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

The technical development of optical tweezers, along with their application in the biological and physical sciences, has progressed significantly since the demonstration of an optical trap for micron-sized particles based on a single, tightly focused laser beam was first reported more than twenty years ago. Bringing together many landmark papers on the field, Optical Tweezers: Methods and Applications covers the techniques and uses of optical tweezers. Each section is introduced by a brief commentary, setting the papers into their historical and contemporary contexts. The first two sections explore the pioneering work of Arthur Ashkin and the use of optical tweezers in biological systems. The book then discusses the extensive use of optical tweezers for the measurement of picoNewton forces and examines various approaches for modeling forces within optical tweezers. The next parts explain how optical tweezers are used in colloid science, how to convert optical tweezers into optical spanners, and how spatial light modulators create holographic tweezers. The book concludes with a section on emerging applications of optical tweezers in microfluidic systems. With contributions from some of the best in the field, this compendium presents important historical and current developments of optical tweezers in a range of scientific areas, from the manipulation of bacteria to the treatment of DNA.

Combining state-of-the-art research with a strong pedagogic approach, this text provides a detailed and complete guide to the theory, practice and applications of optical tweezers. In-depth derivation of the theory of optical trapping and numerical modelling of optical forces are supported by a complete step-by-step design and construction guide for building optical tweezers, with detailed tutorials on collecting and analysing data. Also included are comprehensive reviews of optical tweezers research in fields ranging from cell biology to quantum physics. Featuring numerous exercises and problems throughout, this is an ideal self-contained learning package for advanced lecture and laboratory courses, and an invaluable guide to practitioners wanting to enter the field of optical manipulation. The text is supplemented by www.opticaltweezers.org, a forum for discussion and a source of additional material including free-to-download, customisable research-grade software (OTS) for calculation of optical forces, digital video microscopy, optical tweezers calibration and holographic optical tweezers.

The optical trapping of colloidal matter is an unequalled field of technology for enabling precise handling of particles on microscopic scales, solely by the force of light. Although the basic concept of optical tweezers, which are based on a single laser beam, has matured and found a vast number of exciting applications, in particular in the life sciences, there are strong demands for more sophisticated approaches. This thesis gives an introductory overview of existing optical micromanipulation techniques and reviews the state-of-the-art of the emerging field of structured light fields and their applications in optical trapping, micromanipulation, and organisation. The author presents established, and introduces novel concepts for the holographic and non-holographic shaping of a light field. A special emphasis of the work is the demonstration of advanced applications of the thus created structured light fields in optical micromanipulation, utilising various geometries and unconventional light propagation properties. While most of the concepts developed are demonstrated with artificial microscopic reference particles, the work concludes with a comprehensive demonstration of optical control and alignment of bacterial cells, and hierarchical supramolecular organisation utilising dedicated nanocontainer particles.

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.