Controlling the Trajectories of Nano/Micro Particles Using Light-Actuated Marangoni Flow.

The ability to manipulate small objects and to produce patterns on the nano- and microscale is of great importance, both with respect to fundamentals and technological applications. The manipulation of particles with diameters of the order of 100 nm or below is a challenge because of their Brownian motion but also because of the scaling behavior of methods such as optical trapping. The unification of optical and hydrodynamic forces is a potential route toward the manipulation of tiny objects. Herein we demonstrate the trapping and manipulation of nano- and microparticles based on interfacial flows controlled by visible light, a method we denote as "Light-Actuated Marangoni Tweezer (LAMT)". We experimentally study the manipulation of particles having diameters ranging from 20 nm to 10 μm, including quantum dots and polystyrene nano/microparticles. The particles can be manipulated by scanning a light beam along a liquid surface. In this way, we are able to define almost arbitrary particle trajectories, for example, in the form of letters. In addition, we are able to handle a number of particles in parallel by creating an optical "landscape" consisting of a multitude of laser spots. The inherent advantages of LAMTs are the linear scaling of the trapping force with the particle diameter and the fact that the force is less dependent on particle properties than in the case of conventional methods.