Active control of electroosmotic flow in microchannels using light

The ability to control bulk electroosmotic flow in microchannels via light modulation is demonstrated. Microchannels (1000 μm wide, 20 μm deep) were fabricated and a TiO₂ film was deposited on the inner walls of the channel. TiO₂ is a direct semiconductor that exhibits a change in surface charge upon radiation with UV light; leading to variations in the zeta potential and subsequent flow modulation. The bulk velocity was measured using the current monitoring technique in the presence and absence of UV radiation. Phosphate buffer solutions of different pH values (2.2, 4.7, 8.4) were tested. The magnitude of the change in velocity due to irradiation varied from 7 to 242 μm/s depending on the pH of the buffer. The largest velocity change was observed at pH 4.7, with smaller changes observed at higher and lower pH values. Parameters influencing flow velocity are also discussed.