Optical tweezers: theory and practice

Abstract

The possibility for the manipulation of many different samples using only the light from a laser beam opened the way to a variety of experiments. The technique, known as Optical Tweezers, is nowadays employed in a multitude of applications demonstrating its relevance. Since the pioneering work of Arthur Ashkin, where he used a single strongly focused laser beam, ever more complex experimental set-ups are required in order to perform novel and challenging experiments. Here we provide a comprehensive review of the theoretical background and experimental techniques. We start by giving an overview of the theory of optical forces: first, we consider optical forces in approximated regimes when the particles are much larger (ray optics) or much smaller (dipole approximation) than the light wavelength; then, we discuss the full electromagnetic theory of optical forces with a focus on T-matrix methods. Then, we describe the important aspect of Brownian motion in optical traps and its implementation in optical tweezers simulations. Finally, we provide a general description of typical experimental setups of optical tweezers and calibration techniques with particular emphasis on holographic optical tweezers.

Controlling Liquid Crystal Configuration and Phase Using Multiple Molecular Triggers

“…A home-built optical tweezer was constructed using a fiber laser with a wavelength of 1064 nm and a maximum power of 1 W. The beam was expanded to overfill the back aperture of the objective. A three-dimensional potential well is created when the objective focuses the laser, and this holds an object of high refractive index in place at the focal plane [ 23 , 24 ]. We can estimate the beam waist for the laser.…”

Plasmonic Nanoarchitectures for Single‐Molecule Explorations: An Overview

“…During the last decade, several techniques for the manipulation of biological objects have been developed and probably, the most notable one is the optical tweezers. [58] While standard optical tweezers and trapping systems based on diffraction limited optical setups (Figure 4a) demonstrated to be able to control the position and movement of different species ranging from particles to large molecules or cells, [59] only with the introduction of the nearfield plasmonic optical tweezers (Figure 4b) it has been possible to achieve optical manipulation in a label-free, contactless, and parallel way. [60] Different types of plasmonic nanotweezers based on SP polaritons and localized SP resonances have been proposed and demonstrated to manipulate living cells, DNA, and proteins at a high spatial resolution.…”

Stochastic Modeling of Particle Transport in Confined Geometries: Problems and Peculiarities

“…The rise of microfludics as an autonomous hydrodynamic discipline has informed recent research in the theory of fluid motion, with relevant practical applications in analytical chemistry, molecular biology and biomedicine, production of high-quality pharmaceuticals, etc. [16][17][18][19] The analysis of flow systems at microscale in devices (microchannels, microreactors) of almost comparable size than that of solute particles, necessarily implies a more detailed understanding of all the physical processes at small lengthscales, and thus a unitary and integrated use of theoretical tools deriving from practically all the branches of physics coupled to hydrodynamic problems [20]: optical methods for trapping, particle manipulation and detection [21,22] are of common use in microfluidics, and electrosmotic [23][24][25] and acoustic effects [26,27], either for fluid mixing or for separation purposes can be conveniently integrated within a microfluidic device. On the other hand, microscale hydrodynamics represents the natural realm where thermal and hydrodynamic fluctuations play a leading role.…”