Optofluidic control using photothermal nanoparticles

Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties^1-4. 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 systems⁵. However, our method dispenses with the need for complex pump and valve devices^6-8, surface chemistry^9,10 and electrode patterning^11-14, or any other further effort towards substrate fabrication^15,16. 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.