Optothermal Manipulations of Colloidal Particles and Living Cells

Abstract

Optical manipulation techniques are important in many fields. For instance, they enable bottom-up assembly of nanomaterials and high-resolution and in situ analysis of biological cells and molecules, providing opportunities for discovery of new materials, medical diagnostics, and nanomedicines. Traditional optical tweezers have their applications limited due to the use of rigorous optics and high optical power. New strategies have been established for low-power optical manipulation techniques. Optothermal manipulation, which exploits photon-phonon conversion and matter migration under a light-controlled temperature gradient, is one such emerging technique. Elucidation of the underlying physics of optothermo-matter interaction and rational engineering of optical environments are required to realize diverse optothermal manipulation functionalities. This Account covers the working principles, design concepts, and applications of a series of newly developed optothermal manipulation techniques, including bubble-pen lithography, opto-thermophoretic tweezers, opto-thermoelectric tweezers, optothermal assembly, and opto-thermoelectric printing. In bubble-pen lithography, optical heating of a plasmonic substrate generates microbubbles at the solid-liquid interface to print diverse colloidal particles on the substrates. Programmable bubble printing of semiconductor quantum dots on different substrates and haptic control of printing have also been achieved. The key to optothermal tweezers is the ability to deliver colloidal particles from cold to hot regions of a temperature gradient or a negative Soret effect. We explore different driving forces for the two types of optothermal tweezers. Opto-thermophoretic tweezers rely on an abnormal permittivity gradient built by structured solvent molecules in the electric double layer of colloidal particles and living cells in response to heat-induced entropy, and opto-thermoelectric tweezers exploit a thermophoresis-induced thermoelectric field for the low-power manipulation of small nanoparticles with minimum diameter around 20 nm. Furthermore, by incorporating depletion attraction into the optothermal tweezers system as particle-particle or particle-substrate binding force, we have achieved bottom-up assembly and reconfigurable optical printing of artificial colloidal matter. Beyond optothermal manipulation techniques in liquid environments, we also review recent progress of gas-phase optothermal manipulation based on photophoresis. Photophoretic trapping and transport of light-absorbing materials have been achieved through optical engineering to tune particle-molecule interactions during optical heating, and a novel optical trap display has been demonstrated. An improved understanding of the colloidal response to temperature gradients will surely facilitate further innovations in optothermal manipulation. With their low-power operation, simple optics, and diverse functionalities, optothermal manipulation techniques will find a wide range of applications in life sciences, colloidal...

All optical dynamic nanomanipulation with active colloidal tweezers

“…As far as we know, this is the first all-optical technique for dynamic nanomanipulation in the bulk. Various alternate approaches have relied on combining plasmonic tweezers with additional forcing schemes, such as direct mechanical manipulation of tethered nano-patterned optical fibers 50 , integration with magnetic nanorobots 51 , electro-kinetic flows 14,52 , thermal forces in conjunction with specific chemical moieties 29–31,53 , etc. The ACTs discussed here could be operated remotely to trap and maneuver subwavelength colloidal cargo, using lower optical power than conventional gaussian beam tweezers 5,54 .…”

Opto-thermophoretic separation and trapping of plasmonic nanoparticles

“…13 This photothermal effect drives the thermophoresis as repulsive force, which sweeps the nanoparticles out of trap from hot to cold. [14][15][16][17] By adjusting the ratios of the attractive-and the repulsive forces acting on the nanocolloids, the following three modes on optical manipulation will be available: i) optical trapping mode entirely governed by the gradient force, ii) thermophoretic depletion mode dominated by the thermophoresis, and iii) selective trapping and separation mode based on the interplay of both contributions.…”

Optical Fiber Tweezers: A Versatile Tool for Optical Trapping and Manipulation

“…In addition to the optical force and photothermal effect, the electric fields can also contribute to the trapping and manipulation [101][102][103][104]. Kotnala et al demonstrated an opto-thermophoretic fiber tweezer (OTFT) [105], which combined the photothermal effect and electric field effect into the fiber tweezers.…”