Fig. 8. Proton pumping action of proteorhodopsin immobilized on a POEGMA-NBC/PCysMA binary brush structure. (a) Schematic of the set-up: pR is attached to the surface of the PCysMA brush using His-tag chemistry, which ensures that all pR are oriented in the same direction. Then a lipid bilayer is suspended on the PCysMA brush to form a lipid bilayer. Upon irradiation, pR pumps protons in a given direction through the lipid bilayer. The resulting pH difference is countered by diffusion through the POEGMA brush layers. However, since diffusion occurs more slowly than proton pumping, a net pH gradient is generated during irradiation. Diffusion ensures that equilibrium is achieved following irradiation. The time scale for reaching equilibrium was faster than what could be measured using the current setup. (b) Image formed by mapping the emission between 600 nm and 700 nm from POEGMA-NBC/PCysMA where pR is immobilized on PCysMA using a His-tag, following bilayer formation mediated by addition of a lipid vesicle suspension consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine doped with 0.5 mol% Texas Red® 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt. (c) Emission between 600 nm and 700 nm for POEGMA-NBC/PCysMA without pR following in situ bilayer formation by addition of the lipid vesicle suspension. (d) Emission intensity from POEGMA-NBC walls for samples with and without immobilized pR. The I₆₅₀/I₇₀₀ emission intensity ratio is calculated in each case and inserted.