Holographic Optical Tweezer-based Characterization of In-vivo Cell Mechanics PDF Download

Author: Florian Hörner
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Ling Yao Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 130

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The mechanical response of a cell to external forces carries information about its structure and function. Because cell manipulation should ideally be non-invasive while performing sophisticated biophysical characterization, the radiation force of optical tweezers has become highly attractive. In this thesis, we explore three types of recently-developed optical tweezers: 1) static, 2) time-sharing and 3) oscillating. Using a full three-dimensional finite element method (3DFEM), modeling of each of these regimes allows us to fit experiments and access the cell mechanical properties. Combining optical trapping with cell mechanics requires interdisciplinary efforts. A survey of the various experimental approaches for optical trapping and measurements on isolated cells is presented. We then lay the theoretical background linking the interaction of optical fields to the cell's mechanical response. We are the first to implement a 3DFEM calculation including light scattering and the radiation stress distribution to predict the deformation of a biconcave cell -emulating a red blood cell- in static dual-trap optical tweezers. At equilibrium, the final deformation is given by the separation distance of the two trapping beams, revealing how the cell can be elongated or shrunk. Time-sharing optical tweezers realize multiple traps to manipulate objects ranging from macromolecules to biological cells. Our quantitative analysis shows how, although jumping, the local stress and strain is omnipresent in the cell. The viscoelastic object deformation and internal energy dissipation are analyzed. Another cell shape, a cubic rod, is also studied, elucidating novel symmetrical properties of the mechanical response. Finally, the analysis of the time-dependent deformation -creep testing- of a cell in static and time-sharing optical tweezers, shows that deformation of the object depends altogether on the object's viscoelasticity, significantly on its 3D shape and the mechanical loading. However, dynamic testing with oscillating optical tweezers surprisingly shows a phase shift between the loading stress (external force) and strain (deformation) independent on the 3D cell shape. This is a novel avenue giving access to the cell's viscoelasticity dynamic complex modulus directly in the time-domain.

Author: Changsheng Dai
Publisher: Elsevier
ISBN: 0323952143
Category : Computers
Languages : en
Pages : 402

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Robotics for Cell Manipulation and Characterization provides fundamental principles underpinning robotic cell manipulation and characterization, state-of-the-art technical advances in micro/nano robotics, new discoveries of cell biology enabled by robotic systems, and their applications in clinical diagnosis and treatment. This book covers several areas, including robotics, control, computer vision, biomedical engineering and life sciences using understandable figures and tables to enhance readers’ comprehension and pinpoint challenges and opportunities for biological and biomedical research. Focuses on, and comprehensively covers, robotics for cell manipulation and characterization Highlights recent advances in cell biology and disease treatment enabled by robotic cell manipulation and characterization Provides insightful outlooks on future challenges and opportunities

Author: Matthew A. Cibula
Publisher:
ISBN:
Category : Collagen
Languages : en
Pages : 107

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The development and some applications of holographic optical tweezers (HOT) are presented. Our HOT system uses a spatial light modulator (SLM) to control the location and properties of the optical trap. We have developed a method for optimizing the diffraction efficiency of a SLM that can be applied in situ and addresses the issues of nonlinear phase modulation and phase modulation less than 2[pi]. The method employs a one-dimensional blazed phase grating written on the SLM. For an ideal SLM, the phase shift is linear and covers 0-2[pi], yielding a first-order diffraction efficiency of unity. For a realistic SLM with nonlinear or reduced phase shift, the efficiency is approximately [eta] =1 - [sigma]2, where [sigma]2 is the variance of the phase error from the ideal case. Because each pixel contributes to the phase error independently, this suggests a method to maximize the efficiency by adjusting the phase encoding of the SLM pixel-by-pixel. In practice, we do this by adjusting the gray-scale of each pixel while measuring the first-order diffracted power. The collection of optimal gray values comprises the optimized gray-scale lookup table, which exhibits the nonlinearity required to produce a linear phase grating and the saturated phase encoding that maximizes the efficiency of phase limited SLMs. The optimized SLM enables strong trapping power, even when distributed among multiple traps, which is essential to enable our system to trap multiple nanosensors and simultaneously detect the sensors' fluorescence spectra with an imaging spectrometer. Such nanosensors are capable of detecting changes in their environment such as pH, ion concentration, temperature, and voltage by monitoring changes in the nanosensors' emitted fluorescence spectra. We have used streptavidin labeled quantum dots bound to the surface of biotin labeled polystyrene microspheres to measure temperature changes by observing a corresponding shift in the wavelength of the spectral peak, which is excited with a 532 nm wide field laser source. Particles with diameter greater than the wavelength of light exhibit Mie resonances in their fluorescence spectrum whose spectral locations are dependent on the size of the particle and the relative index of refraction between the particle and the surrounding medium. HOT also provides a useful platform to study the micromechanical properties of elastic materials such as collagen. Collagen gels are widely used in experiments on cell mechanics because collagen is the most abundant protein in the mammalian extracellular matrix and is the primary source of its mechanical properties. Collagen gels are often approximated as homogeneous elastic materials; however, variations in the collagen fiber microstructure and cell adhesion forces cause the mechanical propertiesto be inhomogeneous at the cellular scale. We study the mechanics of type I collagen on the scale of tens to hundreds of microns by using HOT to apply picoNewton forces to micron-sized particles embedded in the collagen fiber network. We measure the local compliance and elastic modulus of the collagen network and find that particle displacements are inhomogeneous, anisotropic and asymmetric. Confocal reflection microscopy is used to reveal the local fiber structure and a simulation treating the network as a triangular lattice is used for comparison to the HOT measurements. Collagen samples prepared at 21°C and 37°C show that gels formed at lower temperature are more inhomogeneous, anisotropic, and compliant than those formed at high temperature, and cellularized samples allow us to characterize the effects of cell adhesion forces on the network mechanics.

Author: Philip H. Jones
Publisher: Cambridge University Press
ISBN: 1107051169
Category : Science
Languages : en
Pages : 565

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A comprehensive guide to the theory, practice and applications of optical tweezers, combining state-of-the-art research with a strong pedagogic approach.

Author: Manlio Tassieri
Publisher: CRC Press
ISBN: 1315341220
Category : Science
Languages : en
Pages : 356

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Thanks to the pioneering works of Ashkin and coworkers, optical tweezers (OTs) have become an invaluable tool for myriad studies throughout the natural sciences. Their success relies on the fact that they can be considered as exceptionally sensitive transducers that are able to resolve pN forces and nm displacements, with high temporal resolution, down to μs. Hence their application to study a wide range of biological phenomena such as measuring the compliance of bacterial tails, the forces exerted by a single motor protein, and the mechanical properties of human red blood cells and of individual biological molecules. The number of articles related to them totals to a whopping 58,000 (source Google Scholar)! Microrheology is a branch of rheology, but it works at micrometer length scales and with microliter sample volumes. Therefore, microrheology techniques have been revealed to be very useful tools for all those rheological/mechanical studies where rare or precious materials are employed, such as in biological and biomedical studies. The aim of this book is to provide a pedagogical introduction to the physics principles governing both the optical tweezers and their application in the field of microrheology of complex materials. This is achieved by following a linear path that starts from a narrative introduction of the "nature of light," followed by a rigorous description of the fundamental equations governing the propagation of light through matter. Moreover, some of the many possible instrumental configurations are presented, especially those that better adapt to perform microrheology measurements. In order to better appreciate the microrheological methods with optical tweezers explored in this book, informative introductions to the basic concepts of linear rheology, statistical mechanics, and the most popular microrheology techniques are also given. Furthermore, an enlightening prologue to the general applications of optical tweezers different from rheological purposes is provided at the end of the book.

Author: Frederic Català i Castro
Publisher:
ISBN:
Category :
Languages : en
Pages : 149

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Mechanics is the branch of physics that studies movement and force, and plays an evident role in life. The swimming dynamics of bacteria in search of nutrients, organelle transport by molecular motors or sensing different kinds of stimuli by neurons, are some of the processes that need to be explained in terms of mechanics. At a human scale, distance and force can be measured with a ruler and a calibrated spring. However, assessing these magnitudes may become an important challenge at a micron scale. Among several techniques, optical tweezers stand out as a non-invasive tool that is capable of using light to grab micron-sized particles and measuring position and force with nanometer (10(-9) and femto-Newton (10(-15) accuracy. Small specimens, such as a bacterium or a cell membrane, can be trapped and effectively manipulated with a focused laser beam. Light momentum exchanged with the trapped sample can be used for eventually measuring the otherwise inaccessible forces that govern biological processes. Optical tweezers have enabled, after trapping cell vesicles in vivo, to measure the pulling force exerted by molecular motors, such as kinesin. Flagellar propulsion forces and energy generation have been investigated by optically trapping the head of a bacterium. Cell membranes have been deformed with optical tweezers and the underlying tension determined. However, the exact forces exerted by optical tweezers are difficult to measure beyond the in vitro approach. In order to calibrate the optical traps, the trapped samples often need to be spherical or present some degree of symmetry, it is important to bear information on the experimental parameters, and one needs high control of several variables that determine the trapping dynamics, such as medium homogeneity and temperature. A cutting-edge method, developed in the Optical Trapping Lab – BiOPT, from the Universitat de Barcelona, targets the light-momentum change as a direct reading of the force exerted by an optical trap. This frees experiments from the necessity of calibrating the optical traps, and makes possible to perform accurate force measurement experiments in vivo and involving irregular samples. In my PhD thesis, the direct force detection method for optical tweezers has been implemented and tested in some of such situations. I first give a technical description of the set-up used for the experiments. The use of a spatial light modulator (SLM) for holographic optical tweezers (HOTs), a piezo-electric platform to induce drag forces, and the trapping laser emission characteristics, are explained in detail. The light-momentum set-up is tested against certain situations deviating from the ideal performance and some steps for optimization of several effects are analyzed. Backscattering light loss is quantified through experiments and numerical simulations and finally assessed to account for an average ±5% uncertainty in force measurements. Then, the method is used to measure forces on irregular samples. First, arbitrary systems composed of microspheres of different kinds are collectively treated as irregular samples, in which the global momentum exchanged with the trapping beam coincides with the total Stokes-drag force. Second, pairs of optical tweezers are used to stably trap cylinders of sizes from 2 milimicras to 50 milimicras and measure forces in accordance with slender-body hydrodynamic theory. Another aspect of the thesis deals with the temperature change induced by water absorption of IR light, which is one of the major concerns within the optical trapping community. As main reasons, accurate knowledge of local temperature is needed for understanding thermally-driven processes, as well as eventual damage to live specimens. Here we use direct force measurements to detect changes in viscosity that are due to laser heating, and compare the results with heat transport simulations to discuss the main conclusions on this effect. The last goal of my thesis has been the implementation of the method inside tissue. The laser beam is affected by the scattering structures present in vivo, such as refractive index mismatches throughout different cells, nuclei, cell membranes or vesicles. As a primary result, despite the trapping beam is captured beyond 95%, I quantified this effect to result in an increase in the standard deviation of force measurements around ±20%. The approach has consisted in comparing the trapping force profiles of spherical probes in vitro (water) and in vivo (zebrafish embryos). To conclude, I here demonstrate that the direct force measurement method can be applied in an increasing number of experiments for which trap calibration becomes intricate or even impossible. Quantitative measurements become feasible in samples with unknown properties, the more important examples being arbitrary, non-spherical samples and the interior of an embryonic tissue.

Author: Arthur Ashkin
Publisher: World Scientific Publishing Company Incorporated
ISBN: 9789810240578
Category : Science
Languages : en
Pages : 915

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This important volume contains selected papers and extensive commentaries on laser trapping and manipulation of neutral particles using radiation pressure forces. Such techniques apply to a variety of small particles, such as atoms, molecules, macroscopic dielectric particles, living cells, and organelles within cells. These optical methods have had a revolutionary impact on the fields of atomic and molecular physics, biophysics, and many aspects of nanotechnology.In atomic physics, the trapping and cooling of atoms down to nanokelvins and even picokelvin temperatures are possible. These are the lowest temperatures in the universe. This made possible the first demonstration of Bose-Einstein condensation of atomic and molecular vapors. Some of the applications are high precision atomic clocks, gyroscopes, the measurement of gravity, cryptology, atomic computers, cavity quantum electrodynamics and coherent atom lasers.A major application in biophysics is the study of the mechanical properties of the many types of motor molecules, mechanoenzymes, and other macromolecules responsible for the motion of organelles within cells and the locomotion of entire cells. Unique in vitro and in vivo assays study the driving forces, stepping motion, kinetics, and efficiency of these motors as they move along the cell's cytoskeleton. Positional and temporal resolutions have been achieved, making possible the study of RNA and DNA polymerases, as they undergo their various copying, backtracking, and error correcting functions on a single base pair basis.Many applications in nanotechnology involve particle and cell sorting, particle rotation, microfabrication of simple machines, microfluidics, and other micrometer devices. The number of applications continues to grow at a rapid rate.The author is the discoverer of optical trapping and optical tweezers. With his colleagues, he first demonstrated optical levitation, the trapping of atoms, and tweezer trapping and manipulation of living cells and biological particles.This is the only review volume covering the many fields of optical trapping and manipulation. The intention is to provide a selective guide to the literature and to teach how optical traps really work.

Author: Victoria Emma Loosemore
Publisher:
ISBN:
Category :
Languages : en
Pages : 96

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Collagen, the most abundant protein in the body, assembles into an extra-cellular fibrillar gel, which has both viscous and elastic properties. These properties can be determined by using optical tweezers to hold a micron-sized bead within the sample. Measurement of the bead's thermally induced motion enables the determination of the frequency-dependent viscoelasticity. Rather than only probing response at a single location, holographic optical tweezers create multiple, independent traps, permitting simultaneous tracking of multiple embedded beads and characterization of their correlated motion. By using this technique in a collagen gel, we will be able to determine local and cross-correlated viscoelastic properties, which vary at different locations during its formation. Implications of this research lie in the fields of health and biomaterials. The aim of this work is to devise and validate protocols for using holographic optical tweezers to measure local and through-space viscoelasticity. Rather than using laser deflection to track particle motion, I use a high-speed camera and image analysis to track the simultaneous motion of multiple beads. This approach provides nanometer-scale resolution of particle position at sampling rates up to 2.5 kHz. I compare tracking data collected from the high-speed camera to those collected by the laser deflection method and find a discrepancy in the perceived motion of the bead. I perform many experimental tests to assess the root of this problem. Additionally, I numerically represent bead motion measurements if collected using both methods (laser-deflection method and high-speed camera method) and compare them to the idealized measurement results. In doing so, I learn about the limitations of each method, and how the viscous and elastic properties inferred from the data are affected by each measurement device. Finally, based on my numerical representations, I suggest a simple procedure to gain more accuracy in the viscous and elastic properties for both simple fluids (such as water) and complex fluids (such as collagen solutions) when using each method. This procedure can be used in future holographic optical tweezers-based experiments to obtain an accurate representation of the local and correlated properties of collagen.

Author: Michael W. Berns
Publisher: Frontiers Media SA
ISBN: 2889742431
Category : Science
Languages : en
Pages : 362

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