Photo-electric biotransducer for activating ionic hydrogel microactuators

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 cm2) 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 pKa 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.