Takafumi Iwaki
Light irradiation can induce the vectorial motion of an aerosol particle. This phenomenon is often explained in terms of inelastic collision between gas molecules and the aerosol particle under a temperature gradient. We considered the photophoresis of a micron-sized liquid droplet in a rarefied gas atmosphere based on the Boltzmann equation for the atmosphere coupled with the Navier-Stokes equation for the droplet. Two features attributable to induced internal flow in the droplet are analyzed: the contribution of homogeneous energy inflow to the motion of the droplet and the nonlinear scaling of the photophoretic velocity depending on the irradiated light intensity.
DOI
Friday, July 9, 2010
Thursday, July 8, 2010
Light-driven nanoscale plasmonic motors
Ming Liu, Thomas Zentgraf, Yongmin Liu, Guy Bartal & Xiang Zhang
When Sir William Crookes developed a four-vaned radiometer, also known as the light-mill, in 1873, it was believed that this device confirmed the existence of linear momentum carried by photons, as predicted by Maxwell's equations. Although Reynolds later proved that the torque on the radiometer was caused by thermal transpiration, researchers continued to search for ways to take advantage of the momentum of photons and to use it for generating rotational forces. The ability to provide rotational force at the nanoscale could open up a range of applications in physics, biology and chemistry, including DNA unfolding and sequencing and nanoelectromechanical systems. Here, we demonstrate a nanoscale plasmonic structure that can, when illuminated with linearly polarized light, generate a rotational force that is capable of rotating a silica microdisk that is 4,000 times larger in volume. Furthermore, we can control the rotation velocity and direction by varying the wavelength of the incident light to excite different plasmonic modes.
DOI
When Sir William Crookes developed a four-vaned radiometer, also known as the light-mill, in 1873, it was believed that this device confirmed the existence of linear momentum carried by photons, as predicted by Maxwell's equations. Although Reynolds later proved that the torque on the radiometer was caused by thermal transpiration, researchers continued to search for ways to take advantage of the momentum of photons and to use it for generating rotational forces. The ability to provide rotational force at the nanoscale could open up a range of applications in physics, biology and chemistry, including DNA unfolding and sequencing and nanoelectromechanical systems. Here, we demonstrate a nanoscale plasmonic structure that can, when illuminated with linearly polarized light, generate a rotational force that is capable of rotating a silica microdisk that is 4,000 times larger in volume. Furthermore, we can control the rotation velocity and direction by varying the wavelength of the incident light to excite different plasmonic modes.
DOI
Wednesday, July 7, 2010
Axon repair: surgical application at a subcellular scale
Wesley C. Chang, Elizabeth Hawkes, Christopher G. Keller, David W. Sretavan
Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.
DOI
Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.
DOI
Comparison of silicon photonic crystal resonator designs for optical trapping of nanomaterials
X Serey, S Mandal and D Erickson
The use of silicon photonic devices for optical manipulation has recently enabled the direct handling of objects like nucleic acids and nanoparticles that are much smaller than could previously be trapped using traditional laser tweezers. The ability to manipulate even smaller matter however requires the development of photonic structures with even stronger trapping potentials. In this work we investigate theoretically several photonic crystal resonator designs and characterize the achievable trapping stiffness and trapping potential depth (sometimes referred to as the trapping stability). Two effects are shown to increase these trapping parameters: field enhancement in the resonator and strong field containment. We find trapping stiffness as high as 22.3 pN nm − 1 for 100 nm polystyrene beads as well as potential depth of 51 000 kBT at T = 300 K, for one Watt of power input to the bus waveguide. Under the same conditions for 70 nm polystyrene beads, we find a stiffness of 69 pN nm − 1 and a potential depth of 177 000 kBT. Our calculations suggest that with input power of 10 mW we could trap particles as small as 7.7 nm diameter with a trapping depth of 500 kBT. We expect these traps to eventually enable the manipulation of small matter such as single proteins, carbon nanotubes and metallic nanoparticles.
DOI
The use of silicon photonic devices for optical manipulation has recently enabled the direct handling of objects like nucleic acids and nanoparticles that are much smaller than could previously be trapped using traditional laser tweezers. The ability to manipulate even smaller matter however requires the development of photonic structures with even stronger trapping potentials. In this work we investigate theoretically several photonic crystal resonator designs and characterize the achievable trapping stiffness and trapping potential depth (sometimes referred to as the trapping stability). Two effects are shown to increase these trapping parameters: field enhancement in the resonator and strong field containment. We find trapping stiffness as high as 22.3 pN nm − 1 for 100 nm polystyrene beads as well as potential depth of 51 000 kBT at T = 300 K, for one Watt of power input to the bus waveguide. Under the same conditions for 70 nm polystyrene beads, we find a stiffness of 69 pN nm − 1 and a potential depth of 177 000 kBT. Our calculations suggest that with input power of 10 mW we could trap particles as small as 7.7 nm diameter with a trapping depth of 500 kBT. We expect these traps to eventually enable the manipulation of small matter such as single proteins, carbon nanotubes and metallic nanoparticles.
DOI
Effect of long- and short-term exposure to laser light at 1070 nm on growth of Saccharomyces cerevisiae
Thomas Aabo, Ivan R. Perch-Nielsen, Jeppe Seidelin Dam, Darwin Z. Palima, Henrik Siegumfeldt, Jesper Glückstad, Nils Arneborg
The effect of a 1070-nm continuous and pulsed wave ytterbium fiber laser on the growth ofSaccharomyces cerevisiae single cells is investigated over a time span of 4 to 5 h. The cells are subjected to optical traps consisting of two counterpropagating plane wavebeams with a uniform flux along the x, y axis. Even at the lowest continuous power investigated—i.e., 0.7 mW—the growth of S. cerevisiae cell clusters is markedly inhibited. The minimum power required to successfully trap single S. cerevisiae cells in three dimensions is estimated to be 3.5 mW. No threshold power for the photodamage, but instead a continuous response to the increased accumulated dose is found in the regime investigated from 0.7 to 2.6 mW. Furthermore, by keeping the delivered dose constant and varying the exposure time and power—i.e. pulsing—we find that the growth of S. cerevisiae cells is increasingly inhibited with increasing power. These results indicate that growth of S. cerevisiae is dependent on both the power as well as the accumulated dose at 1070 nm.
DOI
The effect of a 1070-nm continuous and pulsed wave ytterbium fiber laser on the growth ofSaccharomyces cerevisiae single cells is investigated over a time span of 4 to 5 h. The cells are subjected to optical traps consisting of two counterpropagating plane wavebeams with a uniform flux along the x, y axis. Even at the lowest continuous power investigated—i.e., 0.7 mW—the growth of S. cerevisiae cell clusters is markedly inhibited. The minimum power required to successfully trap single S. cerevisiae cells in three dimensions is estimated to be 3.5 mW. No threshold power for the photodamage, but instead a continuous response to the increased accumulated dose is found in the regime investigated from 0.7 to 2.6 mW. Furthermore, by keeping the delivered dose constant and varying the exposure time and power—i.e. pulsing—we find that the growth of S. cerevisiae cells is increasingly inhibited with increasing power. These results indicate that growth of S. cerevisiae is dependent on both the power as well as the accumulated dose at 1070 nm.
DOI
Shape anisotropy induces rotations in optically trapped red blood cells
Kapil Bambardekar, Jayashree A. Dharmadhikari, Aditya K. Dharmadhikari, Toshihoro Yamada, Tsuyoshi Kato, Hirohiko Kono, Yuichi Fujimura, Shobhona Sharma, Deepak Mathur
A combined experimental and theoretical study is carried out to probe the rotational behavior of red blood cells (RBCs) in a single beam optical trap. We induce shape changes in RBCs by altering the properties of the suspension medium in which live cells float. We find that certain shape anisotropies result in the rotation of optically trapped cells. Indeed, even normal (healthy) RBCs can be made to rotate using linearly polarizedtrapping light by altering the osmotic stress the cells are subjected to. Hyperosmotic stress is found to induce shape anisotropies. We also probe the effect of the medium's viscosity on cell rotation. The observed rotations are modeled using a Langevin-typeequation of motion that takes into account frictional forces that are generated as RBCs rotate in the medium. We observe good correlation between our measured data and calculated results.
DOI
A combined experimental and theoretical study is carried out to probe the rotational behavior of red blood cells (RBCs) in a single beam optical trap. We induce shape changes in RBCs by altering the properties of the suspension medium in which live cells float. We find that certain shape anisotropies result in the rotation of optically trapped cells. Indeed, even normal (healthy) RBCs can be made to rotate using linearly polarizedtrapping light by altering the osmotic stress the cells are subjected to. Hyperosmotic stress is found to induce shape anisotropies. We also probe the effect of the medium's viscosity on cell rotation. The observed rotations are modeled using a Langevin-typeequation of motion that takes into account frictional forces that are generated as RBCs rotate in the medium. We observe good correlation between our measured data and calculated results.
DOI
Power spectrum analysis with least-squares fitting: Amplitude bias and its elimination, with application to optical tweezers and atomic force microscope cantilevers
Simon F. Nørrelykke and Henrik Flyvbjerg
Optical tweezers and atomic force microscope (AFM) cantilevers are often calibrated by fitting their experimental power spectra of Brownian motion. We demonstrate here that if this is done with typical weighted least-squares methods, the result is a bias of relative size between −2/n and +1/n on the value of the fitted diffusion coefficient. Here, n is the number of power spectra averaged over, so typical calibrations contain 10%–20% bias. Both the sign and the size of the bias depend on the weighting scheme applied. Hence, so do length-scale calibrations based on the diffusion coefficient. The fitted value for the characteristic frequency is not affected by this bias. For the AFM then, force measurements are not affected provided an independent length-scale calibration is available. For optical tweezers there is no such luck, since the spring constant is found as the ratio of the characteristic frequency and the diffusion coefficient. We give analytical results for the weight-dependent bias for the wide class of systems whose dynamics is described by a linear (integro)differential equation with additive noise, white or colored. Examples are optical tweezers with hydrodynamic self-interaction and aliasing, calibration of Ornstein–Uhlenbeck models in finance, models for cell migration in biology, etc. Because the bias takes the form of a simple multiplicative factor on the fitted amplitude (e.g. the diffusion coefficient), it is straightforward to remove and the user will need minimal modifications to his or her favorite least-squares fitting programs. Results are demonstrated and illustrated using synthetic data, so we can compare fits with known true values. We also fit some commonly occurring power spectra once-and-for-allin the sense that we give their parameter values and associated error bars as explicit functions of experimental power-spectral values.
DOI
Optical tweezers and atomic force microscope (AFM) cantilevers are often calibrated by fitting their experimental power spectra of Brownian motion. We demonstrate here that if this is done with typical weighted least-squares methods, the result is a bias of relative size between −2/n and +1/n on the value of the fitted diffusion coefficient. Here, n is the number of power spectra averaged over, so typical calibrations contain 10%–20% bias. Both the sign and the size of the bias depend on the weighting scheme applied. Hence, so do length-scale calibrations based on the diffusion coefficient. The fitted value for the characteristic frequency is not affected by this bias. For the AFM then, force measurements are not affected provided an independent length-scale calibration is available. For optical tweezers there is no such luck, since the spring constant is found as the ratio of the characteristic frequency and the diffusion coefficient. We give analytical results for the weight-dependent bias for the wide class of systems whose dynamics is described by a linear (integro)differential equation with additive noise, white or colored. Examples are optical tweezers with hydrodynamic self-interaction and aliasing, calibration of Ornstein–Uhlenbeck models in finance, models for cell migration in biology, etc. Because the bias takes the form of a simple multiplicative factor on the fitted amplitude (e.g. the diffusion coefficient), it is straightforward to remove and the user will need minimal modifications to his or her favorite least-squares fitting programs. Results are demonstrated and illustrated using synthetic data, so we can compare fits with known true values. We also fit some commonly occurring power spectra once-and-for-allin the sense that we give their parameter values and associated error bars as explicit functions of experimental power-spectral values.
DOI
Monday, July 5, 2010
Controlled rotation and orientation of rubrene particles and Escherichia coli using optical tweezers
X. C. Li and X. D. Sun
Optical trapping and rotating of suspended micro-sized rubrene particles were performed using optical tweezers with circularly polarized light. The experimental results show that the rotation speed of the rubrene particles is proportional to the laser power, and the orientation of the rubrene particles can be controlled by the optical tweezers with linearly polarized light. Interestingly, by combining with the rubrene particle, the Escherichia coli (E. coli) can be rotated and oriented by optical tweezers. However, the rotating and orientating are mainly determined by the characteristics of rubrene particles. Our experiment provides a simple and convenient way to orient biological particles even if they are not sensitive to the polarization of the laser beam. Moreover, the rubrene can emit strong fluorescence when excited by the laser at the wavelength of 532 nm, and which can be potential applied to manipulate other particles with the fluorescence characteristics.
DOI
Optical trapping and rotating of suspended micro-sized rubrene particles were performed using optical tweezers with circularly polarized light. The experimental results show that the rotation speed of the rubrene particles is proportional to the laser power, and the orientation of the rubrene particles can be controlled by the optical tweezers with linearly polarized light. Interestingly, by combining with the rubrene particle, the Escherichia coli (E. coli) can be rotated and oriented by optical tweezers. However, the rotating and orientating are mainly determined by the characteristics of rubrene particles. Our experiment provides a simple and convenient way to orient biological particles even if they are not sensitive to the polarization of the laser beam. Moreover, the rubrene can emit strong fluorescence when excited by the laser at the wavelength of 532 nm, and which can be potential applied to manipulate other particles with the fluorescence characteristics.
DOI
Analytical particle measurements in an optical microflume
Joseph D. Taylor, Alex Terray and Sean J. Hart
In this work, microscopic particles in a fluid flow are manipulated using forces generated by a high power laser beam. The resulting manipulations on the particles are imaged using a microscope lens connected to a CCD camera. Differential forces on particles of varying physical and chemical composition have been measured. The goal is to measure the optical forces on a diverse range of particles and catalog the associated chemical and physical differences to understand which properties and mechanisms result in the largest force differentials. Using these measurements our aim is to better understand differences between similar microspheres in terms of size, morphology, or chemical composition. Particles of the same size, but different composition show large variations in optical pressure forces and are easily discernable in the present analytical system. In addition, we have demonstrated the ability to differentiate a 70 nm size difference between two NIST precision size standard polystyrene microspheres, corresponding to a 2.0 pN difference in optical force. Lastly, the instrument was used to measure differences between biological samples of similar size, demonstrating the ability to make precise analytical measurements on microorganism samples.
DOI
In this work, microscopic particles in a fluid flow are manipulated using forces generated by a high power laser beam. The resulting manipulations on the particles are imaged using a microscope lens connected to a CCD camera. Differential forces on particles of varying physical and chemical composition have been measured. The goal is to measure the optical forces on a diverse range of particles and catalog the associated chemical and physical differences to understand which properties and mechanisms result in the largest force differentials. Using these measurements our aim is to better understand differences between similar microspheres in terms of size, morphology, or chemical composition. Particles of the same size, but different composition show large variations in optical pressure forces and are easily discernable in the present analytical system. In addition, we have demonstrated the ability to differentiate a 70 nm size difference between two NIST precision size standard polystyrene microspheres, corresponding to a 2.0 pN difference in optical force. Lastly, the instrument was used to measure differences between biological samples of similar size, demonstrating the ability to make precise analytical measurements on microorganism samples.
DOI
Thursday, July 1, 2010
Published Paper Statistics (first half of 2010)
Here is the results for the first half of 2010 for published papers on optical tweezers, micromanipulation and trapping.
The top Journals (more than 2% hits) are:
- Optics Express 13.5%
- Proceedings of the National Academy of Sciences 4.9%
- Optics Letters 4.3%
- Physical Review E 3.8%
- Physical Review Letters 3.8%
- Biophysical Journal 3.2%
- Lab on a Chip 2.7%
- Nano Letters 2.7%
- Nanotechnology 2.7%
- Physical Review A 2.7%
- Review of Scientific Instruments 2.7 %
Below is a tag cloud for the corresponding words found in the title and abstracts for the period:
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