Noble metal nanoparticles illuminated at their plasmonic resonance wavelength become nanoscale heat sources. This study experimentally demonstrates the optical transport of single and multiple resonant gold nanoparticles (200 nm radius) directed by tailored transverse phase-gradient forces around a 2D optical trap. The phase-gradient force controls nanoparticle speed. Multiple nanoparticles form a quasi-stable group whose motion is also controlled optically, creating a moving heat source and inducing optothermal convective fluid flow, confirmed by tracer particle tracking. A method to control assembly size (and temperature) by manipulating the optical propelling force is presented, enabling indirect control of fluid flows as a micro-optofluidic tool.

José A. Rodrigo, Mercedes Angulo, Tatiana Alieva