Apple iPad Application for Light Actuated Digital Microfluidics

There is an increasing interest for droplet manipulation using light-actuated digital microfluidics (LADM) because it holds many promises in improving biological particle sorting and chemical processing fields. By using a platform that utilizes optoelectrowetting (OEW) and optoelectronic tweezers (OET), on-chip micro to nano volume droplet manipulation can be achieved, respectively. The microfluidic device consists of a liquid layer between a top layer containing Teflon-coated indium-tin-oxide (ITO) and a photosensitive bottom layer with hydrogenated amorphous-Silicon (a-Si:H) and Al₂O₃. By placing light patterns on the bottom layer from a projector, an electric field would be created which places a net force on the liquid droplet towards the light, thus allowing droplet movement. Current methods use a passive feedback system and require manual controlling of light patterns, which is inconvenient for multiple droplet and particle movement. Here, we address the software aspects and introduced an Apple iPad application to simplify the creation of light patterns and controls. By taking advantage of multi-touch and gesture-recognition technology, up to 11 liquid droplets could be controlled simultaneously. Testing was done using an iPad where 9 water droplets were controlled and then merged using multi-touch gestures. This demonstrated a unique and easy to use interface that requires minimal training. By integrating hardware and software, particle manipulation can be easily performed for single cell analysis and sorting.