2-dimensional protein crystals for bioelectronics

A two-dimensional protein crystal that preserves biological function is necessary for the realization of bioelectronic devices. The authors have fabricated a close-packed purple membrane (PM) monolayer by the Langmuir-Blodgett technique and studied the proton transfer through the membrane under the photoexcitation. The PM monolayer is transferred to an indium-tin-oxide or Al-deposited glass substrate and/or a Si wafer by a horizontal transfer technique. The morphology of monolayer film was directly investigated by SEM. From the static and dynamic measurement of photovoltaic effect in the PM multilayer, it was confirmed that the photochemical cycle of the bacteriorhodopsin (membrane protein of PM) was preserved. The two-dimensional packing of globular protein ferritin was also investigated. Depending on the surface pressure applied, the packing changes in a chainlike aggregate or in a fairly good lattice (small patch).