Wenlong Xu, Elaheh Alizadeh, Ashok Prasad
A single-cell assay of active and passive intracellular mechanical properties of mammalian cells could give significant insight into cellular processes. Force spectrum microscopy (FSM) is one such technique, which combines the spontaneous motion of probe particles and the mechanical properties of the cytoskeleton measured by active microrheology using optical tweezers to determine the force spectrum of the cytoskeleton. A simpler and noninvasive method to perform FSM would be very useful, enabling its widespread adoption. Here, we develop an alternative method of FSM using measurement of the fluctuating motion of mitochondria. Mitochondria of the C3H-10T1/2 cell line were labeled and tracked using confocal microscopy. Mitochondrial probes were selected based on morphological characteristics, and their mean-square displacement, creep compliance, and distributions of directional change were measured. We found that the creep compliance of mitochondria resembles that of particles in viscoelastic media. However, comparisons of creep compliance between controls and cells treated with pharmacological agents showed that perturbations to the actomysoin network had surprisingly small effects on mitochondrial fluctuations, whereas microtubule disruption and ATP depletion led to a significantly decreased creep compliance. We used properties of the distribution of directional change to identify a regime of thermally dominated fluctuations in ATP-depleted cells, allowing us to estimate the viscoelastic parameters for a range of timescales. We then determined the force spectrum by combining these viscoelastic properties with measurements of spontaneous fluctuations tracked in control cells. Comparisons with previous measurements made using FSM revealed an excellent match.
DOI
Friday, July 27, 2018
Assembly of Colloidal Particles in Solution
Kun Zhao and Thomas G Mason
Advances in both top-down and bottom-up sytheses of a wide variety of complex colloidal building blocks and also in methods of controlling their assembly in solution have led to new and interesting forms of highly controlled soft matter. In particular, top-down lithographic methods of producing monodisperse colloids now provide precise human-designed control over their sub-particle features, opening up a wide range of new possibilities for assembly structures that had been previously limited by the range of shapes available through bottom-up methods. Moreover, an increasing level of control over anisotropic interactions between these colloidal building blocks, which can be tailored through local geometries of sub-particle features as well as site-specific surface modifications, is giving rise to new demonstrations of massively parallel off-chip self-assembly of specific target structures with low defect rates. In particular, new experimental realizations of hierarchical self-assembly and control over the chiral purity of resulting assembly structures have been achieved. Increasingly, shape-dependent, shape-complementary, and roughness-controlled depletion attractions between non-spherical colloids are being used in novel ways to create assemblies that go far beyond fractal clusters formed by diffusion-limited and reaction-limited aggregation of spheres. As self-assembly methods have progressed, a wide variety of advanced directed assembly methods have also been developed; approaches based on microfluidic control and applying structured electromagnetic fields are particularly promising.
DOI
Advances in both top-down and bottom-up sytheses of a wide variety of complex colloidal building blocks and also in methods of controlling their assembly in solution have led to new and interesting forms of highly controlled soft matter. In particular, top-down lithographic methods of producing monodisperse colloids now provide precise human-designed control over their sub-particle features, opening up a wide range of new possibilities for assembly structures that had been previously limited by the range of shapes available through bottom-up methods. Moreover, an increasing level of control over anisotropic interactions between these colloidal building blocks, which can be tailored through local geometries of sub-particle features as well as site-specific surface modifications, is giving rise to new demonstrations of massively parallel off-chip self-assembly of specific target structures with low defect rates. In particular, new experimental realizations of hierarchical self-assembly and control over the chiral purity of resulting assembly structures have been achieved. Increasingly, shape-dependent, shape-complementary, and roughness-controlled depletion attractions between non-spherical colloids are being used in novel ways to create assemblies that go far beyond fractal clusters formed by diffusion-limited and reaction-limited aggregation of spheres. As self-assembly methods have progressed, a wide variety of advanced directed assembly methods have also been developed; approaches based on microfluidic control and applying structured electromagnetic fields are particularly promising.
DOI
Modeling erythrocyte electrodeformation in response to amplitude modulated electric waveforms
Yuhao Qiang, Jia Liu, Fan Yang, Darryl Dieujuste & E. Du
We present a comprehensive theoretical-experimental framework for quantitative, high-throughput study of cell biomechanics. An improved electrodeformation method has been developed by combing dielectrophoresis and amplitude shift keying, a form of amplitude modulation. This method offers a potential to fully control the magnitude and rate of deformation in cell membranes. In healthy human red blood cells, nonlinear viscoelasticity of cell membranes is obtained through variable amplitude load testing. A mathematical model to predict cellular deformations is validated using the experimental results of healthy human red blood cells subjected to various types of loading. These results demonstrate new capabilities of the electrodeformation technique and the validated mathematical model to explore the effects of different loading configurations on the cellular mechanical behavior. This gives it more advantages over existing methods and can be further developed to study the effects of strain rate and loading waveform on the mechanical properties of biological cells in health and disease.
DOI
We present a comprehensive theoretical-experimental framework for quantitative, high-throughput study of cell biomechanics. An improved electrodeformation method has been developed by combing dielectrophoresis and amplitude shift keying, a form of amplitude modulation. This method offers a potential to fully control the magnitude and rate of deformation in cell membranes. In healthy human red blood cells, nonlinear viscoelasticity of cell membranes is obtained through variable amplitude load testing. A mathematical model to predict cellular deformations is validated using the experimental results of healthy human red blood cells subjected to various types of loading. These results demonstrate new capabilities of the electrodeformation technique and the validated mathematical model to explore the effects of different loading configurations on the cellular mechanical behavior. This gives it more advantages over existing methods and can be further developed to study the effects of strain rate and loading waveform on the mechanical properties of biological cells in health and disease.
DOI
Estimation of thermocapillary force during laser trapping of confined microbubbles in a liquid
Ujitha Abeywickrema; Chenglong Zhao; Partha Banerjee
A theoretical model is introduced to determine the thermocapillary force acting on a microbubble, which adheres to the wall of a container filled with a liquid, during trapping using a focused continuous-wave (CW) laser beam. The model is developed by considering all possible forces acting on the microbubble, which also includes the optical force, the viscous force, and the friction force. The thermocapillary force, estimated from the relative velocity of the trapped microbubble with respect to the container, compares favorably with theoretical predictions based on the temperature gradient induced by the focused laser beam. The proposed experiment can be also used to determine the contact angle and/or the coefficient of friction of the microbubble at the microbubble–container interface. Our results should be useful in the design of efficient systems using microbubbles for drug delivery and water treatment systems.
DOI
A theoretical model is introduced to determine the thermocapillary force acting on a microbubble, which adheres to the wall of a container filled with a liquid, during trapping using a focused continuous-wave (CW) laser beam. The model is developed by considering all possible forces acting on the microbubble, which also includes the optical force, the viscous force, and the friction force. The thermocapillary force, estimated from the relative velocity of the trapped microbubble with respect to the container, compares favorably with theoretical predictions based on the temperature gradient induced by the focused laser beam. The proposed experiment can be also used to determine the contact angle and/or the coefficient of friction of the microbubble at the microbubble–container interface. Our results should be useful in the design of efficient systems using microbubbles for drug delivery and water treatment systems.
DOI
Trapping two types of particles using a focused partially coherent modified Bessel-Gaussian beam
Meiling Duan, Hanghang Zhang, Jinhong Li, Ke Cheng, Gao Wang, Wen Yang
Using the extended Huygens-Fresnel principle and Rayleigh scattering regime, the analytical expressions for the intensity and radiation forces of a focused partially coherent modified Bessel-Gaussian (MBG) beam have been derived, and used to study the optical trapping effect of the focused partially coherent MBG beams acting on dielectric sphere with different refractive indices. The results show that the focused partially coherent MBG beam with m = 0 cannot capture the low index of refraction particles, but can trap the high index of refraction particles. The focused partially coherent MBG beam with m ≥ 1 can trap the high index of refraction particles to a ring on the focal plane, and simultaneously capture the low index of refraction particles to z-axis. When the topological charge m increases, the radiation force decreases while the transverse trapping range increases for low and high index of refractive particles. Besides, larger the value of the spectral degree of coherence ξ is, the easier the two types of particles are trapped by the focused partially coherent MBG beam. Trapping stability is also analysed. The obtained results are useful for analysing the trapping efficiency of focused partially coherent MBG beam applied in micromanipulation and biotechnology.
DOI
Using the extended Huygens-Fresnel principle and Rayleigh scattering regime, the analytical expressions for the intensity and radiation forces of a focused partially coherent modified Bessel-Gaussian (MBG) beam have been derived, and used to study the optical trapping effect of the focused partially coherent MBG beams acting on dielectric sphere with different refractive indices. The results show that the focused partially coherent MBG beam with m = 0 cannot capture the low index of refraction particles, but can trap the high index of refraction particles. The focused partially coherent MBG beam with m ≥ 1 can trap the high index of refraction particles to a ring on the focal plane, and simultaneously capture the low index of refraction particles to z-axis. When the topological charge m increases, the radiation force decreases while the transverse trapping range increases for low and high index of refractive particles. Besides, larger the value of the spectral degree of coherence ξ is, the easier the two types of particles are trapped by the focused partially coherent MBG beam. Trapping stability is also analysed. The obtained results are useful for analysing the trapping efficiency of focused partially coherent MBG beam applied in micromanipulation and biotechnology.
DOI
Optical trapping with planar silicon metalenses
Georgiy Tkachenko, Daan Stellinga, Andrei Ruskuc, Mingzhou Chen, Kishan Dholakia, and Thomas F. Krauss
Contactless manipulation of micron-scale objects in a microfluidic environment is a key ingredient for a range of applications in the biosciences, including sorting, guiding, and analysis of cells and bacteria. Optical forces are powerful for this purpose but, typically, require bulky focusing elements to achieve the appropriate optical field gradients. To this end, realizing the focusing optics in a planar format would be very attractive and conducive to the integration of such microscale devices, either individually or as arrays. Here we report on, to the best of our knowledge, the first experimental demonstration of optical trapping using planar silicon metalenses illuminated with a collimated laser beam. The structures consist of high-contrast gratings with a locally varying period and duty cycle. They are designed to mimic parabolic reflectors with a numerical aperture of 0.56 at a vacuum wavelength of 1064 nm. We achieve both two- and three-dimensional trapping in water, with the latter realized by omitting the central Fresnel zones. This Letter highlights the versatility of such lithographically defined metastructures for exerting optical forces without the need for traditional optical elements.
DOI
Contactless manipulation of micron-scale objects in a microfluidic environment is a key ingredient for a range of applications in the biosciences, including sorting, guiding, and analysis of cells and bacteria. Optical forces are powerful for this purpose but, typically, require bulky focusing elements to achieve the appropriate optical field gradients. To this end, realizing the focusing optics in a planar format would be very attractive and conducive to the integration of such microscale devices, either individually or as arrays. Here we report on, to the best of our knowledge, the first experimental demonstration of optical trapping using planar silicon metalenses illuminated with a collimated laser beam. The structures consist of high-contrast gratings with a locally varying period and duty cycle. They are designed to mimic parabolic reflectors with a numerical aperture of 0.56 at a vacuum wavelength of 1064 nm. We achieve both two- and three-dimensional trapping in water, with the latter realized by omitting the central Fresnel zones. This Letter highlights the versatility of such lithographically defined metastructures for exerting optical forces without the need for traditional optical elements.
DOI
Thursday, July 26, 2018
Dynamic morphing of 3D curved laser traps for all-optical manipulation of particles
José A. Rodrigo, Mercedes Angulo, and Tatiana Alieva
The development of optical manipulation techniques focused on the confinement and transport of micro/nano-particles has attracted increased interest in the last decades. In particular the combination of all-optical confinement and propelling forces, respectively arising from high intensity and phase gradients of a strongly focused laser beam, is promising for optical transport. The recently developed freestyle laser trap exploits this manipulation mechanism to achieve optical transport along arbitrary 3D curves. In practice, reconfigurable 3D optical transport of numerous particles is a challenging problem because it requires the ability to easily adapt the trajectory in real time. In this work, we introduce and experimentally demonstrate a strategy for on-task adaptive design of freestyle laser traps based on a dynamic morphing technique. This provides programmable smooth transformation of the 3D shape of the curved laser trap with independent control of the propelling forces along it, that can be configured according to the considered application. Dynamic morphing, proven here on the example of colloidal dielectric micro-particles, significantly simplifies the important problem of real-time reconfigurable 3D optical transport and opens up routes for other sophisticated optical manipulation tasks.
DOI
The development of optical manipulation techniques focused on the confinement and transport of micro/nano-particles has attracted increased interest in the last decades. In particular the combination of all-optical confinement and propelling forces, respectively arising from high intensity and phase gradients of a strongly focused laser beam, is promising for optical transport. The recently developed freestyle laser trap exploits this manipulation mechanism to achieve optical transport along arbitrary 3D curves. In practice, reconfigurable 3D optical transport of numerous particles is a challenging problem because it requires the ability to easily adapt the trajectory in real time. In this work, we introduce and experimentally demonstrate a strategy for on-task adaptive design of freestyle laser traps based on a dynamic morphing technique. This provides programmable smooth transformation of the 3D shape of the curved laser trap with independent control of the propelling forces along it, that can be configured according to the considered application. Dynamic morphing, proven here on the example of colloidal dielectric micro-particles, significantly simplifies the important problem of real-time reconfigurable 3D optical transport and opens up routes for other sophisticated optical manipulation tasks.
DOI
Raman spectral signature reflects transcriptomic features of antibiotic resistance in Escherichia coli
Arno Germond, Taro Ichimura, Takaaki Horinouchi, Hideaki Fujita, Chikara Furusawa & Tomonobu M. Watanabe
To be able to predict antibiotic resistance in bacteria from fast label-free microscopic observations would benefit a broad range of applications in the biological and biomedical fields. Here, we demonstrate the utility of label-free Raman spectroscopy in monitoring the type of resistance and the mode of action of acquired resistance in a bacterial population of Escherichia coli, in the absence of antibiotics. Our findings are reproducible. Moreover, we identified spectral regions that best predicted the modes of action and explored whether the Raman signatures could be linked to the genetic basis of acquired resistance. Spectral peak intensities significantly correlated (False Discovery Rate, p < 0.05) with the gene expression of some genes contributing to antibiotic resistance genes. These results suggest that the acquisition of antibiotic resistance leads to broad metabolic effects reflected through Raman spectral signatures and gene expression changes, hinting at a possible relation between these two layers of complementary information.
DOI
To be able to predict antibiotic resistance in bacteria from fast label-free microscopic observations would benefit a broad range of applications in the biological and biomedical fields. Here, we demonstrate the utility of label-free Raman spectroscopy in monitoring the type of resistance and the mode of action of acquired resistance in a bacterial population of Escherichia coli, in the absence of antibiotics. Our findings are reproducible. Moreover, we identified spectral regions that best predicted the modes of action and explored whether the Raman signatures could be linked to the genetic basis of acquired resistance. Spectral peak intensities significantly correlated (False Discovery Rate, p < 0.05) with the gene expression of some genes contributing to antibiotic resistance genes. These results suggest that the acquisition of antibiotic resistance leads to broad metabolic effects reflected through Raman spectral signatures and gene expression changes, hinting at a possible relation between these two layers of complementary information.
DOI
Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control
Dylan C. Ullery, Sina Soleymani, Andrew Heaton, Juan Orphee, Les Johnson, Rohan Sood, Patrick Kung & Seongsin M. Kim
We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low-mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force, which can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiencies characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be −30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0:71k0.
DOI
We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low-mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force, which can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiencies characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be −30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0:71k0.
DOI
αβ T Cell Receptor Mechanosensing Forces out Serial Engagement
Yinnian Feng, Ellis L. Reinherz, Matthew J. Lang
The αβ TCR is a mechanosensor whose force-dependent structural transition and allostery regulate peptide discrimination and pMHC bond lifetime. Application of mechanical force on the TCR during ligand recognition promotes its molecular translocation and initiates T cell immunological synapse formation. Synergy of external (cell motility based) and internal (cytoskeletal motor based) forces supports a nonequilibrium (energized) model for T cell activation through reconfiguration of the αβ TCR complex at a critical force threshold.
A digital mechanosensing mechanism defines physicochemical thresholds with significant implications for CTL-based vaccines and immunotherapies. That knowledge affords new insights relative to earlier αβ TCR activation models based on equilibrium processes.
DOI
The αβ TCR is a mechanosensor whose force-dependent structural transition and allostery regulate peptide discrimination and pMHC bond lifetime. Application of mechanical force on the TCR during ligand recognition promotes its molecular translocation and initiates T cell immunological synapse formation. Synergy of external (cell motility based) and internal (cytoskeletal motor based) forces supports a nonequilibrium (energized) model for T cell activation through reconfiguration of the αβ TCR complex at a critical force threshold.
A digital mechanosensing mechanism defines physicochemical thresholds with significant implications for CTL-based vaccines and immunotherapies. That knowledge affords new insights relative to earlier αβ TCR activation models based on equilibrium processes.
DOI
Optical tweezers for trapping in a microfluidic environment
R. Kampmann, S. Sinzinger, and J. G. Korvink
Optical tweezers use the force from a light beam to implement a precise gripping tool. Based purely on an optical principle, it works without any bodily contact with the object. In this paper we describe an optical tweezers that targets an application within the framework of nuclear magnetic resonance (NMR) spectroscopy of small objects, which are embedded inside a microfluidic channel that will be integrated in a micro-NMR detector. In the project’s final stages, the whole system will be installed within the wide bore of a superconducting magnet. The aim is to precisely maintain the position of the object to be measured, without the use of susceptibility disturbing materials or geometries. In this contribution we focus on the design and construction of the tweezers. For the optical force simulation of the system we used a geometrical optics approach, which we combined with a ray fan description of the output beam of an optical system. By embedding both techniques within an iterative design process, we were able to design efficient optical tweezers that met the numerous constraints. Based on details of the constraints and requirements given by the application, different system concepts were derived and studied. Next, a highly adapted and efficient optical trapping system was designed and manufactured. After the components were characterized using vertical scanning interferometry, the system was assembled to achieve a monolithic optical component. The proper function of the optical tweezers was successfully tested by optical trapping of fused silica particles.
DOI
Optical tweezers use the force from a light beam to implement a precise gripping tool. Based purely on an optical principle, it works without any bodily contact with the object. In this paper we describe an optical tweezers that targets an application within the framework of nuclear magnetic resonance (NMR) spectroscopy of small objects, which are embedded inside a microfluidic channel that will be integrated in a micro-NMR detector. In the project’s final stages, the whole system will be installed within the wide bore of a superconducting magnet. The aim is to precisely maintain the position of the object to be measured, without the use of susceptibility disturbing materials or geometries. In this contribution we focus on the design and construction of the tweezers. For the optical force simulation of the system we used a geometrical optics approach, which we combined with a ray fan description of the output beam of an optical system. By embedding both techniques within an iterative design process, we were able to design efficient optical tweezers that met the numerous constraints. Based on details of the constraints and requirements given by the application, different system concepts were derived and studied. Next, a highly adapted and efficient optical trapping system was designed and manufactured. After the components were characterized using vertical scanning interferometry, the system was assembled to achieve a monolithic optical component. The proper function of the optical tweezers was successfully tested by optical trapping of fused silica particles.
DOI
Optomechanical Self-Regulated Coupling of a Suspended Microsphere Cavity and a Waveguide in the Aqueous Medium
Te-Chang Chen; Ming-Chang M. Le
Optomechanics of colloidal microparticles has wide applications in biological analysis and sensing. For colloidal microspheres or microdroplets, the optomechanical force can be magnified through the cavity enhancement effect. However, it is difficult to analyze the force since the colloidal microspheres are suspended in liquid, and addressing a movable microsphere at a specific position in three-dimensional space is also challenging. An on-chip integrated operating platform comprising waveguides and microelectromechanical systems is employed to study the cavity-enhanced optical gradient force on colloidal microspheres, owing to the ability to precisely control the distance between a suspended microsphere and a waveguide through dielectrophoretic force. We introduce two kinds of optomechanical coupling mechanisms at resonance, depending on the initial coupling gap without inclusion of the optical gradient force. One is self-adjusted coupling, where the coupling gap of a suspended microsphere continuously varies with the optical input power, and the other is bistable coupling, where the coupling gap hops from one state to the other as the input power exceeds over a threshold value, which is caused by the nature of nonlinear gap-dependent optical gradient force.
DOI
Optomechanics of colloidal microparticles has wide applications in biological analysis and sensing. For colloidal microspheres or microdroplets, the optomechanical force can be magnified through the cavity enhancement effect. However, it is difficult to analyze the force since the colloidal microspheres are suspended in liquid, and addressing a movable microsphere at a specific position in three-dimensional space is also challenging. An on-chip integrated operating platform comprising waveguides and microelectromechanical systems is employed to study the cavity-enhanced optical gradient force on colloidal microspheres, owing to the ability to precisely control the distance between a suspended microsphere and a waveguide through dielectrophoretic force. We introduce two kinds of optomechanical coupling mechanisms at resonance, depending on the initial coupling gap without inclusion of the optical gradient force. One is self-adjusted coupling, where the coupling gap of a suspended microsphere continuously varies with the optical input power, and the other is bistable coupling, where the coupling gap hops from one state to the other as the input power exceeds over a threshold value, which is caused by the nature of nonlinear gap-dependent optical gradient force.
DOI
Tuesday, July 24, 2018
Tn and STn are members of a family of carbohydrate tumor antigens that possess carbohydrate–carbohydrate interactions
Marit Sletmoen, Thomas A Gerken, Bjørn T Stokke, Joy Burchell, C Fred Brewer
The mucin-type O-glycome in cancer aberrantly expresses the truncated glycans Tn (GalNAcα1-Ser/Thr) and STn (Neu5Acα2,6GalNAcα1-Ser/Thr). However, the role of Tn and STn in cancer and other diseases is not well understood. Our recent discovery of the self-binding properties (carbohydrate–carbohydrate interactions, CCIs) of Tn (Tn–Tn) and STn (STn–STn) provides a model for their possible roles in cellular transformation. We also review evidence that Tn and STn are members of a larger family of glycan tumor antigens that possess CCIs, which may participate in oncogenesis.
DOI
The mucin-type O-glycome in cancer aberrantly expresses the truncated glycans Tn (GalNAcα1-Ser/Thr) and STn (Neu5Acα2,6GalNAcα1-Ser/Thr). However, the role of Tn and STn in cancer and other diseases is not well understood. Our recent discovery of the self-binding properties (carbohydrate–carbohydrate interactions, CCIs) of Tn (Tn–Tn) and STn (STn–STn) provides a model for their possible roles in cellular transformation. We also review evidence that Tn and STn are members of a larger family of glycan tumor antigens that possess CCIs, which may participate in oncogenesis.
DOI
Cooling the motion of a silica microsphere in a magneto-gravitational trap in ultra-high vacuum
Bradley R Slezak, Charles W Lewandowski, Jen-Feng Hsu and Brian D'Urso
Levitated optomechanical systems, and particularly particles trapped in vacuum, provide unique platforms for studying the mechanical behavior of objects well-isolated from their environment. Ultimately, such systems may enable the study of fundamental questions in quantum mechanics, gravity, and other weak forces. While the optical trapping of nanoparticles has emerged as the prototypical levitated optomechanical system, it is not without problems due to the heating from the high optical intensity required, particularly when combined with a high vacuum environment. Here we investigate a magneto-gravitational trap in ultra-high vacuum. In contrast to optical trapping, we create an entirely passive trap for diamagnetic particles by utilizing the magnetic field generated by permanent magnets and the gravitational interaction. We demonstrate cooling the center of mass motion of a trapped silica microsphere from ambient temperature to an effective temperature near or below one milliKelvin in two degrees of freedom by optical feedback damping.
DOI
Levitated optomechanical systems, and particularly particles trapped in vacuum, provide unique platforms for studying the mechanical behavior of objects well-isolated from their environment. Ultimately, such systems may enable the study of fundamental questions in quantum mechanics, gravity, and other weak forces. While the optical trapping of nanoparticles has emerged as the prototypical levitated optomechanical system, it is not without problems due to the heating from the high optical intensity required, particularly when combined with a high vacuum environment. Here we investigate a magneto-gravitational trap in ultra-high vacuum. In contrast to optical trapping, we create an entirely passive trap for diamagnetic particles by utilizing the magnetic field generated by permanent magnets and the gravitational interaction. We demonstrate cooling the center of mass motion of a trapped silica microsphere from ambient temperature to an effective temperature near or below one milliKelvin in two degrees of freedom by optical feedback damping.
DOI
Levitated Nanoparticles for Microscopic Thermodynamics—A Review
Jan Gieseler and James Millen
Levitated Nanoparticles have received much attention for their potential to perform quantum mechanical experiments even at room temperature. However, even in the regime where the particle dynamics are purely classical, there is a lot of interesting physics that can be explored. Here we review the application of levitated nanoparticles as a new experimental platform to explore stochastic thermodynamics in small systems.
DOI
Levitated Nanoparticles have received much attention for their potential to perform quantum mechanical experiments even at room temperature. However, even in the regime where the particle dynamics are purely classical, there is a lot of interesting physics that can be explored. Here we review the application of levitated nanoparticles as a new experimental platform to explore stochastic thermodynamics in small systems.
DOI
Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre
Dmitry S. Bykov, Shangran Xie, Richard Zeltner, Andrey Machnev, Gordon K. L. Wong, Tijmen G. Euser & Philip St.J. Russell
Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.
DOI
Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.
DOI
Control of synchronization in models of hydrodynamically coupled motile cilia
Armando Maestro, Nicolas Bruot, Jurij Kotar, Nariya Uchida, Ramin Golestanian & Pietro Cicuta
In many organisms, multiple motile cilia coordinate their beating to facilitate swimming or driving of surface flows. Simple models are required to gain a quantitative understanding of how such coordination is achieved; there are two scales of phenomena, within and between cilia, and both host complex non-linear and non-thermal effects. We study here a model that is tractable analytically and can be realized by optical trapping colloidal particles: intra-cilia properties are coarse grained into the parameters chosen to drive particles around closed local orbits. Depending on these effective parameters a variety of phase-locked steady states can be achieved. We derive a theory that includes two mechanisms for synchronization: the flexibility of the motion along the predefined orbit and the modulation of the driving force. We show that modest tuning of the cilia beat properties, as could be achieved biologically, results in dramatic changes in the collective motion arising from hydrodynamic coupling.
DOI
In many organisms, multiple motile cilia coordinate their beating to facilitate swimming or driving of surface flows. Simple models are required to gain a quantitative understanding of how such coordination is achieved; there are two scales of phenomena, within and between cilia, and both host complex non-linear and non-thermal effects. We study here a model that is tractable analytically and can be realized by optical trapping colloidal particles: intra-cilia properties are coarse grained into the parameters chosen to drive particles around closed local orbits. Depending on these effective parameters a variety of phase-locked steady states can be achieved. We derive a theory that includes two mechanisms for synchronization: the flexibility of the motion along the predefined orbit and the modulation of the driving force. We show that modest tuning of the cilia beat properties, as could be achieved biologically, results in dramatic changes in the collective motion arising from hydrodynamic coupling.
DOI
Change in collective motion of colloidal particles driven by an optical vortex with driving force and spatial confinement
Keita Saito, Shogo Okuboa and Yasuyuki Kimura
We studied the change in collective behavior of optically driven colloidal particles on a circular path. The particles are simultaneously driven by the orbital angular momentum of an optical vortex beam generated by holographic optical tweezers. The driving force is controlled by the topological charge l of the vortex. By varying the driving force and spatial confinement, four characteristic collective motions were observed. The collective behavior results from the interplay between the optical interaction, hydrodynamic interaction and spatial confinement. Varying the topological charge of an optical vortex not only induces changes in driving force but also alters the stability of three-dimensional optical trapping. The switch between dynamic clustering and stable clustering was observed in this manner. Decreasing the cell thickness diminishes the velocity of the respective particles and increases the spatial confinement. A jamming-like characteristic collective motion appears when the thickness is small and the topological charge is large. In this regime, a ring of equally-spaced doublets was spontaneously formed in systems composed of an even number of particles.
DOI
We studied the change in collective behavior of optically driven colloidal particles on a circular path. The particles are simultaneously driven by the orbital angular momentum of an optical vortex beam generated by holographic optical tweezers. The driving force is controlled by the topological charge l of the vortex. By varying the driving force and spatial confinement, four characteristic collective motions were observed. The collective behavior results from the interplay between the optical interaction, hydrodynamic interaction and spatial confinement. Varying the topological charge of an optical vortex not only induces changes in driving force but also alters the stability of three-dimensional optical trapping. The switch between dynamic clustering and stable clustering was observed in this manner. Decreasing the cell thickness diminishes the velocity of the respective particles and increases the spatial confinement. A jamming-like characteristic collective motion appears when the thickness is small and the topological charge is large. In this regime, a ring of equally-spaced doublets was spontaneously formed in systems composed of an even number of particles.
DOI
Thursday, July 19, 2018
Enhance of optical trapping efficiency by nonlinear optical tweezers
Ho Quang, Quy, Doan Quoc Tuan, Thai Doan Thanh, Nguyen Manh Thang
In this article, enhance of optical trapping efficiency by the nonlinear optical tweezers is investigated. The expressions described the longitudinal and transverse optical trapping efficiencies are theoretically derived. The influence of average laser power on the optical trapping efficiency is observed and discussed in comparison with that of linear optical tweezers. Remarkably, the optical trapping efficiency of nonlinear optical tweezers can be enhanced by using average laser power, and get several times higher than that of the linear optical ones having the same configuration.
DOI
In this article, enhance of optical trapping efficiency by the nonlinear optical tweezers is investigated. The expressions described the longitudinal and transverse optical trapping efficiencies are theoretically derived. The influence of average laser power on the optical trapping efficiency is observed and discussed in comparison with that of linear optical tweezers. Remarkably, the optical trapping efficiency of nonlinear optical tweezers can be enhanced by using average laser power, and get several times higher than that of the linear optical ones having the same configuration.
DOI
A Molecular Grammar Governing the Driving Forces for Phase Separation of Prion-like RNA Binding Proteins
Jie Wang, Jeong-Mo Choi, Alex S. Holehouse, Hyun O. Lee, Xiaojie Zhang, Marcus Jahnel, Shovamayee Maharana, Régis Lemaitre, Andrei Pozniakovsky, David Drechsel, Ina Poser, Rohit V. Pappu, Simon Alberti, Anthony A. Hyman
Proteins such as FUS phase separate to form liquid-like condensates that can harden into less dynamic structures. However, how these properties emerge from the collective interactions of many amino acids remains largely unknown. Here, we use extensive mutagenesis to identify a sequence-encoded molecular grammar underlying the driving forces of phase separation of proteins in the FUS family and test aspects of this grammar in cells. Phase separation is primarily governed by multivalent interactions among tyrosine residues from prion-like domains and arginine residues from RNA-binding domains, which are modulated by negatively charged residues. Glycine residues enhance the fluidity, whereas glutamine and serine residues promote hardening. We develop a model to show that the measured saturation concentrations of phase separation are inversely proportional to the product of the numbers of arginine and tyrosine residues. These results suggest it is possible to predict phase-separation properties based on amino acid sequences.
DOI
Proteins such as FUS phase separate to form liquid-like condensates that can harden into less dynamic structures. However, how these properties emerge from the collective interactions of many amino acids remains largely unknown. Here, we use extensive mutagenesis to identify a sequence-encoded molecular grammar underlying the driving forces of phase separation of proteins in the FUS family and test aspects of this grammar in cells. Phase separation is primarily governed by multivalent interactions among tyrosine residues from prion-like domains and arginine residues from RNA-binding domains, which are modulated by negatively charged residues. Glycine residues enhance the fluidity, whereas glutamine and serine residues promote hardening. We develop a model to show that the measured saturation concentrations of phase separation are inversely proportional to the product of the numbers of arginine and tyrosine residues. These results suggest it is possible to predict phase-separation properties based on amino acid sequences.
DOI
1064 nm Dispersive Raman Microspectroscopy and Optical Trapping of Pharmaceutical Aerosols
Peter J. Gallimore, Nick M. Davidson, Markus Kalberer, Francis D. Pope, and Andrew D. Ward
Raman spectroscopy is a powerful tool for investigating chemical composition. Coupling Raman spectroscopy with optical microscopy (Raman microspectroscopy) and optical trapping (Raman tweezers) allows microscopic length scales and, hence, femtolitre volumes to be probed. Raman microspectroscopy typically uses UV/visible excitation lasers, but many samples, including organic molecules and complex tissue samples, fluoresce strongly at these wavelengths. Here we report the development and application of dispersive Raman microspectroscopy designed around a near-infrared continuous wave 1064 nm excitation light source. We analyze microparticles (1–5 μm diameter) composed of polystyrene latex and from three real-world pressurized metered dose inhalers (pMDIs) used in the treatment of asthma: salmeterol xinafoate (Serevent), salbutamol sulfate (Salamol), and ciclesonide (Alvesco). For the first time, single particles are captured, optically levitated, and analyzed using the same 1064 nm laser, which permits a convenient nondestructive chemical analysis of the true aerosol phase. We show that particles exhibiting overwhelming fluorescence using a visible laser (514.5 nm) can be successfully analyzed with 1064 nm excitation, irrespective of sample composition and irradiation time. Spectra are acquired rapidly (1–5 min) with a wavelength resolution of 2 nm over a wide wavenumber range (500–3100 cm–1). This is despite the microscopic sample size and low Raman scattering efficiency at 1064 nm. Spectra of individual pMDI particles compare well to bulk samples, and the Serevent pMDI delivers the thermodynamically preferred crystal form of salmeterol xinafoate. 1064 nm dispersive Raman microspectroscopy is a promising technique that could see diverse applications for samples where fluorescence-free characterization is required with high spatial resolution.
Raman spectroscopy is a powerful tool for investigating chemical composition. Coupling Raman spectroscopy with optical microscopy (Raman microspectroscopy) and optical trapping (Raman tweezers) allows microscopic length scales and, hence, femtolitre volumes to be probed. Raman microspectroscopy typically uses UV/visible excitation lasers, but many samples, including organic molecules and complex tissue samples, fluoresce strongly at these wavelengths. Here we report the development and application of dispersive Raman microspectroscopy designed around a near-infrared continuous wave 1064 nm excitation light source. We analyze microparticles (1–5 μm diameter) composed of polystyrene latex and from three real-world pressurized metered dose inhalers (pMDIs) used in the treatment of asthma: salmeterol xinafoate (Serevent), salbutamol sulfate (Salamol), and ciclesonide (Alvesco). For the first time, single particles are captured, optically levitated, and analyzed using the same 1064 nm laser, which permits a convenient nondestructive chemical analysis of the true aerosol phase. We show that particles exhibiting overwhelming fluorescence using a visible laser (514.5 nm) can be successfully analyzed with 1064 nm excitation, irrespective of sample composition and irradiation time. Spectra are acquired rapidly (1–5 min) with a wavelength resolution of 2 nm over a wide wavenumber range (500–3100 cm–1). This is despite the microscopic sample size and low Raman scattering efficiency at 1064 nm. Spectra of individual pMDI particles compare well to bulk samples, and the Serevent pMDI delivers the thermodynamically preferred crystal form of salmeterol xinafoate. 1064 nm dispersive Raman microspectroscopy is a promising technique that could see diverse applications for samples where fluorescence-free characterization is required with high spatial resolution.
Physiological Hypoxia (Physioxia) Impairs the Early Adhesion of Single Lymphoma Cell to Marrow Stromal Cell and Extracellular Matrix. Optical Tweezers Study
Kamila Duś-Szachniewicz, Sławomir Drobczyński, Piotr Ziółkowski, Paweł Kołodziej, Kinga M. Walaszek, Aleksandra K. Korzeniewska, Anil Agrawal, Piotr Kupczyk and Marta Woźniak
Adhesion is critical for the maintenance of cellular structures as well as intercellular communication, and its dysfunction occurs prevalently during cancer progression. Recently, a growing number of studies indicated the ability of oxygen to regulate adhesion molecules expression, however, the influence of physiological hypoxia (physioxia) on cell adhesion remains elusive. Thus, here we aimed: (i) to develop an optical tweezers based assay to precisely evaluate single diffuse large B-cell lymphoma (DLBCL) cell adhesion to neighbor cells (mesenchymal stromal cells) and extracellular matrix (Matrigel) under normoxia and physioxia; and, (ii) to explore the role of integrins in adhesion of single lymphoma cell. We identified the pronouncedly reduced adhesive properties of lymphoma cell lines and primary lymphocytes B under physioxia to both stromal cells and Matrigel. Corresponding effects were shown in bulk adhesion assays. Then we emphasized that impaired β1, β2 integrins, and cadherin-2 expression, studied by confocal microscopy, account for reduction in lymphocyte adhesion in physioxia. Additionally, the blockade studies conducted with anti-integrin antibodies have revealed the critical role of integrins in lymphoma adhesion. To summarize, the presented approach allows for precise confirmation of the changes in single cell adhesion properties provoked by physiological hypoxia. Thus, our findings reveal an unprecedented role of using physiologically relevant oxygen conditioning and single cell adhesion approaches when investigating tumor adhesion in vitro.
DOI
Adhesion is critical for the maintenance of cellular structures as well as intercellular communication, and its dysfunction occurs prevalently during cancer progression. Recently, a growing number of studies indicated the ability of oxygen to regulate adhesion molecules expression, however, the influence of physiological hypoxia (physioxia) on cell adhesion remains elusive. Thus, here we aimed: (i) to develop an optical tweezers based assay to precisely evaluate single diffuse large B-cell lymphoma (DLBCL) cell adhesion to neighbor cells (mesenchymal stromal cells) and extracellular matrix (Matrigel) under normoxia and physioxia; and, (ii) to explore the role of integrins in adhesion of single lymphoma cell. We identified the pronouncedly reduced adhesive properties of lymphoma cell lines and primary lymphocytes B under physioxia to both stromal cells and Matrigel. Corresponding effects were shown in bulk adhesion assays. Then we emphasized that impaired β1, β2 integrins, and cadherin-2 expression, studied by confocal microscopy, account for reduction in lymphocyte adhesion in physioxia. Additionally, the blockade studies conducted with anti-integrin antibodies have revealed the critical role of integrins in lymphoma adhesion. To summarize, the presented approach allows for precise confirmation of the changes in single cell adhesion properties provoked by physiological hypoxia. Thus, our findings reveal an unprecedented role of using physiologically relevant oxygen conditioning and single cell adhesion approaches when investigating tumor adhesion in vitro.
DOI
Sub-10 nm particle trapping enabled by a plasmonic dark mode
Fajun Xiao, Yuxuan Ren, Wuyun Shang, Weiren Zhu, Lei Han, Hua Lu, Ting Mei, Malin Premaratne, and Jianlin Zhao
We demonstrate that a highly localized plasmonic dark mode with radial symmetry, termed quadrupole-bonded radial breathing mode, can be used for optically trapping the dielectric nanoparticles. In particular, the annular potential well produced by this dark mode shows a sufficiently large depth to stably trap the 5 nm particles under a relatively low optical power. Our results address the quest for precisely trapping sub-10 nm particles with high yield and pave the way for placing sub-10 nm particles conforming to a specific geometric pattern.
DOI
We demonstrate that a highly localized plasmonic dark mode with radial symmetry, termed quadrupole-bonded radial breathing mode, can be used for optically trapping the dielectric nanoparticles. In particular, the annular potential well produced by this dark mode shows a sufficiently large depth to stably trap the 5 nm particles under a relatively low optical power. Our results address the quest for precisely trapping sub-10 nm particles with high yield and pave the way for placing sub-10 nm particles conforming to a specific geometric pattern.
DOI
Controlled spin of a nonbirefringent droplet trapped in an optical vortex beam
Maksym Ivanov, Dag Hanstorp
The spin part of the angular momentum of light can cause a birefringent particle to spin around its axis, while having no effect on a nonbirefringent particle. The orbital part of light’s angular momentum, on the other hand, can cause both birefringent and nonbirefringent particles to orbit around the axis of a light beam. In this paper, we demonstrate that nonbirefringent particles can also be made to spin around their axis when trapped in an optical vortex beam. The rotation of the particle depends on the ratio of the size of the particle and the diameter of the laser beam in which the particle is trapped. It can therefore be controlled by varying the position of the particle with respect to the focal point of the laser beam. The rotational frequency can also be controlled by changing the polarization state of the beam, since spin–orbit coupling affects the total angular momentum experienced by the trapped particle. The motion of the trapped particle is detected by a photodiode and a high-speed camera. Most microparticles found in nature are nonbirefringent, and the method presented in this paper will therefore open up new applications for optically induced rotations.
DOI
The spin part of the angular momentum of light can cause a birefringent particle to spin around its axis, while having no effect on a nonbirefringent particle. The orbital part of light’s angular momentum, on the other hand, can cause both birefringent and nonbirefringent particles to orbit around the axis of a light beam. In this paper, we demonstrate that nonbirefringent particles can also be made to spin around their axis when trapped in an optical vortex beam. The rotation of the particle depends on the ratio of the size of the particle and the diameter of the laser beam in which the particle is trapped. It can therefore be controlled by varying the position of the particle with respect to the focal point of the laser beam. The rotational frequency can also be controlled by changing the polarization state of the beam, since spin–orbit coupling affects the total angular momentum experienced by the trapped particle. The motion of the trapped particle is detected by a photodiode and a high-speed camera. Most microparticles found in nature are nonbirefringent, and the method presented in this paper will therefore open up new applications for optically induced rotations.
DOI
Monday, July 16, 2018
Low-frequency Noise Reduction in Dual-Fiber Optical Trap using Normalized Differential Signal of Transmission Lights
Tengfang Kuang; Guangzong Xiao; Wei Xiong; Xiang Han; Xinlin Chen; Jie Yuan
The accuracy of long-term position detection in dual-fiber optical trap is limited by low-frequency noise. We propose a technique that can reduce such noise. A position detection system for dual-fiber optical trap using a quadrant photodiode is built. The transmission light from the trapped particle is detected by two photodiodes. The normalized differential signal of transmission lights is demonstrated to carry the noise caused by asymmetric laser power fluctuation irradiating the microsphere, which is proved to dominate low-frequency noise. By subtracting this normalized difference from the position signal, the noise-reduction capability of this technique is remarkably 67% depending on detection bandwidth. It is expected to be applied to integrated and microfluidic fiber-optic trap system.
DOI
The accuracy of long-term position detection in dual-fiber optical trap is limited by low-frequency noise. We propose a technique that can reduce such noise. A position detection system for dual-fiber optical trap using a quadrant photodiode is built. The transmission light from the trapped particle is detected by two photodiodes. The normalized differential signal of transmission lights is demonstrated to carry the noise caused by asymmetric laser power fluctuation irradiating the microsphere, which is proved to dominate low-frequency noise. By subtracting this normalized difference from the position signal, the noise-reduction capability of this technique is remarkably 67% depending on detection bandwidth. It is expected to be applied to integrated and microfluidic fiber-optic trap system.
DOI
Optical levitation measurement on hygroscopic behaviour and SVOC vapour pressure of single organic/inorganic aqueous aerosol
Chen Cai,Chunsheng Zhao
Quantifying the gas/particle partitioning of organic compounds is of great significance to the understanding of atmospheric aerosol indirect effect. Accurate determination of the hygroscopicities and vapour pressures of semi-volatile organic compounds (SVOC) is of crucial importance in studying their partitioning behaviour into atmospheric aerosol, as the influences on SVOCs evaporation from participation of inorganic species remains unclear. In this study we first present thermodynamic quantitative simulation and tweezed single particle measurement of hygroscopicity and volatility of single aerosol droplets. With thermodynamics simulation of the hygroscopicity, SVOC time dependent evaporation and potential chloride depletion reaction in a single trapped droplet, we illustrate influences from different process towards the trapped droplet. In optical tweezers measurement, the trapped droplet in the aerosol optical tweezers acts as a microcavity, which stimulates the cavity enhanced Raman spectroscopy (CERS) signal. Size and composition of the particle are calculated from Mie fit to the positions of the "whispering gallery modes" in the CERS fingerprint. Hygroscopic behaviours and SVOC saturated vapour pressure can then be extracted from the correlation between the changing droplet radius and solute concentration (derived from experimentally determined real part of refractive index (RI)) with good accuracy and reliability.
DOI
Quantifying the gas/particle partitioning of organic compounds is of great significance to the understanding of atmospheric aerosol indirect effect. Accurate determination of the hygroscopicities and vapour pressures of semi-volatile organic compounds (SVOC) is of crucial importance in studying their partitioning behaviour into atmospheric aerosol, as the influences on SVOCs evaporation from participation of inorganic species remains unclear. In this study we first present thermodynamic quantitative simulation and tweezed single particle measurement of hygroscopicity and volatility of single aerosol droplets. With thermodynamics simulation of the hygroscopicity, SVOC time dependent evaporation and potential chloride depletion reaction in a single trapped droplet, we illustrate influences from different process towards the trapped droplet. In optical tweezers measurement, the trapped droplet in the aerosol optical tweezers acts as a microcavity, which stimulates the cavity enhanced Raman spectroscopy (CERS) signal. Size and composition of the particle are calculated from Mie fit to the positions of the "whispering gallery modes" in the CERS fingerprint. Hygroscopic behaviours and SVOC saturated vapour pressure can then be extracted from the correlation between the changing droplet radius and solute concentration (derived from experimentally determined real part of refractive index (RI)) with good accuracy and reliability.
DOI
Optomechanical Cavities for All-Optical Photothermal Sensing
Marcel W. Pruessner, Doewon Park, Todd H. Stievater, Dmitry A. Kozak, and William S. Rabinovich
Cavity optomechanics enables strong coupling of optics and mechanics. Although remarkable progress has been made, practical applications of cavity optomechanics are only recently being realized. In this work we propose an all-optical sensing technique enabling the measurement of photothermally induced strains with ultrahigh-resolution. We demonstrate an optomechanical sensor consisting of a silicon nitride (Si3N4) microring cavity that is evanescently coupled to a suspended SiNx micromechanical (MEMS) oscillator. Experiments show that MEMS resonances are excited purely via cavity-enhanced gradient optical forces. However, small levels of absorption in the oscillator result in photothermally induced strains that shift the mechanical resonance frequencies. By measuring absorption-induced frequency shifts our technique enables high-resolution with nanostrain sensitivity corresponding to fJ-levels of absorption. As a demonstration, we perform absorption spectroscopy on the MEMS device and measure the known Si–H absorption feature of deposited silicon nitride. The unprecedented sensitivity enabled by absorption-induced frequency shifts enables entirely new sensors in fields ranging from materials and chemical sensing to bolometers and imaging arrays.
DOI
Cavity optomechanics enables strong coupling of optics and mechanics. Although remarkable progress has been made, practical applications of cavity optomechanics are only recently being realized. In this work we propose an all-optical sensing technique enabling the measurement of photothermally induced strains with ultrahigh-resolution. We demonstrate an optomechanical sensor consisting of a silicon nitride (Si3N4) microring cavity that is evanescently coupled to a suspended SiNx micromechanical (MEMS) oscillator. Experiments show that MEMS resonances are excited purely via cavity-enhanced gradient optical forces. However, small levels of absorption in the oscillator result in photothermally induced strains that shift the mechanical resonance frequencies. By measuring absorption-induced frequency shifts our technique enables high-resolution with nanostrain sensitivity corresponding to fJ-levels of absorption. As a demonstration, we perform absorption spectroscopy on the MEMS device and measure the known Si–H absorption feature of deposited silicon nitride. The unprecedented sensitivity enabled by absorption-induced frequency shifts enables entirely new sensors in fields ranging from materials and chemical sensing to bolometers and imaging arrays.
DOI
Sorting Metal Nanoparticles with Dynamic and Tunable Optical Driven Forces
Fan Nan and Zijie Yan
Precise sorting of colloidal nanoparticles is a challenging yet necessary task for size-specific applications of nanoparticles in nanophotonics and biochemistry. Here we present a new strategy for all-optical sorting of metal nanoparticles with dynamic and tunable optical driven forces generated by phase gradients of light. Size-dependent optical forces arising from the phase gradients of optical line traps can drive nanoparticles of different sizes with different velocities in solution, leading to their separation along the line traps. By using a sequential combination of optical lines to create differential trapping potentials, we realize precise sorting of silver and gold nanoparticles in the diameter range of 70–150 nm with a resolution down to 10 nm. Separation of the nanoparticles agrees with the analysis of optical forces acting on them and with simulations of their kinetic motions. The results provide new insights into all-optical nanoparticle manipulation and separation and reveal that there is still room to sort smaller nanoparticle with nanometer precision using dynamic phase-gradient forces.
DOI
Precise sorting of colloidal nanoparticles is a challenging yet necessary task for size-specific applications of nanoparticles in nanophotonics and biochemistry. Here we present a new strategy for all-optical sorting of metal nanoparticles with dynamic and tunable optical driven forces generated by phase gradients of light. Size-dependent optical forces arising from the phase gradients of optical line traps can drive nanoparticles of different sizes with different velocities in solution, leading to their separation along the line traps. By using a sequential combination of optical lines to create differential trapping potentials, we realize precise sorting of silver and gold nanoparticles in the diameter range of 70–150 nm with a resolution down to 10 nm. Separation of the nanoparticles agrees with the analysis of optical forces acting on them and with simulations of their kinetic motions. The results provide new insights into all-optical nanoparticle manipulation and separation and reveal that there is still room to sort smaller nanoparticle with nanometer precision using dynamic phase-gradient forces.
DOI
Optical Manipulation along an Optical Axis with a Polarization Sensitive Meta-Lens
Hen Markovich, Ivan I. Shishkin, Netta Hendler, and Pavel Ginzburg
The ability to manipulate small objects with focused laser beams opens a broad spectrum of opportunities in fundamental and applied studies, for which precise control over mechanical path and stability is required. Although conventional optical tweezers are based on refractive optics, the development of compact trapping devices that could be integrated within fluid cells is in high demand. Here, a plasmonic polarization-sensitive metasurface-based lens, embedded within a fluid, is demonstrated to provide several stable trapping centers along the optical axis. The position of a particle is controlled with the polarization of the incident light, interacting with plasmonic nanoscale patch antennas, organized within overlapping Fresnel zones of the lens. While standard diffractive optical elements face challenges in trapping objects in the axial direction outside the depth of focus, bifocal Fresnel meta-lens demonstrates the capability to manipulate a bead along a 4 μm line. An additional fluorescent module, incorporated within the optical trapping setup, was implemented and enabled the accurate mapping of optical potentials via a particle-tracking algorithm. Auxiliary micro- and nanostructures, integrated within fluidic devices, provide numerous opportunities to achieve flexible optomechanical manipulation, including transport, trapping, and sorting, which are in high demand for lab-on-a-chip applications and many others.
DOI
The ability to manipulate small objects with focused laser beams opens a broad spectrum of opportunities in fundamental and applied studies, for which precise control over mechanical path and stability is required. Although conventional optical tweezers are based on refractive optics, the development of compact trapping devices that could be integrated within fluid cells is in high demand. Here, a plasmonic polarization-sensitive metasurface-based lens, embedded within a fluid, is demonstrated to provide several stable trapping centers along the optical axis. The position of a particle is controlled with the polarization of the incident light, interacting with plasmonic nanoscale patch antennas, organized within overlapping Fresnel zones of the lens. While standard diffractive optical elements face challenges in trapping objects in the axial direction outside the depth of focus, bifocal Fresnel meta-lens demonstrates the capability to manipulate a bead along a 4 μm line. An additional fluorescent module, incorporated within the optical trapping setup, was implemented and enabled the accurate mapping of optical potentials via a particle-tracking algorithm. Auxiliary micro- and nanostructures, integrated within fluidic devices, provide numerous opportunities to achieve flexible optomechanical manipulation, including transport, trapping, and sorting, which are in high demand for lab-on-a-chip applications and many others.
DOI
Understanding quantum emitters in plasmonic nanocavities with conformal transformation: Purcell enhancement and forces
V. Pacheco-Peña and M. Navarro-Cía
Nanogaps supporting cavity plasmonic modes with unprecedented small mode volume are attractive platforms for tailoring the properties of light–matter interactions at the nanoscale and revealing new physics. Hitherto, there is a concerning lack of analytical solutions to divide the complex interactions into their different underlying mechanisms to gain a better understanding that can foster enhanced designs. Bowtie apertures are viewed as an effective and appealing nanocavity and are studied here within the analytical frame of conformal transformation. We show how the non-radiative Purcell enhancement of a quantum emitter within the bowtie nanocavity depends strongly not only on the geometry of the nanocavity, but also on the position and orientation of the emitter. For a 20 nm diameter (∅ 20 nm) bowtie nanocavity, we report a change of up to two orders of magnitude in the maximum non-radiative Purcell enhancement and a shift in its peak wavelength from green to infra-red. The changes are tracked down to the overlap between the emitter field and the gap plasmon mode field distribution. This analysis also enables us to understand the self-induced trapping potential of a colloidal quantum dot inside the nanocavity. Since transformations can be cascaded, the technique introduced in this work can also be applied to a wide range of nanocavities found in the literature.
Monday, July 2, 2018
Quantitative Evaluation of Optical Forces by Single Particle Tracking in Slit-like Microfluidic Channels
Fumika Nito, Tetsuya Shiozaki, Ryo Nagura, Tetsuro Tsuji, Kentaro Doi, Chie Hosokawa, and Satoyuki Kawano
Optical trapping and manipulation techniques have attracted significant attention in various research fields. Optical forces divided into two terms, such as a scattering force and gradient one, work to push forward and attract objects, respectively. This is a typical property of optical forces. In particular, a tool known as optical tweezers can be created when a laser beam is converged at a focal point, causing strong forces to be generated so as to trap and manipulate small objects. In this study, we propose a novel method to build up cluster structures of polystyrene particles by using optical trapping techniques. Recording trajectories of single particles, the optical forces are quantitatively evaluated using particle tracking velocimetry. Herein, we treat various particle sizes whose diameters are ranging from 1 to 4 μm and expose them to a converged laser beam of 1064 nm wavelength. As a result, both experimental and theoretical results are in good agreement. The behavior of particles is understood in the framework of Ashkin's ray optics. This finding clarifies optical force fields of microparticles distributed in a slit-like microfluidic channel and will be applicable for effectively forming ordered structures in liquids.
DOI
Optical trapping and manipulation techniques have attracted significant attention in various research fields. Optical forces divided into two terms, such as a scattering force and gradient one, work to push forward and attract objects, respectively. This is a typical property of optical forces. In particular, a tool known as optical tweezers can be created when a laser beam is converged at a focal point, causing strong forces to be generated so as to trap and manipulate small objects. In this study, we propose a novel method to build up cluster structures of polystyrene particles by using optical trapping techniques. Recording trajectories of single particles, the optical forces are quantitatively evaluated using particle tracking velocimetry. Herein, we treat various particle sizes whose diameters are ranging from 1 to 4 μm and expose them to a converged laser beam of 1064 nm wavelength. As a result, both experimental and theoretical results are in good agreement. The behavior of particles is understood in the framework of Ashkin's ray optics. This finding clarifies optical force fields of microparticles distributed in a slit-like microfluidic channel and will be applicable for effectively forming ordered structures in liquids.
DOI
Optical trapping of ultrasmooth gold nanoparticles in liquid and air
Y. Arita, G. Tkachenko, N. McReynolds, N. Marro, W. Edwards, E. R. Kay, and K. Dholakia
Optical manipulation of gold nanoparticles has emerged as an exciting avenue for studies in nanothermometry, cell poration, optical binding, and optomechanics. However, conventional gold nanoparticles usually depart from a spherical shape, making such studies less controlled and leading to potential artifacts in trapping behavior. We synthesize ultrasmooth gold nanoparticles, which offer improved circularity and monodispersity. In this article, we demonstrate the advantages of such nanoparticles through a series of optical trapping experiments in both liquid and air. Compared to their conventional counterparts, ultrasmooth gold nanoparticles exhibit up to a two-fold and ten-fold reduction in standard deviation for trap stiffness measurements in liquid and air, respectively. They will enable more controlled studies of plasmon mediated light-matter interactions.
DOI
Optical manipulation of gold nanoparticles has emerged as an exciting avenue for studies in nanothermometry, cell poration, optical binding, and optomechanics. However, conventional gold nanoparticles usually depart from a spherical shape, making such studies less controlled and leading to potential artifacts in trapping behavior. We synthesize ultrasmooth gold nanoparticles, which offer improved circularity and monodispersity. In this article, we demonstrate the advantages of such nanoparticles through a series of optical trapping experiments in both liquid and air. Compared to their conventional counterparts, ultrasmooth gold nanoparticles exhibit up to a two-fold and ten-fold reduction in standard deviation for trap stiffness measurements in liquid and air, respectively. They will enable more controlled studies of plasmon mediated light-matter interactions.
DOI
Coupling effects in position observations due to residual misalignments of imaging axes in counter-propagating dual-beam optical traps
Qijun Luan, Xiang Han, , Guangzong Xiao, Wei Xiong, Hui Luo
Video microscopy is one of the most versatile and successful measurement techniques in the spatio-temporal characterization of particle manipulations. The orientations of the imaging axes are always manually aligned correspondingly to the axes of the optical traps. We assume a residual misalignment angle as 5° exists between one imaging axis and the optical axis. Generous repeated position fluctuations resulted from Brownian motion are simulated, and the statistical results demonstrate dramatic cross-coupling effects occur in the situation of inconsistent trapping stiffness in orthogonal axes. The coupling effects may cause biased stiffness estimations and deteriorate the accuracy of parameter measurements related to position observations. For misalignment calibrations, multi-position observation methods using power imbalance and optical binding interactions are proposed with detailed discussions. The calibration can help to improve the accuracy of position related parameter measurements using suspended particles.
Video microscopy is one of the most versatile and successful measurement techniques in the spatio-temporal characterization of particle manipulations. The orientations of the imaging axes are always manually aligned correspondingly to the axes of the optical traps. We assume a residual misalignment angle as 5° exists between one imaging axis and the optical axis. Generous repeated position fluctuations resulted from Brownian motion are simulated, and the statistical results demonstrate dramatic cross-coupling effects occur in the situation of inconsistent trapping stiffness in orthogonal axes. The coupling effects may cause biased stiffness estimations and deteriorate the accuracy of parameter measurements related to position observations. For misalignment calibrations, multi-position observation methods using power imbalance and optical binding interactions are proposed with detailed discussions. The calibration can help to improve the accuracy of position related parameter measurements using suspended particles.
Switching of Radiation Force on Optically Trapped Microparticles through Photochromic Reactions of Pyranoquinazoline Derivatives
Kenji Setoura, Ahsan M. Memon, Syoji Ito, Yuki Inagaki, Katsuya Mutoh, Jiro Abe, and Hiroshi Miyasaka
Photocontrol of mechanical motions of small objects has attracted much attention to develop mesoscopic remote actuators. For this purpose, photoinduced morphological changes of molecules, molecular aggregates, and crystals have been extensively studied in the field of chemistry and materials science. Here, we propose direct use of momenta of light (i.e. radiation force) to control the motion of small objects, through photochromic reactions of pyranoquinazoline (PQ) derivatives. PQ is colorless in visible wavelength region while it is in closed form and undergoes photochemical ring-opening reactions to form colored isomers upon UV light irradiation; the open-ring isomers return to the colorless closed isomers mainly through the thermal back reaction. In the experiment, individual polymer microparticles with diameters of 7 μm incorporating PQ were trapped by optical tweezers. When the trapped microparticle was irradiated with UV light, the microparticle was pushed along the axis of light propagation about a few micrometers by absorption force arising from PQ in colored form. In addition, we found that dynamics of trapped microparticles was regulated by the thermal back reaction of PQ. The present results demonstrate that diversity of photochromic reactions can be transcribed into mesoscopic motions through the momentum exchange between light and molecules.
DOI
Photocontrol of mechanical motions of small objects has attracted much attention to develop mesoscopic remote actuators. For this purpose, photoinduced morphological changes of molecules, molecular aggregates, and crystals have been extensively studied in the field of chemistry and materials science. Here, we propose direct use of momenta of light (i.e. radiation force) to control the motion of small objects, through photochromic reactions of pyranoquinazoline (PQ) derivatives. PQ is colorless in visible wavelength region while it is in closed form and undergoes photochemical ring-opening reactions to form colored isomers upon UV light irradiation; the open-ring isomers return to the colorless closed isomers mainly through the thermal back reaction. In the experiment, individual polymer microparticles with diameters of 7 μm incorporating PQ were trapped by optical tweezers. When the trapped microparticle was irradiated with UV light, the microparticle was pushed along the axis of light propagation about a few micrometers by absorption force arising from PQ in colored form. In addition, we found that dynamics of trapped microparticles was regulated by the thermal back reaction of PQ. The present results demonstrate that diversity of photochromic reactions can be transcribed into mesoscopic motions through the momentum exchange between light and molecules.
DOI
Proposing an on/off optical router in telecom wavelength using plasmonic tweezer
Sina Aghili, Saeed Golmohammadi, Aydin Amini
This study proposes a plasmonic tweezer using an array of plasmonic bowties which operates as a narrow band filter in an optical telecommunication window when the core–shell nanoparticle is fixed within the fluidic medium and the incident wave is considered as a polychromatic light. Conversely, in the case of manipulating the nanoparticle, the structure acts as an on/off optical router in a fixed wavelength (λ=1.55 micron). Optical forces acting on the nanoparticle have been calculated using the Maxwell stress tensor which enabled us to obtain the nanoparticle manipulation and consequently, the transmission/reflection spectra of the proposed structure over time during the movement of the nanoparticle. A plane wave source with the intensity of View the MathML source was used to excite this plasmonic structure and the results were investigated using a numerical finite difference time domain (FDTD) method.
DOI
This study proposes a plasmonic tweezer using an array of plasmonic bowties which operates as a narrow band filter in an optical telecommunication window when the core–shell nanoparticle is fixed within the fluidic medium and the incident wave is considered as a polychromatic light. Conversely, in the case of manipulating the nanoparticle, the structure acts as an on/off optical router in a fixed wavelength (λ=1.55 micron). Optical forces acting on the nanoparticle have been calculated using the Maxwell stress tensor which enabled us to obtain the nanoparticle manipulation and consequently, the transmission/reflection spectra of the proposed structure over time during the movement of the nanoparticle. A plane wave source with the intensity of View the MathML source was used to excite this plasmonic structure and the results were investigated using a numerical finite difference time domain (FDTD) method.
DOI
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