Light-Governed Capillary Flow in Microfluidic Systems

Light-based flow systems for point-of-care devices are of interest because, in principle, sunlight could be used to operate them, potentially allowing for high functionality with minimal device complexity and expense. A light-operated method to drive flow using poly(N-isopropylacrylamide), a smart polymer that changes wettability as a function of temperature, is introduced. It is grafted onto a carbon black-polydimethylsiloxane surface, which converts light into a thermal pattern that valves flow at user-defined locations. Flow rates are demonstrated ranging from 4 mu L min-1 at 25 degrees C to 0.1 mu L min-1 at 40 degrees C. The valving dynamics are also characterised, and a response time of less than 4 s is shown. Light-operated flow could provide the simple architecture and advanced functionality needed in low-resource point-of-care devices.