Light-driven hydrogel microvalve based on BR proton pumps

Regulating the directional flow of very small quantities of fluid along narrow microchannels has been an on-going challenge for Lab-on-a-Chip (LOC) technologies. The control and precise delivery of minute quantities of liquid is often accomplished by an externally controlled microvalve. A thin porous photoelectric film that controls the expansion and contraction of an ionic polymer actuator, or hydrogel microvalve, is described in this paper. The light driven transducer is comprised of an ultra-thin layer of oriented photosensitive bacteriorhodopsin (bR) purple membrane (PM) patches which are self-assembled on a bio-functionalized gold (Au) coated porous anodic alumina substrate. When exposed to visible light, the proton pumps formed by the bR PMs generate a unidirectional flow of ions through the very tiny pores of the Aucoated substrate altering the pH of two separated ionic solutions. The change in pH in the target solution is sufficient to induce isomotic pressure within the hydrogel microvalve and drive volume expansion. Preliminary experiments are performed using the light-driven proton pumps and an ionic hydrogel microvalve constructed from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) monomers. The investigative study shows that an 8μm gap in a microchannel could be closed using a focused light beam. Further studies are, however, required to optimize important design parameters and fabrication steps to improve performance.