Photo-electric biotransducer for activating ionic hydrogel microactuators

Abstract

An ionic hydrogel microactuator driven by an organic photo-electric transducer is described in this paper. When exposed to visible light, the ultrathin layer of photosensitive bacteriorhodopsin (bR) purple membrane patches adsorbed on a biofunctionalized porous anodic alumina (PAA) gold coated surface acts as an array of proton pumps that transport H + ions from the acidic gel to a separate ionic solution. The movement of ions across the porous membrane creates a pH gradient that causes the hydroxyethyl methacrylate–acrylic acid (HEMA–AA) gel to swell. Experimental studies show that a 13 nm self-assembled photoelectric layer can generate approximately 1.3 mV/(mW cm 2 ) when exposed to an 18 mW, 568 nm light source. The photo-voltage produced by the monolayer is sufficient to change the pH of the surrounding ionic solution with 0.42. The small change in pH around the phase transition point p K a enabled the hydrogel microactuator to swell by more than 80% of its original volume in less than 85 min. The expansion increased the diameter and length of the gel microstructure by 23% and 22%, respectively.