Carinna N. Lima, Diogenes S. Moura, Yandilla S.S. Silva, Tiago H. Souza, Fabiano A.P. Crisafuli, Diego C.N. Silva, Jaqueline C. Peres, Carlos L. Cesar, R.E. de Araujo, Adriana Fontes
Biomechanical and electrical properties are important to the performance and survival of red blood cells (RBCs) in the microcirculation. This study proposed and explored methodologies based on optical tweezers and cationic quantum dots (QDs) as biophotonic tools to characterize, in a complementary way, viscoelastic properties and membrane electrical charges of RBCs. The methodologies were applied to normal (HbA) and β-thalassemia intermedia (Hbβ) RBCs. The β-thalassemia intermedia disease is a hereditary hemoglobinopathy characterized by a reduction (or absence) of β-globin chains, which leads to α-globin chains precipitation. The apparent elasticity (μ) and membrane viscosity (ηm) of RBCs captured by optical tweezers were obtained in just a single experiment. Besides, the membrane electrical charges were evaluated by flow cytometry, exploring electrostatic interactions between cationic QDs, stabilized with cysteamine, with the negatively charged RBC surfaces. Results showed that Hbβ RBCs are considerably less elastic, have a higher ηm, and presented a reduction in membrane electrical charges, when compared to HbA RBCs. Moreover, the methodologies based on optical tweezers and QDs, here proposed, showed to be capable of providing a deeper and integrated comprehension on RBC rheological and electrical changes, resulting from diverse biological conditions, such as the β-thalassemia intermedia hemoglobinopathy.
DOI
Friday, November 29, 2019
SERS discrimination of single DNA bases in single oligonucleotides by electro-plasmonic trapping
Jian-An Huang, Mansoureh Z. Mousavi, Yingqi Zhao, Aliaksandr Hubarevich, Fatima Omeis, Giorgia Giovannini, Moritz Schütte, Denis Garoli & Francesco De Angelis
Surface-enhanced Raman spectroscopy (SERS) sensing of DNA bases by plasmonic nanopores could pave a way to novel methods for DNA analyses and new generation single-molecule sequencing platforms. The SERS discrimination of single DNA bases depends critically on the time that a DNA strand resides within the plasmonic hot spot. In fact, DNA molecules flow through the nanopores so rapidly that the SERS signals collected are not sufficient for single-molecule analysis. Here, we report an approach to control the residence time of molecules in the hot spot by an electro-plasmonic trapping effect. By directly adsorbing molecules onto a gold nanoparticle and then trapping the single nanoparticle in a plasmonic nanohole up to several minutes, we demonstrate single-molecule SERS detection of all four DNA bases as well as discrimination of single nucleobases in a single oligonucleotide. Our method can be extended easily to label-free sensing of single-molecule amino acids and proteins.
DOI
Surface-enhanced Raman spectroscopy (SERS) sensing of DNA bases by plasmonic nanopores could pave a way to novel methods for DNA analyses and new generation single-molecule sequencing platforms. The SERS discrimination of single DNA bases depends critically on the time that a DNA strand resides within the plasmonic hot spot. In fact, DNA molecules flow through the nanopores so rapidly that the SERS signals collected are not sufficient for single-molecule analysis. Here, we report an approach to control the residence time of molecules in the hot spot by an electro-plasmonic trapping effect. By directly adsorbing molecules onto a gold nanoparticle and then trapping the single nanoparticle in a plasmonic nanohole up to several minutes, we demonstrate single-molecule SERS detection of all four DNA bases as well as discrimination of single nucleobases in a single oligonucleotide. Our method can be extended easily to label-free sensing of single-molecule amino acids and proteins.
DOI
Optimization of metallic nanoapertures at short-wave infrared wavelengths for self-induced back-action trapping
Chenyi Zhang, Jinxin Li, Jin Gyu Park, Yi-Feng Su, Robert E. Goddard, and Ryan M. Gelfand
This paper presents simulation results for double nanohole and inverted bowtie nanoapertures optimized to resonate in the short-wave infrared regime (1050 nm and 1550 nm). These geometries have shown great promise for trapping nanoparticles with applications in optical engineering, physics, and biology. Using a finite element analysis tool, we found that the outline length for inverted bowtie nanoapertures in a 100 nm thick gold film with a 20 nm gap dimension having an optimized transmission resonance for 1050 nm and 1550 nm optical wavelengths is 106.5 nm and 188.5 nm, respectively. With the same gap size, the radii of the circles for the double nanohole nanoapertures are 72 nm and 128 nm. The near-field enhancements of the two structures are almost the same, while the double nanohole geometries have a 20% larger full width at half-maximum than the inverted bowtie. Next, by studying the effect of changing the inner radii of the inverted bowtie corners, we found that the difference between 2 nm and 6 nm corner radii can blue-shift the optical resonance by up to 45 nm. As a result of not having any inner corners, the double nanohole structure requires less precise fabrication and therefore could potentially have a higher successful yield of nanoapertures during the manufacturing process. Lastly, we will show experimental results that confirm the optical resonance of the nanoapertures at 1550 nm. These results will enable better performance and signal-to-noise ratio in nanoaperture trapping for the short-wave infrared wavelength regime.
DOI
This paper presents simulation results for double nanohole and inverted bowtie nanoapertures optimized to resonate in the short-wave infrared regime (1050 nm and 1550 nm). These geometries have shown great promise for trapping nanoparticles with applications in optical engineering, physics, and biology. Using a finite element analysis tool, we found that the outline length for inverted bowtie nanoapertures in a 100 nm thick gold film with a 20 nm gap dimension having an optimized transmission resonance for 1050 nm and 1550 nm optical wavelengths is 106.5 nm and 188.5 nm, respectively. With the same gap size, the radii of the circles for the double nanohole nanoapertures are 72 nm and 128 nm. The near-field enhancements of the two structures are almost the same, while the double nanohole geometries have a 20% larger full width at half-maximum than the inverted bowtie. Next, by studying the effect of changing the inner radii of the inverted bowtie corners, we found that the difference between 2 nm and 6 nm corner radii can blue-shift the optical resonance by up to 45 nm. As a result of not having any inner corners, the double nanohole structure requires less precise fabrication and therefore could potentially have a higher successful yield of nanoapertures during the manufacturing process. Lastly, we will show experimental results that confirm the optical resonance of the nanoapertures at 1550 nm. These results will enable better performance and signal-to-noise ratio in nanoaperture trapping for the short-wave infrared wavelength regime.
DOI
Nonlinear Optical Tweezers As an Optical Method for Controlling Particles with High Trap Efficiency
Ho Quang Quy
Optical tweezers have seen as an essential tool for the manipulation dielectric microparticles and nanoparticles due to its non-contact action and high resolution of optical force. Up to now, there has been a lot of optical tweezers applications in the fields of biophysics, chemistry, medical science and nanoscience. Recently, optical tweezers have been theoretically and experimentally developing for the nanomechanical characterization of various kinds of biological cells. The configuration of optical tweezers has been day after day improving to enhance the trapping efficiency, spatial and temporal resolution and easy to control trapped objects. In common trend of optical tweezers improvements, we will discuss in detail of the several configurations of nonlinear optical tweezers using nonlinear materials as the added lens. We will also address the advantages of nonlinear optical tweezers, such as enhance optical efficiency, reduce trapping region, simplify controlling all-optical method. Finally, we present discussions about the specific properties of nonlinear optical tweezers used for stretch DNA molecule as example and an ideal to improve nonlinear optical tweezers using thin layer of organic dye proposed for going time.
DOI
Optical tweezers have seen as an essential tool for the manipulation dielectric microparticles and nanoparticles due to its non-contact action and high resolution of optical force. Up to now, there has been a lot of optical tweezers applications in the fields of biophysics, chemistry, medical science and nanoscience. Recently, optical tweezers have been theoretically and experimentally developing for the nanomechanical characterization of various kinds of biological cells. The configuration of optical tweezers has been day after day improving to enhance the trapping efficiency, spatial and temporal resolution and easy to control trapped objects. In common trend of optical tweezers improvements, we will discuss in detail of the several configurations of nonlinear optical tweezers using nonlinear materials as the added lens. We will also address the advantages of nonlinear optical tweezers, such as enhance optical efficiency, reduce trapping region, simplify controlling all-optical method. Finally, we present discussions about the specific properties of nonlinear optical tweezers used for stretch DNA molecule as example and an ideal to improve nonlinear optical tweezers using thin layer of organic dye proposed for going time.
DOI
Optical binding of nanoparticles
Kayn A. Forbes, David S. Bradshaw, David L. Andrews
Optical binding is a laser-induced inter-particle force that exists between two or more particles subjected to off-resonant light. It is one of the key tools in optical manipulation of particles. Distinct from the single-particle forces which operate in optical trapping and tweezing, it enables the light-induced self-assembly of non-contact multi-particle arrays and structures. Whilst optical binding at the microscale between microparticles is well-established, it is only within the last few years that the experimental difficulties of observing nanoscale optical binding between nanoparticles have been overcome. This hurdle surmounted, there has been a sudden proliferation in observations of nanoscale optical binding, where the corresponding theoretical understanding and predictions of the underlying nanophotonics have become ever more important. This article covers these new developments, giving an overview of the emergent field of nanoscale optical binding.
DOI
Optical binding is a laser-induced inter-particle force that exists between two or more particles subjected to off-resonant light. It is one of the key tools in optical manipulation of particles. Distinct from the single-particle forces which operate in optical trapping and tweezing, it enables the light-induced self-assembly of non-contact multi-particle arrays and structures. Whilst optical binding at the microscale between microparticles is well-established, it is only within the last few years that the experimental difficulties of observing nanoscale optical binding between nanoparticles have been overcome. This hurdle surmounted, there has been a sudden proliferation in observations of nanoscale optical binding, where the corresponding theoretical understanding and predictions of the underlying nanophotonics have become ever more important. This article covers these new developments, giving an overview of the emergent field of nanoscale optical binding.
DOI
Wednesday, November 27, 2019
Supported Solid Lipid Bilayers as a Platform for Single-Molecule Force Measurements
Swathi Sudhakar, Tobias Jörg Jachowskix, Michael Kittelberger, Ammara Maqbool, Gero Lutz Hermsdorf, Mohammad Kazem Abdosamad and Erik Schäffer
Biocompatible surfaces are important for basic and applied research in life science with experiments ranging from the organismal to the single-molecule level. For the latter, examples include the translocation of kinesin motor proteins along microtubule cytoskeletal filaments or the study of DNA–protein interactions. Such experiments often employ single-molecule fluorescence or force microscopy. In particular for force measurements, a key requirement is to prevent nonspecific interactions of biomolecules and force probes with the surface, while providing specific attachments that can sustain loads. Common approaches to reduce nonspecific interactions include supported lipid bilayers or PEGylated surfaces. However, fluid lipid bilayers do not support loads and PEGylation may require harsh chemical surface treatments and have limited reproducibility. Here, we developed and applied a supported solid lipid bilayer (SSLB) as a platform for specific, load bearing attachments with minimal nonspecific interactions. Apart from single-molecule fluorescence measurements, anchoring molecules to lipids in the solid phase enabled us to perform force measurements of molecular motors and overstretch DNA. Furthermore, using a heating laser, we could switch the SSLB to its fluid state allowing for manipulation of anchoring points. The assay had little nonspecific interactions, was robust, reproducible, and time-efficient, and required less hazardous and toxic chemicals for preparation. In the long term, we expect that SSLBs can be widely employed for single-molecule fluorescence microscopy, force spectroscopy, and cellular assays in mechanobiology.
DOI
Biocompatible surfaces are important for basic and applied research in life science with experiments ranging from the organismal to the single-molecule level. For the latter, examples include the translocation of kinesin motor proteins along microtubule cytoskeletal filaments or the study of DNA–protein interactions. Such experiments often employ single-molecule fluorescence or force microscopy. In particular for force measurements, a key requirement is to prevent nonspecific interactions of biomolecules and force probes with the surface, while providing specific attachments that can sustain loads. Common approaches to reduce nonspecific interactions include supported lipid bilayers or PEGylated surfaces. However, fluid lipid bilayers do not support loads and PEGylation may require harsh chemical surface treatments and have limited reproducibility. Here, we developed and applied a supported solid lipid bilayer (SSLB) as a platform for specific, load bearing attachments with minimal nonspecific interactions. Apart from single-molecule fluorescence measurements, anchoring molecules to lipids in the solid phase enabled us to perform force measurements of molecular motors and overstretch DNA. Furthermore, using a heating laser, we could switch the SSLB to its fluid state allowing for manipulation of anchoring points. The assay had little nonspecific interactions, was robust, reproducible, and time-efficient, and required less hazardous and toxic chemicals for preparation. In the long term, we expect that SSLBs can be widely employed for single-molecule fluorescence microscopy, force spectroscopy, and cellular assays in mechanobiology.
DOI
Time-resolved emission microscopy of light-induced aggregation of luminescent polymers
Yang Xu, Jian Zhou and Trevor Smith
Photon pressure has been used induce the aggregation from solution of a series of photoluminescence conjugated polyelectrolytes containing tetraphenylethene units. These polymers show steady-state and time-resolved emission properties that are dependent on the local chromophore environment that can be influenced by the degree of intra- and inter- molecular interactions, which enables the photoaggregation process to be monitored by time-resolved fluorescence imaging techniques. Structural differences in the polymer lead to variations in the photo-induced aggregation behaviour.
DOI
Photon pressure has been used induce the aggregation from solution of a series of photoluminescence conjugated polyelectrolytes containing tetraphenylethene units. These polymers show steady-state and time-resolved emission properties that are dependent on the local chromophore environment that can be influenced by the degree of intra- and inter- molecular interactions, which enables the photoaggregation process to be monitored by time-resolved fluorescence imaging techniques. Structural differences in the polymer lead to variations in the photo-induced aggregation behaviour.
DOI
Forces between solid surfaces in aqueous electrolyte solutions
Alexander M. Smith, Michal Borkovec, Gregor Trefalt
This review addresses experimental findings obtained with direct force measurements between two similar or dissimilar solid surfaces in aqueous electrolyte solutions. Interpretation of these measurements is mainly put forward in terms of the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). This theory invokes a superposition of attractive van der Waals forces and repulsive double layer forces. DLVO theory is shown to be extremely reliable, even in the case of multivalent ions. However, such a description is only successful, when appropriate surface charge densities, charge regulation characteristics, and ion pairing or complexation equilibria in solution are considered. Deviations from DLVO theory only manifest themselves at distances of typically below few nm. More long-ranged non-DLVO forces can be observed in some situations, particularly, in concentrated electrolyte solutions, in the presence of strongly adsorbed layers, or for hydrophobic surfaces. The latter forces probably originate from patch-charge surface heterogeneities, which can be induced by ion-ion correlation effects, charge fluctuations, or other types of surface heterogeneities.
DOI
This review addresses experimental findings obtained with direct force measurements between two similar or dissimilar solid surfaces in aqueous electrolyte solutions. Interpretation of these measurements is mainly put forward in terms of the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). This theory invokes a superposition of attractive van der Waals forces and repulsive double layer forces. DLVO theory is shown to be extremely reliable, even in the case of multivalent ions. However, such a description is only successful, when appropriate surface charge densities, charge regulation characteristics, and ion pairing or complexation equilibria in solution are considered. Deviations from DLVO theory only manifest themselves at distances of typically below few nm. More long-ranged non-DLVO forces can be observed in some situations, particularly, in concentrated electrolyte solutions, in the presence of strongly adsorbed layers, or for hydrophobic surfaces. The latter forces probably originate from patch-charge surface heterogeneities, which can be induced by ion-ion correlation effects, charge fluctuations, or other types of surface heterogeneities.
DOI
Molecular scaffolds: when DNA becomes the hardware for single-molecule investigations
Charlie Gosse, Terence R. Strick, Dorota Kostrz
Over the past few decades, single-molecule manipulation has been widely applied to the real-time analysis of biomolecular interactions. It has enabled researchers to decipher structure-function relationships for polymers, enzymes, and larger-scale molecular machines, in particular by harnessing force to probe both chemical and mechanical stabilities. Nucleic acids have played a central role in this effort because, in addition to their biological significance, they exhibit unique polymeric properties which have recast them as key components participating in numerous experimental designs. In this review, we introduce recent developments highlighting this dual nature of nucleic acids in biophysics, as objects of study but also as tools allowing novel approaches. More specifically, we present molecular scaffolds as an emerging concept and describe their use in single-molecule force spectroscopy. Aspects related to folding and noncovalent interactions will be presented in parallel to research in enzymology, with a focus on the acquisition of thermodynamic and kinetic data.
DOI
Over the past few decades, single-molecule manipulation has been widely applied to the real-time analysis of biomolecular interactions. It has enabled researchers to decipher structure-function relationships for polymers, enzymes, and larger-scale molecular machines, in particular by harnessing force to probe both chemical and mechanical stabilities. Nucleic acids have played a central role in this effort because, in addition to their biological significance, they exhibit unique polymeric properties which have recast them as key components participating in numerous experimental designs. In this review, we introduce recent developments highlighting this dual nature of nucleic acids in biophysics, as objects of study but also as tools allowing novel approaches. More specifically, we present molecular scaffolds as an emerging concept and describe their use in single-molecule force spectroscopy. Aspects related to folding and noncovalent interactions will be presented in parallel to research in enzymology, with a focus on the acquisition of thermodynamic and kinetic data.
DOI
Cargo adaptors regulate stepping and force generation of mammalian dynein–dynactin
Mohamed M. Elshenawy, John T. Canty, Liya Oster, Luke S. Ferro, Zhou Zhou, Scott C. Blanchard & Ahmet Yildiz
Cytoplasmic dynein is an ATP-driven motor that transports intracellular cargos along microtubules. Dynein adopts an inactive conformation when not attached to a cargo, and motility is activated when dynein assembles with dynactin and a cargo adaptor. It was unclear how active dynein–dynactin complexes step along microtubules and transport cargos under tension. Using single-molecule imaging, we showed that dynein–dynactin advances by taking 8 to 32-nm steps toward the microtubule minus end with frequent sideways and backward steps. Multiple dyneins collectively bear a large amount of tension because the backward stepping rate of dynein is insensitive to load. Recruitment of two dyneins to dynactin increases the force generation and the likelihood of winning against kinesin in a tug-of-war but does not directly affect velocity. Instead, velocity is determined by cargo adaptors and tail–tail interactions between two closely packed dyneins. Our results show that cargo adaptors modulate dynein motility and force generation for a wide range of cellular functions.
DOI
Cytoplasmic dynein is an ATP-driven motor that transports intracellular cargos along microtubules. Dynein adopts an inactive conformation when not attached to a cargo, and motility is activated when dynein assembles with dynactin and a cargo adaptor. It was unclear how active dynein–dynactin complexes step along microtubules and transport cargos under tension. Using single-molecule imaging, we showed that dynein–dynactin advances by taking 8 to 32-nm steps toward the microtubule minus end with frequent sideways and backward steps. Multiple dyneins collectively bear a large amount of tension because the backward stepping rate of dynein is insensitive to load. Recruitment of two dyneins to dynactin increases the force generation and the likelihood of winning against kinesin in a tug-of-war but does not directly affect velocity. Instead, velocity is determined by cargo adaptors and tail–tail interactions between two closely packed dyneins. Our results show that cargo adaptors modulate dynein motility and force generation for a wide range of cellular functions.
DOI
Multiplexed protein force spectroscopy reveals equilibrium protein folding dynamics and the low-force response of von Willebrand factor
Achim Löf, Philipp U. Walker, View ORCID ProfileSteffen M. Sedlak, Sophia Gruber, Tobias Obser, Maria A. Brehm, Martin Benoit, and Jan Lipfert
Single-molecule force spectroscopy has provided unprecedented insights into protein folding, force regulation, and function. So far, the field has relied primarily on atomic force microscope and optical tweezers assays that, while powerful, are limited in force resolution, throughput, and require feedback for constant force measurements. Here, we present a modular approach based on magnetic tweezers (MT) for highly multiplexed protein force spectroscopy. Our approach uses elastin-like polypeptide linkers for the specific attachment of proteins, requiring only short peptide tags on the protein of interest. The assay extends protein force spectroscopy into the low force (<1 pN) regime and enables parallel and ultra-stable measurements at constant forces. We present unfolding and refolding data for the small, single-domain protein ddFLN4, commonly used as a molecular fingerprint in force spectroscopy, and for the large, multidomain dimeric protein von Willebrand factor (VWF) that is critically involved in primary hemostasis. For both proteins, our measurements reveal exponential force dependencies of unfolding and refolding rates. We directly resolve the stabilization of the VWF A2 domain by Ca2+ and discover transitions in the VWF C domain stem at low forces that likely constitute the first steps of VWF’s mechano-activation. Probing the force-dependent lifetime of biotin–streptavidin bonds, we find that monovalent streptavidin constructs with specific attachment geometry are significantly more force stable than commercial, multivalent streptavidin. We expect our modular approach to enable multiplexed force-spectroscopy measurements for a wide range of proteins, in particular in the physiologically relevant low-force regime.
DOI
Single-molecule force spectroscopy has provided unprecedented insights into protein folding, force regulation, and function. So far, the field has relied primarily on atomic force microscope and optical tweezers assays that, while powerful, are limited in force resolution, throughput, and require feedback for constant force measurements. Here, we present a modular approach based on magnetic tweezers (MT) for highly multiplexed protein force spectroscopy. Our approach uses elastin-like polypeptide linkers for the specific attachment of proteins, requiring only short peptide tags on the protein of interest. The assay extends protein force spectroscopy into the low force (<1 pN) regime and enables parallel and ultra-stable measurements at constant forces. We present unfolding and refolding data for the small, single-domain protein ddFLN4, commonly used as a molecular fingerprint in force spectroscopy, and for the large, multidomain dimeric protein von Willebrand factor (VWF) that is critically involved in primary hemostasis. For both proteins, our measurements reveal exponential force dependencies of unfolding and refolding rates. We directly resolve the stabilization of the VWF A2 domain by Ca2+ and discover transitions in the VWF C domain stem at low forces that likely constitute the first steps of VWF’s mechano-activation. Probing the force-dependent lifetime of biotin–streptavidin bonds, we find that monovalent streptavidin constructs with specific attachment geometry are significantly more force stable than commercial, multivalent streptavidin. We expect our modular approach to enable multiplexed force-spectroscopy measurements for a wide range of proteins, in particular in the physiologically relevant low-force regime.
DOI
Monday, November 25, 2019
Optical-fiber-based powerful tools for living cell manipulation
Xiaotong Zhang, Shitai Yang, and Libo Yuan
By using a specialty optical fiber, a series of powerful microparticle manipulation tools, including optical tweezers, a micro-optical hand, and an optical gun, are developed and demonstrated. In this paper, a review of our research activities on the optical manipulation of microparticles is presented. In particular, we will describe a kind of specialty optical fiber designed and fabricated for building optical trapping and manipulating tools. The performances of annular core fiber-based optical tweezers, a multicore fiber-based micro-optical hand, and a coaxial dual waveguide fiber-based optical gun are demonstrated as examples of applications and discussed in detail. The fiber can be used in cell manipulation in life science and drug response in medicine.
DOI
By using a specialty optical fiber, a series of powerful microparticle manipulation tools, including optical tweezers, a micro-optical hand, and an optical gun, are developed and demonstrated. In this paper, a review of our research activities on the optical manipulation of microparticles is presented. In particular, we will describe a kind of specialty optical fiber designed and fabricated for building optical trapping and manipulating tools. The performances of annular core fiber-based optical tweezers, a multicore fiber-based micro-optical hand, and a coaxial dual waveguide fiber-based optical gun are demonstrated as examples of applications and discussed in detail. The fiber can be used in cell manipulation in life science and drug response in medicine.
DOI
All-fiber active tractor beam generator and its application
Xiaoyun Tang, Yu Zhang, Yaxun Zhang, Zhihai Liu, Xinghua Yang, Zhang Jianzhong, Jun Yang, Libo Yuan
We propose and demonstrate an all-fiber probe to generate an active tractor beam by changing the gradients of optical intensity distributions. We grind the tip of a seven-core fiber (SCF) into a truncated hexagonal pyramid shape to integrate three equivalent two-core fiber optical tweezers in an SCF. Three optical tweezers produce three trapping locations along the fiber main axis. By adjusting and controlling the incident laser power in each core, we may perform multiple functions, including microparticles optical trapping, long-distance attraction, bidirectional transportation, and axial-direction position controllable adjustment. The proposed all-fiber active tractor beam generator is convenient to integrate and low cost. The all-fiber probe has the compatibility of optical tweezers and optical tractor beams. The increased effective range of optical pull broadens the scope of feasible optical trapping and will pave the way towards more efficient light-powered miniature machines, tools and applications.
DOI
We propose and demonstrate an all-fiber probe to generate an active tractor beam by changing the gradients of optical intensity distributions. We grind the tip of a seven-core fiber (SCF) into a truncated hexagonal pyramid shape to integrate three equivalent two-core fiber optical tweezers in an SCF. Three optical tweezers produce three trapping locations along the fiber main axis. By adjusting and controlling the incident laser power in each core, we may perform multiple functions, including microparticles optical trapping, long-distance attraction, bidirectional transportation, and axial-direction position controllable adjustment. The proposed all-fiber active tractor beam generator is convenient to integrate and low cost. The all-fiber probe has the compatibility of optical tweezers and optical tractor beams. The increased effective range of optical pull broadens the scope of feasible optical trapping and will pave the way towards more efficient light-powered miniature machines, tools and applications.
DOI
Germanium microparticles as optically induced oscillators in optical tweezers
W. H. Campos, T. A. Moura, O. J. B. J. Marques, J. M. Fonseca, W. A. Moura-Melo, M. S. Rocha, and J. B. S. Mendes
Oscillatory dynamics is a key tool in optical tweezer applications. It is usually implemented by mechanical interventions that cannot be optically controlled. In this paper, we show that germanium semiconductor beads behave as optically induced oscillators when subjected to a highly focused laser beam. In turn, the well-defined direction of oscillations can be manipulated by the polarization of the light beam. Such unusual motion is due to the competition between the usual optical forces and the radiometric force related to thermal effects, which pushes the beads from the focal region. We characterize the behavior of the germanium beads in detail and propose a model accounting for the related forces in good agreement with the experimental data. Such kind of system can potentially revolutionize the field of optical manipulation, contributing to the design of single molecule machines and to the application of oscillatory forces in fundamental physics, cellular manipulation, fluid dynamics, and other soft-matter systems.
DOI
Oscillatory dynamics is a key tool in optical tweezer applications. It is usually implemented by mechanical interventions that cannot be optically controlled. In this paper, we show that germanium semiconductor beads behave as optically induced oscillators when subjected to a highly focused laser beam. In turn, the well-defined direction of oscillations can be manipulated by the polarization of the light beam. Such unusual motion is due to the competition between the usual optical forces and the radiometric force related to thermal effects, which pushes the beads from the focal region. We characterize the behavior of the germanium beads in detail and propose a model accounting for the related forces in good agreement with the experimental data. Such kind of system can potentially revolutionize the field of optical manipulation, contributing to the design of single molecule machines and to the application of oscillatory forces in fundamental physics, cellular manipulation, fluid dynamics, and other soft-matter systems.
DOI
Aerosol Optical Tweezers Constrain the Morphology Evolution of Liquid-Liquid Phase-Separated Atmospheric Particles
Kyle Gorkowski, Neil M. Donahue, Ryan C. Sullivan
Chemical models of atmospheric particles are vital in understanding the role of aerosol particles in atmospheric chemistry, air pollution, human health, and climate change. Advancing these models requires new frameworks that can realistically predict how critical particle properties evolve. We present such a framework for predicting particle phase separation and which morphology will prevail; this controls how each particle interacts with and affects the atmosphere. We studied the mixing behavior of α-pinene secondary organic aerosol (SOA) with different organic phases, as relative humidity was varied to determine the interplay between polarity, miscibility, interfacial tension, and the resulting morphology. Using measurements from aerosol optical tweezers experiments and literature data, a general trend in morphology with increasing atmospheric oxidation was observed, from biphasic partially engulfed (where both phases are immediately accessible to the gas phase) to biphasic core shell (where the organic shell conceals the core) and finally to a single-phase, homogeneous morphology.
DOI
Chemical models of atmospheric particles are vital in understanding the role of aerosol particles in atmospheric chemistry, air pollution, human health, and climate change. Advancing these models requires new frameworks that can realistically predict how critical particle properties evolve. We present such a framework for predicting particle phase separation and which morphology will prevail; this controls how each particle interacts with and affects the atmosphere. We studied the mixing behavior of α-pinene secondary organic aerosol (SOA) with different organic phases, as relative humidity was varied to determine the interplay between polarity, miscibility, interfacial tension, and the resulting morphology. Using measurements from aerosol optical tweezers experiments and literature data, a general trend in morphology with increasing atmospheric oxidation was observed, from biphasic partially engulfed (where both phases are immediately accessible to the gas phase) to biphasic core shell (where the organic shell conceals the core) and finally to a single-phase, homogeneous morphology.
DOI
Autonomous robot-aided optical tweezer system for biological cell manipulation
Mingyang Xie
Over the past few decades, optical tweezers have become a powerful tool that is widely used in cell-based biomedical applications. Their popularity is attributed to their unique advantages in the manipulation of biological cells with high accuracy, degree of freedom, and flexibility in a noninvasive manner. With the trends toward the automation of biological processes with high throughput, precision, and reliability, many autonomous frameworks have been developed for the realization of diverse cell manipulations. This study reviews the latest advancements in automated cell transportation and reorientation control. Moreover, by integrating optical tweezers with other tools, the mechanisms of cell-based physiological activity and subcellular operation are investigated and reviewed. Discussions on the current challenges and potential research trends on optical manipulation of biological cells are finally presented.
DOI
Over the past few decades, optical tweezers have become a powerful tool that is widely used in cell-based biomedical applications. Their popularity is attributed to their unique advantages in the manipulation of biological cells with high accuracy, degree of freedom, and flexibility in a noninvasive manner. With the trends toward the automation of biological processes with high throughput, precision, and reliability, many autonomous frameworks have been developed for the realization of diverse cell manipulations. This study reviews the latest advancements in automated cell transportation and reorientation control. Moreover, by integrating optical tweezers with other tools, the mechanisms of cell-based physiological activity and subcellular operation are investigated and reviewed. Discussions on the current challenges and potential research trends on optical manipulation of biological cells are finally presented.
DOI
Additive manufacturing of laminar flow cells for single-molecule experiments
Arash Ahmadi, Katharina Till, Yngve Hafting, Mark Schüttpelz, Magnar Bjørås, Kyrre Glette, Jim Tørresen, Alexander D. Rowe & Bjørn Dalhus
A microfluidic laminar flow cell (LFC) forms an indispensable component in single-molecule experiments, enabling different substances to be delivered directly to the point under observation and thereby tightly controlling the biochemical environment immediately surrounding single molecules. Despite substantial progress in the production of such components, the process remains relatively inefficient, inaccurate and time-consuming. Here we address challenges and limitations in the routines, materials and the designs that have been commonly employed in the field, and introduce a new generation of LFCs designed for single-molecule experiments and assembled using additive manufacturing. We present single- and multi-channel, as well as reservoir-based LFCs produced by 3D printing to perform single-molecule experiments. Using these flow cells along with optical tweezers, we show compatibility with single-molecule experiments including the isolation and manipulation of single DNA molecules either attached to the surface of a coverslip or as freely movable DNA dumbbells, as well as direct observation of protein-DNA interactions. Using additive manufacturing to produce LFCs with versatility of design and ease of production allow experimentalists to optimize the flow cells to their biological experiments and provide considerable potential for performing multi-component single-molecule experiments.
DOI
A microfluidic laminar flow cell (LFC) forms an indispensable component in single-molecule experiments, enabling different substances to be delivered directly to the point under observation and thereby tightly controlling the biochemical environment immediately surrounding single molecules. Despite substantial progress in the production of such components, the process remains relatively inefficient, inaccurate and time-consuming. Here we address challenges and limitations in the routines, materials and the designs that have been commonly employed in the field, and introduce a new generation of LFCs designed for single-molecule experiments and assembled using additive manufacturing. We present single- and multi-channel, as well as reservoir-based LFCs produced by 3D printing to perform single-molecule experiments. Using these flow cells along with optical tweezers, we show compatibility with single-molecule experiments including the isolation and manipulation of single DNA molecules either attached to the surface of a coverslip or as freely movable DNA dumbbells, as well as direct observation of protein-DNA interactions. Using additive manufacturing to produce LFCs with versatility of design and ease of production allow experimentalists to optimize the flow cells to their biological experiments and provide considerable potential for performing multi-component single-molecule experiments.
DOI
Friday, November 22, 2019
Sustained self-starting orbital motion of a glass-fiber “nanoengine” driven by photophoretic forces
Shangran Xie, Riccardo Pennetta, Zheqi Wang, Philip St. J. Russell
Controllable optically-driven rotation of microscopic objects is desirable in many applications but is difficult to achieve. Here we report sustained self-starting orbital motion of a clamped elongated nanostructure—a glass-fiber nanospike—when a CW laser beam is focused axially on to its tip. Analysis shows that photophoretic anti-trapping forces, acting on the nanospike with a delayed response, introduce optomechanical gain into the mechanical motion, overcoming the intrinsic mechanical dissipation and resulting in growth from noise of oscillations at the resonant frequency of the nanospike. These photophoretic forces further enable phase-locking of the orthogonal fast and slow vibrations of the nanospike (induced by slight mechanical anisotropy), giving rise to a self-sustained orbital motion. The locked phase of orbital motion can be changed by tuning the gas pressure and adjusting the geometrical asymmetry of the system. This light-driven nano-engine opens up a new degree of freedom for controlling the rotational motion of elongated nano-objects.
DOI
Controllable optically-driven rotation of microscopic objects is desirable in many applications but is difficult to achieve. Here we report sustained self-starting orbital motion of a clamped elongated nanostructure—a glass-fiber nanospike—when a CW laser beam is focused axially on to its tip. Analysis shows that photophoretic anti-trapping forces, acting on the nanospike with a delayed response, introduce optomechanical gain into the mechanical motion, overcoming the intrinsic mechanical dissipation and resulting in growth from noise of oscillations at the resonant frequency of the nanospike. These photophoretic forces further enable phase-locking of the orthogonal fast and slow vibrations of the nanospike (induced by slight mechanical anisotropy), giving rise to a self-sustained orbital motion. The locked phase of orbital motion can be changed by tuning the gas pressure and adjusting the geometrical asymmetry of the system. This light-driven nano-engine opens up a new degree of freedom for controlling the rotational motion of elongated nano-objects.
DOI
The post-PAM interaction of RNA-guided spCas9 with DNA dictates its target binding and dissociation
Qian Zhang, Fengcai Wen, Siqi Zhang, Jiachuan Jin, Lulu Bi, Ying Lu, Ming Li, Xu-Guang Xi, Xingxu Huang, Bin Shen and Bo Sun
Cas9 is an RNA-guided endonuclease that targets complementary DNA for cleavage and has been repurposed for many biological usages. Cas9 activities are governed by its direct interactions with DNA. However, information about this interplay and the mechanism involved in its direction of Cas9 activity remain obscure. Using a single-molecule approach, we probed Cas9/sgRNA/DNA interactions along the DNA sequence and found two stable interactions flanking the protospacer adjacent motif (PAM). Unexpectedly, one of them is located approximately 14 base pairs downstream of the PAM (post-PAM interaction), which is beyond the apparent footprint of Cas9 on DNA. Loss or occupation of this interaction site on DNA impairs Cas9 binding and cleavage. Consistently, a downstream helicase could readily displace DNA-bound Cas9 by disrupting this relatively weak post-PAM interaction. Our work identifies a critical interaction of Cas9 with DNA that dictates its binding and dissociation, which may suggest distinct strategies to modulate Cas9 activity.
DOI
Cas9 is an RNA-guided endonuclease that targets complementary DNA for cleavage and has been repurposed for many biological usages. Cas9 activities are governed by its direct interactions with DNA. However, information about this interplay and the mechanism involved in its direction of Cas9 activity remain obscure. Using a single-molecule approach, we probed Cas9/sgRNA/DNA interactions along the DNA sequence and found two stable interactions flanking the protospacer adjacent motif (PAM). Unexpectedly, one of them is located approximately 14 base pairs downstream of the PAM (post-PAM interaction), which is beyond the apparent footprint of Cas9 on DNA. Loss or occupation of this interaction site on DNA impairs Cas9 binding and cleavage. Consistently, a downstream helicase could readily displace DNA-bound Cas9 by disrupting this relatively weak post-PAM interaction. Our work identifies a critical interaction of Cas9 with DNA that dictates its binding and dissociation, which may suggest distinct strategies to modulate Cas9 activity.
DOI
Induction and measurement of the early stage of a host‐parasite interaction using a combined optical trapping and Raman micro‐spectroscopy system
Faris Sinjab, Hany M. Elsheikha, Max Dooley, Ioan Notingher
Understanding and quantifying the temporal acquisition of host cell molecules by intracellular pathogens is fundamentally important in biology. In this study, a recently developed holographic optical trapping (HOT)‐based Raman micro‐spectroscopy (RMS) instrument is applied to detect, characterize and monitor in real time the molecular trafficking of a specific molecular species (isotope‐labelled phenylalanine (L‐Phe(D8)) at the single cell level. This approach enables simultaneous measurement of the chemical composition of human cerebrovascular endothelial cells and the protozoan parasite Toxoplasma gondii in isolation at the very start of the infection process. Using a model to decouple measurement contributions from host and pathogen sampling in the excitation volume, the data indicate that manipulating parasites with HOT coupled with RMS chemical readout was an effective method for measurement of L‐Phe(D8) transfer from host cells to parasites in real‐time, from the moment the parasite enters the host cell.
DOI
Understanding and quantifying the temporal acquisition of host cell molecules by intracellular pathogens is fundamentally important in biology. In this study, a recently developed holographic optical trapping (HOT)‐based Raman micro‐spectroscopy (RMS) instrument is applied to detect, characterize and monitor in real time the molecular trafficking of a specific molecular species (isotope‐labelled phenylalanine (L‐Phe(D8)) at the single cell level. This approach enables simultaneous measurement of the chemical composition of human cerebrovascular endothelial cells and the protozoan parasite Toxoplasma gondii in isolation at the very start of the infection process. Using a model to decouple measurement contributions from host and pathogen sampling in the excitation volume, the data indicate that manipulating parasites with HOT coupled with RMS chemical readout was an effective method for measurement of L‐Phe(D8) transfer from host cells to parasites in real‐time, from the moment the parasite enters the host cell.
DOI
Chirality-dependent optical dipole potential
Seyedeh Hamideh Kazemi and Mohammad Mahmoudi
In this paper, we show the possibility of spatially separating two opposite enantiomers of chiral molecules, using an optical dipole potential. Because of the broken mirror symmetry of effective potential, chiral molecules have a cyclic three-level Δ-configuration structure. Irradiation of these molecules with three femtosecond laser pulses gives rise to an enantiomer-dependent optical force. Interestingly, considerable differences in the direction of the force felt by the enantiomers have been shown to cause the chirality-dependent optical dipole potential which stably captures only one enantiomeric form. Moreover, the proposed scheme provides a complete control over what kind of molecules, the left- or right-handed ones, can be selectively trapped. Note that we have analyzed the optical force, and specifically the trapping effect, by considering the full interaction Hamiltonian, including both rotating and counter-rotating terms.
DOI
In this paper, we show the possibility of spatially separating two opposite enantiomers of chiral molecules, using an optical dipole potential. Because of the broken mirror symmetry of effective potential, chiral molecules have a cyclic three-level Δ-configuration structure. Irradiation of these molecules with three femtosecond laser pulses gives rise to an enantiomer-dependent optical force. Interestingly, considerable differences in the direction of the force felt by the enantiomers have been shown to cause the chirality-dependent optical dipole potential which stably captures only one enantiomeric form. Moreover, the proposed scheme provides a complete control over what kind of molecules, the left- or right-handed ones, can be selectively trapped. Note that we have analyzed the optical force, and specifically the trapping effect, by considering the full interaction Hamiltonian, including both rotating and counter-rotating terms.
DOI
Integrating ultrafast and stochastic dynamics studies of Brownian motion in molecular systems and colloidal particles
Guilherme H. Oliveira, Rene A. Nome
Ultrafast spectroscopy and stochastic dynamics studies of chemical dynamics in solution with high resolution in both space and time have been undertaken for many years, but it is still challenging to connect fundamental knowledge obtained from stroboscopic approaches at ultrashort timescales and small length scales with that obtained by directly measuring individual particle motion at longer timescales. Therefore, it is interesting, conceptually and experimentally, to understand the similarities and differences between these two approaches to the study of chemical dynamics in condensed phase systems. We discuss recent advances in the understanding of the transition from ballistic to diffusive motion and chemical reaction rate theories and describe the significance of the findings in relation to the study of thermally activated processes at multiple time and length scales.
DOI
Ultrafast spectroscopy and stochastic dynamics studies of chemical dynamics in solution with high resolution in both space and time have been undertaken for many years, but it is still challenging to connect fundamental knowledge obtained from stroboscopic approaches at ultrashort timescales and small length scales with that obtained by directly measuring individual particle motion at longer timescales. Therefore, it is interesting, conceptually and experimentally, to understand the similarities and differences between these two approaches to the study of chemical dynamics in condensed phase systems. We discuss recent advances in the understanding of the transition from ballistic to diffusive motion and chemical reaction rate theories and describe the significance of the findings in relation to the study of thermally activated processes at multiple time and length scales.
DOI
Lateral optical forces on linearly polarized emitters near a reciprocal substrate
Hafssaa Latioui and Mário G. Silveirinha
We theoretically investigate the conditions for the emergence of lateral (recoil) optical forces on generic dipole-type emitters positioned nearby a reciprocal translation-invariant substrate. Surprisingly, we find that for linearly polarized electric dipoles and for a gradientless excitation the lateral force invariably vanishes, independent of the anisotropy (e.g., tilted optical axes) or chirality of the substrate. We identify an opportunity to have a recoil force relying on a superposition of two linearly polarized and collinear electric and magnetic dipoles. Counterintuitively, it is shown that when such an emitter stands above a uniaxial dielectric half-space with tilted optical axes it may experience a recoil force oriented along the direction perpendicular to the plane defined by the interface normal and the substrate optical axis.
DOI
We theoretically investigate the conditions for the emergence of lateral (recoil) optical forces on generic dipole-type emitters positioned nearby a reciprocal translation-invariant substrate. Surprisingly, we find that for linearly polarized electric dipoles and for a gradientless excitation the lateral force invariably vanishes, independent of the anisotropy (e.g., tilted optical axes) or chirality of the substrate. We identify an opportunity to have a recoil force relying on a superposition of two linearly polarized and collinear electric and magnetic dipoles. Counterintuitively, it is shown that when such an emitter stands above a uniaxial dielectric half-space with tilted optical axes it may experience a recoil force oriented along the direction perpendicular to the plane defined by the interface normal and the substrate optical axis.
DOI
Thursday, November 21, 2019
In situ Observation of Efflorescence and Deliquescence Phase Transitions of Single NaCl and NaNO3 Mixture Particles in Air using a Laser Trapping Technique
Shoji Ishizaka, Fangqin Guo, Xiaomeng Tian, Samantha Seng, Yeny A. Tobon, and Sophie Sobanska
A novel experimental approach to study the hygroscopic properties of multi-component inorganic aerosols was demonstrated using a laser trapping technique. The efflorescence and deliquescence phase transitions of the equimolar mixture of NaCl and NaNO3 particles levitated in air were reversibly induced by controlling relative humidity. The two-stage phase transitions of the particles during the dehumidifying and humidifying processes were successfully observed in air. To our knowledge, this is the first experimental result to observe the reversible hygroscopic behavior of single optically-levitated multi-component inorganic aerosols in air. Furthermore, to elucidate the influence of solid substrates on the homogeneous and heterogeneous nucleation processes, the efflorescence relative humidity (ERH) and mutual efflorescence relative humidity (MERH) in air were compared with those observed on a hydrophobic glass substrate. The average ERH and MERH values of the NaCl–NaNO3 particles levitated in air were lower than those obtained for the particles deposited on the hydrophobic glass substrate.
DOI
A novel experimental approach to study the hygroscopic properties of multi-component inorganic aerosols was demonstrated using a laser trapping technique. The efflorescence and deliquescence phase transitions of the equimolar mixture of NaCl and NaNO3 particles levitated in air were reversibly induced by controlling relative humidity. The two-stage phase transitions of the particles during the dehumidifying and humidifying processes were successfully observed in air. To our knowledge, this is the first experimental result to observe the reversible hygroscopic behavior of single optically-levitated multi-component inorganic aerosols in air. Furthermore, to elucidate the influence of solid substrates on the homogeneous and heterogeneous nucleation processes, the efflorescence relative humidity (ERH) and mutual efflorescence relative humidity (MERH) in air were compared with those observed on a hydrophobic glass substrate. The average ERH and MERH values of the NaCl–NaNO3 particles levitated in air were lower than those obtained for the particles deposited on the hydrophobic glass substrate.
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Lippia sidoides and Lippia origanoides essential oils affect the viability, motility and ultrastructure of Trypanosoma cruzi
Andrezza Raposo Borges de Melo, Taciana Mirely Maciel Higino, Aline Dulce Pitt da Rocha Oliveira, Adriana Fontes, Diego César Nunes da Silva, Maria Carolina Accioly Brelaz de Castro, José Arimatéia Dantas Lopes, Regina Celia Bressan Queiroz de Figueiredo
Chagas disease, caused by the protozoan Trypanosoma cruzi, is considered a public health problem. The current chemotherapy for this illness causes serious side effects and its use in the chronic phase of the disease is still controversial. In this sense, the investigation of novel therapeutic strategies remains a priority. The essential oils (EOs) from aromatic plants emerge as a promising source of bioactive compounds. In a previous work we reported the trypanocidal activity of the essential oils from the medicinal plants Lippia sidoides (LSEO) and Lippia origanoides (LOEO) against T. cruzi. Herein, we aimed to further investigate, in more details, the mode of action of LSEO and LOEO on the different developmental stages of this parasite. We showed that Lippia sidoides (LSEO) and Lippia origanoides (LOEO) induced a significant reduction in the percentage of macrophages infected by T. cruzi and in the number of intracellular parasites. Ultrastructural analysis showed that the treatment with both oils caused morphological changes consistent with loss of viability and cell death. The reduced staining with calcein and the increase in the proportion of HE–positive cells also demonstrated that LSEO and LOEO caused loss of parasite viability and membrane integrity. A considerable decrease in Rhodamine 123 and an increase in fluorescence intensity of MitoSox in LOEO were indicative of loss of mitochondrial potential and generation of reactive oxygen species, which ultimately lead to parasite death. Moreover, the optical tweezer analysis indicated that LOEO was more effective in reducing the motility of the epimastigotes. Together our results demonstrated that the LSEO and LOEO are active against T. cruzi and constitute a promising drugs for the therapy of Chagas disease.
DOI
Chagas disease, caused by the protozoan Trypanosoma cruzi, is considered a public health problem. The current chemotherapy for this illness causes serious side effects and its use in the chronic phase of the disease is still controversial. In this sense, the investigation of novel therapeutic strategies remains a priority. The essential oils (EOs) from aromatic plants emerge as a promising source of bioactive compounds. In a previous work we reported the trypanocidal activity of the essential oils from the medicinal plants Lippia sidoides (LSEO) and Lippia origanoides (LOEO) against T. cruzi. Herein, we aimed to further investigate, in more details, the mode of action of LSEO and LOEO on the different developmental stages of this parasite. We showed that Lippia sidoides (LSEO) and Lippia origanoides (LOEO) induced a significant reduction in the percentage of macrophages infected by T. cruzi and in the number of intracellular parasites. Ultrastructural analysis showed that the treatment with both oils caused morphological changes consistent with loss of viability and cell death. The reduced staining with calcein and the increase in the proportion of HE–positive cells also demonstrated that LSEO and LOEO caused loss of parasite viability and membrane integrity. A considerable decrease in Rhodamine 123 and an increase in fluorescence intensity of MitoSox in LOEO were indicative of loss of mitochondrial potential and generation of reactive oxygen species, which ultimately lead to parasite death. Moreover, the optical tweezer analysis indicated that LOEO was more effective in reducing the motility of the epimastigotes. Together our results demonstrated that the LSEO and LOEO are active against T. cruzi and constitute a promising drugs for the therapy of Chagas disease.
DOI
The Anti-Aggregation Holdase Hsp33 Promotes the Formation of Folded Protein Structures
Fatemeh Moayed, Sergey Bezrukavnikov, Mohsin M.Naqvi, Bastian Groitl, Claudia M. Cremers, Guenter Kramer, Kingshuk Ghosh, Ursula Jakob, Sander J. Tans
Holdase chaperones are known to be central to suppressing aggregation, but how they affect substrate conformations remains poorly understood. Here, we use optical tweezers to study how the holdase Hsp33 alters folding transitions within single maltose binding proteins and aggregation transitions between maltose binding protein substrates. Surprisingly, we find that Hsp33 not only suppresses aggregation but also guides the folding process. Two modes of action underlie these effects. First, Hsp33 binds unfolded chains, which suppresses aggregation between substrates and folding transitions within substrates. Second, Hsp33 binding promotes substrate states in which most of the chain is folded and modifies their structure, possibly by intercalating its intrinsically disordered regions. A statistical ensemble model shows how Hsp33 function results from the competition between these two contrasting effects. Our findings reveal an unexpectedly comprehensive functional repertoire for Hsp33 that may be more prevalent among holdases and dispels the notion of a strict chaperone hierarchy.
DOI
Holdase chaperones are known to be central to suppressing aggregation, but how they affect substrate conformations remains poorly understood. Here, we use optical tweezers to study how the holdase Hsp33 alters folding transitions within single maltose binding proteins and aggregation transitions between maltose binding protein substrates. Surprisingly, we find that Hsp33 not only suppresses aggregation but also guides the folding process. Two modes of action underlie these effects. First, Hsp33 binds unfolded chains, which suppresses aggregation between substrates and folding transitions within substrates. Second, Hsp33 binding promotes substrate states in which most of the chain is folded and modifies their structure, possibly by intercalating its intrinsically disordered regions. A statistical ensemble model shows how Hsp33 function results from the competition between these two contrasting effects. Our findings reveal an unexpectedly comprehensive functional repertoire for Hsp33 that may be more prevalent among holdases and dispels the notion of a strict chaperone hierarchy.
DOI
Single-cell patterning technology for biological applications
Zihui Wang, Baihe Lang, Yingmin Qu, Li Li, Zhengxun Song, and Zuobin Wang
Single-cell patterning technology has revealed significant contributions of single cells to conduct basic and applied biological studies in vitro such as the understanding of basic cell functions, neuronal network formation, and drug screening. Unlike traditional population-based cell patterning approaches, single-cell patterning is an effective technology of fully understanding cell heterogeneity by precisely controlling the positions of individual cells. Therefore, much attention is currently being paid to this technology, leading to the development of various micro-nanofabrication methodologies that have been applied to locate cells at the single-cell level. In recent years, various methods have been continuously improved and innovated on the basis of existing ones, overcoming the deficiencies and promoting the progress in biomedicine. In particular, microfluidics with the advantages of high throughput, small sample volume, and the ability to combine with other technologies has a wide range of applications in single-cell analysis. Here, we present an overview of the recent advances in single-cell patterning technology, with a special focus on current physical and physicochemical methods including stencil patterning, trap- and droplet-based microfluidics, and chemical modification on surfaces via photolithography, microcontact printing, and scanning probe lithography. Meanwhile, the methods applied to biological studies and the development trends of single-cell patterning technology in biological applications are also described.
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Transportation of dielectric particles along illumination pattern with bend and phase gradient
Kai Niu, Dongjie Bao, Shaohua Tao
Automatic transportation of optically trapped particles along a bend in the plane perpendicular to beam propagation direction was realized with a beam of designed amplitude and phase distributions. The bends were formed with illumination pattern and possessed phase gradients. The relation between the motion of dielectric particles and the bends of different angles was analyzed, and experiment was carried out to demonstrate the automatic transportation. We also investigated influence of the angle of a bend on the transportation speed of a trapped particle. The bend with phase gradients is critical for realization of automatic movement of particles along an arbitrary route which can be constructed with combination of bends, arcs, and lines. The proposed technique can be applied for directional transportation and optical sorting.
DOI
Automatic transportation of optically trapped particles along a bend in the plane perpendicular to beam propagation direction was realized with a beam of designed amplitude and phase distributions. The bends were formed with illumination pattern and possessed phase gradients. The relation between the motion of dielectric particles and the bends of different angles was analyzed, and experiment was carried out to demonstrate the automatic transportation. We also investigated influence of the angle of a bend on the transportation speed of a trapped particle. The bend with phase gradients is critical for realization of automatic movement of particles along an arbitrary route which can be constructed with combination of bends, arcs, and lines. The proposed technique can be applied for directional transportation and optical sorting.
DOI
Tuesday, November 19, 2019
Force interactions between Yersiniae lipopolysaccharides and monoclonal antibodies: An optical tweezers study
Ilya Konyshev, Andrey Byvalov, Boris Ananchenko, Rawil Fakhrullin, Anna Danilushkina, Lyubov Dudina
This article reports the force spectroscopy investigation of interactions between lipopolysaccharides (LPSs) of two species from Yersinia genus and complementary (or heterologous) monoclonal antibodies (mAbs). We have obtained the experimental data by optical trapping on the “sensitized polystyrene microsphere – sensitized glass substrate” model system at its approach – retraction in vertical plane. We detected non-specific interactions in low-amplitude areas on histograms mainly due to physicochemical properties of abiotic surface and specific interactions in complementary pairs “antigen – antibodies” in high-amplitude areas (100–120 pN) on histograms. The developed measurement procedure can be used for detection of rupture forces in other molecular pairs.
DOI
This article reports the force spectroscopy investigation of interactions between lipopolysaccharides (LPSs) of two species from Yersinia genus and complementary (or heterologous) monoclonal antibodies (mAbs). We have obtained the experimental data by optical trapping on the “sensitized polystyrene microsphere – sensitized glass substrate” model system at its approach – retraction in vertical plane. We detected non-specific interactions in low-amplitude areas on histograms mainly due to physicochemical properties of abiotic surface and specific interactions in complementary pairs “antigen – antibodies” in high-amplitude areas (100–120 pN) on histograms. The developed measurement procedure can be used for detection of rupture forces in other molecular pairs.
DOI
X-ray diffraction measurement of a single nanometre-sized particle levitated in air by an optical-trap sample holder
Y. Fukuyama, N. Yasuda, K. Sugimoto and S. Kimura
A single-beam optical-trap sample holder for X-ray diffraction measurements with synchrotron radiation has been developed. The sample holder was used to obtain an X-ray diffraction image of a single ZnO particle levitated in air, without mechanical contact, by the optical gradient force exerted by a focused laser beam. The diffraction image showed a Debye ring pattern, which was similar to a powder diffraction pattern of an assemblage of ZnO particles. While the ZnO particle is held by the optical trap in air, it rotates irregularly. Therefore, the Debye ring pattern of the ZnO particle can be clearly obtained even if the ZnO particle is a single grain. Lattice parameters and crystallite size of the single ZnO particle were determined simultaneously. The lattice parameters were determined to be a = 3.2505 ± 0.0005 Å and c = 5.207 ± 0.006 Å, which are consistent with those of the assemblage of ZnO particles. The crystallite size determined by the Scherrer method was 193.4 ± 26.2 nm.
DOI
A single-beam optical-trap sample holder for X-ray diffraction measurements with synchrotron radiation has been developed. The sample holder was used to obtain an X-ray diffraction image of a single ZnO particle levitated in air, without mechanical contact, by the optical gradient force exerted by a focused laser beam. The diffraction image showed a Debye ring pattern, which was similar to a powder diffraction pattern of an assemblage of ZnO particles. While the ZnO particle is held by the optical trap in air, it rotates irregularly. Therefore, the Debye ring pattern of the ZnO particle can be clearly obtained even if the ZnO particle is a single grain. Lattice parameters and crystallite size of the single ZnO particle were determined simultaneously. The lattice parameters were determined to be a = 3.2505 ± 0.0005 Å and c = 5.207 ± 0.006 Å, which are consistent with those of the assemblage of ZnO particles. The crystallite size determined by the Scherrer method was 193.4 ± 26.2 nm.
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Volatility measurements of 1, 2, 6-hexanetriol in levitated viscous aerosol particles
Xi-Juan Lv, Zhe Chen, Jia-Bi Ma, Yun-Hong Zhang
The partitioning of semi-volatile organic compounds (SVOCs) between particle and gas phases is a primary focus in the study of the formation and lifetime of secondary organic aerosols (SOAs). To predict the temporal and spatial distribution of SOAs, it is essential to retrieve the fundamental parameters of SVOCs that govern the distribution of organic compounds between the condensed and gas phases. In the present work, the volatility of 1,2,6-hexanetriol in sucrose/1,2,6-hexanetriol/water mixed aerosol droplets was studied by employing optical tweezers coupled with cavity-enhanced Raman spectroscopy. The radii and refractive indexes of the levitated droplets were determined in real time using the wavelength positions of stimulated Raman spectra, and the effective vapor pressures of 1,2,6-hexanetriol at different relative humidity (RH) were obtained according to Maxwell equation. For the droplets with sucrose/1,2,6-hexanetriol molar ratio of 1:1, the effective vapor pressure of 1,2,6-hexanetriol decreased with the decrease of RH. When the RH decreased from 70% to 10%, the effective vapor pressure of 1,2,6-hexanetriol decreased from (2.16 to (6.72. Compared to the vapor pressure of pure 1,2,6-hexanetriol (1.16 ± 0.025), the evaporation of 1,2,6-hexanetriol in the mixed droplet was suppressed by sucrose, especially at low RH. For the mixed droplets with sucrose/1,2,6-hexanetriol molar ratio of 3:1, 1:3, a similar phenomenon was observed. Besides, for the mixed droplets under constant RH, the effective vapor pressure of 1,2,6-hexanetriol decreased with the sucrose increasing, and the presence of 1,2,6-hexanetriol caused viscosity decline of sucrose in the meantime. To characterize the water mass transfer of mixed droplets at different RH, the characteristic time ratios between the droplet radius and the RH were calculated. Compared to the characteristic time ratio of pure sucrose droplets, the characteristic time ratio of the mixed droplets apparently decreased. And for constant RH, the characteristic time of sucrose/1,2,6-hexanetriol/H2O decreased with the increase of 1,2,6-hexanetriol. In general, we report the studies of both volatility and molecular diffusion process in the aerosol phase for the sucrose/1,2,6-hexanetriol/H2O ternary system, these results may provide a theoretical basis for subsequent research concerning the volatility of SVOCs in super viscous aerosols.
DOI
The partitioning of semi-volatile organic compounds (SVOCs) between particle and gas phases is a primary focus in the study of the formation and lifetime of secondary organic aerosols (SOAs). To predict the temporal and spatial distribution of SOAs, it is essential to retrieve the fundamental parameters of SVOCs that govern the distribution of organic compounds between the condensed and gas phases. In the present work, the volatility of 1,2,6-hexanetriol in sucrose/1,2,6-hexanetriol/water mixed aerosol droplets was studied by employing optical tweezers coupled with cavity-enhanced Raman spectroscopy. The radii and refractive indexes of the levitated droplets were determined in real time using the wavelength positions of stimulated Raman spectra, and the effective vapor pressures of 1,2,6-hexanetriol at different relative humidity (RH) were obtained according to Maxwell equation. For the droplets with sucrose/1,2,6-hexanetriol molar ratio of 1:1, the effective vapor pressure of 1,2,6-hexanetriol decreased with the decrease of RH. When the RH decreased from 70% to 10%, the effective vapor pressure of 1,2,6-hexanetriol decreased from (2.16 to (6.72. Compared to the vapor pressure of pure 1,2,6-hexanetriol (1.16 ± 0.025), the evaporation of 1,2,6-hexanetriol in the mixed droplet was suppressed by sucrose, especially at low RH. For the mixed droplets with sucrose/1,2,6-hexanetriol molar ratio of 3:1, 1:3, a similar phenomenon was observed. Besides, for the mixed droplets under constant RH, the effective vapor pressure of 1,2,6-hexanetriol decreased with the sucrose increasing, and the presence of 1,2,6-hexanetriol caused viscosity decline of sucrose in the meantime. To characterize the water mass transfer of mixed droplets at different RH, the characteristic time ratios between the droplet radius and the RH were calculated. Compared to the characteristic time ratio of pure sucrose droplets, the characteristic time ratio of the mixed droplets apparently decreased. And for constant RH, the characteristic time of sucrose/1,2,6-hexanetriol/H2O decreased with the increase of 1,2,6-hexanetriol. In general, we report the studies of both volatility and molecular diffusion process in the aerosol phase for the sucrose/1,2,6-hexanetriol/H2O ternary system, these results may provide a theoretical basis for subsequent research concerning the volatility of SVOCs in super viscous aerosols.
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Optical fiber-based manipulation of microparticles in microfluidic channel through thermal convection
Wei Zhan, Mingjun Yang and Wuzhou Song
We demonstrate a simple optical fiber microfluidic control device based on photothermal effect induced convection, which can realize flexible manipulation and particle sorting over a range of hundreds of microns. Three single-mode optical fibers in a regular arrangement were utilized for the realization of the particle capture function, which simplifies the complex equipment and reduces the cost in traditional optical tweezers. We also display a unique control mode: the horizontal manipulation of particles by moving the fiber vertically. It will hopefully be applied in biomedical, chemical analysis, material testing and other fields.
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We demonstrate a simple optical fiber microfluidic control device based on photothermal effect induced convection, which can realize flexible manipulation and particle sorting over a range of hundreds of microns. Three single-mode optical fibers in a regular arrangement were utilized for the realization of the particle capture function, which simplifies the complex equipment and reduces the cost in traditional optical tweezers. We also display a unique control mode: the horizontal manipulation of particles by moving the fiber vertically. It will hopefully be applied in biomedical, chemical analysis, material testing and other fields.
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Optimal wave fields for micromanipulation in complex scattering environments
Michael Horodynski, Matthias Kühmayer, Andre Brandstötter, Kevin Pichler, Yan V. Fyodorov, Ulrich Kuhl & Stefan Rotter
The manipulation of small objects with light has become an indispensable tool in many areas of research, ranging from physics to biology and medicine. Here, we demonstrate how to implement micromanipulation at the optimal level of efficiency for arbitrarily shaped targets and inside complex environments such as disordered media. Our approach is to design wavefronts in the far field with optimal properties in the near field of the target to apply the strongest possible force, pressure or torque as well as to achieve the most efficient focus inside the target. This non-iterative technique only relies on a simple eigenvalue problem established from the system’s scattering matrix and its dependence on small shifts in specific target parameters (access to the near field of the target is not required). To illustrate this concept, we perform a proof-of-principle experiment in the microwave regime, fully confirming our predictions.
DOI
The manipulation of small objects with light has become an indispensable tool in many areas of research, ranging from physics to biology and medicine. Here, we demonstrate how to implement micromanipulation at the optimal level of efficiency for arbitrarily shaped targets and inside complex environments such as disordered media. Our approach is to design wavefronts in the far field with optimal properties in the near field of the target to apply the strongest possible force, pressure or torque as well as to achieve the most efficient focus inside the target. This non-iterative technique only relies on a simple eigenvalue problem established from the system’s scattering matrix and its dependence on small shifts in specific target parameters (access to the near field of the target is not required). To illustrate this concept, we perform a proof-of-principle experiment in the microwave regime, fully confirming our predictions.
DOI
Angular momentum properties of hybrid cylindrical vector vortex beams in tightly focused optical systems
Peiwen Meng, Zhongsheng Man, A. P. Konijnenberg, and H. P. Urbach
Optical angular momenta (AM) have attracted tremendous research interest in recent years. In this paper we theoretically investigate the electromagnetic field and angular momentum properties of tightly focused arbitrary cylindrical vortex vector (CVV) input beams. An absorptive particle is placed in focused CVV fields to analyze the optical torques. The spin-orbit motions of the particle can be predicted and controlled when the influences of different parameters, such as the topological charge, the polarization and the initial phases, are taken into account. These findings will be helpful in optical beam shaping, optical spin-orbit interaction and practical optical manipulation.
DOI
Optical angular momenta (AM) have attracted tremendous research interest in recent years. In this paper we theoretically investigate the electromagnetic field and angular momentum properties of tightly focused arbitrary cylindrical vortex vector (CVV) input beams. An absorptive particle is placed in focused CVV fields to analyze the optical torques. The spin-orbit motions of the particle can be predicted and controlled when the influences of different parameters, such as the topological charge, the polarization and the initial phases, are taken into account. These findings will be helpful in optical beam shaping, optical spin-orbit interaction and practical optical manipulation.
DOI
Thursday, November 14, 2019
Lateral Subunit Coupling Determines Intermediate Filament Mechanics
Charlotta Lorenz, Johanna Forsting, Anna V. Schepers, Julia Kraxner, Susanne Bauch, Hannes Witt, Stefan Klumpp, and Sarah Köster
The cytoskeleton is a composite network of three types of protein filaments, among which intermediate filaments (IFs) are the most extensible ones. Two very important IFs are keratin and vimentin, which have similar molecular architectures but different mechanical behaviors. Here we compare the mechanical response of single keratin and vimentin filaments using optical tweezers. We show that the mechanics of vimentin strongly depends on the ionic strength of the buffer and that its force-strain curve suggests a high degree of cooperativity between subunits. Indeed, a computational model indicates that in contrast to keratin, vimentin is characterized by strong lateral subunit coupling of its charged monomers during unfolding of α helices. We conclude that cells can tune their mechanics by differential use of keratin versus vimentin.
DOI
The cytoskeleton is a composite network of three types of protein filaments, among which intermediate filaments (IFs) are the most extensible ones. Two very important IFs are keratin and vimentin, which have similar molecular architectures but different mechanical behaviors. Here we compare the mechanical response of single keratin and vimentin filaments using optical tweezers. We show that the mechanics of vimentin strongly depends on the ionic strength of the buffer and that its force-strain curve suggests a high degree of cooperativity between subunits. Indeed, a computational model indicates that in contrast to keratin, vimentin is characterized by strong lateral subunit coupling of its charged monomers during unfolding of α helices. We conclude that cells can tune their mechanics by differential use of keratin versus vimentin.
DOI
Wednesday, November 13, 2019
Laser Controlled 65 Micrometer Long Microrobot Made of Ni‐Ti Shape Memory Alloy
Min‐Soo Kim Hyun‐Taek Lee Sung‐Hoon Ahn
Microrobotics has many potential applications, such as environmental remediation, in the biomedical arena. However, existing microrobots exhibit practical limitations including inadequate biocompatibility and imprecise control. Here, a microrobot made of shape memory alloy (SMA) actuator which can be driven by laser scanning to perform microscale motions is introduced. The 65 µm long microrobot having crawling‐like motion can demonstrate the movement with 10.0 µm s−1 of the maximum speed. The microrobot is controlled by a laser affording wireless, spatiotemporally selective capabilities. During actuation, the robot exhibits crawling‐like motions including trigger via the SMA as removal of adhesion to surface, propulsion induced by optothermal and optical trapping effects. Both theoretical predictions and experimental results confirm that the SMA microrobot can be actuated and controlled via laser scanning. The principle of SMA microrobots, and the optical actuation method, can be broadened to other applications that require deformable microscale structures suitable for mass production.
DOI
Microrobotics has many potential applications, such as environmental remediation, in the biomedical arena. However, existing microrobots exhibit practical limitations including inadequate biocompatibility and imprecise control. Here, a microrobot made of shape memory alloy (SMA) actuator which can be driven by laser scanning to perform microscale motions is introduced. The 65 µm long microrobot having crawling‐like motion can demonstrate the movement with 10.0 µm s−1 of the maximum speed. The microrobot is controlled by a laser affording wireless, spatiotemporally selective capabilities. During actuation, the robot exhibits crawling‐like motions including trigger via the SMA as removal of adhesion to surface, propulsion induced by optothermal and optical trapping effects. Both theoretical predictions and experimental results confirm that the SMA microrobot can be actuated and controlled via laser scanning. The principle of SMA microrobots, and the optical actuation method, can be broadened to other applications that require deformable microscale structures suitable for mass production.
DOI
Single molecule mechanics resolves the earliest events in force generation by cardiac myosin
Michael S Woody, Donald A Winkelmann, Marco Capitanio, E Michael Ostap, Yale E Goldman
Key steps of cardiac mechanochemistry, including the force-generating working stroke and the release of phosphate (Pi), occur rapidly after myosin-actin attachment. An ultra-high-speed optical trap enabled direct observation of the timing and amplitude of the working stroke, which can occur within <200 μs of actin binding by β-cardiac myosin. The initial actomyosin state can sustain loads of at least 4.5 pN and proceeds directly to the stroke or detaches before releasing ATP hydrolysis products. The rates of these processes depend on the force. The time between binding and stroke is unaffected by 10 mM Pi which, along with other findings, indicates the stroke precedes phosphate release. After Pi release, Pi can rebind enabling reversal of the working stroke. Detecting these rapid events under physiological loads provides definitive indication of the dynamics by which actomyosin converts biochemical energy into mechanical work.
DOI
Key steps of cardiac mechanochemistry, including the force-generating working stroke and the release of phosphate (Pi), occur rapidly after myosin-actin attachment. An ultra-high-speed optical trap enabled direct observation of the timing and amplitude of the working stroke, which can occur within <200 μs of actin binding by β-cardiac myosin. The initial actomyosin state can sustain loads of at least 4.5 pN and proceeds directly to the stroke or detaches before releasing ATP hydrolysis products. The rates of these processes depend on the force. The time between binding and stroke is unaffected by 10 mM Pi which, along with other findings, indicates the stroke precedes phosphate release. After Pi release, Pi can rebind enabling reversal of the working stroke. Detecting these rapid events under physiological loads provides definitive indication of the dynamics by which actomyosin converts biochemical energy into mechanical work.
DOI
Three-Dimensional Pose Estimation of Optically Transparent Microrobots
Maria Grammatikopoulou, Guang-Zhong Yang
The use of microrobots for cell manipulation has a range of applications in biomedical research. Direct sensing of microrobot three-dimensional (3D) position and orientation, however, is practically challenging due to the small scale involved. This letter proposes a vision-based method for estimating the 3D pose of optically transparent microrobots based on Optical Tweezers (OT) manipulation by using Convolutional Neural Networks (CNNs). A model-based approach is used to generate the large training set required for CNNs. Detailed validation is performed to demonstrate the experimental use of the technique.
DOI
The use of microrobots for cell manipulation has a range of applications in biomedical research. Direct sensing of microrobot three-dimensional (3D) position and orientation, however, is practically challenging due to the small scale involved. This letter proposes a vision-based method for estimating the 3D pose of optically transparent microrobots based on Optical Tweezers (OT) manipulation by using Convolutional Neural Networks (CNNs). A model-based approach is used to generate the large training set required for CNNs. Detailed validation is performed to demonstrate the experimental use of the technique.
DOI
Photonic crystal nanobeam/micro-ring hybrid-cavities for optical trapping
Shoubao Han, Yaocheng Shi
We propose a new type of hybrid-cavity structure for trapping nanoscale particles. The hybrid cavity is based on a ring waveguide with the incorporation of a photonic crystal nanobeam cavity (PCNC). We design the cavity and investigate the influence of geometric parameters on its performance and optical trapping ability. The numerical results show that high quality factor, low mode volume and strong optical trapping ability can be achieved. The radii of holes are quadratically tapered from the center to two sides with a smaller period in the mirrors of the PCNC and the optical trapping force is proportional to (1−T)Q/V of the cavity. Furthermore, a hybrid cavity with optimal trapping ability is realized with quality factor up to 1.98106, mode volume as low as 1.90()3 and its optical trapping force can be as high as −855 pN/mW, which is 15 times enhanced compared to that of a microring resonator with the same radius.
DOI
We propose a new type of hybrid-cavity structure for trapping nanoscale particles. The hybrid cavity is based on a ring waveguide with the incorporation of a photonic crystal nanobeam cavity (PCNC). We design the cavity and investigate the influence of geometric parameters on its performance and optical trapping ability. The numerical results show that high quality factor, low mode volume and strong optical trapping ability can be achieved. The radii of holes are quadratically tapered from the center to two sides with a smaller period in the mirrors of the PCNC and the optical trapping force is proportional to (1−T)Q/V of the cavity. Furthermore, a hybrid cavity with optimal trapping ability is realized with quality factor up to 1.98106, mode volume as low as 1.90()3 and its optical trapping force can be as high as −855 pN/mW, which is 15 times enhanced compared to that of a microring resonator with the same radius.
DOI
Tuesday, November 12, 2019
Structural characterization of the saxitoxin-targeting APTSTX1 aptamer using optical tweezers and molecular dynamics simulations
Nathalie Casanova-Morales, Nataniel L. Figueroa, Karol Alfaro, Felipe Montenegro, Nelson P. Barrera, J. R. Maze, Christian A. M. Wilson, Pablo Conejeros
Optical tweezers have enabled the exploration of picoNewton forces and dynamics in single–molecule systems such as DNA and molecular motors. In this work, we used optical tweezers to study the folding/unfolding dynamics of the APTSTX1–aptamer, a single-stranded DNA molecule with high affinity for saxitoxin (STX), a lethal neurotoxin. By measuring the transition force during (un)folding processes, we were able to characterize and distinguish the conformational changes of this aptamer in the presence of magnesium ions and toxin. This work was supported by molecular dynamics (MD) simulations to propose an unfolding mechanism of the aptamer–Mg+2 complex. Our results are a step towards the development of new aptamer-based STX sensors that are potentially cheaper and more sensitive than current alternatives.
DOI
Optical tweezers have enabled the exploration of picoNewton forces and dynamics in single–molecule systems such as DNA and molecular motors. In this work, we used optical tweezers to study the folding/unfolding dynamics of the APTSTX1–aptamer, a single-stranded DNA molecule with high affinity for saxitoxin (STX), a lethal neurotoxin. By measuring the transition force during (un)folding processes, we were able to characterize and distinguish the conformational changes of this aptamer in the presence of magnesium ions and toxin. This work was supported by molecular dynamics (MD) simulations to propose an unfolding mechanism of the aptamer–Mg+2 complex. Our results are a step towards the development of new aptamer-based STX sensors that are potentially cheaper and more sensitive than current alternatives.
DOI
On-the-fly particle metrology in hollow-core photonic crystal fibre
Abhinav Sharma, Shangran Xie, Richard Zeltner, and Philip St.J. Russell
Efficient monitoring of airborne particulate matter (PM), especially particles with aerodynamic diameter less than 2.5 µm (PM2.5), is crucial for improving public health. Reliable information on the concentration, size distribution and chemical characteristics of PMs is key to evaluating air pollution and identifying its sources. Standard methods for PM2.5 characterization require sample collection from the atmosphere and post-analysis using sophisticated equipment in a laboratory environment, and are normally very time-consuming. Although optical methods based on analysis of scattering of free-space laser beams or evanescent fields are in principle suitable for real-time particle counting and sizing, lack of knowledge of the refractive index in these methods not only leads to inevitable sizing ambiguity but also prevents identification of the particle material. In the case of evanescent wave detection, the system lifetime is strongly limited by adhesion of particles to the surfaces. Here we report a novel technique for airborne particle metrology based on hollow-core photonic crystal fibre. It offers in situ particle counting, sizing and refractive index measurement with effectively unlimited device lifetime, and relies on optical forces that automatically capture airborne particles in front of the hollow core and propel them into the fibre. The resulting transmission drop, together with the time-of-flight of the particles passing through the fibre, provide unambiguous mapping of particle size and refractive index with high accuracy. The technique offers unique advantages over currently available real-time particle metrology systems, and can be directly applied to monitoring air pollution in the open atmosphere as well as precise particle characterization in a local environment such as a closed room or a reaction vessel.
DOI
Efficient monitoring of airborne particulate matter (PM), especially particles with aerodynamic diameter less than 2.5 µm (PM2.5), is crucial for improving public health. Reliable information on the concentration, size distribution and chemical characteristics of PMs is key to evaluating air pollution and identifying its sources. Standard methods for PM2.5 characterization require sample collection from the atmosphere and post-analysis using sophisticated equipment in a laboratory environment, and are normally very time-consuming. Although optical methods based on analysis of scattering of free-space laser beams or evanescent fields are in principle suitable for real-time particle counting and sizing, lack of knowledge of the refractive index in these methods not only leads to inevitable sizing ambiguity but also prevents identification of the particle material. In the case of evanescent wave detection, the system lifetime is strongly limited by adhesion of particles to the surfaces. Here we report a novel technique for airborne particle metrology based on hollow-core photonic crystal fibre. It offers in situ particle counting, sizing and refractive index measurement with effectively unlimited device lifetime, and relies on optical forces that automatically capture airborne particles in front of the hollow core and propel them into the fibre. The resulting transmission drop, together with the time-of-flight of the particles passing through the fibre, provide unambiguous mapping of particle size and refractive index with high accuracy. The technique offers unique advantages over currently available real-time particle metrology systems, and can be directly applied to monitoring air pollution in the open atmosphere as well as precise particle characterization in a local environment such as a closed room or a reaction vessel.
DOI
Orientation of swimming cells with annular beam optical tweezers
Isaac C.D. Lenton, Declan J. Armstrong, Alexander B. Stilgoe, Timo A. Nieminen, Halina Rubinsztein-Dunlop
Optical tweezers are a versatile tool that can be used to manipulate small particles including both motile and non-motile bacteria and cells. The orientation of a non-spherical particle within a beam depends on the shape of the particle and the shape of the light field. By using multiple beams, sculpted light fields or dynamically changing beams, it is possible to control the orientation of certain particles. In this paper we discuss the orientation of the rod-shaped bacteria Escherichia coli (E. coli) using dynamically shifting annular beam optical tweezers. We begin with examples of different beams used for the orientation of rod-shaped particles. We discuss the differences between orientation of motile and non-motile particles, and explore annular beams and the circumstances when they may be beneficial for manipulation of non-spherical particles or cells. Using simulations we map out the trajectory the E. coli takes. Estimating the trap stiffness along the trajectory gives us an insight into how stable an intermediate rotation is with respect to the desired orientation. Using this method, we predict and experimentally verify the change in the orientation of motile E. coli from vertical to near-horizontal with only one intermediate step. The method is not specific to exploring the orientation of particles and could be easily extended to quantify the stability of an arbitrary particle trajectory.
DOI
Optical tweezers are a versatile tool that can be used to manipulate small particles including both motile and non-motile bacteria and cells. The orientation of a non-spherical particle within a beam depends on the shape of the particle and the shape of the light field. By using multiple beams, sculpted light fields or dynamically changing beams, it is possible to control the orientation of certain particles. In this paper we discuss the orientation of the rod-shaped bacteria Escherichia coli (E. coli) using dynamically shifting annular beam optical tweezers. We begin with examples of different beams used for the orientation of rod-shaped particles. We discuss the differences between orientation of motile and non-motile particles, and explore annular beams and the circumstances when they may be beneficial for manipulation of non-spherical particles or cells. Using simulations we map out the trajectory the E. coli takes. Estimating the trap stiffness along the trajectory gives us an insight into how stable an intermediate rotation is with respect to the desired orientation. Using this method, we predict and experimentally verify the change in the orientation of motile E. coli from vertical to near-horizontal with only one intermediate step. The method is not specific to exploring the orientation of particles and could be easily extended to quantify the stability of an arbitrary particle trajectory.
DOI
X-typed curvilinear transport of strongly absorbing particle in a dual-beam fiber optical trap
Zhihai Liu, Lu Wang, Yu Zhang, Siyu Lin, Yaxun Zhang, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan
We propose and demonstrate a novel approach to transport a strongly absorbing particle in an X-typed trajectory reciprocally in pure liquid glycerol based on a dual-beam optical fiber trap. We perform the X-typed light field by integrating a glass microsphere on the tip of a two-core fiber. The motion of the absorbing particle in pure liquid glycerol is dominated by the Δα-type photophoretic forces (FΔα). The incident laser power determines the direction of FΔα. Therefore, we may perform the reciprocating transport of the absorbing particle by changing and controlling the laser power. It is simple to manufacture the fiber probe and convenient to operate the transport of the microparticle. Our research expands the applications of absorbing particles in targeted drug delivery, biological sampling, and optically mediated particle clearing.
DOI
We propose and demonstrate a novel approach to transport a strongly absorbing particle in an X-typed trajectory reciprocally in pure liquid glycerol based on a dual-beam optical fiber trap. We perform the X-typed light field by integrating a glass microsphere on the tip of a two-core fiber. The motion of the absorbing particle in pure liquid glycerol is dominated by the Δα-type photophoretic forces (FΔα). The incident laser power determines the direction of FΔα. Therefore, we may perform the reciprocating transport of the absorbing particle by changing and controlling the laser power. It is simple to manufacture the fiber probe and convenient to operate the transport of the microparticle. Our research expands the applications of absorbing particles in targeted drug delivery, biological sampling, and optically mediated particle clearing.
DOI
Characterization of non-linearities through mechanical squeezing in levitated optomechanics
Ashley Setter, Jamie Vovrosh, and Hendrik Ulbricht
We demonstrate a technique to estimate the strength of nonlinearities present in the trapping potential of an optically levitated nanoparticle. By applying a brief pulsed reduction in the trapping laser power of the system such as to squeeze the phase space distribution and then matching the time evolution of the shape of the phase space distribution to that of numerical simulations, one can estimate the strength of the nonlinearity present in the system. We apply this technique to estimate the strength of the Duffing nonlinearity present in the optical trapping potential.We would like to thank C. Timberlake for comments on this manuscript as well as M. Toroš, T. Georgescu, and M. Rashid for discussions. We also wish to thank the Leverhulme Trust and the Foundational Questions Institute (FQXi) for funding. A. Setter is supported by the Engineering and Physical Sciences Research Council (EPSRC) under the Center for Doctoral Training Grant No. EP/L015382/1. We also acknowledge support from the EU FET project TEQ (Grant Agreement No. 766900). In addition, the authors acknowledge the use of the IRIDIS High Performance Computing Facility and associated support services at the University of Southampton. All data supporting this study are openly available from the University of Southampton repository at https://doi.org/10.5258/SOTON/D0967. The code used to analyze the data is openly available at https://doi.org/10.5281/zenodo.1042526.
DOI
We demonstrate a technique to estimate the strength of nonlinearities present in the trapping potential of an optically levitated nanoparticle. By applying a brief pulsed reduction in the trapping laser power of the system such as to squeeze the phase space distribution and then matching the time evolution of the shape of the phase space distribution to that of numerical simulations, one can estimate the strength of the nonlinearity present in the system. We apply this technique to estimate the strength of the Duffing nonlinearity present in the optical trapping potential.We would like to thank C. Timberlake for comments on this manuscript as well as M. Toroš, T. Georgescu, and M. Rashid for discussions. We also wish to thank the Leverhulme Trust and the Foundational Questions Institute (FQXi) for funding. A. Setter is supported by the Engineering and Physical Sciences Research Council (EPSRC) under the Center for Doctoral Training Grant No. EP/L015382/1. We also acknowledge support from the EU FET project TEQ (Grant Agreement No. 766900). In addition, the authors acknowledge the use of the IRIDIS High Performance Computing Facility and associated support services at the University of Southampton. All data supporting this study are openly available from the University of Southampton repository at https://doi.org/10.5258/SOTON/D0967. The code used to analyze the data is openly available at https://doi.org/10.5281/zenodo.1042526.
DOI
Monday, November 11, 2019
Optically oriented attachment of nanoscale metal-semiconductor heterostructures in organic solvents via photonic nanosoldering
Matthew J. Crane, Elena P. Pandres, E. James Davis, Vincent C. Holmberg & Peter J. Pauzauskie
As devices approach the single-nanoparticle scale, the rational assembly of nanomaterial heterojunctions remains a persistent challenge. While optical traps can manipulate objects in three dimensions, to date, nanoscale materials have been trapped primarily in aqueous solvents or vacuum. Here, we demonstrate the use of optical traps to manipulate, align, and assemble metal-seeded nanowire building blocks in a range of organic solvents. Anisotropic radiation pressure generates an optical torque that orients each nanowire, and subsequent trapping of aligned nanowires enables deterministic fabrication of arbitrarily long heterostructures of periodically repeating bismuth-nanocrystal/germanium-nanowire junctions. Heat transport calculations, back-focal-plane interferometry, and optical images reveal that the bismuth nanocrystal melts during trapping, facilitating tip-to-tail “nanosoldering” of the germanium nanowires. These bismuth-semiconductor interfaces may be useful for quantum computing or thermoelectric applications. In addition, the ability to trap nanostructures in oxygen- and water-free organic media broadly expands the library of materials available for optical manipulation and single-particle spectroscopy.
DOI
As devices approach the single-nanoparticle scale, the rational assembly of nanomaterial heterojunctions remains a persistent challenge. While optical traps can manipulate objects in three dimensions, to date, nanoscale materials have been trapped primarily in aqueous solvents or vacuum. Here, we demonstrate the use of optical traps to manipulate, align, and assemble metal-seeded nanowire building blocks in a range of organic solvents. Anisotropic radiation pressure generates an optical torque that orients each nanowire, and subsequent trapping of aligned nanowires enables deterministic fabrication of arbitrarily long heterostructures of periodically repeating bismuth-nanocrystal/germanium-nanowire junctions. Heat transport calculations, back-focal-plane interferometry, and optical images reveal that the bismuth nanocrystal melts during trapping, facilitating tip-to-tail “nanosoldering” of the germanium nanowires. These bismuth-semiconductor interfaces may be useful for quantum computing or thermoelectric applications. In addition, the ability to trap nanostructures in oxygen- and water-free organic media broadly expands the library of materials available for optical manipulation and single-particle spectroscopy.
DOI
Detection of self-generated nanowaves on the interface of an evaporating sessile water droplet
Dhanush Bhatt, Rahul Vaippully, Bhavesh Kharbanda, Anand Dev Ranjan, Sulochana R, Viraj Dharod, Dillip Satapathy, and Basudev Roy
Evaporating sessile droplets have been known to exhibit oscillations on the air-liquid interface. These are generally over millimeter scales. Using a novel approach, we are able to measure surface height changes of 500 nm amplitude using optical trapping of a set of microscopic particles at the interface, particularly when the vertical thickness of the droplet reduces to less than 50 𝜇m. We find that at the later stages of the droplet evaporation, particularly when the convection currents become large, the top air-water interface starts to spontaneously oscillate vertically as a function of time in consistency with predictions. We also detect travelling wave trains moving in the azimuthal direction of the drop surface which are consistent with hydrothermal waves at a different combination of Reynolds, Prandtl and Evaporation numbers than previously observed. This is the first time that wave-trains have been observed in water, being extremely challenging to detect both interferometrically and with infra-red cameras. We also find that such waves apply a force parallel to the interface along the propagation direction.
DOI
Evaporating sessile droplets have been known to exhibit oscillations on the air-liquid interface. These are generally over millimeter scales. Using a novel approach, we are able to measure surface height changes of 500 nm amplitude using optical trapping of a set of microscopic particles at the interface, particularly when the vertical thickness of the droplet reduces to less than 50 𝜇m. We find that at the later stages of the droplet evaporation, particularly when the convection currents become large, the top air-water interface starts to spontaneously oscillate vertically as a function of time in consistency with predictions. We also detect travelling wave trains moving in the azimuthal direction of the drop surface which are consistent with hydrothermal waves at a different combination of Reynolds, Prandtl and Evaporation numbers than previously observed. This is the first time that wave-trains have been observed in water, being extremely challenging to detect both interferometrically and with infra-red cameras. We also find that such waves apply a force parallel to the interface along the propagation direction.
DOI
Detection of Specific Antibody-Ligand Interactions with a Self-Induced Back-Action Actuated Nanopore Electrophoresis (SANE) Sensor
Sai Santosh Sasank Peri, Manoj K Sabnani, Muhammad Usman Raza, Soroush Ghaffari, Susanne Gimlin, Debra D Wawro, JungSoo Lee, MinJun Kim, Jon A Weidanz and George Alexandrakis
Recent advances in plasmonic nanopore technologies have enabled the use of concurrently acquired bimodal optical-electrical data for improved quantification of molecular interactions. This work presents the use of a new plasmonic nanosensor employing Self-Induced Back-Action (SIBA) for optical trapping to enable SIBA-Actuated Nanopore Electrophoresis (SANE) for quantifying antibody-ligand interactions. T-cell receptor-like antibodies (TCRmAbs) engineered to target peptide-presenting Major Histocompatibility Complex (pMHC) ligands, representing a model of target ligands presented on the surface of cancer cells, were used to test the SANE sensor's ability to identify specific antibody-ligand binding. Cancer-irrelevant TCRmAbs targeting the same pMHCs were also tested as a control. It was found that the sensor could provide bimodal molecular signatures that could differentiate between antibody, ligand and the complexes that they formed, as well as distinguish between specific and non-specific interactions. Furthermore, the results suggested an interesting phenomenon of increased antibody-ligand complex bound fraction detected by the SANE sensor compared to that expected for corresponding bulk solution concentrations. A possible physical mechanism and potential advantages for the sensor's ability to augment complex formation near its active sensing volume at concentrations lower than the free solution equilibrium binding constant (KD ) are discussed.
DOI
Recent advances in plasmonic nanopore technologies have enabled the use of concurrently acquired bimodal optical-electrical data for improved quantification of molecular interactions. This work presents the use of a new plasmonic nanosensor employing Self-Induced Back-Action (SIBA) for optical trapping to enable SIBA-Actuated Nanopore Electrophoresis (SANE) for quantifying antibody-ligand interactions. T-cell receptor-like antibodies (TCRmAbs) engineered to target peptide-presenting Major Histocompatibility Complex (pMHC) ligands, representing a model of target ligands presented on the surface of cancer cells, were used to test the SANE sensor's ability to identify specific antibody-ligand binding. Cancer-irrelevant TCRmAbs targeting the same pMHCs were also tested as a control. It was found that the sensor could provide bimodal molecular signatures that could differentiate between antibody, ligand and the complexes that they formed, as well as distinguish between specific and non-specific interactions. Furthermore, the results suggested an interesting phenomenon of increased antibody-ligand complex bound fraction detected by the SANE sensor compared to that expected for corresponding bulk solution concentrations. A possible physical mechanism and potential advantages for the sensor's ability to augment complex formation near its active sensing volume at concentrations lower than the free solution equilibrium binding constant (KD ) are discussed.
DOI
Influence of static electric field on Raman polarizability of optically trapped polystyrene beads Author links open overlay panel
U. K. Adarsh, Aseefhali Bankapur, Mahendra Acharya, Santhosh Chidangil
The influence of static electric field of about 4.9 kV/cm on optically trapped polystyrene bead has been studied using micro-Raman spectroscopy. This experimental method could explore the response of electronic polarizability of molecules to the static electric field by measuring the Raman intensity. It is observed that, the atomic electrons in polystyrene will polarize to the extent that they induce a Raman intensity enhancements by a factor ranging from 0.004 to 0.64 for various spectral bands of polystyrene when exposed to the electric field from ∼4.90 to 4.96 kV/cm.
DOI
The influence of static electric field of about 4.9 kV/cm on optically trapped polystyrene bead has been studied using micro-Raman spectroscopy. This experimental method could explore the response of electronic polarizability of molecules to the static electric field by measuring the Raman intensity. It is observed that, the atomic electrons in polystyrene will polarize to the extent that they induce a Raman intensity enhancements by a factor ranging from 0.004 to 0.64 for various spectral bands of polystyrene when exposed to the electric field from ∼4.90 to 4.96 kV/cm.
DOI
Elucidating optical field directed hierarchical self-assembly of homogenous versus heterogeneous nanoclusters with femtosecond optical tweezers
Dipankar Mondal, Soumendra Nath Bandyopadhyay, Debabrata Goswami
Insights into the morphology of nanoclusters would facilitate the design of nano-devices with improved optical, electrical, and magnetic responses. We have utilized optical gradient forces for the directed self-assembly of colloidal clusters using high-repetition-rate femtosecond laser pulses to delineate their structure and dynamics. We have ratified our experiments with theoretical models derived from the Langevin equation and defined the valid ranges of applicability. Our femtosecond optical tweezer-based technique characterizes the in-situ formation of hierarchical self-assembled clusters of homomers as well as heteromers by analyzing the back focal plane displacement signal. This technique is able to efficiently distinguish between nano-particles in heterogeneous clusters and is in accordance with our theory. Herein, we report results from our technique, and also develop a model to describe the mechanism of such processes where corner frequency changes. We show how the corner frequency changes enables us to recognize the structure and dynamics of the coagulation of colloidal homogeneous and heterogeneous clusters in condensed media over a broad range of nanoparticle sizes. The methods described here are advantageous, as the backscatter position-sensitive detection probes the in-situ self-assembly process while other light scattering approaches are leveraged for the characterization of isolated clusters.
DOI
Insights into the morphology of nanoclusters would facilitate the design of nano-devices with improved optical, electrical, and magnetic responses. We have utilized optical gradient forces for the directed self-assembly of colloidal clusters using high-repetition-rate femtosecond laser pulses to delineate their structure and dynamics. We have ratified our experiments with theoretical models derived from the Langevin equation and defined the valid ranges of applicability. Our femtosecond optical tweezer-based technique characterizes the in-situ formation of hierarchical self-assembled clusters of homomers as well as heteromers by analyzing the back focal plane displacement signal. This technique is able to efficiently distinguish between nano-particles in heterogeneous clusters and is in accordance with our theory. Herein, we report results from our technique, and also develop a model to describe the mechanism of such processes where corner frequency changes. We show how the corner frequency changes enables us to recognize the structure and dynamics of the coagulation of colloidal homogeneous and heterogeneous clusters in condensed media over a broad range of nanoparticle sizes. The methods described here are advantageous, as the backscatter position-sensitive detection probes the in-situ self-assembly process while other light scattering approaches are leveraged for the characterization of isolated clusters.
DOI
Friday, November 8, 2019
Towards biological applications of nanophotonic tweezers
Ryan P. Badman, Fan Ye, Michelle D.Wang
Optical trapping (synonymous with optical tweezers) has become a core biophysical technique widely used for interrogating fundamental biological processes on size scales ranging from the single-molecule to the cellular level. Recent advances in nanotechnology have led to the development of ‘nanophotonic tweezers,’ an exciting new class of ‘on-chip’ optical traps. Here, we describe how nanophotonic tweezers are making optical trap technology more broadly accessible and bringing unique biosensing and manipulation capabilities to biological applications of optical trapping.
DOI
Optical trapping (synonymous with optical tweezers) has become a core biophysical technique widely used for interrogating fundamental biological processes on size scales ranging from the single-molecule to the cellular level. Recent advances in nanotechnology have led to the development of ‘nanophotonic tweezers,’ an exciting new class of ‘on-chip’ optical traps. Here, we describe how nanophotonic tweezers are making optical trap technology more broadly accessible and bringing unique biosensing and manipulation capabilities to biological applications of optical trapping.
DOI
Effect of waiting time on the water transport kinetics of magnesium sulfate aerosol at gel-forming relative humidity using optical tweezers
Pianpian Chang, Xiaoyan Gao, Chen Cai, Jiabi Ma, Yunhong Zhang
With the loss of water, the amorphous gel states in aqueous magnesium sulfate (MgSO4) aerosol forms and results in nonequilibrium dynamics, owing to the extended time scales for diffusive mixing. The mass transfer resistance in MgSO4 aerosol droplets during evaporation or condensation is investigated using aerosol optical tweezers (AOTs) coupled with Raman spectroscopy. In addition, the kinetics of water transport during hydration and dehydration after different waiting time is studied. With the cyclic change of the relative humidity (RH) below gel-forming, the waiting time is varied to examine the effect of the duration of drying and humidifying on water transport kinetics during subsequent hydration and dehydration process. Apparent diffusion coefficients (Dap) of water molecules in the gel state after different waiting time are obtained. The results indicate that the duration of drying will affect water transport kinetics for subsequent humidifying process due to the different structure and composition in MgSO4 aerosol droplet at different ambient humidities. However, the duration of humidifying has little effect on water transport kinetics for subsequent drying process below gel-forming RH.
DOI
With the loss of water, the amorphous gel states in aqueous magnesium sulfate (MgSO4) aerosol forms and results in nonequilibrium dynamics, owing to the extended time scales for diffusive mixing. The mass transfer resistance in MgSO4 aerosol droplets during evaporation or condensation is investigated using aerosol optical tweezers (AOTs) coupled with Raman spectroscopy. In addition, the kinetics of water transport during hydration and dehydration after different waiting time is studied. With the cyclic change of the relative humidity (RH) below gel-forming, the waiting time is varied to examine the effect of the duration of drying and humidifying on water transport kinetics during subsequent hydration and dehydration process. Apparent diffusion coefficients (Dap) of water molecules in the gel state after different waiting time are obtained. The results indicate that the duration of drying will affect water transport kinetics for subsequent humidifying process due to the different structure and composition in MgSO4 aerosol droplet at different ambient humidities. However, the duration of humidifying has little effect on water transport kinetics for subsequent drying process below gel-forming RH.
DOI
Single-Molecule Analysis and Engineering of DNA Motors
Sonisilpa Mohapatra, Chang-Ting Lin, Xinyu A. Feng, Aakash Basu, Taekjip Ha
Molecular motors are diverse enzymes that transduce chemical energy into mechanical work and, in doing so, perform critical cellular functions such as DNA replication and transcription, DNA supercoiling, intracellular transport, and ATP synthesis. Single-molecule techniques have been extensively used to identify structural intermediates in the reaction cycles of molecular motors and to understand how substeps in energy consumption drive transitions between the intermediates. Here, we review a broad spectrum of single-molecule tools and techniques such as optical and magnetic tweezers, atomic force microscopy (AFM), single-molecule fluorescence resonance energy transfer (smFRET), nanopore tweezers, and hybrid techniques that increase the number of observables. These methods enable the manipulation of individual biomolecules via the application of forces and torques and the observation of dynamic conformational changes in single motor complexes. We also review how these techniques have been applied to study various motors such as helicases, DNA and RNA polymerases, topoisomerases, nucleosome remodelers, and motors involved in the condensation, segregation, and digestion of DNA. In-depth analysis of mechanochemical coupling in molecular motors has made the development of artificially engineered motors possible. We review techniques such as mutagenesis, chemical modifications, and optogenetics that have been used to re-engineer existing molecular motors to have, for instance, altered speed, processivity, or functionality. We also discuss how single-molecule analysis of engineered motors allows us to challenge our fundamental understanding of how molecular motors transduce energy.
DOI
Molecular motors are diverse enzymes that transduce chemical energy into mechanical work and, in doing so, perform critical cellular functions such as DNA replication and transcription, DNA supercoiling, intracellular transport, and ATP synthesis. Single-molecule techniques have been extensively used to identify structural intermediates in the reaction cycles of molecular motors and to understand how substeps in energy consumption drive transitions between the intermediates. Here, we review a broad spectrum of single-molecule tools and techniques such as optical and magnetic tweezers, atomic force microscopy (AFM), single-molecule fluorescence resonance energy transfer (smFRET), nanopore tweezers, and hybrid techniques that increase the number of observables. These methods enable the manipulation of individual biomolecules via the application of forces and torques and the observation of dynamic conformational changes in single motor complexes. We also review how these techniques have been applied to study various motors such as helicases, DNA and RNA polymerases, topoisomerases, nucleosome remodelers, and motors involved in the condensation, segregation, and digestion of DNA. In-depth analysis of mechanochemical coupling in molecular motors has made the development of artificially engineered motors possible. We review techniques such as mutagenesis, chemical modifications, and optogenetics that have been used to re-engineer existing molecular motors to have, for instance, altered speed, processivity, or functionality. We also discuss how single-molecule analysis of engineered motors allows us to challenge our fundamental understanding of how molecular motors transduce energy.
DOI
Synthetic asters as elastic and radial skeletons
Qingqiao Xie, Xixi Chen, Tianli Wu, Tiankuo Wang, Yi Cao, Steve Granick, Yuchao Li & Lingxiang Jiang
The radial geometry with rays radiated from a common core occurs ubiquitously in nature for its symmetry and functions. Herein, we report a class of synthetic asters with well-defined core-ray geometry that can function as elastic and radial skeletons to harbor nano- and microparticles. We fabricate the asters in a single, facile, and high-yield step that can be readily scaled up; specifically, amphiphilic gemini molecules self-assemble in water into asters with an amorphous core and divergently growing, twisted crystalline ribbons. The asters can spontaneously position microparticles in the cores, along the radial ribbons, or by the outer rims depending on particle sizes and surface chemistry. Their mechanical properties are determined on single- and multiple-aster levels. We further maneuver the synthetic asters as building blocks to form higher-order structures in virtue of aster-aster adhesion induced by ribbon intertwining. We envision the astral structures to act as rudimentary spatial organizers in nanoscience for coordinated multicomponent systems, possibly leading to emergent, synergistic functions.
DOI
The radial geometry with rays radiated from a common core occurs ubiquitously in nature for its symmetry and functions. Herein, we report a class of synthetic asters with well-defined core-ray geometry that can function as elastic and radial skeletons to harbor nano- and microparticles. We fabricate the asters in a single, facile, and high-yield step that can be readily scaled up; specifically, amphiphilic gemini molecules self-assemble in water into asters with an amorphous core and divergently growing, twisted crystalline ribbons. The asters can spontaneously position microparticles in the cores, along the radial ribbons, or by the outer rims depending on particle sizes and surface chemistry. Their mechanical properties are determined on single- and multiple-aster levels. We further maneuver the synthetic asters as building blocks to form higher-order structures in virtue of aster-aster adhesion induced by ribbon intertwining. We envision the astral structures to act as rudimentary spatial organizers in nanoscience for coordinated multicomponent systems, possibly leading to emergent, synergistic functions.
DOI
Nonphotochemical pulsed-laser-induced nucleation in a cw-laser-induced phase-separated solution droplet of aqueous glycine formed by optical gradient forces
Omar Gowayed, Tasfia Tasnim, José J. Fuentes-Rivera, Janice E. Aber, Bruce A. Garetz
A centimeter-sized laser-induced phase-separated (LIPS) solution droplet, which was formed by tightly focusing a continuous-wave, near-infrared laser beam at the glass/solution interface of a millimeter-thick layer of glycine in D2O with a supersaturation ratio, S, of 1.36 was irradiated with a single unfocused nanosecond near-infrared laser pulse in order to study the effect of nonphotochemical laser-induced nucleation (NPLIN) on the droplet, as well as to help characterize the behavior of the LIPS droplet. Additionally, a control NPLIN experiment was conducted on an S=1.50 supersaturated solution of glycine/D2O in the same cell to better understand the differences between NPLIN in a LIPS droplet and an ordinary supersaturated solution. These experiments revealed that NPLIN could nucleate crystals within a LIPS droplet, although the growth of these crystals was inhibited during the first 5 minutes of the droplet’s relaxation. For the first 40 minutes of its relaxation, the LIPS droplet was observed to be more labile to spontaneous nucleation than the control S=1.50 solution, although the growth of spontaneously nucleated crystals was also inhibited during the first 5 minutes of the droplet’s relaxation. This suggests that although the macroscopic phase boundary between the LIPS droplet and the surrounding solution disappeared after approximately 5 minutes, the full microscopic relaxation of the LIPS droplet took at least 40 minutes. The resulting crystals were analyzed using powder X-ray diffraction (PXRD), and 100% of crystals formed within the LIPS droplet induced by NPLIN with linearly polarized light and by spontaneous nucleation were α-glycine, while crystals formed outside of the LIPS droplet, or in the periphery, were mixtures of α- and γ-glycine. The results indicate that the LIPS droplet and the surrounding solution are not equilibrium phases of aqueous glycine, but phases in which gradient optical forces have induced a partitioning of large and small solute clusters.
DOI
A centimeter-sized laser-induced phase-separated (LIPS) solution droplet, which was formed by tightly focusing a continuous-wave, near-infrared laser beam at the glass/solution interface of a millimeter-thick layer of glycine in D2O with a supersaturation ratio, S, of 1.36 was irradiated with a single unfocused nanosecond near-infrared laser pulse in order to study the effect of nonphotochemical laser-induced nucleation (NPLIN) on the droplet, as well as to help characterize the behavior of the LIPS droplet. Additionally, a control NPLIN experiment was conducted on an S=1.50 supersaturated solution of glycine/D2O in the same cell to better understand the differences between NPLIN in a LIPS droplet and an ordinary supersaturated solution. These experiments revealed that NPLIN could nucleate crystals within a LIPS droplet, although the growth of these crystals was inhibited during the first 5 minutes of the droplet’s relaxation. For the first 40 minutes of its relaxation, the LIPS droplet was observed to be more labile to spontaneous nucleation than the control S=1.50 solution, although the growth of spontaneously nucleated crystals was also inhibited during the first 5 minutes of the droplet’s relaxation. This suggests that although the macroscopic phase boundary between the LIPS droplet and the surrounding solution disappeared after approximately 5 minutes, the full microscopic relaxation of the LIPS droplet took at least 40 minutes. The resulting crystals were analyzed using powder X-ray diffraction (PXRD), and 100% of crystals formed within the LIPS droplet induced by NPLIN with linearly polarized light and by spontaneous nucleation were α-glycine, while crystals formed outside of the LIPS droplet, or in the periphery, were mixtures of α- and γ-glycine. The results indicate that the LIPS droplet and the surrounding solution are not equilibrium phases of aqueous glycine, but phases in which gradient optical forces have induced a partitioning of large and small solute clusters.
DOI
Optical-trapping of particles in air using parabolic reflectors and a hollow laser beam
Yong-Le Pan, Aimable Kalume, Isaac C. D. Lenton, Timo A. Nieminen, Alex B. Stilgoe, Halina Rubinsztein-Dunlop, Leonid A. Beresnev, Chuji Wang, and Joshua L. Santarpia
We present an advanced optical-trapping method that is capable of trapping arbitrary shapes of transparent and absorbing particles in air. Two parabolic reflectors were used to reflect the inner and outer parts of a single hollow laser beam, respectively, to form two counter-propagating conical beams and bring them into a focal point for trapping. This novel design demonstrated high trapping efficiency and strong trapping robustness with a simple optical configuration. Instead of using expensive microscope objectives, the parabolic reflectors can not only achieved large numerical aperture (N.A.) focusing, but were also able to focus the beam far away from optical surfaces to minimize optics contamination. This design also offered a large free space for flexible integration with other measuring techniques, such as optical-trapping Raman spectroscopy, for on-line single particle characterization.
DOI
We present an advanced optical-trapping method that is capable of trapping arbitrary shapes of transparent and absorbing particles in air. Two parabolic reflectors were used to reflect the inner and outer parts of a single hollow laser beam, respectively, to form two counter-propagating conical beams and bring them into a focal point for trapping. This novel design demonstrated high trapping efficiency and strong trapping robustness with a simple optical configuration. Instead of using expensive microscope objectives, the parabolic reflectors can not only achieved large numerical aperture (N.A.) focusing, but were also able to focus the beam far away from optical surfaces to minimize optics contamination. This design also offered a large free space for flexible integration with other measuring techniques, such as optical-trapping Raman spectroscopy, for on-line single particle characterization.
DOI
N-Heterocyclic Carbene-Platinum Complexes Featuring an Anthracenyl Moiety: Anti-Cancer Activity and DNA Interaction
Sébastien Harlepp, Edith Chardon, Mathilde Bouché, Georges Dahm, Mounir Maaloum, Stéphane Bellemin-Laponnaz
A platinum (II) complex stabilized by a pyridine and an N-heterocyclic carbene ligand featuring an anthracenyl moiety was prepared. The compound was fully characterized and its molecular structure was determined by single-crystal X-ray diffraction. The compound demonstrated high in vitro antiproliferative activities against cancer cell lines with IC50 ranging from 10 to 80 nM. The presence of the anthracenyl moiety on the N-heterocyclic carbene (NHC) Pt complex was used as a luminescent tag to probe the metal interaction with the nucleobases of the DNA through a pyridine-nucleobase ligand exchange. Such interaction of the platinum complex with DNA was corroborated by optical tweezers techniques and liquid phase atomic force microscopy (AFM). The results revealed a two-state interaction between the platinum complex and the DNA strands. This two-state behavior was quantified from the different experiments due to contour length variations. At 24 h incubation, the stretching curves revealed multiple structural breakages, and AFM imaging revealed a highly compact and dense structure of platinum complexes bridging the DNA strands.
DOI
A platinum (II) complex stabilized by a pyridine and an N-heterocyclic carbene ligand featuring an anthracenyl moiety was prepared. The compound was fully characterized and its molecular structure was determined by single-crystal X-ray diffraction. The compound demonstrated high in vitro antiproliferative activities against cancer cell lines with IC50 ranging from 10 to 80 nM. The presence of the anthracenyl moiety on the N-heterocyclic carbene (NHC) Pt complex was used as a luminescent tag to probe the metal interaction with the nucleobases of the DNA through a pyridine-nucleobase ligand exchange. Such interaction of the platinum complex with DNA was corroborated by optical tweezers techniques and liquid phase atomic force microscopy (AFM). The results revealed a two-state interaction between the platinum complex and the DNA strands. This two-state behavior was quantified from the different experiments due to contour length variations. At 24 h incubation, the stretching curves revealed multiple structural breakages, and AFM imaging revealed a highly compact and dense structure of platinum complexes bridging the DNA strands.
DOI
Monday, November 4, 2019
Optomechanical control of stacking patterns of h-BN bilayer
Haowei Xu, Jian Zhou, Yifei Li, Rafael Jaramillo, Ju Li
Few-layer two-dimensional (2D) materials usually have different (meta)-stable stacking patterns, which have distinct electronic and optical properties. Inspired by optical tweezers, we show that a laser with selected frequency can modify the generalized stacking-fault energy landscape of bilayer hexagonal boron nitride (BBN), by coupling to the slip-dependent dielectric response. Consequently, BBN can be reversibly and barrier-freely switched between its stacking patterns in a controllable way. We simulate the dynamics of the stacking transition with a simplified equation of motion and demonstrate that it happens at picosecond timescale. When one layer of BBN has a nearly-free surface boundary condition, BBN can be locked in its metastable stacking modes for a long time. Such a fast, reversible and non-volatile transition makes BBN a potential media for data storage and optical phase mask.
DOI
Few-layer two-dimensional (2D) materials usually have different (meta)-stable stacking patterns, which have distinct electronic and optical properties. Inspired by optical tweezers, we show that a laser with selected frequency can modify the generalized stacking-fault energy landscape of bilayer hexagonal boron nitride (BBN), by coupling to the slip-dependent dielectric response. Consequently, BBN can be reversibly and barrier-freely switched between its stacking patterns in a controllable way. We simulate the dynamics of the stacking transition with a simplified equation of motion and demonstrate that it happens at picosecond timescale. When one layer of BBN has a nearly-free surface boundary condition, BBN can be locked in its metastable stacking modes for a long time. Such a fast, reversible and non-volatile transition makes BBN a potential media for data storage and optical phase mask.
DOI
Synchronized Rayleigh and Raman scattering for the characterization of single optically trapped extracellular vesicles
Agustin Enciso-Martinez, Edwin van der Pol, Aufried T.M. Lenferink, Leon W.M.M. Terstappen, Ton G.Van Leeuwen, Cees Otto
Extracellular Vesicles (EVs) can be used as biomarkers in diseases like cancer, as their lineage of origin and molecular composition depend on the presence of cancer cells. Recognition of tumor-derived EVs (tdEVs) from other particles and EVs in body fluids requires characterization of single EVs to exploit their biomarker potential. We present here a new method based on synchronized Rayleigh and Raman light scattering from a single laser beam, which optically traps single EVs. Rapidly measured sequences of the Rayleigh scattering amplitude show precisely when an individual EV is trapped and the synchronously acquired Raman spectrum labels every time interval with chemical information. Raman spectra of many single EVs can thus be acquired with great fidelity in an automated manner by blocking the laser beam at regular time intervals. This new method enables single EV characterization from fluids at the single particle level.
DOI
Extracellular Vesicles (EVs) can be used as biomarkers in diseases like cancer, as their lineage of origin and molecular composition depend on the presence of cancer cells. Recognition of tumor-derived EVs (tdEVs) from other particles and EVs in body fluids requires characterization of single EVs to exploit their biomarker potential. We present here a new method based on synchronized Rayleigh and Raman light scattering from a single laser beam, which optically traps single EVs. Rapidly measured sequences of the Rayleigh scattering amplitude show precisely when an individual EV is trapped and the synchronously acquired Raman spectrum labels every time interval with chemical information. Raman spectra of many single EVs can thus be acquired with great fidelity in an automated manner by blocking the laser beam at regular time intervals. This new method enables single EV characterization from fluids at the single particle level.
DOI
Interactions between polystyrene particles with diameters of several tens to hundreds of micrometers at the oil–water interface
Ha Eun Lee, Kyu Hwan Choi, Xia Ming, Dong Woo Kang, Bum Jun Park
The charged spherical colloidal particles at the fluid–fluid interface experience considerably strong and long-ranged electrostatic and capillary interactions. The contribution of capillary force becomes more significant as the particle size increases beyond a certain limit. The relative strengths of the two competing interactions between the spherical polystyrene particles at the oil–water interface are quantified depending on their size. The studied particles, obtained using the microfluidic method, have diameters of tens to hundreds of micrometers. The scaling behaviors of the commercially available colloidal particles with diameters of ∼3 μm are also compared. An optical laser tweezer apparatus is used to directly or indirectly measure the interparticle force. Subsequently, the capillary force that can be attributed to the gravity-induced interface deformation and contact line undulation is calculated and compared with the measured interaction force. Regardless of the particle diameter (∼3–330 μm), the measured force is observed to decay as r−4, where r denotes the center-to-center separation, demonstrating that the dipolar electrostatic interaction is important and that the gravity-induced capillary interaction is negligible. Furthermore, numerical calculations with respect to the undulated meniscus confirm that the magnitude of capillary interaction is significantly smaller than that of the measured electrostatic interaction.
DOI
The charged spherical colloidal particles at the fluid–fluid interface experience considerably strong and long-ranged electrostatic and capillary interactions. The contribution of capillary force becomes more significant as the particle size increases beyond a certain limit. The relative strengths of the two competing interactions between the spherical polystyrene particles at the oil–water interface are quantified depending on their size. The studied particles, obtained using the microfluidic method, have diameters of tens to hundreds of micrometers. The scaling behaviors of the commercially available colloidal particles with diameters of ∼3 μm are also compared. An optical laser tweezer apparatus is used to directly or indirectly measure the interparticle force. Subsequently, the capillary force that can be attributed to the gravity-induced interface deformation and contact line undulation is calculated and compared with the measured interaction force. Regardless of the particle diameter (∼3–330 μm), the measured force is observed to decay as r−4, where r denotes the center-to-center separation, demonstrating that the dipolar electrostatic interaction is important and that the gravity-induced capillary interaction is negligible. Furthermore, numerical calculations with respect to the undulated meniscus confirm that the magnitude of capillary interaction is significantly smaller than that of the measured electrostatic interaction.
DOI
A spiral-like curve with an adjustable opening generated by a modified helico-conical beam
Tian Xia, Shaohua Tao, Shubo Cheng
A modified helico-conical beam (MHCB) is proposed to generate a spiral-like curve with an adjustable opening at the focal plane of a lens. Moreover, the opening of a spiral-like curve can be adjustable finely, which firstly increases quickly and then increases slowly with the increasement of the fraction n. For the MHCB, there is not also stray light around the opening at the focal plane. In addition, the intensity profile for the MHCB approaching the focal plane of the lens along the optic axis rotates. Furthermore, it is also proved in the experiments that the spiral-like beam with the opening can be used to transport particles. The generating method of the MHCB is illustrated. In addition, we also prove numerically and experimentally that the MHCB can produce a spiral-like intensity distribution. The proposed beam can be applied to induce transportation of particles, and collect multiple particles in the center of the spiral-like curve, and sort the particles into different positions.
DOI
A modified helico-conical beam (MHCB) is proposed to generate a spiral-like curve with an adjustable opening at the focal plane of a lens. Moreover, the opening of a spiral-like curve can be adjustable finely, which firstly increases quickly and then increases slowly with the increasement of the fraction n. For the MHCB, there is not also stray light around the opening at the focal plane. In addition, the intensity profile for the MHCB approaching the focal plane of the lens along the optic axis rotates. Furthermore, it is also proved in the experiments that the spiral-like beam with the opening can be used to transport particles. The generating method of the MHCB is illustrated. In addition, we also prove numerically and experimentally that the MHCB can produce a spiral-like intensity distribution. The proposed beam can be applied to induce transportation of particles, and collect multiple particles in the center of the spiral-like curve, and sort the particles into different positions.
DOI
Drag controlled formation of polymeric colloids with optical traps
Erel Lasnoy, Omer Wagner, Eitan Edri and Hagay Shpaisman
Optical trapping is a powerful optical manipulation technique for controlling various mesoscopic systems that allows formation of tailor-made polymeric micro-sized colloids by directed coalescence of nucleation sites. However, control over the size of a single colloid requires constant monitoring of the growth process and deactivation of the optical trap once it reaches the required dimensions. Moreover, producing more than one colloid requires moving the sample to a pristine location where the process must be repeated. Here, we present a novel method for continuous control over formation of polydimethylsiloxane colloids based on directed coalescence induced by optical traps under flow inside microfluidic channels. Once the drag force on a growing colloid exceeds the trapping force, it leaves the optical trap, and a new colloid starts to form at the same location. We demonstrate repeatability of the process and selectively produce colloids with radii of ∼1–14 μm by controlling the laser intensity and flow rate. In addition, holographic optical tweezers are used to show how multiple optical traps in 3D could be used to influence a significant cross section of the micro-channel, thus forming a light-controlled assembly line for colloidal formation.
DOI
Optical trapping is a powerful optical manipulation technique for controlling various mesoscopic systems that allows formation of tailor-made polymeric micro-sized colloids by directed coalescence of nucleation sites. However, control over the size of a single colloid requires constant monitoring of the growth process and deactivation of the optical trap once it reaches the required dimensions. Moreover, producing more than one colloid requires moving the sample to a pristine location where the process must be repeated. Here, we present a novel method for continuous control over formation of polydimethylsiloxane colloids based on directed coalescence induced by optical traps under flow inside microfluidic channels. Once the drag force on a growing colloid exceeds the trapping force, it leaves the optical trap, and a new colloid starts to form at the same location. We demonstrate repeatability of the process and selectively produce colloids with radii of ∼1–14 μm by controlling the laser intensity and flow rate. In addition, holographic optical tweezers are used to show how multiple optical traps in 3D could be used to influence a significant cross section of the micro-channel, thus forming a light-controlled assembly line for colloidal formation.
DOI
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