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Light-driven microfluidic platforms for droplet-based biochemical analysis

We report on two light-induced droplet actuation mechanisms, floating electrode optoelectronic tweezers (FEOET) and lateral field optoelectrowetting (LOEW), for manipulating aqueous droplets immersed in oil on a featureless photoconductive surface with an open chamber configuration. Droplet functions including transporting, merging, mixing, and splitting, and multi-droplet manipulation have been accomplished. Droplet manipulation in FEOET is based on light-induced dielectrophoretic forces in an electrically insulating medium such as oil. It has been shown that oilimmersed aqueous droplets can be actuated by a light beam with an intensity as low as 400 μW/cm2 in FEOET. However, due to the weak force generated by the DEP-based droplet actuation, the droplet moving speed is limited to hundreds of μm/s and performing other droplet manipulation functions such as splitting and injection is challenging on FEOET. On the other hand, LOEW-based droplet actuation is realized by modulating the interfacial surface tension of a droplet on a hydrophobic surface through a light-induced electrowetting effect. Since surface tension provides large forces than DEP on a droplet with a diameter from mm to hundreds of μm, LOEW allows transporting droplets at a speed in the range of cm/s and performing droplet-based functions such as splitting and injection. The open chamber configuration of these platforms provides flexibility in integration with other microfluidic components such as external reservoirs and tubing for broad chemical and biochemical applications.