LAUSR

Intelligent contactless microfluidic pumping strategies have been increasingly desirable in operation of lab-on-a-chip devices. Herein, we present a photothermal microfluidic pumping strategy for on-chip multiplexed cargo transport in a contactless and spatiotemporally controllable fashion, based on the application of near-infrared laser-driven photothermal effect in microfluidic paper-based devices (μPDs). Graphene oxide (GO)-doped thermoresponsive poly (N-isopropylacrylamide)-acrylamide (NIPAM-AcAm) hydrogels served as the photothermally responsive cargo reservoirs on the μPDs. In response to remote contactless irradiation by an 808 nm laser, on-chip phase transition of the composite hydrogels was actuated in a switch-like manner as a result of the photothermal effect of GO, enabling robust on-chip pumping of cargoes from the hydrogels to pre-defined arrays of reaction zones. The thermal imaging technique was employed to monitor the on-chip photothermal pumping process. The microfluidic pumping performance can be spatiotemporally controlled in a quantitative way by remotely tuning the laser power, irradiation time, and GO concentration. The pumping strategy was exemplified by using FeCl3 and horseradish peroxidase (HRP) as the model cargoes to implement on-chip Prussian blue (PB)- and 3,3',5,5'-tetramethylbenzidine (TMB)-based colorimetric reactions, respectively. Furthermore, multiplexed on-demand microfluidic pumping was achieved by flexibly adjusting the irradiation pathway and the microfluidic pattern. The new microfluidic pumping strategy shows great promise for diverse microfluidic applications due to its flexibility, high integratability into lab-on-a-chip devices, and contactless and spatiotemporal controllability.