Tan, Y.; Sun, D.; Wang, J.; Huang, W.
The physiological functions of human red blood cells (RBCs) play a crucial role to human health and are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. The osmotic condition is an important factor to the physiological environment, but its effect on RBCs has been little studied. To investigate this effect, robotic manipulation technology with optical tweezers is utilized in this paper to characterize the mechanical properties of RBCs in different osmotic conditions. The effectiveness of this technology is demonstrated first in the manipulation of microbeads. Then the optical tweezers are used to stretch RBCs to acquire the force–deformation relationships. To extract cell properties from the experimental data, a mechanical model is developed for RBCs in hypotonic conditions by extending our previous work , and the finite element model is utilized for RBCs in isotonic and hypertonic conditions. Through comparing the modeling results to the experimental data, the shear moduli of RBCs in different osmotic solutions are characterized, which shows that the cell stiffness increases with elevated osmolality. Furthermore, the property variation and potential biomedical significance of this study are discussed. In conclusion, this study indicates that the osmotic stress has a significant effect on the cell properties of human RBCs, which may provide insight into the pathology analysis and therapy of some human diseases.
DOI
Tuesday, June 29, 2010
Measurement of the Instantaneous Velocity of a Brownian Particle
Tongcang Li, Simon Kheifets, David Medellin, Mark G. Raizen
Brownian motion of particles affects many branches of science. We report on the Brownian motion of micrometer-sized beads of glass held in air by an optical tweezer, over a wide range of pressures, and we measured the instantaneous velocity of a Brownian particle. Our results provide direct verification of the energy equipartition theorem for a Brownian particle. For short times, the ballistic regime of Brownian motion was observed, in contrast to the usual diffusive regime. We discuss the applications of these methods toward cooling the center-of-mass motion of a bead in vacuum to the quantum ground motional state.
Brownian motion of particles affects many branches of science. We report on the Brownian motion of micrometer-sized beads of glass held in air by an optical tweezer, over a wide range of pressures, and we measured the instantaneous velocity of a Brownian particle. Our results provide direct verification of the energy equipartition theorem for a Brownian particle. For short times, the ballistic regime of Brownian motion was observed, in contrast to the usual diffusive regime. We discuss the applications of these methods toward cooling the center-of-mass motion of a bead in vacuum to the quantum ground motional state.
Optical vortex beams for trapping and transport of particles in air
V. G. Shvedov, A. S. Desyatnikov, A. V. Rode, Y. V. Izdebskaya, W. Z. Krolikowski and Y. S. Kivshar
In this paper we show that laser beams containing phase singularity can be used for trapping and guiding light-absorbing particles in air. The experiments were performed with agglomerates of carbon nanoparticles with the size in the range 0.1–10 μm; the typical cw laser power was of a few mW. The stability of open-air three-dimensional trapping was within ±2 μm in both the transverse and the longitudinal directions. The particle position on the beams axis within the trap can be controlled by changing the relative intensity of two beams. The distinguishing feature of the trapping strategy is that particles are trapped at the intensity minimum of the beam, thus with minimum heating and intervention into the particle properties, which is important for direct studies of particle properties and for air-trapping of living cells.
DOI
In this paper we show that laser beams containing phase singularity can be used for trapping and guiding light-absorbing particles in air. The experiments were performed with agglomerates of carbon nanoparticles with the size in the range 0.1–10 μm; the typical cw laser power was of a few mW. The stability of open-air three-dimensional trapping was within ±2 μm in both the transverse and the longitudinal directions. The particle position on the beams axis within the trap can be controlled by changing the relative intensity of two beams. The distinguishing feature of the trapping strategy is that particles are trapped at the intensity minimum of the beam, thus with minimum heating and intervention into the particle properties, which is important for direct studies of particle properties and for air-trapping of living cells.
DOI
The evaluation of interaction between red blood cells in blood coagulation by optical tweezers
Yang, Bor-Wen; Mu, Yu-Hong; Huang, Kui-Teng; Li, Zhe; Wu, Jie-Lung; Lin, Yu-An
To maintain the life of patients with hemophilia, apoplexy or hemorrhage, appropriate blood coagulation is crucial. To study the microscopic phenomena of blood coagulation and the therapeutic effects of blood medication, optical tweezers were applied to estimate the interaction between red blood cells in the coagulation process. By measuring minimum optical power required to trap the coagulating blood cells, the pN-scale interaction between them can be evaluated. In normal blood sample, the interaction rises in accordance with coagulation time. The addition of heparin attenuates the interaction and postpones the coagulation, whereas the addition of tranexamic acid starts the coagulation early at the beginning and allows the process completed in less time.
DOI
To maintain the life of patients with hemophilia, apoplexy or hemorrhage, appropriate blood coagulation is crucial. To study the microscopic phenomena of blood coagulation and the therapeutic effects of blood medication, optical tweezers were applied to estimate the interaction between red blood cells in the coagulation process. By measuring minimum optical power required to trap the coagulating blood cells, the pN-scale interaction between them can be evaluated. In normal blood sample, the interaction rises in accordance with coagulation time. The addition of heparin attenuates the interaction and postpones the coagulation, whereas the addition of tranexamic acid starts the coagulation early at the beginning and allows the process completed in less time.
DOI
Friday, June 25, 2010
Protein-Mediated DNA Loop Formation and Breakdown in a Fluctuating Environment
Yih-Fan Chen, J. N. Milstein, and Jens-Christian Meiners
Living cells provide a fluctuating, out-of-equilibrium environment in which genes must coordinate cellular function. DNA looping, which is a common means of regulating transcription, is very much a stochastic process; the loops arise from the thermal motion of the DNA and other fluctuations of the cellular environment. We present single-molecule measurements of DNA loop formation and breakdown when an artificial fluctuating force, applied to mimic a fluctuating cellular environment, is imposed on the DNA. We show that loop formation is greatly enhanced in the presence of noise of only a fraction of kBT, yet find that hypothetical regulatory schemes that employ mechanical tension in the DNA—as a sensitive switch to control transcription—can be surprisingly robust due to a fortuitous cancellation of noise effects.
DOI
Living cells provide a fluctuating, out-of-equilibrium environment in which genes must coordinate cellular function. DNA looping, which is a common means of regulating transcription, is very much a stochastic process; the loops arise from the thermal motion of the DNA and other fluctuations of the cellular environment. We present single-molecule measurements of DNA loop formation and breakdown when an artificial fluctuating force, applied to mimic a fluctuating cellular environment, is imposed on the DNA. We show that loop formation is greatly enhanced in the presence of noise of only a fraction of kBT, yet find that hypothetical regulatory schemes that employ mechanical tension in the DNA—as a sensitive switch to control transcription—can be surprisingly robust due to a fortuitous cancellation of noise effects.
DOI
Radiation force of highly focused cosine-Gaussian beam on a particle in the Rayleigh scattering regime
Jiang Yun-Feng, Lu Xuan-Hui, Zhao Cheng-Liang
The radiation force of highly focused cosine-Gaussian beam acting on a particle in the Rayleigh scattering regime is theoretically investigated in this paper. The results show that it is feasible to utilize cosine-Gaussian beam in optical trapping system. Unlike the conventional optical beams, the cosine-Gaussian beam could simultaneously trap particles whose refractive index is lower or higher than the ambient.
The radiation force of highly focused cosine-Gaussian beam acting on a particle in the Rayleigh scattering regime is theoretically investigated in this paper. The results show that it is feasible to utilize cosine-Gaussian beam in optical trapping system. Unlike the conventional optical beams, the cosine-Gaussian beam could simultaneously trap particles whose refractive index is lower or higher than the ambient.
Thursday, June 24, 2010
Stable trapping and manually controlled rotation of an asymmetric or birefringent microparticle using dual-mode split-beam optical tweezers
Fang-Wen Sheu, Tzu-Kai Lan, Yu-Chung Lin, Shiung Chen, and Chyung Ay
Inserting a coverslip into half of a Gaussian laser beam at a suitable tilting angle can make the single-mode laser beam become closely spaced dual light spots at the laser focus. In this way, we can reform the conventional single-beam optical tweezers easily and construct a set of dual-mode split-beam optical tweezers, which can be used to manually rotate a trapped and twisted red blood cell around the optical axis. Furthermore, we demonstrate that the split-beam optical tweezers can also stably trap and orient a birefringent polystyrene micro strip particle, which otherwise will self rotate at a varying speed along the structural principal axes, fast spin about the optical axis in a tilting pose, or precess like a gyroscope, in the original linearly polarized single-beam optical tweezers.
DOI
Inserting a coverslip into half of a Gaussian laser beam at a suitable tilting angle can make the single-mode laser beam become closely spaced dual light spots at the laser focus. In this way, we can reform the conventional single-beam optical tweezers easily and construct a set of dual-mode split-beam optical tweezers, which can be used to manually rotate a trapped and twisted red blood cell around the optical axis. Furthermore, we demonstrate that the split-beam optical tweezers can also stably trap and orient a birefringent polystyrene micro strip particle, which otherwise will self rotate at a varying speed along the structural principal axes, fast spin about the optical axis in a tilting pose, or precess like a gyroscope, in the original linearly polarized single-beam optical tweezers.
DOI
Wednesday, June 23, 2010
A force detection technique for single-beam optical traps based on direct measurement of light momentum changes
Arnau Farré and Mario Montes-Usategui
Despite the tremendous success of force-measuring optical traps in recent years, the calibration methods most commonly used in the field have been plagued with difficulties and limitations. Force sensing based on direct measurement of light momentum changes stands out among these as an exception. Especially significant is this method’s potential for working within living cells, with non-spherical particles or with non-Gaussian beams. However, so far, the technique has only been implemented in counter-propagating dual-beam traps, which are difficult to align and integrate with other microscopy techniques. Here, we show the feasibility of a single-beam gradient-trap system working with a force detection technique based on this same principle.
DOI
Despite the tremendous success of force-measuring optical traps in recent years, the calibration methods most commonly used in the field have been plagued with difficulties and limitations. Force sensing based on direct measurement of light momentum changes stands out among these as an exception. Especially significant is this method’s potential for working within living cells, with non-spherical particles or with non-Gaussian beams. However, so far, the technique has only been implemented in counter-propagating dual-beam traps, which are difficult to align and integrate with other microscopy techniques. Here, we show the feasibility of a single-beam gradient-trap system working with a force detection technique based on this same principle.
DOI
Tuesday, June 22, 2010
Regulation of a heterodimeric kinesin-2 through an unprocessive motor domain that is turned processive by its partner
Melanie Brunnbauer, Felix Mueller-Planitz, Süleyman Kösem, Thi Hieu Ho, Renate Dombi, J. Christof M. Gebhardt, Matthias Rief, and Zeynep Ökten
Cilia are microtubule-based protrusions of the plasma membrane found on most eukaryotic cells. Their assembly is mediated through the conserved intraflagellar transport mechanism. One class of motor proteins involved in intraflagellar transport, kinesin-2, is unique among kinesin motors in that some of its members are composed of two distinct polypeptides. However, the biological reason for heterodimerization has remained elusive. Here we provide several interdependent reasons for the heterodimerization of the kinesin-2 motor KLP11/KLP20 of Caenorhabditis elegans cilia. One motor domain is unprocessive as a homodimer, but heterodimerization with a processive partner generates processivity. The “unprocessive” subunit is kept in this partnership as it mediates an asymmetric autoregulation of the motor activity. Finally, heterodimerization is necessary to bind KAP1, the in vivo link between motor and cargo.
DOI
Cilia are microtubule-based protrusions of the plasma membrane found on most eukaryotic cells. Their assembly is mediated through the conserved intraflagellar transport mechanism. One class of motor proteins involved in intraflagellar transport, kinesin-2, is unique among kinesin motors in that some of its members are composed of two distinct polypeptides. However, the biological reason for heterodimerization has remained elusive. Here we provide several interdependent reasons for the heterodimerization of the kinesin-2 motor KLP11/KLP20 of Caenorhabditis elegans cilia. One motor domain is unprocessive as a homodimer, but heterodimerization with a processive partner generates processivity. The “unprocessive” subunit is kept in this partnership as it mediates an asymmetric autoregulation of the motor activity. Finally, heterodimerization is necessary to bind KAP1, the in vivo link between motor and cargo.
DOI
Sunday, June 20, 2010
Raman tweezers sorting of single microbial cells
Wei E. Huang, Andrew D. Ward and Andrew S. Whiteley
We have selectively isolated microbial cells by identifying and then manipulating cells using a combination of Raman microspectroscopy and optical trapping. The criterion for cell discrimination is based on spectral peak shifts within the Raman spectrum of individual cells. A specific shift in the phenylalanine peak position from 1001 rel. cm−1 to 965 rel. cm−1 is utilized to indicate the uptake of 13C within the cell that utilized 13C-substrate. Cells were captured and manipulated using an infrared (1064 nm) laser while Raman spectra were acquired over shorter timescales (30 s) using a co-aligned 514.5 nm laser beam. Selected cells were manoeuvred to a clean part of a capillary tube and the tubes were cleaved to physically separate the cells. The technique was tested for cell viability and cross-contamination effects using 70 single yeast cells (Saccharomyces cerevisia). Following these tests, 58 single bacterial cells (Escherichia coli DH5α, and Pseudomonas fluorescens SBW25::Km-RFP) that exhibited 13C uptake were sorted from bacterial populations. Among those isolated cells, 11 out of 18 yeast cells and 7 out of 18 single SBW25::Km-RFP cells were recovered by incubation; 2 out of 7 sorted yeast cells and 3 out of 8 sorted bacterial cells (single SBW25::Km-RFP) were genome amplified correctly. We show that the Raman tweezers approach has the potential to open a new frontier to study unculturable microorganisms, which account for more than 99% microbes in natural environment.
DOI
We have selectively isolated microbial cells by identifying and then manipulating cells using a combination of Raman microspectroscopy and optical trapping. The criterion for cell discrimination is based on spectral peak shifts within the Raman spectrum of individual cells. A specific shift in the phenylalanine peak position from 1001 rel. cm−1 to 965 rel. cm−1 is utilized to indicate the uptake of 13C within the cell that utilized 13C-substrate. Cells were captured and manipulated using an infrared (1064 nm) laser while Raman spectra were acquired over shorter timescales (30 s) using a co-aligned 514.5 nm laser beam. Selected cells were manoeuvred to a clean part of a capillary tube and the tubes were cleaved to physically separate the cells. The technique was tested for cell viability and cross-contamination effects using 70 single yeast cells (Saccharomyces cerevisia). Following these tests, 58 single bacterial cells (Escherichia coli DH5α, and Pseudomonas fluorescens SBW25::Km-RFP) that exhibited 13C uptake were sorted from bacterial populations. Among those isolated cells, 11 out of 18 yeast cells and 7 out of 18 single SBW25::Km-RFP cells were recovered by incubation; 2 out of 7 sorted yeast cells and 3 out of 8 sorted bacterial cells (single SBW25::Km-RFP) were genome amplified correctly. We show that the Raman tweezers approach has the potential to open a new frontier to study unculturable microorganisms, which account for more than 99% microbes in natural environment.
DOI
Subscribe to:
Posts (Atom)