Colloidal Manipulation through Plasmonic and Non-plasmonic Laser-Assisted Heating

In spite of the long-term awareness of the conversion of light to heat even in materials with low absorption coefficient via the photothermal effect and consequent usage of the effect to evaluate thermo-optic properties of the materials, only recently has the thermal field created via photon-to-phonon conversion been exploited for manipulation of colloidal objects as well as living cells. As compared to conventional direct photon-assisted manipulation via optical tweezers, the optothermal manipulation technique employs much lower optical source power and can manipulate particles over a long range. In this review, the working mechanisms, concepts, and applications of a series of recently established optothermal techniques are discussed for the manipulation of diverse species including micro/nanoparticles, biological cells, molecules, and micelles in various fluidic environments. The physical mechanism of the optical manipulation that relies on the coordinated action of thermal convection, Marangoni convection, thermophoresis, thermoelectricity, depletion attraction, and thermo-osmotic flow is discussed in detail. With their low-power operation, diverse functionalities, and simple optics employed, optothermal manipulation techniques are increasingly finding a wide range of applications in colloidal science, life sciences, materials science, and nanoscience, as well as in the developments of colloidal functional devices and nanomedicine.