Photothermal heating enabled by plasmonic nanostructures for electrokinetic manipulation and sorting of particles.

Plasmonic nanostructures support strong electromagnetic field enhancement or optical "hot spots" that are accompanied by local heat generation. This heating effect is generally seen as an obstacle to stable trapping of particles on a plasmonic substrate. In this work, instead of treating the heating effect as a hindrance, we utilized the collective photoinduced heating of the nanostructure array for high-throughput trapping of particles on a plasmonic nanostructured substrate. The photoinduced heating of the nanostructures is combined with an ac electric field of less than 100 kHz, which results in creation of a strong electrothermal microfluidic flow. This flow rapidly transports suspended particles toward the plasmonic substrate, where they are captured by local electric field effects. This work is envisioned to have application in biosensing and surface-enhanced spectroscopies such as SERS.