Fabrication of an optically driven pH gradient generator based on self-assembled proton pumps

Abstract

Optically manipulating the local pH of a target solution in a microchannel, or reservoir, provides a mechanism for activating and controlling a variety of biological and chemical processes on Lab-on-a-Chip (LOC) devices and micro-total analysis systems (l-TAS). A microscale pH gradient generator that exploits the lightactivated molecular proton pumps found in the purple membranes (PM) of bacteriorhodopsin is described in this paper. The photo-electro-chemical transducer is an ultrathin layer (*13 nm) of oriented PM patches self-assembled on an Au-coated porous substrate. A biotin labeling and streptavidin molecular recognition technique is used to ensure that the extracellular side of all PM patches is attached to the porous substrate enabling unidirectional and efficient transport of ions across the transducer surface. The photo-induced proton pumps generate a flow of ions that produce a measurable change in pH between the separated solutions. The self-assembly procedure is experimentally quantified based on the capacitance characteristics of the bR membranes. The investigation confirms that the transducer is covered with the bR proton pumps at a mass density of 2.33 ng/cm 2 . Experimental tests also show that the proposed transducer can repeatedly generate pH gradients as high as 0.42 and absolute voltage differences as high as 25 mV when illuminated by an 18 mW, 568 nm light source. Furthermore, the DpH is observed to be nonlinear with respect to light intensity and exposure time. The DpH of the target solution is sufficient to cause a phenolphthalein indicator dye to change color or an ionic hydrogel micro-valve to expand.

Ionic Polymer Microactuator Activated by Photoresponsive Organic Proton Pumps

“…Prior studies have shown that biotin labeling is highly effective and can produce a very thin bR PM layer that is <13 nm [16,22]. Figure 3 shows SEM photographs of the self-assembled ultra-thin bR films on the biofunctionalized PAA substrate at different magnifications.…”

Light Color‐Controlled pH‐Adjustment of Aqueous Solutions Using Engineered Proteoliposomes

“…There are examples of the successful application of microbial rhodopsin proton pumps such as BR and proteorhodopsin for the light‐driven control of pH in aqueous solutions using pro‐ and eukaryotic cells, [ 8 ] proteoliposomes, [ 9 ] polymerosomes, [ 10 ] and functionalized surfaces. [ 11 ] From a bioenergetical and engineering point of view the combination of light‐driven proton pumps with ATP synthesis utilizing an established proton gradient across a membrane as a power source is an important achievement. [ 12 ] To the best of our knowledge, the utilization of two proton pumps positioned in opposite orientations within the membrane for controlling proton gradients in synthetic systems has not been reported.…”