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

Abstract Controlling the pH at the microliter scale can be useful for applications in research, medicine, and industry, and therefore represents a valuable application for synthetic biology and microfluidics. The presented vesicular system translates light of different colors into specific pH changes in the surrounding solution. It works with the two light‐driven proton pumps bacteriorhodopsin and blue light‐absorbing proteorhodopsin Med12, that are oriented in opposite directions in the lipid membrane. A computer‐controlled measuring device implements a feedback loop for automatic adjustment and maintenance of a selected pH value. A pH range spanning more than two units can be established, providing fine temporal and pH resolution. As an application example, a pH‐sensitive enzyme reaction is presented where the light color controls the reaction progress. In summary, light color‐controlled pH‐adjustment using engineered proteoliposomes opens new possibilities to control processes at the microliter scale in different contexts, such as in synthetic biology applications.