Jason W. Merrill, Sunil K. Sainis, and Eric R. Dufresne
Electrostatic forces between small groups of colloidal particles are measured using blinking optical tweezers. When the electrostatic screening length is longer than the interparticle separation, forces are found to be non-pairwise-additive. Both pair and multiparticle forces are well described by the linearized Poisson-Boltzmann equation with constant potential boundary conditions. These findings may play an important role in understanding the structure and stability of a wide variety of systems, from micron-sized particles in oil to aqueous nanocolloids.
DOI
Friday, October 9, 2009
Deterministic Ratchet from Stationary Light Fields
I. Zapata, S. Albaladejo, J. M. R. Parrondo, J. J. Sáenz, and F. Sols
Ratchets are dynamic systems where particle transport is induced by zero-average forces due to the interplay between nonlinearity and asymmetry. Generally, they rely on the effect of a strong external driving. We show that stationary optical lattices can be designed to generate particle flow in one direction while requiring neither noise nor driving. Such optical fields must be arranged to yield a combination of conservative (dipole) and nonconservative (radiation pressure) forces. Under strong friction all paths converge to a discrete set of limit periodic trajectories flowing in the same direction.
Ratchets are dynamic systems where particle transport is induced by zero-average forces due to the interplay between nonlinearity and asymmetry. Generally, they rely on the effect of a strong external driving. We show that stationary optical lattices can be designed to generate particle flow in one direction while requiring neither noise nor driving. Such optical fields must be arranged to yield a combination of conservative (dipole) and nonconservative (radiation pressure) forces. Under strong friction all paths converge to a discrete set of limit periodic trajectories flowing in the same direction.
Radiation force of a sphere with an eccentric inclusion illuminated by a laser beam
Han GX, Han YP
Based on the theory of the scattering of an eccentric sphere arbitrarily illuminated by a shaped beam which is recently presented by us, and according to generalized Lorenz - Mie theory (GLMT), we derived the series expressions of radiation forces exerted by the incident beam on an eccentric sphere by using the conservation law of electromagnetic momentum and the Mexwell - Tensor. As an example, numerical results of radiation force of absorbing eccentric spheres for off - axis incidence of Gaussian beam are given, along with a discussion about the influence of the beam - waist radius, relative complex refractive index, relative size and location of the inclusion on the forces.
DOI
Based on the theory of the scattering of an eccentric sphere arbitrarily illuminated by a shaped beam which is recently presented by us, and according to generalized Lorenz - Mie theory (GLMT), we derived the series expressions of radiation forces exerted by the incident beam on an eccentric sphere by using the conservation law of electromagnetic momentum and the Mexwell - Tensor. As an example, numerical results of radiation force of absorbing eccentric spheres for off - axis incidence of Gaussian beam are given, along with a discussion about the influence of the beam - waist radius, relative complex refractive index, relative size and location of the inclusion on the forces.
DOI
Validation, In-Depth Analysis, and Modification of the Micropipette Aspiration Technique
Yong Chen, Baoyu Liu, Gang Xu and Jin-Yu Shao
The micropipette aspiration technique (MAT) has been successfully applied to many studies in cell adhesion such as leukocyte–endothelium interactions. However, this technique has never been validated experimentally and it has been only employed to impose constant forces. In this study, we validated the force measurement of the MAT with the optical trap and analyzed two technical issues of the MAT, force-transducer offset and cell-micropipette gap, with finite element simulation. We also modified the MAT so that increasing or decreasing forces can be applied. With the modified MAT, we studied tether extraction from endothelial cells by pulling single tethers at increasing velocities and constant force loading rates. Before the onset of tether extraction, an apparently linear surface protrusion of a few hundred nanometers was observed, which is likely related to membrane receptors pulling on the underlying cytoskeleton. The strength of the modified MAT lies in its capability and consistency to apply a wide range of force loading rates from several piconewtons per second up to thousands of piconewtons per second. With this modification, the MAT becomes more versatile in the study of single molecule and single cell biophysics.
DOI
The micropipette aspiration technique (MAT) has been successfully applied to many studies in cell adhesion such as leukocyte–endothelium interactions. However, this technique has never been validated experimentally and it has been only employed to impose constant forces. In this study, we validated the force measurement of the MAT with the optical trap and analyzed two technical issues of the MAT, force-transducer offset and cell-micropipette gap, with finite element simulation. We also modified the MAT so that increasing or decreasing forces can be applied. With the modified MAT, we studied tether extraction from endothelial cells by pulling single tethers at increasing velocities and constant force loading rates. Before the onset of tether extraction, an apparently linear surface protrusion of a few hundred nanometers was observed, which is likely related to membrane receptors pulling on the underlying cytoskeleton. The strength of the modified MAT lies in its capability and consistency to apply a wide range of force loading rates from several piconewtons per second up to thousands of piconewtons per second. With this modification, the MAT becomes more versatile in the study of single molecule and single cell biophysics.
DOI
On the interaction of nano-sized organic carbon particles with model lipid membranes
G. Rusciano, A.C. De Luca, G. Pesce and A. Sasso
The cytotoxic character of atmospheric ultra-fine-particles (UFPs) has been reported in numerous, mainly epidemiological, investigations. However, the detailed mechanism, at the molecular level, leading to UFP cytotoxicity is not yet fully understood. To address this question, a better characterization of UFP toxicity in relation to chemical composition, surface area and particle number is needed. To follow this bottom-up approach, we have investigated the interaction of nano-sized organic carbon particles (NOCs), produced in ordinary combustion processes, with cell-sized unilamellar vesicles. These particles have a size in the 1–5 nm range and constitute an abundant fraction of the total carbon emission to the environment due to human activity. The investigation was performed by spectroscopically analyzing the chemical modifications of membrane lipid tails in optically trapped vesicles after exposure to NOCs. Our experimental outcomes demonstrate that they are able to induce oxidative damage to liposome membranes. This modification, in turn, leads to a change in membrane permeability, as observed by surface enhanced Raman scattering. It should be noticed that the method reported herein paves the way for a deeper comprehension of the interaction of nanomaterials with lipid membranes, in relation to both nanoparticles characteristics and membrane lipid composition.
The cytotoxic character of atmospheric ultra-fine-particles (UFPs) has been reported in numerous, mainly epidemiological, investigations. However, the detailed mechanism, at the molecular level, leading to UFP cytotoxicity is not yet fully understood. To address this question, a better characterization of UFP toxicity in relation to chemical composition, surface area and particle number is needed. To follow this bottom-up approach, we have investigated the interaction of nano-sized organic carbon particles (NOCs), produced in ordinary combustion processes, with cell-sized unilamellar vesicles. These particles have a size in the 1–5 nm range and constitute an abundant fraction of the total carbon emission to the environment due to human activity. The investigation was performed by spectroscopically analyzing the chemical modifications of membrane lipid tails in optically trapped vesicles after exposure to NOCs. Our experimental outcomes demonstrate that they are able to induce oxidative damage to liposome membranes. This modification, in turn, leads to a change in membrane permeability, as observed by surface enhanced Raman scattering. It should be noticed that the method reported herein paves the way for a deeper comprehension of the interaction of nanomaterials with lipid membranes, in relation to both nanoparticles characteristics and membrane lipid composition.
Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration
Richard D. L. Hanes, Matthew C. Jenkins, and Stefan U. Egelhaaf
A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45°, smaller angles give a full 2pi phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.
A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45°, smaller angles give a full 2pi phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.
Thursday, October 8, 2009
Line optical tweezers: A tool to induce transformations in stained liposomes and to estimate shear modulus
E. Spyratou, E.A. Mourelatou, A. Georgopoulos, C. Demetzos, M. Makropoulou and A.A. Serafetinides
Liposomes have been actively studied as models of cell membranes and are currently used as drug delivery systems of bioactive molecules. Liposome transformations that mimic cellular processes and are associated with their physicochemical properties have become field of interest the last decade. However, there has been little experimental work on controlled vesicle transformations by non-contact, optical handling methods.In this paper we present the use of line optical tweezers to observe liposome state transitions and transformations. Dynamic shape deformations were induced by line optical tweezers in giant stained liposomes leading to budding transition, fission and pearling creation. Under the controlled effect of line optical tweezers reversible liposome deformations were observed. The shear modulus μ of the membrane was inferred by measuring deformation of stained liposomes induced by the applied optical force. Further laser radiation caused irreversible shape deformations of liposomes, which were transformed from spherical to tubular vesicles. The ability of the selective manipulation of liposomes brings us closer to study their physicochemical properties which play a key role in cellular–liposome interactions, drug encapsulation and delivery efficiency.
Liposomes have been actively studied as models of cell membranes and are currently used as drug delivery systems of bioactive molecules. Liposome transformations that mimic cellular processes and are associated with their physicochemical properties have become field of interest the last decade. However, there has been little experimental work on controlled vesicle transformations by non-contact, optical handling methods.In this paper we present the use of line optical tweezers to observe liposome state transitions and transformations. Dynamic shape deformations were induced by line optical tweezers in giant stained liposomes leading to budding transition, fission and pearling creation. Under the controlled effect of line optical tweezers reversible liposome deformations were observed. The shear modulus μ of the membrane was inferred by measuring deformation of stained liposomes induced by the applied optical force. Further laser radiation caused irreversible shape deformations of liposomes, which were transformed from spherical to tubular vesicles. The ability of the selective manipulation of liposomes brings us closer to study their physicochemical properties which play a key role in cellular–liposome interactions, drug encapsulation and delivery efficiency.
Tuesday, October 6, 2009
Frequency dependence of the optical force between two coupled waveguides
Lin Zhu
We investigate the frequency dependence of the optical force between two coupled waveguides using the supermode theory. We show that the frequency dependence of the optical force in a coupled waveguide system is determined by the dispersion relations of uncoupled individual waveguides. We further numerically calculate the optical force of three representative coupled systems at different frequencies and show that these results agree well with the supermode analysis.
We investigate the frequency dependence of the optical force between two coupled waveguides using the supermode theory. We show that the frequency dependence of the optical force in a coupled waveguide system is determined by the dispersion relations of uncoupled individual waveguides. We further numerically calculate the optical force of three representative coupled systems at different frequencies and show that these results agree well with the supermode analysis.
Monday, October 5, 2009
Enhanced particle transport in an oscillating sinusoidal optical potential
W Mu, Z Liu, L Luan, G Wang, G C Spalding and J B Ketterson
We have studied the delivery of a colloidal particle in the presence of an oscillating, spatially periodic, optical potential. The average particle velocity relative to the fluid velocity in this potential depends greatly on the oscillation amplitude and frequency. The results of both our simulations and experiments show that for some combinations of these parameters, the average particle transportation velocity can be enhanced due to the synchronization of the particle's movement with the oscillating potential.
We have studied the delivery of a colloidal particle in the presence of an oscillating, spatially periodic, optical potential. The average particle velocity relative to the fluid velocity in this potential depends greatly on the oscillation amplitude and frequency. The results of both our simulations and experiments show that for some combinations of these parameters, the average particle transportation velocity can be enhanced due to the synchronization of the particle's movement with the oscillating potential.
Thursday, October 1, 2009
Published Papers
Published papers on Optical Tweezers added in this Blog for the months of 01-09 of 2009.
Here is the results for these first half year of the published papers on optical tweezers, micromanipulation and trapping.
The top 10 Journals are:
Optics Express 13.1%
Here is the results for these first half year of the published papers on optical tweezers, micromanipulation and trapping.
The top 10 Journals are:
Optics Express 13.1%
Physical Review Letters 5.1%
Journal of Optics A 4.2%
Journal of Optics A 4.2%
Physical Review E 4.2%
Biophysical Journal 3.8%
Lab on a Chip 3.8%
Applied Optics 3.4%
Applied Physics Letters 3.0%
Nano Letters 3.0%
Optics Letters 3.0%
Lab on a Chip 3.8%
Applied Optics 3.4%
Applied Physics Letters 3.0%
Nano Letters 3.0%
Optics Letters 3.0%
Physical Review A 3.0%
Below is also a cloud tag from the words found in the title and abstracts:
Below is also a cloud tag from the words found in the title and abstracts:
analysis, approach, beam, beams, behavior, binding, cell, cells, colloidal, complex, dielectric, DNA, dynamics, energy, experimental, field, focal, focused, force, forces, found, holographic, individual, interaction, laser, light, manipulation, measurements, mechanical, membrane, method, model, molecular, molecule, momentum, motion, motor, observed, Optical, optically, particle, particles, phase, position, potential, power, probe, properties, Raman, results, scattering, single, spherical, stiffness, studies, surface, technique, time, trap, trapped, trapping, tweezers
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