Optofluidic control using photothermal nanoparticles.

Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties. Here, we introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid-air interface. Using light beams with submilliwatt power, we can drive and guide liquid flow in microfluidic channels to transport biomolecules and living cells at controlled speeds and directions. Previously, a variety of methods for controlling microscale liquid flow have been developed owing to the increasing interest for microfluidics-based biochemical analysis systems. However, our method dispenses with the need for complex pump and valve devices, surface chemistry and electrode patterning, or any other further effort towards substrate fabrication. Instead, our optofluidic control method will allow the fabrication of all-optical large-scale integrated microfluidic circuits for biomolecular and cellular processing without any physical valve or mechanical pumping device.