Size-tunable capture of mesoscopic matters using thermocapillary vortex

The hydrodynamics in lab-on-a-chip provides an efficient and tunable platform for manipulating mesoscopic particles. Current capture-tunable technology has been mainly focused on inertial flow with little attention on a thermocapillary vortex. The boundary condition is one of the most important factors on particle manipulation in a microvortex. By integrating a photothermal waveguide with a triangular channel in lab-on-a-chip, we present a tunable microvortex array for achieving size-tunable capture. Ellipticity of the temperature field and intensity of vortices are continuously adjustable by moving the photothermal waveguide along the triangular channel, resulting in tunable particle trajectories. Particles can be trapped in a vortex center and driven out of the vortex along with external flow. The detailed theoretical results reveal that a threshold size of trapped particles can be adjustable by the channel width. We believe that the approach, the thermocapillary vortex on chip, will provide a facile way for seamless connection between photonics and microfluidics. Published by AIP Publishing.