Light-driven Microfluidics towards Solar-powered Point-of-care Diagnostics

Point-of-care diagnostics for resource limited settings is a much-researched application of microfluidics technology due to its great potential. Unfortunately, one of the current limitations is the difficulty in creating tools that are both inexpensive and simple to use but also able to perform complex tasks. Light-governed microfluidic systems are of interest because, in principle, sunlight could provide the power source to operate these tools, potentially allowing for increased functionality with minimal device complexity. Here, we study the use of light to perform both the fundamental function of fluid actuation and valving and the more sophisticated process of on-chip polymerase chain reaction (PCR). To facilitate light-driven flow, we use poly(N-isopropylacrylamide) (PNIPAAm), a “smart” polymer that changes wettability as a function of temperature. It is grafted onto a carbon black-polydimethylsiloxane (PDMS) surface, which absorbs light and converts it to heat, to produce various temperature profiles. We use this to create switchable hydrophobic and hydrophilic regions that respectively stop and activate flow and show that light can valve off flow within 4 s after illumination. We also perform continuous-flow PCR by fabricating PDMS lenses that concentrate light onto a carbon black layer to produce the necessary heat pattern, and demonstrate amplification of a 43bp segment of genomic DNA. These investigations show the potential for development of light-operated microfluidics to provide both the simple architecture and advanced functionality needed in point-of-care devices for low resource environments.