Towards biochemical microreactor: Nonlocal photovoltaic actuation of aqueous microdroplets in oil-infused PDMS channels based on LiNbO3: Fe crystal

Abstract

Biocompatible, pump-free microfluidic actuation is a challenging task for optically integrated lab-on-chips. Herein, photovoltaic actuation of aqueous microdroplets is demonstrated inside the oil-infused PDMS channels fabricated on a c-cut LiNbO3:Fe (LN:Fe) substrate. This photovoltaic actuation is based on the repulsive response of aqueous microdroplets to laser illumination, and its “nonlocal” feature can avoid the direct laser illumination on aqueous microdroplets containing fragile biochemical targets. Both the direct electrostatic force acting on the aqueous microdroplet and the repulsive force induced by the compressed convection flow of infused oil are found contributing to this “nonlocal” feature. Due to the transition of electrostatic action from the dielectrophoretic (DEP) to electrophoretic (EP) mechanism, the maximal velocity of photovoltaic actuation in the straight-line channel exhibits a pronounced threshold effect on the laser illumination intensity. Thanking to the strong EP action, the aqueous microdroplet can be actuated to squeeze through a narrow pass in the right-angle channel. Precipitation and chromogenic chemical microreactions as well as mortal reactions of a single paramecium using the photovoltaic actuation are demonstrated for the future on-chip biochemical applications.