Light-actuated ac electroosmosis for nanoparticle manipulation

We present a novel light-actuated ac electroosmosis (LACE) mechanism that allows the concentration and transportation of micro- and nanoscopic particles using light-patterned dynamically reconfigured microfluidic vortices on a photoconductive surface. LACE is realized by sandwiching an aqueous liquid medium between a featureless photoconductive surface and a transparent indium tin oxide electrode. By applying an ac electrical bias with a frequency that is close to the electric double-layer relaxation frequency, a light-patterned virtual electrode can induce ac electroosmotic flow to concentrate and transport nanoscopic particles on the photoconductive surface. By integrating with a spatial light modulator such as a digital micromirror device microdisplay, we can create 31 000 microfluidic vortices on a 1.3 x 1-mm(2) area for massively parallel trapping of 2- and 1-mu m polystyrene beads. We have also demonstrated LACE concentration and transportation of nanoscopic particles including 200- and 50-nm polystyrene beads, lambda-phage DNA molecules, and quantum dots.