Theodor Asavei, Timo A Nieminen, Vincent L Y Loke, Alexander B Stilgoe, Richard Bowman, Daryl Preece, Miles J Padgett, Norman R Heckenberg and Halina Rubinsztein-Dunlop
We demonstrate the control and rotation of an optically trapped object, an optical paddle-wheel, with the rotation direction normal to the beam axis. This is in contrast to the usual situation where the rotation is about the beam axis. The paddle-wheel can be optically driven and moved to any position in the field of view of the microscope, which can be of interest for various biological applications where controlled application of a fluid flow is needed in a particular location and in a specific direction. This is of particular interest in signal transduction studies in cells, especially when a cell is flat and spread out on a surface.
DOI
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Tuesday, June 18, 2013
Microcrystal manipulation with laser tweezers
A. Wagner, R. Duman, B. Stevens and A. Ward
X-ray crystallography is the method of choice to deduce atomic resolution structural information from macromolecules. In recent years, significant investments in structural genomics initiatives have been undertaken to automate all steps in X-ray crystallography from protein expression to structure solution. Robotic systems are widely used to prepare crystallization screens and change samples on synchrotron beamlines for macromolecular crystallography. The only remaining manual handling step is the transfer of the crystal from the mother liquor onto the crystal holder. Manual mounting is relatively straightforward for crystals with dimensions of >25 µm; however, this step is nontrivial for smaller crystals. The mounting of microcrystals is becoming increasingly important as advances in microfocus synchrotron beamlines now allow data collection from crystals with dimensions of only a few micrometres. To make optimal usage of these beamlines, new approaches have to be taken to facilitate and automate this last manual handling step. Optical tweezers, which are routinely used for the manipulation of micrometre-sized objects, have successfully been applied to sort and mount macromolecular crystals on newly designed crystal holders. Diffraction data from CPV type 1 polyhedrin microcrystals mounted with laser tweezers are presented.
DOI
X-ray crystallography is the method of choice to deduce atomic resolution structural information from macromolecules. In recent years, significant investments in structural genomics initiatives have been undertaken to automate all steps in X-ray crystallography from protein expression to structure solution. Robotic systems are widely used to prepare crystallization screens and change samples on synchrotron beamlines for macromolecular crystallography. The only remaining manual handling step is the transfer of the crystal from the mother liquor onto the crystal holder. Manual mounting is relatively straightforward for crystals with dimensions of >25 µm; however, this step is nontrivial for smaller crystals. The mounting of microcrystals is becoming increasingly important as advances in microfocus synchrotron beamlines now allow data collection from crystals with dimensions of only a few micrometres. To make optimal usage of these beamlines, new approaches have to be taken to facilitate and automate this last manual handling step. Optical tweezers, which are routinely used for the manipulation of micrometre-sized objects, have successfully been applied to sort and mount macromolecular crystals on newly designed crystal holders. Diffraction data from CPV type 1 polyhedrin microcrystals mounted with laser tweezers are presented.
DOI
Self-Organized Chiral Microspheres
A. Mazzulla, G. Cipparrone, R. J. Hernandez, A. Pane & R. Bartolino
A variety of chiral microspheres, each one possessing distinctive configurations of the molecular director, are studied. The process to obtain the solid particles is illustrated and some of their optical features is discussed.The optical properties of these objects depend from the emulsion preparation standards. The self-organized structures have been tailored by means of both the chiral dopant concentration and the molecular anchoring at the surface. The microspheres reveal exciting optical properties, i.e. they show specific kinds of selective reflection that can be sorted as radial, conical and cylindrical. The features of these micro-photonic devices are confirmed through experiments of polarized optical manipulation and laser emission.
These complex structures constitute very peculiar micro-systems, inspiring attractive technological applications.
DOI
A variety of chiral microspheres, each one possessing distinctive configurations of the molecular director, are studied. The process to obtain the solid particles is illustrated and some of their optical features is discussed.The optical properties of these objects depend from the emulsion preparation standards. The self-organized structures have been tailored by means of both the chiral dopant concentration and the molecular anchoring at the surface. The microspheres reveal exciting optical properties, i.e. they show specific kinds of selective reflection that can be sorted as radial, conical and cylindrical. The features of these micro-photonic devices are confirmed through experiments of polarized optical manipulation and laser emission.
These complex structures constitute very peculiar micro-systems, inspiring attractive technological applications.
DOI
Assessment of the Elasticity of Erythrocytes in Different Physiological Fluids by Laser Traps
Taylor Barnes, Adam Shulman, Anthony Farone, Mary Farone, Daniel Erenso
In the study of the mechanical properties of the erythrocytes (red blood cells-RBCs) the blood sample is commonly diluted in fluids that do not compromise the integrity of the cells. Fetal bovine serum (FBS), newborn bovine serum (NBBS), and phosphate buffer (PBS) solution with a concentration that can provide the right osmotic pressure are fluids commonly used to dilute the blood samples in such studies. Here we have presented the effect of these fluids on the elastic properties of the RBCs that we studied using laser traps. Two laser traps are directly used to trap and deform the cell by exerting a force distributed on the entire cell. The relative changes in size of the cell are studied as a function of the applied force to investigate any effects on the mechanical deformability of RBCs when the cells are suspended in these fluids. The results have shown that the elasticity of the RBCs in the NBBS is not statistically different from the elasticity of the cells in the PBS solution; however the results for the elasticity of the cells in FBS are found to be significantly higher.
DOI
In the study of the mechanical properties of the erythrocytes (red blood cells-RBCs) the blood sample is commonly diluted in fluids that do not compromise the integrity of the cells. Fetal bovine serum (FBS), newborn bovine serum (NBBS), and phosphate buffer (PBS) solution with a concentration that can provide the right osmotic pressure are fluids commonly used to dilute the blood samples in such studies. Here we have presented the effect of these fluids on the elastic properties of the RBCs that we studied using laser traps. Two laser traps are directly used to trap and deform the cell by exerting a force distributed on the entire cell. The relative changes in size of the cell are studied as a function of the applied force to investigate any effects on the mechanical deformability of RBCs when the cells are suspended in these fluids. The results have shown that the elasticity of the RBCs in the NBBS is not statistically different from the elasticity of the cells in the PBS solution; however the results for the elasticity of the cells in FBS are found to be significantly higher.
DOI
Exploring how infrared radiation enhances the attractive interaction between a cell pair by its electromagnetic nature
Bor-Wen Yang, Chu Yeh, Po-Cheng Lin, Chi-Tse Chao
Electromagnetic radiation can be categorized into ionizing and non-ionizing varieties. To determine the mechanism how non-ionizing radiation affects biological cells, we analyzed the difference between its thermal and electromagnetic effects. Two-beam optical tweezers were designed to demonstrate that infrared radiation could enhance the cellular interaction between red blood cells by its electromagnetic nature. An IR spot in the optical tweezers was irradiated on two RBCs to polarize them and induce electromagnetic attraction, while the other focused visible spot was used to quantify the intensity of the intercellular interaction. It was found that 0.1 mW/μm2 infrared radiation was adequate to cause pN-scale interaction between a cell pair, which was only 1/1000 of the power density used in a CD-R drive. We then set up a model to describe how non-ionizing radiation affected a cell assembly by deriving electromagnetic micro-stress transverse to its propagation axis.
DOI
Electromagnetic radiation can be categorized into ionizing and non-ionizing varieties. To determine the mechanism how non-ionizing radiation affects biological cells, we analyzed the difference between its thermal and electromagnetic effects. Two-beam optical tweezers were designed to demonstrate that infrared radiation could enhance the cellular interaction between red blood cells by its electromagnetic nature. An IR spot in the optical tweezers was irradiated on two RBCs to polarize them and induce electromagnetic attraction, while the other focused visible spot was used to quantify the intensity of the intercellular interaction. It was found that 0.1 mW/μm2 infrared radiation was adequate to cause pN-scale interaction between a cell pair, which was only 1/1000 of the power density used in a CD-R drive. We then set up a model to describe how non-ionizing radiation affected a cell assembly by deriving electromagnetic micro-stress transverse to its propagation axis.
DOI
Sunday, June 16, 2013
Laser guidance–based cell detection in a microfluidic biochip
Wan Qin; Lucas Schmidt; Xiaoqi Yang; Lina Wei; Ting Huang; Julie X. Yuan; Xiang Peng; Xiaocong Yuan; Bruce Z. Gao
We developed a microfluidic biochip to perform laser guidance on two cell types, chick embryonic forebrain neurons and spinal cord neurons. Observation of neurons under a high-magnification microscope, which we obtained from these two cell types, showed no difference in morphology. However, when flowing in the microfluidic channel and simultaneously being laser guided, the two cell types gained quite different guidance speeds under the same experimental conditions. The results demonstrate that different cell types with the same morphology (e.g., size, shape, etc.) can be effectively distinguished from each other by measuring the difference in guidance speeds (the maximum flow speed minus the initial flow speed). This technique is expected to provide a new approach to high-throughput, label-free cell sorting with high sensitivity.
DOI
We developed a microfluidic biochip to perform laser guidance on two cell types, chick embryonic forebrain neurons and spinal cord neurons. Observation of neurons under a high-magnification microscope, which we obtained from these two cell types, showed no difference in morphology. However, when flowing in the microfluidic channel and simultaneously being laser guided, the two cell types gained quite different guidance speeds under the same experimental conditions. The results demonstrate that different cell types with the same morphology (e.g., size, shape, etc.) can be effectively distinguished from each other by measuring the difference in guidance speeds (the maximum flow speed minus the initial flow speed). This technique is expected to provide a new approach to high-throughput, label-free cell sorting with high sensitivity.
DOI
Dynamical and phase-diagram study on stable optical pulling force in Bessel beams
Neng Wang, Jun Chen, Shiyang Liu, and Zhifang Lin
Based on the generalized Lorenz-Mie theory and Maxwell stress tensor formulism, we calculate the transverse force constant matrix and perform a linear stability analysis on a spherical particle that is subject to negative longitudinal optical force (NLOF) under the illumination of Bessel beams. Phase diagrams with respect to the material parameters are presented, which exhibit the possibility of the appearance of NLOF. From dynamical simulations of the particle performed both in the transverse plane and along the longitudinal direction, an even clearer picture of the realization of stable NLOF is presented. It is shown that, due to rotation induced by the orbital angular-momentum of light, higher order Bessel beams cannot stably confine a particle to the beam center where NLOF occurs in the absence of ambient damping, which largely limits their applications for long-distance, stable, backward particle transportation. On the other hand, zero-order Bessel beams can achieve stable transverse confinement of the manipulated particle and act as an optical tractor beam per se. In addition, for a nonmagnetic particle with relative permeability μ=1, a Bessel beam with transverse electric polarization is more favorable for the realization of NLOF than a transverse magnetic beam. Finally, a brief discussion is also presented of the conditions under which an off-beam-axis particle could be suitable for backward transportation using NLOF.
DOI
Based on the generalized Lorenz-Mie theory and Maxwell stress tensor formulism, we calculate the transverse force constant matrix and perform a linear stability analysis on a spherical particle that is subject to negative longitudinal optical force (NLOF) under the illumination of Bessel beams. Phase diagrams with respect to the material parameters are presented, which exhibit the possibility of the appearance of NLOF. From dynamical simulations of the particle performed both in the transverse plane and along the longitudinal direction, an even clearer picture of the realization of stable NLOF is presented. It is shown that, due to rotation induced by the orbital angular-momentum of light, higher order Bessel beams cannot stably confine a particle to the beam center where NLOF occurs in the absence of ambient damping, which largely limits their applications for long-distance, stable, backward particle transportation. On the other hand, zero-order Bessel beams can achieve stable transverse confinement of the manipulated particle and act as an optical tractor beam per se. In addition, for a nonmagnetic particle with relative permeability μ=1, a Bessel beam with transverse electric polarization is more favorable for the realization of NLOF than a transverse magnetic beam. Finally, a brief discussion is also presented of the conditions under which an off-beam-axis particle could be suitable for backward transportation using NLOF.
DOI
Intraflagellar transport drives flagellar surface motility
Sheng Min Shih, Benjamin D Engel, Fatih Kocabas, Thomas Bilyard, Arne Gennerich, Wallace F Marshall, Ahmet Yildiz
The assembly and maintenance of all cilia and flagella require intraflagellar transport (IFT) along the axoneme. IFT has been implicated in sensory and motile ciliary functions, but the mechanisms of this relationship remain unclear. Here, we used Chlamydomonas flagellar surface motility (FSM) as a model to test whether IFT provides force for gliding of cells across solid surfaces. We show that IFT trains are coupled to flagellar membrane glycoproteins (FMGs) in a Ca2+-dependent manner. IFT trains transiently pause through surface adhesion of their FMG cargos, and dynein-1b motors pull the cell towards the distal tip of the axoneme. Each train is transported by at least four motors, with only one type of motor active at a time. Our results demonstrate the mechanism of Chlamydomonas gliding motility and suggest that IFT plays a major role in adhesion-induced ciliary signaling pathways.
DOI
The assembly and maintenance of all cilia and flagella require intraflagellar transport (IFT) along the axoneme. IFT has been implicated in sensory and motile ciliary functions, but the mechanisms of this relationship remain unclear. Here, we used Chlamydomonas flagellar surface motility (FSM) as a model to test whether IFT provides force for gliding of cells across solid surfaces. We show that IFT trains are coupled to flagellar membrane glycoproteins (FMGs) in a Ca2+-dependent manner. IFT trains transiently pause through surface adhesion of their FMG cargos, and dynein-1b motors pull the cell towards the distal tip of the axoneme. Each train is transported by at least four motors, with only one type of motor active at a time. Our results demonstrate the mechanism of Chlamydomonas gliding motility and suggest that IFT plays a major role in adhesion-induced ciliary signaling pathways.
DOI
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