Hydrodynamic Manipulation of Nano-Objects by Thermo-Osmotic Flows

TL;DR

This paper demonstrates that thermo-osmotic boundary flows, induced by optically modulating surface interactions, can be used to trap and manipulate nano-objects with high precision and reconfigurability.

Contribution

It introduces a novel hydrodynamic approach for nano-object manipulation using thermo-osmotic flows generated by localized optical heating.

Findings

Convergent boundary flows with velocities of tens of micrometres per second observed.

Hydrodynamic forces enable precise nanoparticle positioning and guiding.

Fast multiplexing allows parallel manipulation of multiple nano-objects.

Abstract

The manipulation of micro- and nano-objects is of great technological significance to construct new materials, manipulate tiny amounts of liquids in fluidic systems, or detect minute concentrations of analytes. It is commonly approached by the generation of potential energy landscapes, for example, with optical fields. Here we show that strong hydrodynamic boundary flows enable the trapping and manipulation of nano-objects near surfaces. These thermo-osmotic flows are induced by modulating the van der Waals interaction at a solid-liquid interface with optically induced temperature fields. We use a thin gold film on a glass substrate to provide localized but reconfigurable point-like optical heating. Convergent boundary flows with velocities of tens of micrometres per second are observed and substantiated by a quantitative physical model. The hydrodynamic forces acting on suspended nanoparticles and attractive van der Waals or depletion induced forces to enable precise positioning and guiding of the nanoparticles. Fast multiplexing of flow fields further provides the means for parallel manipulation of many nano-objects. Our findings have direct consequences for the field of plasmonic nano-tweezers and other thermo-plasmonic trapping schemes and pave the way for a general scheme of nanoscopic manipulation with boundary flows.