title: Light-governed capillary flow in microfluidic systems.
abstract: 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 μL min(-1)  at 25 °C to 0.1 μL min(-1)  at 40 °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.
authors.affiliation: Cornell University, 240 Upson Hall, Ithaca, New York 14853, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Jiang
authors.forename: David
authors.initials: D
authors.lastname: Erickson
mesh_terms: D000042:Absorption; D000178:Acrylamides / Q000737:chemistry; D000180:Acrylic Resins; D004247:DNA / Q000032:analysis*; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D004867:Equipment Design; D006801:Humans; D008027:Light; D046210:Microfluidic Analytical Techniques; D044085:Microfluidics; D036103:Nanotechnology / Q000379:methods*; D011108:Polymers / Q000737:chemistry; D012993:Solar Energy; D013696:Temperature
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D004129:Dimethylpolysiloxanes; D011108:Polymers; C052970:poly-N-isopropylacrylamide; C013830:baysilon; D004247:DNA