Towards light-addressable flow control: Responsive hydrogels with incorporated graphene oxide as laser-driven actuator structures within microfluidic channels

Light-driven valves based on polymer actuators are obtained by introducing responsive hydrogels into the channels of glass microfluidics. The actuators are consisting of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with incorporated graphene oxide (GO) nanoparticles fabricated by in situ photopolymerization. Upon optothermal heating with a laser, the hydrogels change their volume significantly from a swollen to a collapsed state after exceeding the switching temperature. Applied as valve, the hydrogel blocks the channel without illumination and the channel is opened by light stimulation. Important parameters like the maximum pressure resistance as well as the time constants for opening to a flow rate of 20 mu l/min and the closing procedure are evaluated by flow experiments with repeated operation. In addition to completely open or close the channels, the regulation of the flow rate to intermediate values between 10 and 20 mu l/min by adjusting the power supply of the light source is studied. Furthermore, the ability to control the supply of a particular analyte for an amperometric biosensor by switching between two hydrogel valves is demonstrated as a proof-of-concept experiment.