Mariela R. Otazo, Rob Ward, Graeme Gillies, Reuben S. Osborne, Matt Golding and Martin A. K. Williams
The solid content of viscoelastic emulsion drops is known to affect their propensity for aggregation and their subsequent coalescence behaviour, where the balance between the drive to reduce surface tension and the straining of an internal viscoelastic network is able to create a plethora of stable partially-coalesced states. The latter has previously been elegantly demonstrated in synthetic systems, generated using oil containing different phase volumes of added solids, with micro-pipette experiments carried out on emulsion drops of several tens of microns in size. Herein we carry out experiments in the same spirit but aided by optical tweezers (OT) and using smaller micron-sized emulsion drops generated from milk fat. Given the size dependence of Brownian fluctuations and Laplace pressure the experimental investigation of these smaller drops is not necessarily a trivial extension of the previous work. The solid content of initially separated drops is controlled using a temperature-cycling regime in the sample preparation protocol, and subsequently the propensity for drops to remain joined or not after being brought into contact was examined. Aggregated pairs of drops were then subjected to an increase in temperature, either locally using a high-powered laser, or more globally using a custom-made Peltier temperature-controller. By heating to different degrees, the amount of fat crystals in the drops was able to be controlled, with progressively more compact partially-coalesced states, and eventually complete coalescence generated as the solid content was reduced. While in contrast to previous studies, the emulsion studied here was quite different in size and nature, and the solid content was controlled using temperature, the same underlying physics was nevertheless observed.
DOI
Thursday, August 22, 2019
Size-scaling effects for microparticles and cells manipulated by optoelectronic tweezers
Shuailong Zhang, Weizhen Li, Mohamed Elsayed, Pengfei Tian, Alasdair W. Clark, Aaron R. Wheeler, and Steven L. Neale
In this work, we investigated the use of optoelectronic tweezers (OET) to manipulate objects that are larger than those commonly positioned with standard optical tweezers. We studied the forces that could be produced on differently sized polystyrene microbeads and MCF-7 breast cancer cells with light-induced dielectrophoresis (DEP). It was found that the DEP force imposed on the bead/cell did not increase linearly with the volume of the bead/cell, primarily because of the non-uniform distribution of the electric field above the OET bottom plate. Although this size-scaling work focuses on microparticles and cells, we propose that the physical mechanism elucidated in this research will be insightful for other micro-objects, biological samples, and micro-actuators undergoing OET manipulation.
In this work, we investigated the use of optoelectronic tweezers (OET) to manipulate objects that are larger than those commonly positioned with standard optical tweezers. We studied the forces that could be produced on differently sized polystyrene microbeads and MCF-7 breast cancer cells with light-induced dielectrophoresis (DEP). It was found that the DEP force imposed on the bead/cell did not increase linearly with the volume of the bead/cell, primarily because of the non-uniform distribution of the electric field above the OET bottom plate. Although this size-scaling work focuses on microparticles and cells, we propose that the physical mechanism elucidated in this research will be insightful for other micro-objects, biological samples, and micro-actuators undergoing OET manipulation.
Brillouin optomechanics in nanophotonic structures
Gustavo S. Wiederhecker, Paulo Dainese, and Thiago P. Mayer Alegre
The interaction between light and mesoscopic mechanical degrees of freedom has been investigated under various perspectives, from spectroscopy in condensed matter, optical tweezer particle trapping, and long-haul optical fiber communication system penalties to gravitational-wave detector noise. In the context of integrated photonics, two topics with dissimilar origins—cavity optomechanics and guided wave Brillouin scattering—are rooted in the manipulation and control of the energy exchange between trapped light and mechanical modes. In this tutorial, we explore the impact of optical and mechanical subwavelength confinement on the interaction among these waves, coined as Brillouin optomechanics. At this spatial scale, optical and mechanical fields are fully vectorial and the common intuition that more intense fields lead to stronger interaction may fail. Here, we provide a thorough discussion on how the two major physical effects responsible for the Brillouin interaction—photoelastic and moving-boundary effects—interplay to foster exciting possibilities in this field. In order to stimulate beginners into this growing research field, this tutorial is accompanied by all the discussed simulation material based on a widespread commercial finite-element solver.
DOI
The interaction between light and mesoscopic mechanical degrees of freedom has been investigated under various perspectives, from spectroscopy in condensed matter, optical tweezer particle trapping, and long-haul optical fiber communication system penalties to gravitational-wave detector noise. In the context of integrated photonics, two topics with dissimilar origins—cavity optomechanics and guided wave Brillouin scattering—are rooted in the manipulation and control of the energy exchange between trapped light and mechanical modes. In this tutorial, we explore the impact of optical and mechanical subwavelength confinement on the interaction among these waves, coined as Brillouin optomechanics. At this spatial scale, optical and mechanical fields are fully vectorial and the common intuition that more intense fields lead to stronger interaction may fail. Here, we provide a thorough discussion on how the two major physical effects responsible for the Brillouin interaction—photoelastic and moving-boundary effects—interplay to foster exciting possibilities in this field. In order to stimulate beginners into this growing research field, this tutorial is accompanied by all the discussed simulation material based on a widespread commercial finite-element solver.
DOI
Optomechanical cooling and self-trapping of low field seeking point-like particles
Arthur Jungkind, Wolfgang Niedenzu and Helmut Ritsch
Atoms in spatially dependent light fields are attracted to local intensity maxima or minima depending on the sign of the frequency difference between the light and the atomic resonance. For light fields confined in open high-Q optical resonators the backaction of the atoms onto the light field generates dissipative dynamic opto-mechanical potentials, which can be used to cool and trap the atoms. Extending the conventional case of high field seekers to the regime of blue atom-field detuning, where the particles are low field seeking, we show that inherent nonlinear atom field dynamics still can be tailored to cool and trap near zero field intensity. Studying field intensity, particle localization and kinetic energy for cavity driving or pumping the particle from the side, we identify optimal parameter regimes, where sub-Doppler cooling comes with trapping and minimal atomic saturation.
DOI
Atoms in spatially dependent light fields are attracted to local intensity maxima or minima depending on the sign of the frequency difference between the light and the atomic resonance. For light fields confined in open high-Q optical resonators the backaction of the atoms onto the light field generates dissipative dynamic opto-mechanical potentials, which can be used to cool and trap the atoms. Extending the conventional case of high field seekers to the regime of blue atom-field detuning, where the particles are low field seeking, we show that inherent nonlinear atom field dynamics still can be tailored to cool and trap near zero field intensity. Studying field intensity, particle localization and kinetic energy for cavity driving or pumping the particle from the side, we identify optimal parameter regimes, where sub-Doppler cooling comes with trapping and minimal atomic saturation.
DOI
Real time single TiO2 nanoparticle monitoring of the photodegradation of methylene blue
Guilherme H. Oliveira, Miguel T. Galante, Thalyta T. Martins, Leonardo F. L. S. dos Santos, Fernando Ely, Claudia Longo, Renato V. Gonçalves, Sérgio R. Muniz, René A. Nome
We report a proof-of-concept micro-spectroscopy, stochastic dynamics, and optical trapping study of a well-known reaction for methylene blue photodegradation catalyzed by titanium dioxide aggregates and nanotubes. Photocatalysis is performed under a high concentration of reactants and catalyst loading to characterize the fundamental chemical kinetics and dynamics aspects of this reaction under in operando conditions. We also report the effect of substrate concentration, light intensity, and substrate/catalyst ratio on the kinetic profiles. Optical imaging is used to quantify how spatial and concentration variations affect the reaction kinetics. To study the dynamics of individual nanoparticle catalysts under in operando conditions, we use optical trapping to characterize the stochastic dynamics of single TiO2 nanotubes. Overall, the results presented here indicate that the setup can be used to monitor photocatalytic degradation of methylene blue with simultaneous measurements of images and spectra while also monitoring the catalyst Brownian motion at the single-particle level.
DOI
We report a proof-of-concept micro-spectroscopy, stochastic dynamics, and optical trapping study of a well-known reaction for methylene blue photodegradation catalyzed by titanium dioxide aggregates and nanotubes. Photocatalysis is performed under a high concentration of reactants and catalyst loading to characterize the fundamental chemical kinetics and dynamics aspects of this reaction under in operando conditions. We also report the effect of substrate concentration, light intensity, and substrate/catalyst ratio on the kinetic profiles. Optical imaging is used to quantify how spatial and concentration variations affect the reaction kinetics. To study the dynamics of individual nanoparticle catalysts under in operando conditions, we use optical trapping to characterize the stochastic dynamics of single TiO2 nanotubes. Overall, the results presented here indicate that the setup can be used to monitor photocatalytic degradation of methylene blue with simultaneous measurements of images and spectra while also monitoring the catalyst Brownian motion at the single-particle level.
DOI
Bottle Beams in Nonlocally Defocusing Nonlinear Media
Yuanqiang Peng; Yunqi Li; Xiaolin Wu; Weiyi Hong
The dynamics of the inward-focusing ring Airy beam in nonlocally defocusing nonlinear media is investigated in detail, and a bottle beam shape can be observed by adjusting the amplitude of the inward-focusing ring Airy beam and the nonlocality of the media. The gradient force of the bottle beam is numerically studied. It is worth mentioning that the bottle beams are formed in the nonlinear regime, which indicates that much higher intensity is allowable for these beams than those in the linear regime. Our approach and results may pave the way to the optical tweezers in the nonlinear regime.
DOI
The dynamics of the inward-focusing ring Airy beam in nonlocally defocusing nonlinear media is investigated in detail, and a bottle beam shape can be observed by adjusting the amplitude of the inward-focusing ring Airy beam and the nonlocality of the media. The gradient force of the bottle beam is numerically studied. It is worth mentioning that the bottle beams are formed in the nonlinear regime, which indicates that much higher intensity is allowable for these beams than those in the linear regime. Our approach and results may pave the way to the optical tweezers in the nonlinear regime.
DOI
Hydrophobic catalysis and a potential biological role of DNA unstacking induced by environment effects
Bobo Feng, Robert P. Sosa, Anna K. F. Mårtensson, Kai Jiang, Alex Tong, Kevin D. Dorfman, Masayuki Takahashi, Per Lincoln, Carlos J. Bustamante, Fredrik Westerlund, and Bengt Nordén
Hydrophobic base stacking is a major contributor to DNA double-helix stability. We report the discovery of specific unstacking effects in certain semihydrophobic environments. Water-miscible ethylene glycol ethers are found to modify structure, dynamics, and reactivity of DNA by mechanisms possibly related to a biologically relevant hydrophobic catalysis. Spectroscopic data and optical tweezers experiments show that base-stacking energies are reduced while base-pair hydrogen bonds are strengthened. We propose that a modulated chemical potential of water can promote “longitudinal breathing” and the formation of unstacked holes while base unpairing is suppressed. Flow linear dichroism in 20% diglyme indicates a 20 to 30% decrease in persistence length of DNA, supported by an increased flexibility in single-molecule nanochannel experiments in poly(ethylene glycol). A limited (3 to 6%) hyperchromicity but unaffected circular dichroism is consistent with transient unstacking events while maintaining an overall average B-DNA conformation. Further information about unstacking dynamics is obtained from the binding kinetics of large thread-intercalating ruthenium complexes, indicating that the hydrophobic effect provides a 10 to 100 times increased DNA unstacking frequency and an “open hole” population on the order of 10−2 compared to 10−4 in normal aqueous solution. Spontaneous DNA strand exchange catalyzed by poly(ethylene glycol) makes us propose that hydrophobic residues in the L2 loop of recombination enzymes RecA and Rad51 may assist gene recombination via modulation of water activity near the DNA helix by hydrophobic interactions, in the manner described here. We speculate that such hydrophobic interactions may have catalytic roles also in other biological contexts, such as in polymerases.
DOI
Hydrophobic base stacking is a major contributor to DNA double-helix stability. We report the discovery of specific unstacking effects in certain semihydrophobic environments. Water-miscible ethylene glycol ethers are found to modify structure, dynamics, and reactivity of DNA by mechanisms possibly related to a biologically relevant hydrophobic catalysis. Spectroscopic data and optical tweezers experiments show that base-stacking energies are reduced while base-pair hydrogen bonds are strengthened. We propose that a modulated chemical potential of water can promote “longitudinal breathing” and the formation of unstacked holes while base unpairing is suppressed. Flow linear dichroism in 20% diglyme indicates a 20 to 30% decrease in persistence length of DNA, supported by an increased flexibility in single-molecule nanochannel experiments in poly(ethylene glycol). A limited (3 to 6%) hyperchromicity but unaffected circular dichroism is consistent with transient unstacking events while maintaining an overall average B-DNA conformation. Further information about unstacking dynamics is obtained from the binding kinetics of large thread-intercalating ruthenium complexes, indicating that the hydrophobic effect provides a 10 to 100 times increased DNA unstacking frequency and an “open hole” population on the order of 10−2 compared to 10−4 in normal aqueous solution. Spontaneous DNA strand exchange catalyzed by poly(ethylene glycol) makes us propose that hydrophobic residues in the L2 loop of recombination enzymes RecA and Rad51 may assist gene recombination via modulation of water activity near the DNA helix by hydrophobic interactions, in the manner described here. We speculate that such hydrophobic interactions may have catalytic roles also in other biological contexts, such as in polymerases.
DOI
The TCR is an allosterically regulated macromolecular machinery changing its conformation while working
Wolfgang W. Schamel Balbino Alarcon Susana Minguet
The αβ T‐cell receptor (TCR) is a multiprotein complex controlling the activation of T cells. Although the structure of the complete TCR is not known, cumulative evidence supports that the TCR cycles between different conformational states that are promoted either by thermal motion or by force. These structural transitions determine whether the TCR engages intracellular effectors or not, regulating TCR phosphorylation and signaling. As for other membrane receptors, ligand binding selects and stabilizes the TCR in active conformations, and/or switches the TCR to activating states that were not visited before ligand engagement. Here we review the main models of TCR allostery, that is, ligand binding at TCRαβ changes the structure at CD3 and ζ. (a) The ITAM and proline‐rich sequence exposure model, in which the TCR's cytoplasmic tails shield each other and ligand binding exposes them for phosphorylation. (b) The membrane‐ITAM model, in which the CD3ε and ζ tails are sequestered inside the membrane and again ligand binding exposes them. (c) The mechanosensor model in which ligand binding exerts force on the TCR, inducing structural changes that allow signaling. Since these models are complementary rather than competing, we propose a unified model that aims to incorporate all existing data.
DOI
The αβ T‐cell receptor (TCR) is a multiprotein complex controlling the activation of T cells. Although the structure of the complete TCR is not known, cumulative evidence supports that the TCR cycles between different conformational states that are promoted either by thermal motion or by force. These structural transitions determine whether the TCR engages intracellular effectors or not, regulating TCR phosphorylation and signaling. As for other membrane receptors, ligand binding selects and stabilizes the TCR in active conformations, and/or switches the TCR to activating states that were not visited before ligand engagement. Here we review the main models of TCR allostery, that is, ligand binding at TCRαβ changes the structure at CD3 and ζ. (a) The ITAM and proline‐rich sequence exposure model, in which the TCR's cytoplasmic tails shield each other and ligand binding exposes them for phosphorylation. (b) The membrane‐ITAM model, in which the CD3ε and ζ tails are sequestered inside the membrane and again ligand binding exposes them. (c) The mechanosensor model in which ligand binding exerts force on the TCR, inducing structural changes that allow signaling. Since these models are complementary rather than competing, we propose a unified model that aims to incorporate all existing data.
DOI
Wednesday, August 21, 2019
High stretchability, strength, and toughness of living cells enabled by hyperelastic vimentin intermediate filaments
Jiliang Hu, Yiwei Li, Yukun Hao, Tianqi Zheng, Satish K. Gupta, German Alberto Parada, Huayin Wu, Shaoting Lin, Shida Wang, Xuanhe Zhao, Robert D. Goldman, Shengqiang Cai, and Ming Guo
In many developmental and pathological processes, including cellular migration during normal development and invasion in cancer metastasis, cells are required to withstand severe deformations. The structural integrity of eukaryotic cells under small deformations has been known to depend on the cytoskeleton including actin filaments (F-actin), microtubules (MT), and intermediate filaments (IFs). However, it remains unclear how cells resist severe deformations since both F-actin and microtubules yield or disassemble under moderate strains. Using vimentin containing IFs (VIFs) as a model for studying the large family of IF proteins, we demonstrate that they dominate cytoplasmic mechanics and maintain cell viability at large deformations. Our results show that cytoskeletal VIFs form a stretchable, hyperelastic network in living cells. This network works synergistically with other cytoplasmic components, substantially enhancing the strength, stretchability, resilience, and toughness of cells. Moreover, we find the hyperelastic VIF network, together with other quickly recoverable cytoskeletal components, forms a mechanically robust structure which can mechanically recover after damage.
DOI
In many developmental and pathological processes, including cellular migration during normal development and invasion in cancer metastasis, cells are required to withstand severe deformations. The structural integrity of eukaryotic cells under small deformations has been known to depend on the cytoskeleton including actin filaments (F-actin), microtubules (MT), and intermediate filaments (IFs). However, it remains unclear how cells resist severe deformations since both F-actin and microtubules yield or disassemble under moderate strains. Using vimentin containing IFs (VIFs) as a model for studying the large family of IF proteins, we demonstrate that they dominate cytoplasmic mechanics and maintain cell viability at large deformations. Our results show that cytoskeletal VIFs form a stretchable, hyperelastic network in living cells. This network works synergistically with other cytoplasmic components, substantially enhancing the strength, stretchability, resilience, and toughness of cells. Moreover, we find the hyperelastic VIF network, together with other quickly recoverable cytoskeletal components, forms a mechanically robust structure which can mechanically recover after damage.
DOI
Water diffusion measurements of single charged aerosols using H2O/D2O isotope exchange and Raman spectroscopy in an electrodynamic balance
Katherine A. Nadler, Pyeongeun Kim, Dao-Ling Huang, Wei Xionga and Robert E. Continetti
Sea spray aerosols contain a large array of organic compounds that contribute to high viscosities at low relative humidity and temperature thereby slowing translational diffusion of water. The Stokes–Einstein equation describes how viscosity is inversely correlated with the translational diffusion coefficient of the diffusing species. However, recent studies indicate that the Stokes–Einstein equation breaks down at high viscosities achieved in the particle phase (>1012 Pa s), underestimating the predicted water diffusion coefficient by orders of magnitude and revealing the need for directly studying the diffusion of water in single aerosols. A new method is reported for measuring the water diffusion coefficient in single suspended charged sucrose–water and citric acid (CA)–water microdroplets in the 30–60 micron diameter range. The translational water diffusion coefficient is quantified using the H2O/D2O isotope exchange technique between 26 and 54% relative humidity (RH) for sucrose and 7 and 25% RH for CA using a recently developed mobile electrodynamic balance apparatus. The results are in good agreement with the literature, particularly the Vignes-type parameterization from experiments using isotope exchange and optical tweezers. Below 15% RH, CA droplets show incomplete H2O/D2O exchange. This mobile electrodynamic balance will allow future studies of atmospherically relevant chemical systems, including field studies.
DOI
Sea spray aerosols contain a large array of organic compounds that contribute to high viscosities at low relative humidity and temperature thereby slowing translational diffusion of water. The Stokes–Einstein equation describes how viscosity is inversely correlated with the translational diffusion coefficient of the diffusing species. However, recent studies indicate that the Stokes–Einstein equation breaks down at high viscosities achieved in the particle phase (>1012 Pa s), underestimating the predicted water diffusion coefficient by orders of magnitude and revealing the need for directly studying the diffusion of water in single aerosols. A new method is reported for measuring the water diffusion coefficient in single suspended charged sucrose–water and citric acid (CA)–water microdroplets in the 30–60 micron diameter range. The translational water diffusion coefficient is quantified using the H2O/D2O isotope exchange technique between 26 and 54% relative humidity (RH) for sucrose and 7 and 25% RH for CA using a recently developed mobile electrodynamic balance apparatus. The results are in good agreement with the literature, particularly the Vignes-type parameterization from experiments using isotope exchange and optical tweezers. Below 15% RH, CA droplets show incomplete H2O/D2O exchange. This mobile electrodynamic balance will allow future studies of atmospherically relevant chemical systems, including field studies.
DOI
Effect of small forces on microsphere under optical trap
Rajesh Kumar, Lalit M Bharadwaj and Arun K Lall
In this era of technological development, greater impact of nanotechnology now can be seen in many fields due to better properties and precise control. Many functions are being executed by bio nano-materials or biomolecules in living systems in a very efficient manner. The functional behaviour and their properties need to be examined to use them for various nano-device applications. The mechanical properties of the biomolecules can be studied by attaching them with microspheres and measuring forces on these microspheres through optical trap. Microspheres of three-micrometer diameter were trapped at the focus of infrared laser and viscous drag forces were applied to measure the effect of these forces on the trapped microsphere. It was observed that with 28mW intensity Laser, the trapped microsphere was displaced by 0.19 μm at 2.1 pN force and trap stiffness was determined as 0.011pN/nm. The findings can be useful while attaching these microspheres as cargos along the bionanomotors for nanorobotics and drug delivery applications.
DOI
In this era of technological development, greater impact of nanotechnology now can be seen in many fields due to better properties and precise control. Many functions are being executed by bio nano-materials or biomolecules in living systems in a very efficient manner. The functional behaviour and their properties need to be examined to use them for various nano-device applications. The mechanical properties of the biomolecules can be studied by attaching them with microspheres and measuring forces on these microspheres through optical trap. Microspheres of three-micrometer diameter were trapped at the focus of infrared laser and viscous drag forces were applied to measure the effect of these forces on the trapped microsphere. It was observed that with 28mW intensity Laser, the trapped microsphere was displaced by 0.19 μm at 2.1 pN force and trap stiffness was determined as 0.011pN/nm. The findings can be useful while attaching these microspheres as cargos along the bionanomotors for nanorobotics and drug delivery applications.
DOI
The transmembrane protein fibrocystin/polyductin regulates cell mechanics and cell motility
Stefanie Puder, Tony Fischer and Claudia Tanja Mierke
Polycystic kidney disease is a disorder that leads to fluid filled cysts that replace normal renal tubes. During the process of cellular development and in the progression of the diseases, fibrocystin can lead to impaired organ formation and even cause organ defects. Besides cellular polarity, mechanical properties play major roles in providing the optimal apical-basal or anterior-posterior symmetry within epithelial cells. A breakdown of the cell symmetry that is usually associated with mechanical property changes is known to be essential in many biological processes such as cell migration, polarity and pattern formation especially during development and diseases such as the autosomal recessive cystic kidney disease. Since the breakdown of the cell symmetry can be evoked by several proteins including fibrocystin, we hypothesized that cell mechanics are altered by fibrocystin. However, the effect of fibrocystin on cell migration and cellular mechanical properties is still unclear. In order to explore the function of fibrocystin on cell migration and mechanics, we analyzed fibrocystin knockdown epithelial cells in comparison to fibrocystin control cells. We found that invasiveness of fibrocystin knockdown cells into dense 3D matrices was increased and more efficient compared to control cells. Using optical cell stretching and atomic force microscopy, fibrocystin knockdown cells were more deformable and exhibited weaker cell-matrix as well as cell-cell adhesion forces, respectively. In summary, these findings show that fibrocystin knockdown cells displayed increased 3D matrix invasion through providing increased cellular deformability, decreased cell-matrix and reduced cell-cell adhesion forces.
DOI
Polycystic kidney disease is a disorder that leads to fluid filled cysts that replace normal renal tubes. During the process of cellular development and in the progression of the diseases, fibrocystin can lead to impaired organ formation and even cause organ defects. Besides cellular polarity, mechanical properties play major roles in providing the optimal apical-basal or anterior-posterior symmetry within epithelial cells. A breakdown of the cell symmetry that is usually associated with mechanical property changes is known to be essential in many biological processes such as cell migration, polarity and pattern formation especially during development and diseases such as the autosomal recessive cystic kidney disease. Since the breakdown of the cell symmetry can be evoked by several proteins including fibrocystin, we hypothesized that cell mechanics are altered by fibrocystin. However, the effect of fibrocystin on cell migration and cellular mechanical properties is still unclear. In order to explore the function of fibrocystin on cell migration and mechanics, we analyzed fibrocystin knockdown epithelial cells in comparison to fibrocystin control cells. We found that invasiveness of fibrocystin knockdown cells into dense 3D matrices was increased and more efficient compared to control cells. Using optical cell stretching and atomic force microscopy, fibrocystin knockdown cells were more deformable and exhibited weaker cell-matrix as well as cell-cell adhesion forces, respectively. In summary, these findings show that fibrocystin knockdown cells displayed increased 3D matrix invasion through providing increased cellular deformability, decreased cell-matrix and reduced cell-cell adhesion forces.
DOI
Myosin IIA and formin dependent mechanosensitivity of filopodia adhesion
N. O. Alieva, A. K. Efremov, S. Hu, D. Oh, Z. Chen, M. Natarajan, H. T. Ong, A. Jégou, G. Romet-Lemonne, J. T. Groves, M. P. Sheetz, J. Yan & A. D. Bershadsky
Filopodia, dynamic membrane protrusions driven by polymerization of an actin filament core, can adhere to the extracellular matrix and experience both external and cell-generated pulling forces. The role of such forces in filopodia adhesion is however insufficiently understood. Here, we study filopodia induced by overexpression of myosin X, typical for cancer cells. The lifetime of such filopodia positively correlates with the presence of myosin IIA filaments at the filopodia bases. Application of pulling forces to the filopodia tips through attached fibronectin-coated laser-trapped beads results in sustained growth of the filopodia. Pharmacological inhibition or knockdown of myosin IIA abolishes the filopodia adhesion to the beads. Formin inhibitor SMIFH2, which causes detachment of actin filaments from formin molecules, produces similar effect. Thus, centripetal force generated by myosin IIA filaments at the base of filopodium and transmitted to the tip through actin core in a formin-dependent fashion is required for filopodia adhesion.
DOI
Filopodia, dynamic membrane protrusions driven by polymerization of an actin filament core, can adhere to the extracellular matrix and experience both external and cell-generated pulling forces. The role of such forces in filopodia adhesion is however insufficiently understood. Here, we study filopodia induced by overexpression of myosin X, typical for cancer cells. The lifetime of such filopodia positively correlates with the presence of myosin IIA filaments at the filopodia bases. Application of pulling forces to the filopodia tips through attached fibronectin-coated laser-trapped beads results in sustained growth of the filopodia. Pharmacological inhibition or knockdown of myosin IIA abolishes the filopodia adhesion to the beads. Formin inhibitor SMIFH2, which causes detachment of actin filaments from formin molecules, produces similar effect. Thus, centripetal force generated by myosin IIA filaments at the base of filopodium and transmitted to the tip through actin core in a formin-dependent fashion is required for filopodia adhesion.
DOI
The Hsp90 isoforms from S. cerevisiae differ in structure, function and client range
Hannah Girstmair, Franziska Tippel, Abraham Lopez, Katarzyna Tych, Frank Stein, Per Haberkant, Philipp Werner Norbert Schmid, Dominic Helm, Matthias Rief, Michael Sattler & Johannes Buchner
The molecular chaperone Hsp90 is an important regulator of proteostasis. It has remained unclear why S. cerevisiae possesses two Hsp90 isoforms, the constitutively expressed Hsc82 and the stress-inducible Hsp82. Here, we report distinct differences despite a sequence identity of 97%. Consistent with its function under stress conditions, Hsp82 is more stable and refolds more efficiently than Hsc82. The two isoforms also differ in their ATPases and conformational cycles. Hsc82 is more processive and populates closed states to a greater extent. Variations in the N-terminal ATP-binding domain modulate its dynamics and conformational cycle. Despite these differences, the client interactomes are largely identical, but isoform-specific interactors exist both under physiological and heat shock conditions. Taken together, changes mainly in the N-domain create a stress-specific, more resilient protein with a shifted activity profile. Thus, the precise tuning of the Hsp90 isoforms preserves the basic mechanism but adapts it to specific needs.
DOI
The molecular chaperone Hsp90 is an important regulator of proteostasis. It has remained unclear why S. cerevisiae possesses two Hsp90 isoforms, the constitutively expressed Hsc82 and the stress-inducible Hsp82. Here, we report distinct differences despite a sequence identity of 97%. Consistent with its function under stress conditions, Hsp82 is more stable and refolds more efficiently than Hsc82. The two isoforms also differ in their ATPases and conformational cycles. Hsc82 is more processive and populates closed states to a greater extent. Variations in the N-terminal ATP-binding domain modulate its dynamics and conformational cycle. Despite these differences, the client interactomes are largely identical, but isoform-specific interactors exist both under physiological and heat shock conditions. Taken together, changes mainly in the N-domain create a stress-specific, more resilient protein with a shifted activity profile. Thus, the precise tuning of the Hsp90 isoforms preserves the basic mechanism but adapts it to specific needs.
DOI
PIP2 reshapes membranes through asymmetric desorption
Sankalp Shukla, Rui Jin, Jaclyn Robustelli, Zachary E. Zimmerman, Tobias Baumgart
Phosphatidylinositol-4,5-bisphosphate [PIP2] is an important signaling lipid in eukaryotic cell plasma membranes, playing an essential role in diverse cellular processes. The headgroup of PIP2 is highly negatively charged and this lipid displays a high critical micellar concentration compared to housekeeping phospholipid analogs. Given the crucial role of PIP2, it is imperative to study its localization, interaction with proteins, and membrane shaping properties. Biomimetic membranes have served extensively to elucidate aspects including protein-lipid and lipid-lipid interactions, as well as membrane mechanics. Incorporation of PIP2 into biomimetic membranes, however, has at times resulted in discrepant findings described in the literature. With the goal to elucidate the mechanical consequences of PIP2 incorporation, we studied the desorption of PIP2 from biomimetic giant unilamellar vesicles [GUVs] by means of a fluorescent marker. A decrease in fluorescence intensity with the age of the vesicles suggested that PIP2 lipids were being desorbed from the outer leaflet of the membrane. To evaluate whether this desorption was asymmetric, the vesicles were systematically diluted. This resulted in an increase in the number of internally tubulated vesicles within minutes after dilution, suggesting that the desorption was asymmetric and also generated membrane curvature. By means of a saturated chain homolog of PIP2, we showed that the fast desorption of PIP2 is facilitated by presence of an arachidonic lipid tail and possibly due to its oxidation. Through measurements of the pulling force of membrane tethers, we quantified the effect of this asymmetric desorption on the spontaneous membrane curvature. Furthermore, we found that the spontaneous curvature could be modulated by externally increasing the concentration of PIP2 micelles. Given that the local concentration of PIP2 in biological membranes is variable, spontaneous curvature generated by PIP2 may affect the formation of highly curved structures which can serve as initiators for signaling events.
DOI
Phosphatidylinositol-4,5-bisphosphate [PIP2] is an important signaling lipid in eukaryotic cell plasma membranes, playing an essential role in diverse cellular processes. The headgroup of PIP2 is highly negatively charged and this lipid displays a high critical micellar concentration compared to housekeeping phospholipid analogs. Given the crucial role of PIP2, it is imperative to study its localization, interaction with proteins, and membrane shaping properties. Biomimetic membranes have served extensively to elucidate aspects including protein-lipid and lipid-lipid interactions, as well as membrane mechanics. Incorporation of PIP2 into biomimetic membranes, however, has at times resulted in discrepant findings described in the literature. With the goal to elucidate the mechanical consequences of PIP2 incorporation, we studied the desorption of PIP2 from biomimetic giant unilamellar vesicles [GUVs] by means of a fluorescent marker. A decrease in fluorescence intensity with the age of the vesicles suggested that PIP2 lipids were being desorbed from the outer leaflet of the membrane. To evaluate whether this desorption was asymmetric, the vesicles were systematically diluted. This resulted in an increase in the number of internally tubulated vesicles within minutes after dilution, suggesting that the desorption was asymmetric and also generated membrane curvature. By means of a saturated chain homolog of PIP2, we showed that the fast desorption of PIP2 is facilitated by presence of an arachidonic lipid tail and possibly due to its oxidation. Through measurements of the pulling force of membrane tethers, we quantified the effect of this asymmetric desorption on the spontaneous membrane curvature. Furthermore, we found that the spontaneous curvature could be modulated by externally increasing the concentration of PIP2 micelles. Given that the local concentration of PIP2 in biological membranes is variable, spontaneous curvature generated by PIP2 may affect the formation of highly curved structures which can serve as initiators for signaling events.
DOI
The mechanical properties of microbial surfaces and biofilms
Glauber R. de S.Araújo, Nathan B.Viana, Fran Gómez, Bruno Pontes, Susana Frases
Microbes can modify their surface structure as an adaptive mechanism for survival and dissemination in the environment or inside the host. Altering their ability to respond to mechanical stimuli is part of this adaptive process. Since the 1990s, powerful micromanipulation tools have been developed that allow mechanical studies of microbial cell surfaces, exploring little known aspects of their dynamic behavior. This review concentrates on the study of mechanical and rheological properties of bacteria and fungi, focusing on their cell surface dynamics and biofilm formation.
DOI
Microbes can modify their surface structure as an adaptive mechanism for survival and dissemination in the environment or inside the host. Altering their ability to respond to mechanical stimuli is part of this adaptive process. Since the 1990s, powerful micromanipulation tools have been developed that allow mechanical studies of microbial cell surfaces, exploring little known aspects of their dynamic behavior. This review concentrates on the study of mechanical and rheological properties of bacteria and fungi, focusing on their cell surface dynamics and biofilm formation.
DOI
Existence of periodic solutions for a scalar differential equation modelling optical conveyor belts
Luis Carretero, José Valero
We study a one-dimensional ordinary differential equation modelling optical conveyor belts, showing in particular cases of physical interest that periodic solutions exist. Moreover, under rather general assumptions it is proved that the set of periodic solutions is bounded.
DOI
We study a one-dimensional ordinary differential equation modelling optical conveyor belts, showing in particular cases of physical interest that periodic solutions exist. Moreover, under rather general assumptions it is proved that the set of periodic solutions is bounded.
DOI
Tuesday, August 20, 2019
A Universal Assay for Making DNA, RNA, and RNA–DNA Hybrid Configurations for Single-Molecule Manipulation in Two or Three Steps without Ligation
Ya-Jun Yang, Lun Song, Xiao-Cong Zhao, Chen Zhang, Wen-Qiang Wu, Hui-Juan You, Hang Fu, Er-Chi Zhou, Xing-Hua Zhang
Despite having a great variety of topologies, most DNA, RNA, and RNA–DNA hybrid (RDH) configurations for single-molecule manipulation are composed of several single-stranded (ss) DNA and ssRNA strands, with functional labels at the two ends for surface tethering. On this basis, we developed a simple, robust, and universal amplification-annealing (AA) assay for making all these configurations in two or three steps without inefficient digestion and ligation reactions. As examples, we made ssDNA, short ssDNA with double-stranded (ds) DNA handles, dsDNA with ssDNA handles, replication-fork shaped DNA/RDH/RNA, DNA holiday junction, three-site multiple-labeled and nicked DNA, torsion-constrained RNA/RDH, and short ssRNA with RDH handles. In addition to single-molecule manipulation techniques including optical tweezers, magnetic tweezers, and atomic force microscopy, these configurations can be applied in other surface-tethering techniques as well.
DOI
Despite having a great variety of topologies, most DNA, RNA, and RNA–DNA hybrid (RDH) configurations for single-molecule manipulation are composed of several single-stranded (ss) DNA and ssRNA strands, with functional labels at the two ends for surface tethering. On this basis, we developed a simple, robust, and universal amplification-annealing (AA) assay for making all these configurations in two or three steps without inefficient digestion and ligation reactions. As examples, we made ssDNA, short ssDNA with double-stranded (ds) DNA handles, dsDNA with ssDNA handles, replication-fork shaped DNA/RDH/RNA, DNA holiday junction, three-site multiple-labeled and nicked DNA, torsion-constrained RNA/RDH, and short ssRNA with RDH handles. In addition to single-molecule manipulation techniques including optical tweezers, magnetic tweezers, and atomic force microscopy, these configurations can be applied in other surface-tethering techniques as well.
DOI
Quantifying the Local Mechanical Properties of Cells in a Fibrous Three-Dimensional Microenvironment
Amy Dagro, Labchan Rajbhandari, Santiago Orrego, Sung Hoon Kang, Arun Venkatesan, Kaliat T. Ramesh
Measurements of the mechanical response of biological cells are critical for understanding injury and disease, for developing diagnostic tools, and for computational models in mechanobiology. Although it is well known that cells are sensitive to the topography of their microenvironment, the current paradigm in mechanical testing of adherent cells is mostly limited to specimens grown on flat two-dimensional substrates. In this study, we introduce a technique in which cellular indentation via optical trapping is performed on cells at a high spatial resolution to obtain their regional mechanical properties while they exist in a more favorable three-dimensional microenvironment. We combine our approach with nonlinear contact mechanics theory to consider the effects of a large deformation. This allows us to probe length scales that are relevant for obtaining overall cell stiffness values. The experimental results herein provide the hyperelastic material properties at both high (∼100 s−1) and low (∼1–10 s−1) strain rates of murine central nervous system glial cells. The limitations due to possible misalignment of the indenter in the three-dimensional space are examined using a computational model.
DOI
Measurements of the mechanical response of biological cells are critical for understanding injury and disease, for developing diagnostic tools, and for computational models in mechanobiology. Although it is well known that cells are sensitive to the topography of their microenvironment, the current paradigm in mechanical testing of adherent cells is mostly limited to specimens grown on flat two-dimensional substrates. In this study, we introduce a technique in which cellular indentation via optical trapping is performed on cells at a high spatial resolution to obtain their regional mechanical properties while they exist in a more favorable three-dimensional microenvironment. We combine our approach with nonlinear contact mechanics theory to consider the effects of a large deformation. This allows us to probe length scales that are relevant for obtaining overall cell stiffness values. The experimental results herein provide the hyperelastic material properties at both high (∼100 s−1) and low (∼1–10 s−1) strain rates of murine central nervous system glial cells. The limitations due to possible misalignment of the indenter in the three-dimensional space are examined using a computational model.
DOI
Robust orientation control of multi‐DOF cell based on uncertainty and disturbance estimation
Mingyang Xie, Adnan Shakoor, Chuntao Li, Dong Sun
Multiple degrees‐of‐freedom (multi‐DOF) cell orientation control is a vital important technique involved in single cell surgery applications. Currently, few studies have been performed toward automation of multi‐DOF cell orientation control using robotically controlled optical tweezers. In this paper, a robust control framework is developed to perform multi‐DOF cell rotational control with consideration of model uncertainties and external disturbances. Both simulation and experimental studies are presented to illustrate the performance of the proposed control strategy. The main contributions of this work lie in that this is the first time to develop a unified framework to achieve multi‐DOF cell orientation control without the need for accurate dynamic model parameters and/or any knowledge about uncertainty characteristic, which greatly enhances the robustness of the overall system.
DOI
Multiple degrees‐of‐freedom (multi‐DOF) cell orientation control is a vital important technique involved in single cell surgery applications. Currently, few studies have been performed toward automation of multi‐DOF cell orientation control using robotically controlled optical tweezers. In this paper, a robust control framework is developed to perform multi‐DOF cell rotational control with consideration of model uncertainties and external disturbances. Both simulation and experimental studies are presented to illustrate the performance of the proposed control strategy. The main contributions of this work lie in that this is the first time to develop a unified framework to achieve multi‐DOF cell orientation control without the need for accurate dynamic model parameters and/or any knowledge about uncertainty characteristic, which greatly enhances the robustness of the overall system.
DOI
Suppressed Spontaneous Emission for Coherent Momentum Transfer
Xueping Long, Scarlett S. Yu, Andrew M. Jayich, and Wesley C. Campbell
Strong optical forces with minimal spontaneous emission are desired for molecular deceleration and atom interferometry applications. We report experimental benchmarking of such a stimulated optical force driven by ultrafast laser pulses. We apply this technique to accelerate atoms, demonstrating up to an average of 19ℏk momentum transfers per spontaneous emission event. This represents more than an order of magnitude improvement in suppression of spontaneous emission compared to radiative scattering forces. For molecular beam slowing, this technique is capable of delivering a many-fold increase in the achievable time-averaged force to significantly reduce both the slowing distance and detrimental losses to dark vibrational states.
DOI
Strong optical forces with minimal spontaneous emission are desired for molecular deceleration and atom interferometry applications. We report experimental benchmarking of such a stimulated optical force driven by ultrafast laser pulses. We apply this technique to accelerate atoms, demonstrating up to an average of 19ℏk momentum transfers per spontaneous emission event. This represents more than an order of magnitude improvement in suppression of spontaneous emission compared to radiative scattering forces. For molecular beam slowing, this technique is capable of delivering a many-fold increase in the achievable time-averaged force to significantly reduce both the slowing distance and detrimental losses to dark vibrational states.
DOI
Advances in surface-enhanced optical forces and optical manipulations
Wang Han-Cong, Li Zhi-Peng
The localized surface plasmons in metal nanostructures under optical excitation will lead to near-field localization and enhancement, which have shown important applications in surface enhancement spectroscopy, ultra-sensitive sensing, microfluidic chip, enhanced optical force, etc. The plasmon resonance and the resulting electric field enhancement strongly depend on wavelength and structure geometry. As a result, the optical force will be closely related to the field distribution, that is, the optical force can be used to manipulate and sort plasmonic metal structures. The large near-field enhancement and gradient of metal nanoparticle aggregates can also be used as a "plasmonic tweezer" to manipulate other particles. Furthermore, in the case of changing the incident polarization and even for a new type of structured laser beam, the optical manipulation has a higher degree of freedom. In this review, having briefly introduced the plasmon-enhanced optical force, we focus on the recent advances in the following three aspects:1) the manipulation of plasmonic nanoparticles by optical tweezer, 2) the manipulation of other particles by plasmonic tweezer, and 3) dependence of plasmonic optical force on the polarization, optical angular momentum, structured light and the structured chirality. Comparing with other topics of plasmon-enhanced light-interactions, there is plenty of room for further developing the plasmon-enhanced optical force and optical manipulation. Several research trends can be foreseen. 1) More precise optical manipulating and sorting of nanoparticles (even sub-nanometer). For example, more sensitive special resonant modes (e.g. Fano resonance) of plasmonic nanostructure can be utilized. For some nanostructures with small feature sizes, especially when the gap size is close to 1 nm, the non-local effect has a certain effect on the plasmon resonance. Therefore, when calculating the optical force in this case, non-local effects and possibly other quantum effects should be considered. 2) Richer laser fields, that is, using various new structured fields and chiral structures provides a higher degree of freedom for the optical forces and optical manipulation. Also, the localized surface plasmons can be combined with propagating surface plasmons. 3) Wider applications of plasmonic optical forces, especially in combination with other effects and even interdiscipline, e.g. enhanced spectroscopy, enhanced single particle chemical reactions, nonlinear optical effects, and photothermal manipulations.
DOI
The localized surface plasmons in metal nanostructures under optical excitation will lead to near-field localization and enhancement, which have shown important applications in surface enhancement spectroscopy, ultra-sensitive sensing, microfluidic chip, enhanced optical force, etc. The plasmon resonance and the resulting electric field enhancement strongly depend on wavelength and structure geometry. As a result, the optical force will be closely related to the field distribution, that is, the optical force can be used to manipulate and sort plasmonic metal structures. The large near-field enhancement and gradient of metal nanoparticle aggregates can also be used as a "plasmonic tweezer" to manipulate other particles. Furthermore, in the case of changing the incident polarization and even for a new type of structured laser beam, the optical manipulation has a higher degree of freedom. In this review, having briefly introduced the plasmon-enhanced optical force, we focus on the recent advances in the following three aspects:1) the manipulation of plasmonic nanoparticles by optical tweezer, 2) the manipulation of other particles by plasmonic tweezer, and 3) dependence of plasmonic optical force on the polarization, optical angular momentum, structured light and the structured chirality. Comparing with other topics of plasmon-enhanced light-interactions, there is plenty of room for further developing the plasmon-enhanced optical force and optical manipulation. Several research trends can be foreseen. 1) More precise optical manipulating and sorting of nanoparticles (even sub-nanometer). For example, more sensitive special resonant modes (e.g. Fano resonance) of plasmonic nanostructure can be utilized. For some nanostructures with small feature sizes, especially when the gap size is close to 1 nm, the non-local effect has a certain effect on the plasmon resonance. Therefore, when calculating the optical force in this case, non-local effects and possibly other quantum effects should be considered. 2) Richer laser fields, that is, using various new structured fields and chiral structures provides a higher degree of freedom for the optical forces and optical manipulation. Also, the localized surface plasmons can be combined with propagating surface plasmons. 3) Wider applications of plasmonic optical forces, especially in combination with other effects and even interdiscipline, e.g. enhanced spectroscopy, enhanced single particle chemical reactions, nonlinear optical effects, and photothermal manipulations.
DOI
Optical manipulation of Rayleigh particles by metalenses—a numerical study
Zhe Shen, Hongchao Liu, Shuang Zhang, Yao-Chun Shen, Baifu Zhang, and Saiyu Luo
Based on the focusing feature of a metalens, we numerically studied its application in optical manipulation of Rayleigh particles. Three types of metalenses—point focusing, line focusing, and line focusing with phase gradient—were designed. Simulation results using the finite-difference time-domain method showed that the incident optical beams could be focused into a spot or a line for stable particle trapping. Through engineering a gradient phase in the direction of the focal line, the proposed metalens can push the particles along the line. This provides a unique capability to move particles along a line without the need of any mechanical movement. Given its thin sheet structure and compactness, the proposed metalens can be easily integrated into microfluidic and optical tweezers systems, and it can find potential applications in optical sorting of biological cells.
DOI
Based on the focusing feature of a metalens, we numerically studied its application in optical manipulation of Rayleigh particles. Three types of metalenses—point focusing, line focusing, and line focusing with phase gradient—were designed. Simulation results using the finite-difference time-domain method showed that the incident optical beams could be focused into a spot or a line for stable particle trapping. Through engineering a gradient phase in the direction of the focal line, the proposed metalens can push the particles along the line. This provides a unique capability to move particles along a line without the need of any mechanical movement. Given its thin sheet structure and compactness, the proposed metalens can be easily integrated into microfluidic and optical tweezers systems, and it can find potential applications in optical sorting of biological cells.
DOI
Molecular mechanism of cytoplasmic dynein tension sensing
Lu Rao, Florian Berger, Matthew P. Nicholas & Arne Gennerich
Cytoplasmic dynein is the most complex cytoskeletal motor protein and is responsible for numerous biological functions. Essential to dynein’s function is its capacity to respond anisotropically to tension, so that its microtubule-binding domains bind microtubules more strongly when under backward load than forward load. The structural mechanisms by which dynein senses directional tension, however, are unknown. Using a combination of optical tweezers, mutagenesis, and chemical cross-linking, we show that three structural elements protruding from the motor domain—the linker, buttress, and stalk—together regulate directional tension-sensing. We demonstrate that dynein’s anisotropic response to directional tension is mediated by sliding of the coiled-coils of the stalk, and that coordinated conformational changes of dynein’s linker and buttress control this process. We also demonstrate that the stalk coiled-coils assume a previously undescribed registry during dynein’s stepping cycle. We propose a revised model of dynein’s mechanochemical cycle which accounts for our findings.
DOI
Cytoplasmic dynein is the most complex cytoskeletal motor protein and is responsible for numerous biological functions. Essential to dynein’s function is its capacity to respond anisotropically to tension, so that its microtubule-binding domains bind microtubules more strongly when under backward load than forward load. The structural mechanisms by which dynein senses directional tension, however, are unknown. Using a combination of optical tweezers, mutagenesis, and chemical cross-linking, we show that three structural elements protruding from the motor domain—the linker, buttress, and stalk—together regulate directional tension-sensing. We demonstrate that dynein’s anisotropic response to directional tension is mediated by sliding of the coiled-coils of the stalk, and that coordinated conformational changes of dynein’s linker and buttress control this process. We also demonstrate that the stalk coiled-coils assume a previously undescribed registry during dynein’s stepping cycle. We propose a revised model of dynein’s mechanochemical cycle which accounts for our findings.
DOI
All-optical tunable plasmonic nano-aggregations for surface-enhanced Raman scattering
Lei Chen, Wei Liu, Dongyi Shen, Yuehan Liu, Zhihao Zhou, Xiaogan Liang and Wenjie Wan
Interparticle forces play a crucial role in nanoparticle-based nanoscience and nanoengineering for synthesizing new materials, manipulating nanoscale structures, understanding biological processes and ultrasensitive sensing. Complicated by the fluid-dynamical and chemical nature of the liquid environment of nanoparticles, previous attempts are limited to electromagnetic and chemical methods. Alternatively, optically induced forces provide a convenient and fabrication-free route to manipulate nanoparticles at the nanoscale. Here we demonstrate a new double laser trapping scheme for metallic nano-aggregation by inducing strong near-field optical interparticle forces without any chemical agents or complicated fabrication processes. These induced optical forces arising from strong localized plasmon resonance strongly depend on the interparticle separation well beyond the diffraction limit and the polarization of the incident laser field. We examine such sub-resolved interparticle separation in trapped nanoaggregates by measuring surface-enhanced Raman scattering, and further demonstrate the single-molecule sensitivity by implementing such nanostructures. This new technique opens a new avenue for all-optical manipulation of nanomaterials as well as ultra-sensitive bio-chemical sensing applications.
DOI
Interparticle forces play a crucial role in nanoparticle-based nanoscience and nanoengineering for synthesizing new materials, manipulating nanoscale structures, understanding biological processes and ultrasensitive sensing. Complicated by the fluid-dynamical and chemical nature of the liquid environment of nanoparticles, previous attempts are limited to electromagnetic and chemical methods. Alternatively, optically induced forces provide a convenient and fabrication-free route to manipulate nanoparticles at the nanoscale. Here we demonstrate a new double laser trapping scheme for metallic nano-aggregation by inducing strong near-field optical interparticle forces without any chemical agents or complicated fabrication processes. These induced optical forces arising from strong localized plasmon resonance strongly depend on the interparticle separation well beyond the diffraction limit and the polarization of the incident laser field. We examine such sub-resolved interparticle separation in trapped nanoaggregates by measuring surface-enhanced Raman scattering, and further demonstrate the single-molecule sensitivity by implementing such nanostructures. This new technique opens a new avenue for all-optical manipulation of nanomaterials as well as ultra-sensitive bio-chemical sensing applications.
DOI
Replication Fork Activation Is Enabled by a Single-Stranded DNA Gate in CMG Helicase
Michael R. Wasserman, Grant D. Schauer, Michael E. O’Donnell, Shixin Liu
The eukaryotic replicative helicase CMG is a closed ring around double-stranded (ds)DNA at origins yet must transition to single-stranded (ss)DNA for helicase action. CMG must also handle repair intermediates, such as reversed forks that lack ssDNA. Here, using correlative single-molecule fluorescence and force microscopy, we show that CMG harbors a ssDNA gate that enables transitions between ss and dsDNA. When coupled to DNA polymerase, CMG remains on ssDNA, but when uncoupled, CMG employs this gate to traverse forked junctions onto dsDNA. Surprisingly, CMG undergoes rapid diffusion on dsDNA and can transition back onto ssDNA to nucleate a functional replisome. The gate—distinct from that between Mcm2/5 used for origin loading—is intrinsic to CMG; however, Mcm10 promotes strand passage by enhancing the affinity of CMG to DNA. This gating process may explain the dsDNA-to-ssDNA transition of CMG at origins and help preserve CMG on dsDNA during fork repair.
Monday, August 19, 2019
Oxaliplatin effects on the DNA molecule studied by force spectroscopy
L Oliveira, J M Caquito Jr and M S Rocha
In the present study we investigated the binding of the anticancer compound Oxaliplatin to DNA. Using optical tweezers to perform single molecule force spectroscopy, we determined the changes of the mechanical parameters of DNA complexes formed with Oxaliplatin, at high and low ionic strengths. The interaction mechanism and the physical chemistry of the binding were determined from these measurements. In addition, kinetic information on covalent diadduct formation and on DNA compaction by Oxaliplatin were also obtained. All these results were critically compared to those obtained for the related anti-neoplastic compounds Cisplatin and Carboplatin, previously determined under similar experimental conditions. These results provide new information about the action of platinum-based compounds on DNA, being useful to the improvement of current chemotherapies and to the design of novel correlated drugs.
DOI
In the present study we investigated the binding of the anticancer compound Oxaliplatin to DNA. Using optical tweezers to perform single molecule force spectroscopy, we determined the changes of the mechanical parameters of DNA complexes formed with Oxaliplatin, at high and low ionic strengths. The interaction mechanism and the physical chemistry of the binding were determined from these measurements. In addition, kinetic information on covalent diadduct formation and on DNA compaction by Oxaliplatin were also obtained. All these results were critically compared to those obtained for the related anti-neoplastic compounds Cisplatin and Carboplatin, previously determined under similar experimental conditions. These results provide new information about the action of platinum-based compounds on DNA, being useful to the improvement of current chemotherapies and to the design of novel correlated drugs.
DOI
Hidden Symmetries in Bowtie Nanocavities and Diabolo Nanoantennas
Victor Pacheco-Peña, Rúben Alves, Miguel Navarro-Cía
Symmetries play an important role in many branches of physics and enable simplification of the mathematical description of problems. In some cases, symmetries are hidden and are only evident under suitable coordinate systems. With the help of conformal transformation, it is shown analytically here how asymmetric-looking plasmonics diabolo nanoantennas and bowtie nanocavities display a hidden symmetry that justifies the unforeseen symmetric nonradiative Purcell enhancement of a nanoemitter in their immediacy. The conformal transformation also provides physical insight on the dissimilar self-induced trapping potential experienced by such nanoemitter nearby/inside the diabolo nanoantenna/bowtie nanocavity. The analytical results are confirmed with full-wave simulations. This work highlights the elegant and cost-effective (in terms of computational burden) solution that conformal transformation provides to understand the underlying physics of and to design/model plasmonic nanostructures that are becoming key elements in sensing, quantum optics, and so on.
DOI
Symmetries play an important role in many branches of physics and enable simplification of the mathematical description of problems. In some cases, symmetries are hidden and are only evident under suitable coordinate systems. With the help of conformal transformation, it is shown analytically here how asymmetric-looking plasmonics diabolo nanoantennas and bowtie nanocavities display a hidden symmetry that justifies the unforeseen symmetric nonradiative Purcell enhancement of a nanoemitter in their immediacy. The conformal transformation also provides physical insight on the dissimilar self-induced trapping potential experienced by such nanoemitter nearby/inside the diabolo nanoantenna/bowtie nanocavity. The analytical results are confirmed with full-wave simulations. This work highlights the elegant and cost-effective (in terms of computational burden) solution that conformal transformation provides to understand the underlying physics of and to design/model plasmonic nanostructures that are becoming key elements in sensing, quantum optics, and so on.
DOI
Flow-Through Optical Chromatography in Combination with Confocal Raman Microspectroscopy: A Novel Label-Free Approach To Detect Responses of Live Macrophages to Environmental Stimuli
Qin Lu, Daniel E. Barlow, Dhanya Haridas, Braden C. Giordano, Harold D. Ladouceur, Joel D. Gaston, Greg E. Collins, Alex V. Terray
Flow-through optical chromatography (FT-OC), an advanced mode of optical chromatography, achieved baseline separation of a mixture of silica microparticles (SiO2, 1.00 and 2.50 μm) and a mixture of polystyrene microparticles (PS, 1.00, 2.00, and 3.00 μm) based on particle size. Comparisons made between experimentally determined velocities for the microparticles and theoretically derived velocities from Mie theory and Stokes’ law validated the data collection setup and the data analysis for FT-OC. A population shift in live macrophages (cell line IC-21, ATCC TIB-186) responding to environmental stimuli was sensitively detected by FT-OC. The average velocity of macrophages stressed by nutritional deprivation was decreased considerably together with a small but statistically significant increase in cell size. Mie scattering calculations demonstrated that the small increase in cell size of macrophages stressed by nutritional deprivation was not entirely responsible for this decrease. Confocal fluorescence microscopy and atomic force microscopy (AFM) studies revealed morphological changes of macrophages induced by nutritional deprivation, and these changes were more likely responsible for the decrease in average velocity detected by FT-OC. Confocal Raman microspectroscopy was used to shed light upon biochemical transformations of macrophages suffering from nutritional deprivation.
DOI
Flow-through optical chromatography (FT-OC), an advanced mode of optical chromatography, achieved baseline separation of a mixture of silica microparticles (SiO2, 1.00 and 2.50 μm) and a mixture of polystyrene microparticles (PS, 1.00, 2.00, and 3.00 μm) based on particle size. Comparisons made between experimentally determined velocities for the microparticles and theoretically derived velocities from Mie theory and Stokes’ law validated the data collection setup and the data analysis for FT-OC. A population shift in live macrophages (cell line IC-21, ATCC TIB-186) responding to environmental stimuli was sensitively detected by FT-OC. The average velocity of macrophages stressed by nutritional deprivation was decreased considerably together with a small but statistically significant increase in cell size. Mie scattering calculations demonstrated that the small increase in cell size of macrophages stressed by nutritional deprivation was not entirely responsible for this decrease. Confocal fluorescence microscopy and atomic force microscopy (AFM) studies revealed morphological changes of macrophages induced by nutritional deprivation, and these changes were more likely responsible for the decrease in average velocity detected by FT-OC. Confocal Raman microspectroscopy was used to shed light upon biochemical transformations of macrophages suffering from nutritional deprivation.
DOI
Optical Tweezers: Phototoxicity and Thermal Stress in Cells and Biomolecules
Alfonso Blázquez-Castro
For several decades optical tweezers have proven to be an invaluable tool in the study and analysis of myriad biological responses and applications. However, as with every tool, they can have undesirable or damaging effects upon the very sample they are helping to study. In this review the main negative effects of optical tweezers upon biostructures and living systems will be presented. There are three main areas on which the review will focus: linear optical excitation within the tweezers, non-linear photonic effects, and thermal load upon the sampled volume. Additional information is provided on negative mechanical effects of optical traps on biological structures. Strategies to avoid or, at least, minimize these negative effects will be introduced. Finally, all these effects, undesirable for the most, can have positive applications under the right conditions. Some hints in this direction will also be discussed.
DOI
For several decades optical tweezers have proven to be an invaluable tool in the study and analysis of myriad biological responses and applications. However, as with every tool, they can have undesirable or damaging effects upon the very sample they are helping to study. In this review the main negative effects of optical tweezers upon biostructures and living systems will be presented. There are three main areas on which the review will focus: linear optical excitation within the tweezers, non-linear photonic effects, and thermal load upon the sampled volume. Additional information is provided on negative mechanical effects of optical traps on biological structures. Strategies to avoid or, at least, minimize these negative effects will be introduced. Finally, all these effects, undesirable for the most, can have positive applications under the right conditions. Some hints in this direction will also be discussed.
DOI
Non-Stokes drag coefficient in single-particle electrophoresis: New insights on a classical problem
Mai-Jia Liao, Ming-Tzo Wei, Shi-Xin Xu, H Daniel Ou-Yang and Ping Sheng
We measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field, and found it to be markedly different from that of the Stokes drag. The drag coefficient, along with the measured electrical force, yield a mobility-zeta potential relation that agrees with the literature. By using the measured mobility as input, numerical calculations based on the Poisson–Nernst–Planck equations, coupled to the Navier–Stokes equation, reveal an intriguing microscopic electroosmotic flow near the particle surface, with a well-defined transition between an inner flow field and an outer flow field in the vicinity of electric double layer's outer boundary. This distinctive interface delineates the surface that gives the correct drag coefficient and the effective electric charge. The consistency between experiments and theoretical predictions provides new insights into the classic electrophoresis problem, and can shed light on new applications of electrophoresis to investigate biological nanoparticles.
DOI
We measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field, and found it to be markedly different from that of the Stokes drag. The drag coefficient, along with the measured electrical force, yield a mobility-zeta potential relation that agrees with the literature. By using the measured mobility as input, numerical calculations based on the Poisson–Nernst–Planck equations, coupled to the Navier–Stokes equation, reveal an intriguing microscopic electroosmotic flow near the particle surface, with a well-defined transition between an inner flow field and an outer flow field in the vicinity of electric double layer's outer boundary. This distinctive interface delineates the surface that gives the correct drag coefficient and the effective electric charge. The consistency between experiments and theoretical predictions provides new insights into the classic electrophoresis problem, and can shed light on new applications of electrophoresis to investigate biological nanoparticles.
DOI
The applications of nanopores in studies of proteins
Taoli Ding, Antony K.Chen, Zuhong Lu
Nanopores are a label-free platform with the ability to detect subtle changes in the activities of individual biomolecules under physiological conditions. Here, we comprehensively review the technological development of nanopores, focusing on their applications in studying the physicochemical properties and dynamic conformations of peptides, individual proteins, protein-protein complexes and protein-DNA complexes. This is followed by a brief discussion of the potential challenges that need to be overcome before the technology can be widely accepted by the scientific community. We believe that with continued refinement of the technology, significant understanding can be gained to help clarify the role of protein activities in the regulation of cellular physiology and pathogenesis.
DOI
Nanopores are a label-free platform with the ability to detect subtle changes in the activities of individual biomolecules under physiological conditions. Here, we comprehensively review the technological development of nanopores, focusing on their applications in studying the physicochemical properties and dynamic conformations of peptides, individual proteins, protein-protein complexes and protein-DNA complexes. This is followed by a brief discussion of the potential challenges that need to be overcome before the technology can be widely accepted by the scientific community. We believe that with continued refinement of the technology, significant understanding can be gained to help clarify the role of protein activities in the regulation of cellular physiology and pathogenesis.
DOI
Lateral optical force on linearly polarized dipoles near a magneto-optical surface based on polarization conversion
J. A. Girón-Sedas, Jack J. Kingsley-Smith, and Francisco J. Rodríguez-Fortuño
Novel lateral optical forces acting on dipoles near surfaces have been investigated in the past few years: circularly polarized dipoles experience lateral optical forces when in proximity to a surface due to the recoil of directionally excited modes. Recent work shows that even linearly polarized dipoles may experience lateral forces when nonreciprocal substrates are used, due to the asymmetric propagation of modes in the surface. We theoretically show that a linearly polarized particle emitting in close proximity to a magneto-optical substrate may experience a lateral optical force even if the external magnetic field is normal to the surface plane. The polarization conversion of the magneto-optic material introduces a gradient in the quasistatic fields reflected from the surface, resulting in a lateral optical force, and also gives surface plasmons a hybrid polarization character, which alters the surface plasmon directional excitation from the dipole, resulting in an optical recoil force. We envisage potential applications in nanomechanical devices, since similar magnetoplasmonic architectures have already been developed experimentally.
DOI
Novel lateral optical forces acting on dipoles near surfaces have been investigated in the past few years: circularly polarized dipoles experience lateral optical forces when in proximity to a surface due to the recoil of directionally excited modes. Recent work shows that even linearly polarized dipoles may experience lateral forces when nonreciprocal substrates are used, due to the asymmetric propagation of modes in the surface. We theoretically show that a linearly polarized particle emitting in close proximity to a magneto-optical substrate may experience a lateral optical force even if the external magnetic field is normal to the surface plane. The polarization conversion of the magneto-optic material introduces a gradient in the quasistatic fields reflected from the surface, resulting in a lateral optical force, and also gives surface plasmons a hybrid polarization character, which alters the surface plasmon directional excitation from the dipole, resulting in an optical recoil force. We envisage potential applications in nanomechanical devices, since similar magnetoplasmonic architectures have already been developed experimentally.
DOI
Nanometric plasmonic optical trapping on gold nanostructures
Domna G. Kotsifaki, Mersini Makropoulou and Alexander A. Searfetinides
The precise noninvasive optical manipulation of nanometer-sized particles by evanescent fields, instead of the conventional optical tweezers, has recently awaken an increasing interest, opening a way for investigating phenomena relevant to both fundamental and applied science. In this work, the optical trapping force exerted on trapped dielectric nanoparticle was theoretically investigated as a function on the trapping beam wavelength and as a function of several plasmonic nanostructures schemes based on numerical simulation. The maximum optical trapping forces are obtained at the resonance wavelength for each plasmonic nanostructure geometry. Prominent tunabilities, such as radius and separation of gold nanoparticles as well as the numerical aperture of objective lens were examined. This work will provide theoretical support for developing new types of plasmonic sensing substrates for exciting biomedical applications such as single-molecule fluorescence.
DOI
The precise noninvasive optical manipulation of nanometer-sized particles by evanescent fields, instead of the conventional optical tweezers, has recently awaken an increasing interest, opening a way for investigating phenomena relevant to both fundamental and applied science. In this work, the optical trapping force exerted on trapped dielectric nanoparticle was theoretically investigated as a function on the trapping beam wavelength and as a function of several plasmonic nanostructures schemes based on numerical simulation. The maximum optical trapping forces are obtained at the resonance wavelength for each plasmonic nanostructure geometry. Prominent tunabilities, such as radius and separation of gold nanoparticles as well as the numerical aperture of objective lens were examined. This work will provide theoretical support for developing new types of plasmonic sensing substrates for exciting biomedical applications such as single-molecule fluorescence.
DOI
Thursday, August 15, 2019
Rheological properties of cryptococcal polysaccharide change with fiber size, antibody binding and temperature
Glauber R de S Araújo, Nathan B Viana, Bruno Pontes‡ & Susana Frases‡
Aim:Cryptococcus neoformans is the major agent of cryptococcosis. The main virulence factor is the polysaccharide (PS) capsule. Changes in cryptococcal PS properties have been poorly elucidated. Materials & methods: We analyzed the mechanical properties of secreted PS and intact capsules, using dynamic light scattering and optical tweezers. Results: Storage and loss moduli showed that secreted PS behaves as a viscoelastic liquid, while capsular PS behaves as a viscoelastic solid. The secreted PS remains as a viscoelastic fluid at different temperatures with thermal hysteresis after 85°C. Antibody binding altered the viscoelastic behavior of both secreted and capsular PS. Conclusion: Deciphering the mechanical aspects of these structures could reveal features that may have consequences in novel therapies against cryptococcosis.
DOI
Aim:Cryptococcus neoformans is the major agent of cryptococcosis. The main virulence factor is the polysaccharide (PS) capsule. Changes in cryptococcal PS properties have been poorly elucidated. Materials & methods: We analyzed the mechanical properties of secreted PS and intact capsules, using dynamic light scattering and optical tweezers. Results: Storage and loss moduli showed that secreted PS behaves as a viscoelastic liquid, while capsular PS behaves as a viscoelastic solid. The secreted PS remains as a viscoelastic fluid at different temperatures with thermal hysteresis after 85°C. Antibody binding altered the viscoelastic behavior of both secreted and capsular PS. Conclusion: Deciphering the mechanical aspects of these structures could reveal features that may have consequences in novel therapies against cryptococcosis.
DOI
Grafted optical vortex with controllable orbital angular momentum distribution
Hao Zhang, Xinzhong Li, Haixiang Ma, Miaomiao Tang, Hehe Li, Jie Tang, and Yangjian Cai
In an optical vortex (OV) field, the orbital angular momentum (OAM) distribution strongly depends on the intensity, which results in difficulty in OAM independent modulation. To overcome this limitation, we propose a grafted optical vortex (GOV) via spiral phase reconstruction of two or more OVs with different topological charges (TCs). To remain the annular shape of the GOV’s intensity, the Dirac δ-function is employed to restrict the energy in a ring. Theoretical analysis and manipulation experiments of polystyrene microspheres show that the magnitude and direction of the GOV’s local OAM are controllable by modulating the grafted TCs while the intensity remains constant. The results of this work provide an ingenious method to control the local tangential force on the light ring, which will promote potential applications in optical trapping and rotating micro-particles.
DOI
In an optical vortex (OV) field, the orbital angular momentum (OAM) distribution strongly depends on the intensity, which results in difficulty in OAM independent modulation. To overcome this limitation, we propose a grafted optical vortex (GOV) via spiral phase reconstruction of two or more OVs with different topological charges (TCs). To remain the annular shape of the GOV’s intensity, the Dirac δ-function is employed to restrict the energy in a ring. Theoretical analysis and manipulation experiments of polystyrene microspheres show that the magnitude and direction of the GOV’s local OAM are controllable by modulating the grafted TCs while the intensity remains constant. The results of this work provide an ingenious method to control the local tangential force on the light ring, which will promote potential applications in optical trapping and rotating micro-particles.
DOI
Digital Assembly of Colloidal Particles for Nanoscale Manufacturing
Abhay Kotnala, Yuebing Zheng
From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology, and medicine. However, the extent of its practical realization relies on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom‐up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top‐down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or “digitally” has been heavily sought as it mimics the natural method of making matter and enables construction of nanomaterials with sophisticated architectures. An insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies, is provided. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing.
DOI
From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology, and medicine. However, the extent of its practical realization relies on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom‐up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top‐down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or “digitally” has been heavily sought as it mimics the natural method of making matter and enables construction of nanomaterials with sophisticated architectures. An insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies, is provided. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing.
DOI
Periodic propagation properties and radiation forces of focusing off-axis hollow vortex Gaussian beams in a harmonic potential
Gengxin Chen, Jintao Xie, Dongsen Cai, Qiliang Sun, Dongmei Deng
Obtaining the analytical expression of focusing off-axis hollow vortex Gaussian (HVG) beams by solving the (2 + 1) dimensionless linear Schrödinger-like equation, we perform the propagation path, the intensity and phase distributions, the center of mass, the peak intensity and the beam width with different potential widths , different hollow orders , different topological charges , different off-axis coordinates (). In general, the off-axis HVG beams are swirled counterclockwise and periodically focus during the propagation. The topological charge separates the focusing center but the hollow order concentrates the focusing area. Moreover, the off-axis coordinate () significantly increases the focusing intensity and the potential width can also increase the focusing frequency during the propagation. Interestingly, the influences of the hollow order , the topological charge and off-axis coordinate () are the same on the peak intensity, which are different with the beam width. Furthermore, we also discuss the Poynting vector, angular momentum and radiation forces. In terms of the radiation forces, we can easily explore the position trapping particles stably regardless of the off-axis coordinate () selection.
DOI
Obtaining the analytical expression of focusing off-axis hollow vortex Gaussian (HVG) beams by solving the (2 + 1) dimensionless linear Schrödinger-like equation, we perform the propagation path, the intensity and phase distributions, the center of mass, the peak intensity and the beam width with different potential widths , different hollow orders , different topological charges , different off-axis coordinates (). In general, the off-axis HVG beams are swirled counterclockwise and periodically focus during the propagation. The topological charge separates the focusing center but the hollow order concentrates the focusing area. Moreover, the off-axis coordinate () significantly increases the focusing intensity and the potential width can also increase the focusing frequency during the propagation. Interestingly, the influences of the hollow order , the topological charge and off-axis coordinate () are the same on the peak intensity, which are different with the beam width. Furthermore, we also discuss the Poynting vector, angular momentum and radiation forces. In terms of the radiation forces, we can easily explore the position trapping particles stably regardless of the off-axis coordinate () selection.
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Multiple trapping using a focused hybrid vector beam
Li Zhang, Xiaodong Qiu, Lingwei Zeng and Lixiang Chen
This paper proposes a simple and efficient method that uses a single focused hybrid vector beam to confine metallic Rayleigh particles at multiple positions. We study the force mechanisms of multiple trapping by analyzing gradient and scattering forces. It is observed that the wavelength and topological charges of the hybrid vector beam regulates the trapping positions and number of optical trap sites. The proposed method can be implemented easily in three-dimensional spaces, and it facilitates both trapping and organization of particles. Thus, it can provide an effective and controllable means for nanoparticle manipulation.
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This paper proposes a simple and efficient method that uses a single focused hybrid vector beam to confine metallic Rayleigh particles at multiple positions. We study the force mechanisms of multiple trapping by analyzing gradient and scattering forces. It is observed that the wavelength and topological charges of the hybrid vector beam regulates the trapping positions and number of optical trap sites. The proposed method can be implemented easily in three-dimensional spaces, and it facilitates both trapping and organization of particles. Thus, it can provide an effective and controllable means for nanoparticle manipulation.
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Properties of a Tightly Focused Circularly Polarized Anomalous Vortex Beam and Its Optical Forces on Trapped Nanoparticles
Yihua Bai, Miao Dong, Mingyan Zhang, Yuanjie Yang
The characteristics of a circularly polarized anomalous vortex beam (CPAVB), focused by an objective lens with a high numerical aperture (NA), are studied analytically and theoretically. It shows that the topological charge can affect the beam profile significantly and a flat-topped (FT) beam can be obtained by modulating the NA and topological charge. It is interesting to find that spin-to-orbital angular momentum conversion can occur in the longitudinal component after tight focusing. Furthermore, optical forces of the tightly focused CPAVB on nanoparticles are analyzed in detail. It can be expected to trap two kinds of nanoparticles using such beam near the focus.
DOI
The characteristics of a circularly polarized anomalous vortex beam (CPAVB), focused by an objective lens with a high numerical aperture (NA), are studied analytically and theoretically. It shows that the topological charge can affect the beam profile significantly and a flat-topped (FT) beam can be obtained by modulating the NA and topological charge. It is interesting to find that spin-to-orbital angular momentum conversion can occur in the longitudinal component after tight focusing. Furthermore, optical forces of the tightly focused CPAVB on nanoparticles are analyzed in detail. It can be expected to trap two kinds of nanoparticles using such beam near the focus.
DOI
Investigation on the laser trapping mechanism of light-absorbing particles in air
Bo He, Xuemei Cheng, Yongjie Zhan, Qian Zhang, Haowei Chen, Zhaoyu Ren, Chen Niu, Jingjing Yao, Tengfei Jiao and Jintao Bai
We report on the micron-sized light-absorbing particle trapping in two configurations (horizontal and vertical), in order to elucidate the laser trapping mechanism based on the photophoretic force. Two types of carbon particles (irregular graphite particles and carbon microspheres) were tested in both Gaussian and hollow beam traps. By comparing the trapping efficiency and stability under various circumstances, we confirmed that there are two types of photophoretic forces: $F_{\Delta \alpha}$ and $F_{\Delta T}$ forces on the laser irradiating particle. Furthermore, the forces and moments exerting the particles in various traps were analyzed, which explained the experimental phenomena very well. It was found that the $F_{\Delta \alpha}$ force due to the thermal accommodation difference among the irregular particles helps the irregular particles to be balanced more easily and of higher trapping efficiency and stability. This work provides important references for people to choose a suitable trapping scheme according to the particles, which would be of significance in the applications of single-particle analysis.
DOI
We report on the micron-sized light-absorbing particle trapping in two configurations (horizontal and vertical), in order to elucidate the laser trapping mechanism based on the photophoretic force. Two types of carbon particles (irregular graphite particles and carbon microspheres) were tested in both Gaussian and hollow beam traps. By comparing the trapping efficiency and stability under various circumstances, we confirmed that there are two types of photophoretic forces: $F_{\Delta \alpha}$ and $F_{\Delta T}$ forces on the laser irradiating particle. Furthermore, the forces and moments exerting the particles in various traps were analyzed, which explained the experimental phenomena very well. It was found that the $F_{\Delta \alpha}$ force due to the thermal accommodation difference among the irregular particles helps the irregular particles to be balanced more easily and of higher trapping efficiency and stability. This work provides important references for people to choose a suitable trapping scheme according to the particles, which would be of significance in the applications of single-particle analysis.
DOI
Self-Assembly and Biogenesis of the Cellular Membrane are Dictated by Membrane Stretch and Composition
Akshata R. Naik, Eric R. Kuhn, Kenneth T. Lewis, Keith M. Kokotovich, Krishna R. Maddipati, Xuequn Chen, J. H. K. Hörber, Douglas J. Taatjes, Jeffrey J. Potoff, Bhanu P. Jena
The cell plasma membrane is a highly dynamic organelle governing a wide range of cellular activities including ion transport, secretion, cell division, growth, and development. The fundamental process involved in the addition of new membranes to pre-existing plasma membranes, however, is unclear. Here, we report, using biophysical, morphological, biochemical, and molecular dynamic simulations, the selective incorporation of proteins and lipids from the cytosol into the cell plasma membrane dictated by membrane stretch and composition. Stretching of the cell membrane as a consequence of volume increase following incubation in a hypotonic solution and results in the incorporation of cytosolic proteins and lipids into the existing plasma membrane. Molecular dynamic simulations further confirm that increased membrane stretch results in the rapid insertion of lipids into the existing plasma membrane. Similarly, depletion of cholesterol from the cell plasma membrane selectively alters the incorporation of lipids into the membrane.
DOI
The cell plasma membrane is a highly dynamic organelle governing a wide range of cellular activities including ion transport, secretion, cell division, growth, and development. The fundamental process involved in the addition of new membranes to pre-existing plasma membranes, however, is unclear. Here, we report, using biophysical, morphological, biochemical, and molecular dynamic simulations, the selective incorporation of proteins and lipids from the cytosol into the cell plasma membrane dictated by membrane stretch and composition. Stretching of the cell membrane as a consequence of volume increase following incubation in a hypotonic solution and results in the incorporation of cytosolic proteins and lipids into the existing plasma membrane. Molecular dynamic simulations further confirm that increased membrane stretch results in the rapid insertion of lipids into the existing plasma membrane. Similarly, depletion of cholesterol from the cell plasma membrane selectively alters the incorporation of lipids into the membrane.
DOI
Monday, August 12, 2019
Plasmonic optical tweezers based on nanostructures: fundamentals, advances and prospects
Domna G. Kotsifaki, Síle Nic Chormaic
The ability of metallic nanostructures to confine light at the sub-wavelength scale enables new perspectives and opportunities in the field of nanotechnology. Making use of this unique advantage, nano-optical trapping techniques have been developed to tackle new challenges in a wide range of areas from biology to quantum optics. In this work, starting from basic theories, we present a review of research progress in near-field optical manipulation techniques based on metallic nanostructures, with an emphasis on some of the most promising advances in molecular technology, such as the precise control of single biomolecules. We also provide an overview of possible future research directions of nanomanipulation techniques.
The ability of metallic nanostructures to confine light at the sub-wavelength scale enables new perspectives and opportunities in the field of nanotechnology. Making use of this unique advantage, nano-optical trapping techniques have been developed to tackle new challenges in a wide range of areas from biology to quantum optics. In this work, starting from basic theories, we present a review of research progress in near-field optical manipulation techniques based on metallic nanostructures, with an emphasis on some of the most promising advances in molecular technology, such as the precise control of single biomolecules. We also provide an overview of possible future research directions of nanomanipulation techniques.
Nanopore-based sensing interface for single molecule electrochemistry
Rui Gao, Yao Lin, Yi-Lun Ying, Yi-Tao Long
Nanopore techniques are experiencing a gallop since it walked out the notebook and show its charm on the science arena. The nanoscale pore offers a single-molecule resolution with a label-free and high-selective manner for the research of molecular structures, molecular dynamics, single-molecule reactions and for a variety of applications in biophysics and bionanotechnology. In this review, we introduce the construction of three types of nanopore platforms along with the latest progress in DNA sensing, structure and dynamics analysis of peptides/proteins, and the detection of redox reactions with new sensing mechanisms. Then, we depict nanopore data processing methods which provide an insight of data mining under the background of big data. We could fully expect the great impact of nanopore techniques on not only for DNA sequencing and sensing applications, but also in protein sequencing and clinical diagnostics.
DOI
Nanopore techniques are experiencing a gallop since it walked out the notebook and show its charm on the science arena. The nanoscale pore offers a single-molecule resolution with a label-free and high-selective manner for the research of molecular structures, molecular dynamics, single-molecule reactions and for a variety of applications in biophysics and bionanotechnology. In this review, we introduce the construction of three types of nanopore platforms along with the latest progress in DNA sensing, structure and dynamics analysis of peptides/proteins, and the detection of redox reactions with new sensing mechanisms. Then, we depict nanopore data processing methods which provide an insight of data mining under the background of big data. We could fully expect the great impact of nanopore techniques on not only for DNA sequencing and sensing applications, but also in protein sequencing and clinical diagnostics.
DOI
Optical fan for single‐cell screening
Xiaoshuai Liu, Yuchao Li, Xiaohao Xu, Yao Zhang, Baojun Li
The single‐cell screening has attracted great attentions in advanced biomedicine and tissue biology, especially for the early disease diagnosis and treatment monitoring. In this work, by using a specific‐designed fiber probe with a flat facet, we propose an “optical fan” strategy to screen K562 cells at the single‐cell level from a populations of RBCs. After the 980‐nm laser beam injected into the fiber probe, the RBCs were blown away but holding target K562 cells in place. Further, multiple leukemic cells can be screened from hundreds of red blood cells, providing an efficient approach for the cell screening. The experimental results were interpreted by the numerical simulation, and the stiffness of optical fan was also discussed.
DOI
The single‐cell screening has attracted great attentions in advanced biomedicine and tissue biology, especially for the early disease diagnosis and treatment monitoring. In this work, by using a specific‐designed fiber probe with a flat facet, we propose an “optical fan” strategy to screen K562 cells at the single‐cell level from a populations of RBCs. After the 980‐nm laser beam injected into the fiber probe, the RBCs were blown away but holding target K562 cells in place. Further, multiple leukemic cells can be screened from hundreds of red blood cells, providing an efficient approach for the cell screening. The experimental results were interpreted by the numerical simulation, and the stiffness of optical fan was also discussed.
DOI
Cell patterning via optimized dielectrophoretic force within hexagonal electrodes in vitro for skin tissue engineering
Zhijie Huan, Weicheng Ma, Min Xu, Zhixiong Zhong, Xiangpeng Li, Zhenhong Zhu
Tissue reconstruction through in vitro cell seeding is a popular method for tissue engineering. In this paper, we proposed a thin-layer structure consisting of multiple hexagons for the regeneration of skin tissue. Cells could be seeded and cultured within the structure via dielectrophoresis (DEP) actively. A thin layer of the structure was fabricated with biocompatible medical-grade stainless steel via precise laser cutting. The fabricated layers were stacked together to form a 3D electrode pair, which could be used to generate a 3D electric field. Thus, the suspended cells within the structure could be patterned via DEP manipulation. The input voltage was examined and optimized to ensure cell viability and patterning efficiency during the DEP manipulation process. As soon as we applied the optimized voltage, human foreskin fibroblast (HFF) cells could be attracted along the edge of the electrodes, forming hexagonal cellular patterns. After that, a single layer of the patterned cells was further cultured in an incubator for 7 days and observed under a microscope. The obtained images showed that the seeded cells could proliferate and fill in the hexagonal wells, which could be used for further skin tissue regeneration. As shown in the experimental results, this structure could be used for active cell seeding and proliferation for the development of skin tissue engineering.
DOI
Tissue reconstruction through in vitro cell seeding is a popular method for tissue engineering. In this paper, we proposed a thin-layer structure consisting of multiple hexagons for the regeneration of skin tissue. Cells could be seeded and cultured within the structure via dielectrophoresis (DEP) actively. A thin layer of the structure was fabricated with biocompatible medical-grade stainless steel via precise laser cutting. The fabricated layers were stacked together to form a 3D electrode pair, which could be used to generate a 3D electric field. Thus, the suspended cells within the structure could be patterned via DEP manipulation. The input voltage was examined and optimized to ensure cell viability and patterning efficiency during the DEP manipulation process. As soon as we applied the optimized voltage, human foreskin fibroblast (HFF) cells could be attracted along the edge of the electrodes, forming hexagonal cellular patterns. After that, a single layer of the patterned cells was further cultured in an incubator for 7 days and observed under a microscope. The obtained images showed that the seeded cells could proliferate and fill in the hexagonal wells, which could be used for further skin tissue regeneration. As shown in the experimental results, this structure could be used for active cell seeding and proliferation for the development of skin tissue engineering.
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Solar “Meta-Sails” for Agile Optical Force Control
Karim Achouri ; Oscar V. Cespedes ; Christophe Caloz
We propose to use metasurfaces as a means of controlling optical forces for increasing the range of motions in spacecraft solar sails. Specifically, we present a theoretical study of metasurface structures that allow one to achieve attractive, lateral and rotational forces, in addition to the conventional repulsive force. Such solar “meta-sails” may facilitate future travels in the solar system and toward exoplanets.
DOI
We propose to use metasurfaces as a means of controlling optical forces for increasing the range of motions in spacecraft solar sails. Specifically, we present a theoretical study of metasurface structures that allow one to achieve attractive, lateral and rotational forces, in addition to the conventional repulsive force. Such solar “meta-sails” may facilitate future travels in the solar system and toward exoplanets.
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Single-shot phase-sensitive wideband active microrheology of viscoelastic fluids using pulse-scanned optical tweezers
Shuvojit Paul, Avijit Kundu and Ayan Banerjee
We present a fast phase sensitive active microrheology technique exploring the phase response of a microscopic probe particle trapped in a linear viscoelastic fluid using optical tweezers under an external perturbation. Thus, we experimentally
 determine the cumulative response of the probe to an entire repertoire of sinusoidal excitations simultaneously by applying a spatial square pulse as an excitation to the trapped probe. The square pulse naturally contains the fundamental sinusoidal frequency component and higher odd harmonics, so that we measure the phase response of the probe over a wide frequency band in a single shot, with the band being tunable over the spectrum by choosing suitable experimental parameters. We then determine the responses to individual harmonics using a lock-in algorithm, and compare the phase shifts to those obtained theoretically by solving the equation of motion of the probe particle conned in a harmonic potential in the fluid in the presence of a sinusoidal perturbation. We go on to relate the phase response of the probe to the complex shear modulus G"(ω), and proceed to verify our technique in a mixture of polyacrylamide and water, which we compare with known values in literature and obtain very good agreement. Our method increases the robustness of active microrheology in general and ensures that any drifts in time are almost entirely ruled out from the data, with
 the added advantage of high speed and ease of use.
DOI
We present a fast phase sensitive active microrheology technique exploring the phase response of a microscopic probe particle trapped in a linear viscoelastic fluid using optical tweezers under an external perturbation. Thus, we experimentally
 determine the cumulative response of the probe to an entire repertoire of sinusoidal excitations simultaneously by applying a spatial square pulse as an excitation to the trapped probe. The square pulse naturally contains the fundamental sinusoidal frequency component and higher odd harmonics, so that we measure the phase response of the probe over a wide frequency band in a single shot, with the band being tunable over the spectrum by choosing suitable experimental parameters. We then determine the responses to individual harmonics using a lock-in algorithm, and compare the phase shifts to those obtained theoretically by solving the equation of motion of the probe particle conned in a harmonic potential in the fluid in the presence of a sinusoidal perturbation. We go on to relate the phase response of the probe to the complex shear modulus G"(ω), and proceed to verify our technique in a mixture of polyacrylamide and water, which we compare with known values in literature and obtain very good agreement. Our method increases the robustness of active microrheology in general and ensures that any drifts in time are almost entirely ruled out from the data, with
 the added advantage of high speed and ease of use.
DOI
Polarization-dependent center-of-mass motion of an optically levitated nanosphere
Yuanbin Jin, Xudong Yu, and Jing Zhang
In this study, we report the influence on the center-of-mass translational motion of a levitated nanosphere in the case of the combination of an elliptical polarization with an elliptical [Math Processing Error]-mode Gaussian beam. A fundamental-mode Gaussian laser with a slightly elliptical profile is focused using a high numerical aperture objective lens for trapping a nanosphere. The field distribution of the strongly focused laser in the focus region depends on its polarization according to vector diffraction theory. Therefore, the motion of the nanosphere depends on the relative orientation and ellipticity of the two ellipses’ parameters. For a linearly polarized light field, the eigenfrequencies and corresponding power spectra of the radial motions change periodically with the rotation of the linear polarization direction relative to the orientation of the elliptical [Math Processing Error]-mode Gaussian beam. We further demonstrate that these effects could be enhanced or canceled by controlling the relative orientation and ellipticity of the two ellipses’ parameters. This work provides a more flexible method for manipulating an optically levitated nanosphere. Furthermore, the above-mentioned effects can be used to evaluate a tightly focused laser using the motion of the nanosphere.
DOI
In this study, we report the influence on the center-of-mass translational motion of a levitated nanosphere in the case of the combination of an elliptical polarization with an elliptical [Math Processing Error]-mode Gaussian beam. A fundamental-mode Gaussian laser with a slightly elliptical profile is focused using a high numerical aperture objective lens for trapping a nanosphere. The field distribution of the strongly focused laser in the focus region depends on its polarization according to vector diffraction theory. Therefore, the motion of the nanosphere depends on the relative orientation and ellipticity of the two ellipses’ parameters. For a linearly polarized light field, the eigenfrequencies and corresponding power spectra of the radial motions change periodically with the rotation of the linear polarization direction relative to the orientation of the elliptical [Math Processing Error]-mode Gaussian beam. We further demonstrate that these effects could be enhanced or canceled by controlling the relative orientation and ellipticity of the two ellipses’ parameters. This work provides a more flexible method for manipulating an optically levitated nanosphere. Furthermore, the above-mentioned effects can be used to evaluate a tightly focused laser using the motion of the nanosphere.
DOI
Dual-laser-actuated operation of small size objects at a liquid interface
Xinbin Zhang, Yahui Kong, Jihong Yan, and Jie Zhao
This work focuses on the use, for the first time to our knowledge, of dual laser beams in photothermal-effect-based propulsion of small size objects at liquid interfaces. Compared with the single-laser mode, dual-laser-actuated operation turns out to be much more controllable with high quality, efficiency, and anti-interference capacity, which can be achieved through automated programming instead of through manual operation. A series of experiments were carried out to verify the principle, with the effects of laser power, laser-spot distance, and movement speed discussed in detail. The findings of this work might provide some insights into the development of intelligent macro/micro-operation systems for manipulating objects at different scales, such as drug particles and cells at liquid interfaces in the future.
DOI
This work focuses on the use, for the first time to our knowledge, of dual laser beams in photothermal-effect-based propulsion of small size objects at liquid interfaces. Compared with the single-laser mode, dual-laser-actuated operation turns out to be much more controllable with high quality, efficiency, and anti-interference capacity, which can be achieved through automated programming instead of through manual operation. A series of experiments were carried out to verify the principle, with the effects of laser power, laser-spot distance, and movement speed discussed in detail. The findings of this work might provide some insights into the development of intelligent macro/micro-operation systems for manipulating objects at different scales, such as drug particles and cells at liquid interfaces in the future.
DOI
Friday, August 9, 2019
Hollow-Bottle microstructure beam shape transformation based on the confocal optical system
Zhikun Yang, Xiaohui Ma, Xinglei Lin, Yingtian Xu, Liang Jin, Yonggang Zou, He Zhang
In this study, a confocal optical system formed by a combination of two axicon lenses, a parabolic annular mirror and a concave mirror was used to obtain an adjustable microstructured beam. The two axicons were used to create a collimated hollow annular beam whose diameter varies with the distance between the two components, and the duty cycle of the hollow beam changes accordingly. At the same time, the annular factor also changes correspondingly after the hollow beam was concentrated. According to the scalar diffraction integral theory, the change of focusing characteristics of different annular factor after a parabolic annular mirror was studied. The concentrated beam was reflected by a concave mirror to form a confocal optical system. According to the numerical simulation, the size of the focused spot varies from 2.8 to in the range of the annular factor from 1.19 to 1.09. Detailed characteristics of the microstructure beam shape changes were analyzed. These results have important implications for particle manipulation and other applications.
DOI
In this study, a confocal optical system formed by a combination of two axicon lenses, a parabolic annular mirror and a concave mirror was used to obtain an adjustable microstructured beam. The two axicons were used to create a collimated hollow annular beam whose diameter varies with the distance between the two components, and the duty cycle of the hollow beam changes accordingly. At the same time, the annular factor also changes correspondingly after the hollow beam was concentrated. According to the scalar diffraction integral theory, the change of focusing characteristics of different annular factor after a parabolic annular mirror was studied. The concentrated beam was reflected by a concave mirror to form a confocal optical system. According to the numerical simulation, the size of the focused spot varies from 2.8 to in the range of the annular factor from 1.19 to 1.09. Detailed characteristics of the microstructure beam shape changes were analyzed. These results have important implications for particle manipulation and other applications.
DOI
Optical assessment of alterations of microrheologic and microcirculation parameters in cardiovascular diseases
Andrei E. Lugovtsov, Yury I. Gurfinkel, Petr B. Ermolinskiy, Anastasiya I. Maslyanitsina, Larisa I. Dyachuk, and Alexander V. Priezzhev
In this work, we compare the blood aggregation parameters measured in vitro by laser aggregometry and optical trapping techniques in blood samples with the parameters of blood rheology measured in vivo by digital capillaroscopy in the nail bed capillaries of patients suffering from the hypertension and coronary heart disease. We show that the alterations of the parameters measured in vivo and in vitro for patients with different stages of these diseases are interrelated. Good agreement between the results obtained with different techniques, and their applicability for the diagnostics of abnormalities of rheological properties of blood are demonstrated.
DOI
In this work, we compare the blood aggregation parameters measured in vitro by laser aggregometry and optical trapping techniques in blood samples with the parameters of blood rheology measured in vivo by digital capillaroscopy in the nail bed capillaries of patients suffering from the hypertension and coronary heart disease. We show that the alterations of the parameters measured in vivo and in vitro for patients with different stages of these diseases are interrelated. Good agreement between the results obtained with different techniques, and their applicability for the diagnostics of abnormalities of rheological properties of blood are demonstrated.
DOI
Enhancement of trapping efficiency by utilizing a hollow sinh-Gaussian beam
Zhirong Liu, Xun Wang & Kelin Hang
Propagation properties and optical forces upon a Rayleigh dielectric sphere for a newly proposed hollow sinh-Gaussian beam (HsGB) are intensively investigated. In view of the targeted laser beam’s unique tight focusing properties that a significantly sharp, peak-centered, and adjustable intensity distribution would be produced in the focal vicinity, the tightly focused HsGB could be exploited to trap and manipulate nano-sized dielectric spheres with high-refractive index in the focal region. The interesting and meaningful features for the novel HsGB mainly include that, compared with the conventional fundamental Gaussian beams under the same optical power, the tightly focused HsGB has much higher intensity gradient and deeper potential well through optimizing targeted laser beam’s parameters. Theretofore, the novel HsGB optical tweezers could drastically enhance its trapping efficiency. Finally, the trapping stability conditions are discussed in detail. The analytical and numerical results obtained here could provide a directive suggestion for researchers in optimizing experimental parameters in constructing a novel HsGB tweezers and making use of a HsGB.
DOI
Propagation properties and optical forces upon a Rayleigh dielectric sphere for a newly proposed hollow sinh-Gaussian beam (HsGB) are intensively investigated. In view of the targeted laser beam’s unique tight focusing properties that a significantly sharp, peak-centered, and adjustable intensity distribution would be produced in the focal vicinity, the tightly focused HsGB could be exploited to trap and manipulate nano-sized dielectric spheres with high-refractive index in the focal region. The interesting and meaningful features for the novel HsGB mainly include that, compared with the conventional fundamental Gaussian beams under the same optical power, the tightly focused HsGB has much higher intensity gradient and deeper potential well through optimizing targeted laser beam’s parameters. Theretofore, the novel HsGB optical tweezers could drastically enhance its trapping efficiency. Finally, the trapping stability conditions are discussed in detail. The analytical and numerical results obtained here could provide a directive suggestion for researchers in optimizing experimental parameters in constructing a novel HsGB tweezers and making use of a HsGB.
DOI
Titration of Aerosol pH through Droplet Coalescence
Ellen M. Coddens, Kyle J. Angle, Vicki H. Grassian
The pH of aqueous aerosols, as well as cloud and fog droplets, has an important influence on the chemistry that takes place within these unique microenvironments. Utilizing conjugate acid/base pairs to infer pH changes, we investigate, for the first time, changes in aerosol pH upon coalescence. In particular, we show that the pH within individual aqueous aerosols that are ∼8 μm in diameter can be titrated via droplet coalescence in an aerosol optical tweezer. Using sulfate/bisulfate and carbonate/bicarbonate as model systems, the pH of trapped aerosols is determined before and after introduction of smaller aerosols containing a strong acid. The pH change upon coalescence with the smaller, acidic aerosol is calculated using specific ion interaction theory. Furthermore, we show that the pH of an individual aerosol can be altered along a fairly wide range of pH values, paving the way for future studies requiring rigorous pH control of an aqueous aerosol.
DOI
The pH of aqueous aerosols, as well as cloud and fog droplets, has an important influence on the chemistry that takes place within these unique microenvironments. Utilizing conjugate acid/base pairs to infer pH changes, we investigate, for the first time, changes in aerosol pH upon coalescence. In particular, we show that the pH within individual aqueous aerosols that are ∼8 μm in diameter can be titrated via droplet coalescence in an aerosol optical tweezer. Using sulfate/bisulfate and carbonate/bicarbonate as model systems, the pH of trapped aerosols is determined before and after introduction of smaller aerosols containing a strong acid. The pH change upon coalescence with the smaller, acidic aerosol is calculated using specific ion interaction theory. Furthermore, we show that the pH of an individual aerosol can be altered along a fairly wide range of pH values, paving the way for future studies requiring rigorous pH control of an aqueous aerosol.
DOI
Automated Indirect Transportation of Biological Cells with Optical Tweezers and a 3D Printed Microtool
Songyu Hu, Heng Xie, Tanyong Wei, Shuxun Chen and Dong Sun
Optical tweezers are widely used for noninvasive and precise micromanipulation of living cells to understand biological processes. By focusing laser beams on cells, direct cell manipulation with optical tweezers can achieve high precision and flexibility. However, direct exposure to the laser beam can lead to negative effects on the cells. These phenomena are also known as photobleaching and photodamage. In this study, we proposed a new indirect cell micromanipulation approach combined with a robot-aided holographic optical tweezer system and 3D nano-printed microtool. The microtool was designed with a V-shaped head and an optical handle part. The V-shaped head can push and trap different sizes of cells as the microtool moves forward by optical trapping of the handle part. In this way, cell exposure to the laser beam can be effectively reduced. The microtool was fabricated with a laser direct writing system by two-photon photopolymerization. A control strategy combined with an imaging processing algorithm was introduced for automated manipulation of the microtool and cells. Experiments were performed to verify the effectiveness of our approach. First, automated microtool transportation and rotation were demonstrated with high precision. Second, indirect optical transportations of cells, with and without an obstacle, were performed to demonstrate the effectiveness of the proposed approach. Third, experiments of fluorescent cell manipulation were performed to confirm that, indicated by the photobleaching effect, indirect manipulation with the microtool could induce less laser exposure compared with direct optical manipulation. The proposed method could be useful in complex biomedical applications where precise cell manipulation and less laser exposure are required.
DOI
Optical tweezers are widely used for noninvasive and precise micromanipulation of living cells to understand biological processes. By focusing laser beams on cells, direct cell manipulation with optical tweezers can achieve high precision and flexibility. However, direct exposure to the laser beam can lead to negative effects on the cells. These phenomena are also known as photobleaching and photodamage. In this study, we proposed a new indirect cell micromanipulation approach combined with a robot-aided holographic optical tweezer system and 3D nano-printed microtool. The microtool was designed with a V-shaped head and an optical handle part. The V-shaped head can push and trap different sizes of cells as the microtool moves forward by optical trapping of the handle part. In this way, cell exposure to the laser beam can be effectively reduced. The microtool was fabricated with a laser direct writing system by two-photon photopolymerization. A control strategy combined with an imaging processing algorithm was introduced for automated manipulation of the microtool and cells. Experiments were performed to verify the effectiveness of our approach. First, automated microtool transportation and rotation were demonstrated with high precision. Second, indirect optical transportations of cells, with and without an obstacle, were performed to demonstrate the effectiveness of the proposed approach. Third, experiments of fluorescent cell manipulation were performed to confirm that, indicated by the photobleaching effect, indirect manipulation with the microtool could induce less laser exposure compared with direct optical manipulation. The proposed method could be useful in complex biomedical applications where precise cell manipulation and less laser exposure are required.
DOI
Femtosecond laser is effective tool for zona pellucida engraving and tagging of preimplantation mammalian embryos
Inna V. Ilina, Yulia V. Khramova, Maxim A. Filatov, Dmitry S. Sitnikov
Our purpose was to study whether application of femtosecond laser pulses for alphanumeric code marking in the volume of zona pellucida (ZP) could be effective and reliable approach for direct tagging of preimplantation embryos. Femtosecond laser pulses (wavelength of 514 nm, pulse duration of 280 fs, repetition rate of 2.5 kHz, pulse energy of 20 nJ) were applied for precise alphanumeric code engraving on the ZP of mouse embryos at the zygote stage for individual embryo marking and their accurate identification. Embryo quality assessment every 24 h post laser-assisted marking as well as immunofluorescence staining (for ICM/TE cell number ratio calculation) were performed. Initial experiments have started with embryo marking in a single equatorial plane. The codes engraved could be clearly recognized until the thinning of the ZP prior to hatching. Since embryo may change its orientation during the ART cycle, multi-plane code engraving seems to be more practical for simplifying the process of code searching and embryo identification. We have marked the ZP in three planes, and no decrease in developmental rates as well as no morphological changes of embryos post laser-assisted engraving have been observed as compared to control group embryos. Our results demonstrate the suitability of femtosecond laser as a novel tool for noninvasive embryo tagging, enabling embryo identification from day 0.5 post coitum to at least early blastocyst stage. Thus, the versatility and the potential use of femtosecond lasers in the field of developmental biology and assisted reproduction have been shown.
DOI
Our purpose was to study whether application of femtosecond laser pulses for alphanumeric code marking in the volume of zona pellucida (ZP) could be effective and reliable approach for direct tagging of preimplantation embryos. Femtosecond laser pulses (wavelength of 514 nm, pulse duration of 280 fs, repetition rate of 2.5 kHz, pulse energy of 20 nJ) were applied for precise alphanumeric code engraving on the ZP of mouse embryos at the zygote stage for individual embryo marking and their accurate identification. Embryo quality assessment every 24 h post laser-assisted marking as well as immunofluorescence staining (for ICM/TE cell number ratio calculation) were performed. Initial experiments have started with embryo marking in a single equatorial plane. The codes engraved could be clearly recognized until the thinning of the ZP prior to hatching. Since embryo may change its orientation during the ART cycle, multi-plane code engraving seems to be more practical for simplifying the process of code searching and embryo identification. We have marked the ZP in three planes, and no decrease in developmental rates as well as no morphological changes of embryos post laser-assisted engraving have been observed as compared to control group embryos. Our results demonstrate the suitability of femtosecond laser as a novel tool for noninvasive embryo tagging, enabling embryo identification from day 0.5 post coitum to at least early blastocyst stage. Thus, the versatility and the potential use of femtosecond lasers in the field of developmental biology and assisted reproduction have been shown.
DOI
Ultrafast Welding Dynamics of Plasmonic Nanorod Dimers
Paul Johns, Ryan J. Suess, Nicholas Charipar, Jake Fontana
Transient absorption (TA) experiments were performed to determine the mechanisms controlling the welding process of plasmonic nanorod dimers using ultrafast light pulses. The TA signals during the self-assembly and welding of the nanorod dimers were temporally and spectrally resolved, enabling each potential mechanism to be isolated by their associated time scales. For all the TA measurements collected between 5 and 1000 ps, no abrupt or anomalous TA signals were observed that would indicate a welding event had occurred during this temporal regime. A cumulative multipulse welding mechanism beyond 1000 ps is unlikely since the nanorods return to their ground state before the next laser pulse arrives. To understand the dynamics below 5 ps, we fit the welding kinetics data to a rate equation and determined a threshold fluence of 79 μJ/cm2 was needed to initiate welding. To correlate the threshold fluence to a physical mechanism, finite element calculations were used to show the nanorods reached temperatures of 635 K, sufficient to cause surface melting when irradiated with a 75 μJ/cm2 pulse. We then demonstrate the optical forces in the nanojunction are attractive and sufficiently large to displace the molecules linking the unwelded dimer structures. Accordingly, these experiments suggest the welding mechanism is governed by a threshold fluence from a single laser pulse, resulting in the surface of the individual nanorods melting, which are then pulled together by attractive optical forces forming a welded dimer structure. Globally, these results set an upper bound on the rate these materials can be produced.
DOI
Transient absorption (TA) experiments were performed to determine the mechanisms controlling the welding process of plasmonic nanorod dimers using ultrafast light pulses. The TA signals during the self-assembly and welding of the nanorod dimers were temporally and spectrally resolved, enabling each potential mechanism to be isolated by their associated time scales. For all the TA measurements collected between 5 and 1000 ps, no abrupt or anomalous TA signals were observed that would indicate a welding event had occurred during this temporal regime. A cumulative multipulse welding mechanism beyond 1000 ps is unlikely since the nanorods return to their ground state before the next laser pulse arrives. To understand the dynamics below 5 ps, we fit the welding kinetics data to a rate equation and determined a threshold fluence of 79 μJ/cm2 was needed to initiate welding. To correlate the threshold fluence to a physical mechanism, finite element calculations were used to show the nanorods reached temperatures of 635 K, sufficient to cause surface melting when irradiated with a 75 μJ/cm2 pulse. We then demonstrate the optical forces in the nanojunction are attractive and sufficiently large to displace the molecules linking the unwelded dimer structures. Accordingly, these experiments suggest the welding mechanism is governed by a threshold fluence from a single laser pulse, resulting in the surface of the individual nanorods melting, which are then pulled together by attractive optical forces forming a welded dimer structure. Globally, these results set an upper bound on the rate these materials can be produced.
DOI
Interface-Dependent Radiative Lifetimes of Yb3+, Er3+ Co-doped Single NaYF4 Upconversion Nanowires
Xuezhe Zhou, Xiaojing Xia, Bennett E. Smith, Matthew B. Lim, Alexander B. Bard, Anupum Pant, Peter J. Pauzauskie
The development of upconversion nanomaterials for many photonic applications requires a detailed understanding of their radiative lifetimes that in turn depend critically on local environmental conditions. In this work, hexagonal (β-phase) sodium-yttrium-fluoride (NaYF4) nanowires (NWs) were synthesized and substitutionally co-doped with a luminescent solid solution of trivalent erbium and ytterbium ions. A single-beam laser trapping instrument was used in tandem with a piezo-controlled, variable-temperature stage to precisely vary the nanowire’s distance from the substrate. The spontaneous photoluminescence lifetime of the 4S3/2 → 4I15/2 transition from Er3+ ions was observed to change by >60% depending on the ions’ separation distance from a planar (water/glass) dielectric interface. The 4S3/2 state lifetime is observed to increase by a factor of 1.62 ± 0.01 as the distance from the quartz coverslip increases from ∼0 nm to ∼40 μm. Less significant changes in the luminescence lifetime (≤10%) were observed over a temperature range between 25 and 50 °C. The distance dependence of the lifetime is interpreted quantitatively in the context of classical electromagnetic coupling between Er3+ ions within the nanowire and the adjacent dielectric interface. We also demonstrate potential applications of the NaYF4 NWs for both controlling and probing temperatures at nanometer scales by integrating them within a poly(dimethylsiloxane) composite matrix.
DOI
The development of upconversion nanomaterials for many photonic applications requires a detailed understanding of their radiative lifetimes that in turn depend critically on local environmental conditions. In this work, hexagonal (β-phase) sodium-yttrium-fluoride (NaYF4) nanowires (NWs) were synthesized and substitutionally co-doped with a luminescent solid solution of trivalent erbium and ytterbium ions. A single-beam laser trapping instrument was used in tandem with a piezo-controlled, variable-temperature stage to precisely vary the nanowire’s distance from the substrate. The spontaneous photoluminescence lifetime of the 4S3/2 → 4I15/2 transition from Er3+ ions was observed to change by >60% depending on the ions’ separation distance from a planar (water/glass) dielectric interface. The 4S3/2 state lifetime is observed to increase by a factor of 1.62 ± 0.01 as the distance from the quartz coverslip increases from ∼0 nm to ∼40 μm. Less significant changes in the luminescence lifetime (≤10%) were observed over a temperature range between 25 and 50 °C. The distance dependence of the lifetime is interpreted quantitatively in the context of classical electromagnetic coupling between Er3+ ions within the nanowire and the adjacent dielectric interface. We also demonstrate potential applications of the NaYF4 NWs for both controlling and probing temperatures at nanometer scales by integrating them within a poly(dimethylsiloxane) composite matrix.
DOI
Wednesday, August 7, 2019
Tunable optofluidic sorting and manipulation on micro-ring resonators from a statistics perspective
Wenhao Xu, Yuye Wang, Wenxiang Jiao, Feng Wang, Xiaofu Xu, Min Jiang, Ho-Pui Ho, and Guanghui Wang
Based on the optical trapping force of an evanescent wave at a micro-ring resonator alongside a waveguide, we propose a tunable optofluidic sorting unit for micro-nanoparticles by localized thermal phase tuning. With the tuning of field build-up factor of resonator, the depth of trapping potential well and the size of trapped particle are adjustable. Furthermore, by considering the Brownian motion of trapped particles from a statistics perspective, we verify the critical trapping threshold of a potential well, which is usually assumed to be 1𝑘𝐵𝑇. The threshold depends not only on the optical power and particle size, but also on the length of the coupling region. Compared with a wavelength tuning mechanism, localized thermal tuning enables large-scale integration of many independent tunable resonators. As a demonstration, we propose a set of operations with three resonators for nanoparticle manipulation, including sorting, storing, and mixing. Our proposed function units are of great importance for on-chip large-scale integration of optofluidic systems.
DOI
Based on the optical trapping force of an evanescent wave at a micro-ring resonator alongside a waveguide, we propose a tunable optofluidic sorting unit for micro-nanoparticles by localized thermal phase tuning. With the tuning of field build-up factor of resonator, the depth of trapping potential well and the size of trapped particle are adjustable. Furthermore, by considering the Brownian motion of trapped particles from a statistics perspective, we verify the critical trapping threshold of a potential well, which is usually assumed to be 1𝑘𝐵𝑇. The threshold depends not only on the optical power and particle size, but also on the length of the coupling region. Compared with a wavelength tuning mechanism, localized thermal tuning enables large-scale integration of many independent tunable resonators. As a demonstration, we propose a set of operations with three resonators for nanoparticle manipulation, including sorting, storing, and mixing. Our proposed function units are of great importance for on-chip large-scale integration of optofluidic systems.
DOI
Delayed feedback control of active particles: a controlled journey towards the destination
S. M. J. Khadem and Sabine H. L. Klappa
We explore theoretically the navigation of an active particle based on delayed feedback control. The delayed feedback enters in our expression for the particle orientation which, for an active particle, determines (up to noise) the direction of motion in the next time step. Here we estimate the orientation by comparing the delayed position of the particle with the actual one. This method does not require any real-time monitoring of the particle orientation and may thus be relevant also for controlling sub-micron sized particles, where the imaging process is not easily feasible. We apply the delayed feedback strategy to two experimentally relevant situations, namely, optical trapping and photon nudging. To investigate the performance of our strategy, we calculate the mean arrival time analytically (exploiting a small-delay approximation) and by simulations.
DOI
We explore theoretically the navigation of an active particle based on delayed feedback control. The delayed feedback enters in our expression for the particle orientation which, for an active particle, determines (up to noise) the direction of motion in the next time step. Here we estimate the orientation by comparing the delayed position of the particle with the actual one. This method does not require any real-time monitoring of the particle orientation and may thus be relevant also for controlling sub-micron sized particles, where the imaging process is not easily feasible. We apply the delayed feedback strategy to two experimentally relevant situations, namely, optical trapping and photon nudging. To investigate the performance of our strategy, we calculate the mean arrival time analytically (exploiting a small-delay approximation) and by simulations.
DOI
Fabrication of Monodisperse Colloids of Resonant Spherical Silicon Nanoparticles: Applications in Optical Trapping and Printing
Vytautas Valuckas, Ramón Paniagua-Domínguez, Aili Maimaiti, Partha Pratim Patra, Seng Kai Wong, Ruggero Verre, Mikael Käll, Arseniy I. Kuznetsov
We present a new method for making monodisperse highly spherical polycrystalline silicon (Si) nanoparticles dispersed in solution and a method for trapping, moving, and printing these nanoparticles on a substrate. Spherical Si nanoparticles with low dispersion in size (<3.5%) and diameter of 130 and 210 nm were fabricated using combined hole-mask colloidal lithography and laser-induced transfer. The particles are highly crystalline and possess electric and magnetic dipole resonances in the visible spectrum varying with the diameter. They could be trapped in 2D against a substrate using an optical tweezer and then printed onto the substrate by means of radiation pressure. The proposed method paves the way for the use of optical forces for assembling complex resonant dielectric nanostructures with engineered optical properties.
DOI
We present a new method for making monodisperse highly spherical polycrystalline silicon (Si) nanoparticles dispersed in solution and a method for trapping, moving, and printing these nanoparticles on a substrate. Spherical Si nanoparticles with low dispersion in size (<3.5%) and diameter of 130 and 210 nm were fabricated using combined hole-mask colloidal lithography and laser-induced transfer. The particles are highly crystalline and possess electric and magnetic dipole resonances in the visible spectrum varying with the diameter. They could be trapped in 2D against a substrate using an optical tweezer and then printed onto the substrate by means of radiation pressure. The proposed method paves the way for the use of optical forces for assembling complex resonant dielectric nanostructures with engineered optical properties.
DOI
Optical Tweezers Microrheology Maps the Dynamics of Strain-Induced Local Inhomogeneities in Entangled Polymers
Manas Khan, Kathryn Regan, and Rae M. Robertson-Anderson
Optical tweezers microrheology (OTM) offers a powerful approach to probe the nonlinear response of complex soft matter systems, such as networks of entangled polymers, over wide-ranging spatiotemporal scales. OTM can also uniquely characterize the microstructural dynamics that lead to the intriguing nonlinear rheological properties that these systems exhibit. However, the strain in OTM measurements, applied by optically forcing a microprobe through the material, induces network inhomogeneities in and around the strain path, and the resultant flow field complicates the measured response of the system. Through a robust set of custom-designed OTM protocols, coupled with modeling and analytical calculations, we characterize the time-varying inhomogeneity fields induced by OTM measurements. We show that homogenization following strain does not interfere with the intrinsic stress relaxation dynamics of the system, rather it manifests as an independent component in the stress decay, even in highly nonlinear regimes such as with the microrheological large-amplitude-oscillatory-shear (MLAOS) protocols we introduce. Our specific results show that Rouse-like elastic retraction, rather than disentanglement and disengagement, dominates the nonlinear stress relaxation of entangled polymers at micro- and mesoscales. Thus, our study opens up possibilities of performing precision nonlinear microrheological measurements, such as MLAOS, on a wide range of complex macromolecular systems.
DOI
Optical tweezers microrheology (OTM) offers a powerful approach to probe the nonlinear response of complex soft matter systems, such as networks of entangled polymers, over wide-ranging spatiotemporal scales. OTM can also uniquely characterize the microstructural dynamics that lead to the intriguing nonlinear rheological properties that these systems exhibit. However, the strain in OTM measurements, applied by optically forcing a microprobe through the material, induces network inhomogeneities in and around the strain path, and the resultant flow field complicates the measured response of the system. Through a robust set of custom-designed OTM protocols, coupled with modeling and analytical calculations, we characterize the time-varying inhomogeneity fields induced by OTM measurements. We show that homogenization following strain does not interfere with the intrinsic stress relaxation dynamics of the system, rather it manifests as an independent component in the stress decay, even in highly nonlinear regimes such as with the microrheological large-amplitude-oscillatory-shear (MLAOS) protocols we introduce. Our specific results show that Rouse-like elastic retraction, rather than disentanglement and disengagement, dominates the nonlinear stress relaxation of entangled polymers at micro- and mesoscales. Thus, our study opens up possibilities of performing precision nonlinear microrheological measurements, such as MLAOS, on a wide range of complex macromolecular systems.
DOI
Testing collapse models with levitated nanoparticles: Detection challenge
A. Vinante, A. Pontin, M. Rashid, M. Toroš, P. F. Barker, and H. Ulbricht
We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic vacuum, and look for the conditions which allow for a stringent noninterferometric test of spontaneous collapse models. In particular we compare different possible techniques to detect the particle motion. Key conditions which need to be achieved are extremely low residual pressure and the ability to detect the particle at ultralow power. We compare three different detection approaches based, respectively, on an optical cavity, an optical tweezer, and an electrical readout, and for each one we assess advantages, drawbacks, and technical challenges.
DOI
We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic vacuum, and look for the conditions which allow for a stringent noninterferometric test of spontaneous collapse models. In particular we compare different possible techniques to detect the particle motion. Key conditions which need to be achieved are extremely low residual pressure and the ability to detect the particle at ultralow power. We compare three different detection approaches based, respectively, on an optical cavity, an optical tweezer, and an electrical readout, and for each one we assess advantages, drawbacks, and technical challenges.
DOI
Optical trapping forces on Rayleigh particles by a focused Bessel-Gaussian correlated Schell-model beam
Zhang Hanghang, Han Yiping, Wang Jiajie, Guo Jirong
Optical trapping forces exerted by a focused Bessel-Gaussian correlated Schell-model (BGCSM) beam on Rayleigh dielectric spheres with different refractive indices are analyzed. The dependence of radiation forces on the transverse coherence width δ0, the coherence parameter β, refractive index of the particle, and particle radius are investigated. It is shown that the focused BGCSM beam can be used to trap particles with both high and low index of refraction near the focus, and as the transverse coherence width δ0 or the relative refractive indices of the particle with respect to the host medium increases, or the coherence parameter β decreases, the trapping stability increase. Furthermore, the limits of the radius for two types of particles stably captured are determined.
DOI
Optical trapping forces exerted by a focused Bessel-Gaussian correlated Schell-model (BGCSM) beam on Rayleigh dielectric spheres with different refractive indices are analyzed. The dependence of radiation forces on the transverse coherence width δ0, the coherence parameter β, refractive index of the particle, and particle radius are investigated. It is shown that the focused BGCSM beam can be used to trap particles with both high and low index of refraction near the focus, and as the transverse coherence width δ0 or the relative refractive indices of the particle with respect to the host medium increases, or the coherence parameter β decreases, the trapping stability increase. Furthermore, the limits of the radius for two types of particles stably captured are determined.
DOI
Propagation properties of Airy hollow Gaussian vortex beams through the strongly nonlocal nonlinear media
Gengxin Chen, Qiliang Sun, Jintao Xie, Dongmei Deng
We introduce a class of Airy hollow Gaussian vortex (AiHGV) beams and derive the analytical propagating expression of the AiHGV beams in strongly nonlocal nonlinear media (SNNM) using the transfer matrix method for the first time. The nonlinear factor 𝛺 can significantly increase the intensity of the side lobe and the hollow range becomes obvious, which causes the propagation pattern to dramatically change. Moreover, the distribution factor 𝛼 can prominently affect the focusing range and the decay factor a can also flexibly change the focusing position. In addition, 3D propagation and the center of mass are fully described to enrich the propagation properties of the AiHGV beams. Interestingly, the variations of the nonlinear factor 𝛺 and the decay factor a are proportional to the Poynting vector, the angular momentum and the gradient force at the focusing position, in which the effect of the distribution factor 𝛼 is totally different.
DOI
We introduce a class of Airy hollow Gaussian vortex (AiHGV) beams and derive the analytical propagating expression of the AiHGV beams in strongly nonlocal nonlinear media (SNNM) using the transfer matrix method for the first time. The nonlinear factor 𝛺 can significantly increase the intensity of the side lobe and the hollow range becomes obvious, which causes the propagation pattern to dramatically change. Moreover, the distribution factor 𝛼 can prominently affect the focusing range and the decay factor a can also flexibly change the focusing position. In addition, 3D propagation and the center of mass are fully described to enrich the propagation properties of the AiHGV beams. Interestingly, the variations of the nonlinear factor 𝛺 and the decay factor a are proportional to the Poynting vector, the angular momentum and the gradient force at the focusing position, in which the effect of the distribution factor 𝛼 is totally different.
DOI
Tuesday, August 6, 2019
The optoelectronic microrobot: A versatile toolbox for micromanipulation
Shuailong Zhang, Erica Y. Scott, Jastaranpreet Singh, Yujie Chen, Yanfeng Zhang, Mohamed Elsayed, M. Dean Chamberlain, Nika Shakiba, Kelsey Adams, Siyuan Yu, Cindi M. Morshead, Peter W. Zandstra, and Aaron R. Wheeler
Microrobotics extends the reach of human-controlled machines to submillimeter dimensions. We introduce a microrobot that relies on optoelectronic tweezers (OET) that is straightforward to manufacture, can take nearly any desirable shape or form, and can be programmed to carry out sophisticated, multiaxis operations. One particularly useful program is a serial combination of “load,” “transport,” and “deliver,” which can be applied to manipulate a wide range of micrometer-dimension payloads. Importantly, microrobots programmed in this manner are much gentler on fragile mammalian cells than conventional OET techniques. The microrobotic system described here was demonstrated to be useful for single-cell isolation, clonal expansion, RNA sequencing, manipulation within enclosed systems, controlling cell–cell interactions, and isolating precious microtissues from heterogeneous mixtures. We propose that the optoelectronic microrobotic system, which can be implemented using a microscope and consumer-grade optical projector, will be useful for a wide range of applications in the life sciences and beyond.
DOI
Microrobotics extends the reach of human-controlled machines to submillimeter dimensions. We introduce a microrobot that relies on optoelectronic tweezers (OET) that is straightforward to manufacture, can take nearly any desirable shape or form, and can be programmed to carry out sophisticated, multiaxis operations. One particularly useful program is a serial combination of “load,” “transport,” and “deliver,” which can be applied to manipulate a wide range of micrometer-dimension payloads. Importantly, microrobots programmed in this manner are much gentler on fragile mammalian cells than conventional OET techniques. The microrobotic system described here was demonstrated to be useful for single-cell isolation, clonal expansion, RNA sequencing, manipulation within enclosed systems, controlling cell–cell interactions, and isolating precious microtissues from heterogeneous mixtures. We propose that the optoelectronic microrobotic system, which can be implemented using a microscope and consumer-grade optical projector, will be useful for a wide range of applications in the life sciences and beyond.
DOI
Overstretching Double-Stranded RNA, Double-Stranded DNA, and RNA-DNA Duplexes
Lena Melkonyan, Mathilde Bercy, Thierry Bizebard, Ulrich Bockelmann
Using single-molecule force measurements, we compare the overstretching transition of the four types of duplexes composed of DNA or RNA strands. Three of the four extremities of each double helix are attached to two microscopic beads, and a stretching force is applied with a dual-beam optical trapping interferometer. We find that overstretching occurs for all four duplexes with small differences between the plateau forces. Double-stranded RNA (dsRNA) exhibits a smooth transition in contrast to the other three duplexes that show sawtooth patterns, the latter being a characteristic signature of peeling. This difference is observed for a wide range of experimental conditions. We present a theoretical description that explains the difference and predicts that peeling and bubble formation do not occur in overstretching double-stranded RNA. Formation of S-RNA is proposed, an overstretching mechanism that contrary to the other two does not generate single strands. We suggest that this singular RNA property helps RNA structures to assemble and play their essential roles in the biological cell.
DOI
Using single-molecule force measurements, we compare the overstretching transition of the four types of duplexes composed of DNA or RNA strands. Three of the four extremities of each double helix are attached to two microscopic beads, and a stretching force is applied with a dual-beam optical trapping interferometer. We find that overstretching occurs for all four duplexes with small differences between the plateau forces. Double-stranded RNA (dsRNA) exhibits a smooth transition in contrast to the other three duplexes that show sawtooth patterns, the latter being a characteristic signature of peeling. This difference is observed for a wide range of experimental conditions. We present a theoretical description that explains the difference and predicts that peeling and bubble formation do not occur in overstretching double-stranded RNA. Formation of S-RNA is proposed, an overstretching mechanism that contrary to the other two does not generate single strands. We suggest that this singular RNA property helps RNA structures to assemble and play their essential roles in the biological cell.
DOI
Research of laser cooling by the optical force between light field and the atoms
X.X. Zhang, Y.H. Ji, Z.L. Yan, H. Wang
The interaction force in the four-waving mixing of a two-level atoms system is analyzed. A new rate equation and the formula of the optical force are obtained. By simulation and analysis with MATLAB software, the impulse curve is obtained. The impulse increases with probe-wave detuning increasing and then tends to saturation. When the Ra-bi frequency takes a certain value, the impulse can obtain relative maximum and the relative maximum increases with the Ra-bi frequency increasing. The relation between the most value and the parameters of Ra-bi frequency and probe-wave detuning is also researched. The impulse occurs minimum when probe-wave detuning is zero and Ra-bi frequency is zero, there is no maximum for the impulse, which is close to 0.02 infinitely, the lowest temperature that can be reached is 248 μk. In addition, T2/T1 also has a significant influence on the impulse.
DOI
The interaction force in the four-waving mixing of a two-level atoms system is analyzed. A new rate equation and the formula of the optical force are obtained. By simulation and analysis with MATLAB software, the impulse curve is obtained. The impulse increases with probe-wave detuning increasing and then tends to saturation. When the Ra-bi frequency takes a certain value, the impulse can obtain relative maximum and the relative maximum increases with the Ra-bi frequency increasing. The relation between the most value and the parameters of Ra-bi frequency and probe-wave detuning is also researched. The impulse occurs minimum when probe-wave detuning is zero and Ra-bi frequency is zero, there is no maximum for the impulse, which is close to 0.02 infinitely, the lowest temperature that can be reached is 248 μk. In addition, T2/T1 also has a significant influence on the impulse.
DOI
Differentiation of single lymphoma primary cells and normal B-cells based on their adhesion to mesenchymal stromal cells in optical tweezers
Kamila Duś-Szachniewicz, Sławomir Drobczyński, Marta Woźniak, Krzysztof Zduniak, Katarzyna Ostasiewicz, Piotr Ziółkowski, Aleksandra K. Korzeniewska, Anil K. Agrawal, Paweł Kołodziej, Kinga Walaszek, Zbigniew Bystydzieński & Grzegorz Rymkiewicz
We have adapted a non-invasive method based on optical tweezers technology to differentiate between the normal B-cells and the B-cell non-Hodgkin lymphoma (B-NHL) cells derived from clinical samples. Our approach bases on the nascent adhesion between an individual B-cell and a mesenchymal stromal cell. In this study, a single B-cell was trapped and optically seeded on a mesenchymal stromal cell and kept in a direct contact with it until a stable connection between the cells was formed in time scale. This approach allowed us to avoid the introduction of any exogenous beads or chemicals into the experimental setup which would have affected the cell-to-cell adhesion. Here, we have provided new evidence that aberrant adhesive properties found in transformed B-cells are related to malignant neoplasia. We have demonstrated that the mean time required for establishing adhesive interactions between an individual normal B-cell and a mesenchymal stromal cell was 26.7 ± 16.6 s, while for lymphoma cell it was 208.8 ± 102.3 s, p < 0.001. The contact time for adhesion to occur ranged from 5 to 90 s and from 60 to 480 s for normal B-cells and lymphoma cells, respectively. This method for optically controlled cell-to-cell adhesion in time scale is beneficial to the successful differentiation of pathological cells from normal B-cells within the fine needle aspiration biopsy of a clinical sample. Additionally, variations in time-dependent adhesion among subtypes of B-NHL, established here by the optical trapping, confirm earlier results pertaining to cell heterogeneity.
DOI
We have adapted a non-invasive method based on optical tweezers technology to differentiate between the normal B-cells and the B-cell non-Hodgkin lymphoma (B-NHL) cells derived from clinical samples. Our approach bases on the nascent adhesion between an individual B-cell and a mesenchymal stromal cell. In this study, a single B-cell was trapped and optically seeded on a mesenchymal stromal cell and kept in a direct contact with it until a stable connection between the cells was formed in time scale. This approach allowed us to avoid the introduction of any exogenous beads or chemicals into the experimental setup which would have affected the cell-to-cell adhesion. Here, we have provided new evidence that aberrant adhesive properties found in transformed B-cells are related to malignant neoplasia. We have demonstrated that the mean time required for establishing adhesive interactions between an individual normal B-cell and a mesenchymal stromal cell was 26.7 ± 16.6 s, while for lymphoma cell it was 208.8 ± 102.3 s, p < 0.001. The contact time for adhesion to occur ranged from 5 to 90 s and from 60 to 480 s for normal B-cells and lymphoma cells, respectively. This method for optically controlled cell-to-cell adhesion in time scale is beneficial to the successful differentiation of pathological cells from normal B-cells within the fine needle aspiration biopsy of a clinical sample. Additionally, variations in time-dependent adhesion among subtypes of B-NHL, established here by the optical trapping, confirm earlier results pertaining to cell heterogeneity.
DOI
Extended linear detection range for optical tweezers using a stop at the back focal plane of the condenser
S Masoumeh Mousavi, Akbar Samadi, Faegheh Hajizadeh and S Nader S Reihani
Optical tweezers are indispensable micro-manipulation tools. It is known that optical tweezers are force rather than position sensors due to the shorter linear range of their position detection system. In this paper, we have shown for the first time, that positioning an optical stop at the BFP of the condenser can overcome this problem by extending the linear detection range. This method would be valuable for the force spectroscopy applications of optical tweezers.
DOI
Optical tweezers are indispensable micro-manipulation tools. It is known that optical tweezers are force rather than position sensors due to the shorter linear range of their position detection system. In this paper, we have shown for the first time, that positioning an optical stop at the BFP of the condenser can overcome this problem by extending the linear detection range. This method would be valuable for the force spectroscopy applications of optical tweezers.
DOI
Anomalous optical forces in PT-symmetric waveguides
Mohammad-Ali Miri, Michele Cotrufo, and Andrea Alù
Evanescently coupled passive waveguides experience optical forces of attractive or repulsive nature, depending on the mode of operation. Here we explore the optical forces between parity-time-symmetric coupled waveguides, with balanced levels of gain and loss. We find that, besides the diagonal stress components that result in a pressure normal to the surface of the waveguides, this system exhibits an off-diagonal stress component that creates a shear along the propagation direction. In addition, for a critical value of balanced gain and loss, the normal pressure can be reduced to zero. These anomalous optical forces are related to the unusual power flow in coupled active-passive channels, and open interesting opportunities for microfluidics and micro-optomechanical systems.
DOI
Evanescently coupled passive waveguides experience optical forces of attractive or repulsive nature, depending on the mode of operation. Here we explore the optical forces between parity-time-symmetric coupled waveguides, with balanced levels of gain and loss. We find that, besides the diagonal stress components that result in a pressure normal to the surface of the waveguides, this system exhibits an off-diagonal stress component that creates a shear along the propagation direction. In addition, for a critical value of balanced gain and loss, the normal pressure can be reduced to zero. These anomalous optical forces are related to the unusual power flow in coupled active-passive channels, and open interesting opportunities for microfluidics and micro-optomechanical systems.
DOI
Two-dimensional photonic crystals for engineering atom–light interactions
Su-Peng Yu, Juan A. Muniz, Chen-Lung Hung, and H. J. Kimble
We present a 2D photonic crystal system for interacting with cold cesium (Cs) atoms. The band structures of the 2D photonic crystals are predicted to produce unconventional atom–light interaction behaviors, including anisotropic emission, suppressed spontaneous decay, and photon-mediated atom–atom interactions controlled by the position of the atomic array relative to the photonic crystal. An optical conveyor technique is presented for continuously loading atoms into the desired trapping positions with optimal coupling to the photonic crystal. The device configuration also enables application of optical tweezers for controlled placement of atoms. Devices can be fabricated reliably from a 200-nm silicon nitride device layer using a lithography-based process, producing predicted optical properties in transmission and reflection measurements. These 2D photonic crystal devices can be readily deployed to experiments for many-body physics with neutral atoms and engineering of exotic quantum matter.
DOI
We present a 2D photonic crystal system for interacting with cold cesium (Cs) atoms. The band structures of the 2D photonic crystals are predicted to produce unconventional atom–light interaction behaviors, including anisotropic emission, suppressed spontaneous decay, and photon-mediated atom–atom interactions controlled by the position of the atomic array relative to the photonic crystal. An optical conveyor technique is presented for continuously loading atoms into the desired trapping positions with optimal coupling to the photonic crystal. The device configuration also enables application of optical tweezers for controlled placement of atoms. Devices can be fabricated reliably from a 200-nm silicon nitride device layer using a lithography-based process, producing predicted optical properties in transmission and reflection measurements. These 2D photonic crystal devices can be readily deployed to experiments for many-body physics with neutral atoms and engineering of exotic quantum matter.
DOI
Construction of 3D Cellular Composites with Stem Cells Derived from Adipose Tissue and Endothelial Cells by Use of Optical Tweezers in a Natural Polymer Solution
Takehiro Yamazaki, Toshifumi Kishimoto, Paweł Leszczyński, Koichiro Sadakane, Takahiro Kenmotsu, Hirofumi Watanabe, Tomohiko Kazama, Taro Matsumoto, Kenichi Yoshikawa and Hiroaki Taniguchi
To better understand the regulation and function of cellular interactions, three-dimensional (3D) assemblies of single cells and subsequent functional analysis are gaining popularity in many research fields. While we have developed strategies to build stable cellular structures using optical tweezers in a minimally invasive state, methods for manipulating a wide range of cell types have yet to be established. To mimic organ-like structures, the construction of 3D cellular assemblies with variety of cell types is essential. Our recent studies have shown that the presence of nonspecific soluble polymers in aqueous solution is the key to creating stable 3D cellular assemblies efficiently. The present study further expands on the construction of 3D single cell assemblies using two different cell types. We have successfully generated 3D cellular assemblies, using GFP-labeled adipose tissue-derived stem cells and endothelial cells by using optical tweezers. Our findings will support the development of future applications to further characterize cellular interactions in tissue regeneration.
DOI
To better understand the regulation and function of cellular interactions, three-dimensional (3D) assemblies of single cells and subsequent functional analysis are gaining popularity in many research fields. While we have developed strategies to build stable cellular structures using optical tweezers in a minimally invasive state, methods for manipulating a wide range of cell types have yet to be established. To mimic organ-like structures, the construction of 3D cellular assemblies with variety of cell types is essential. Our recent studies have shown that the presence of nonspecific soluble polymers in aqueous solution is the key to creating stable 3D cellular assemblies efficiently. The present study further expands on the construction of 3D single cell assemblies using two different cell types. We have successfully generated 3D cellular assemblies, using GFP-labeled adipose tissue-derived stem cells and endothelial cells by using optical tweezers. Our findings will support the development of future applications to further characterize cellular interactions in tissue regeneration.
DOI
Monday, August 5, 2019
Positioning of space objects by laser-induced jets
E Y Loktionov and D S Sitnikov
Laser-induced thrust provides a number of significant advantages over the currently used methods: virtually any material can be used as a working medium; radiation source and its power unit can be located outside the spacecraft; it is possible to provide a minimum impulse bit of 1 nN s or less; momentum imparted at single impact can be controlled within 2 orders of magnitude dynamic range. We have considered recoil momentum generation at femtosecond to continuous laser impact range on different materials normalized by laser output performance to evaluate momentum coupling to on-board energy system. It is shown that better momentum coupling at short wavelength is not worth of associated energy losses, but laser pulse shortening to picosecond range is. Data reported here on laser thrust generation efficiency and methods of laser impact layout are of interest not for small spacecraft application range broadening only, but also for the prevention of emergency situations development (launch to unplanned orbit, uncontrolled rotation, etc.), space debris removal, and anti-asteroid protection of the Earth – possible impact layouts for such missions are considered.
DOI
Laser-induced thrust provides a number of significant advantages over the currently used methods: virtually any material can be used as a working medium; radiation source and its power unit can be located outside the spacecraft; it is possible to provide a minimum impulse bit of 1 nN s or less; momentum imparted at single impact can be controlled within 2 orders of magnitude dynamic range. We have considered recoil momentum generation at femtosecond to continuous laser impact range on different materials normalized by laser output performance to evaluate momentum coupling to on-board energy system. It is shown that better momentum coupling at short wavelength is not worth of associated energy losses, but laser pulse shortening to picosecond range is. Data reported here on laser thrust generation efficiency and methods of laser impact layout are of interest not for small spacecraft application range broadening only, but also for the prevention of emergency situations development (launch to unplanned orbit, uncontrolled rotation, etc.), space debris removal, and anti-asteroid protection of the Earth – possible impact layouts for such missions are considered.
DOI
Solenoidal optical forces from a plasmonic Archimedean spiral
Mohammad Asif Zaman, Punnag Padhy, and Lambertus Hesselink
The optical forces generated by a right-handed plasmonic Archimedean spiral (PAS) have been mapped and analyzed. By changing the handedness of the circularly polarized excitation, the structure can switch from a trapping force profile to a rotating force profile. The Helmholtz-Hodge decomposition method has been used to separate the solenoidal component and the conservative component of the force and quantify their relative magnitude. It is shown that the for right-hand circularly polarized excitation, the PAS creates a significant amount of solenoidal forces. Using the decomposed force components, an intuitive explanation of the motion of micro- and nanoparticles in the force field is presented. Vector field topology is used to visualize the force components. The analysis is found to be consistent with numerical and experimental results. Due to the intuitive nature of the analysis, it can be used in the initial design process of complex laboratory-on-a-chip systems where a rigorous analysis is computationally expensive.
DOI
The optical forces generated by a right-handed plasmonic Archimedean spiral (PAS) have been mapped and analyzed. By changing the handedness of the circularly polarized excitation, the structure can switch from a trapping force profile to a rotating force profile. The Helmholtz-Hodge decomposition method has been used to separate the solenoidal component and the conservative component of the force and quantify their relative magnitude. It is shown that the for right-hand circularly polarized excitation, the PAS creates a significant amount of solenoidal forces. Using the decomposed force components, an intuitive explanation of the motion of micro- and nanoparticles in the force field is presented. Vector field topology is used to visualize the force components. The analysis is found to be consistent with numerical and experimental results. Due to the intuitive nature of the analysis, it can be used in the initial design process of complex laboratory-on-a-chip systems where a rigorous analysis is computationally expensive.
DOI
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