Continuous Colloidal Concentration and Patterning with Optically Induced AC Electrokinetics

We demonstrate an optically induced AC electrokinetic technique that rapidly and continuously accumulates colloids (49 nm to 3.0 microns) on both ITO and gold electrode surfaces resulting in a crystalline-like monolayer aggregation. This is done without photosensitive materials. Electrothermal hydrodynamics produce a microfluidic vortex that carries particles in suspension towards its center where they are trapped by low-frequency AC electrokinetic forces. We characterize the rate of particle aggregation as a function of the applied AC voltage, AC frequency, and illumination intensity. Further, we have selectively captured and separated 2.0 micron from 1.0 micron polystyrene particles as well as 1.0 micron silica from 1.0 micron polystyrene particles. This dynamic optically-induced technique rapidly and selectively concentrates, patterns, and translates colloidal aggregates and can be used for a variety of lab-on-a-chip applications.