Optical manipulation in conjunction with photochemical/photothermal responses of materials

Abstract

This article reviews optical manipulation coupled with photochemical/photothermal responses of nanometer sized materials including molecular systems, polymers, and inorganic nanoparticles. After the introduction, section 2 overviews the optical trapping of nanometer sized molecular systems including early-stage studies, such as trapping of polymer chains, micelles, and molecular aggregates in solution at room temperatures. Then, the conformation control of macromolecule assemblies and gels by optical force are introduced, followed by micro-fabrications achieved by combining optical trapping and photochemical reactions. Section 3 summarizes studies on the evaluation of optical force acting on nanometric molecular systems using fluorescence correlation techniques. Approaches to control optical force by using photochemical reactions are show in section 4, where the absorption band of target materials are modified through photochromic reactions, leading to micromechanical motion of small particles synchronizing with the photochemical reactions. Section 5 overviews photothermal effect in optical manipulation such as natural convection, Marangoni convection and thermophoresis, and applications of the thermal effects to develop new methods of micromanipulation achieved by combining optical force and photothermal responses.

Fluctuation-mediated orbital rotation of microparticles in non-coaxially counter-propagating optical tweezers

“…Optical manipulation techniques using pressure of photons, invented by Ashkin, have been widely applied to capture, transport and analyze tiny objects in various research fields. [1][2][3] In principle, when target objects of optical manipulation are illuminated with parallel light, they exhibit linear translational motions because that light carries linear momenta; microparticles will be blow off by dissipative force (sum of scattering and absorption forces) along the direction of light propagation. [4,5] On the other hand, when laser light is tightly focused using a microscope objective with a high numerical aperture, microparticles will be pushed into a minimum of optical potential because of the momenta of photons pouring down from wide angles; this is commonly known as optical tweezers.…”