Enhanced Optoelectronics by Oriented Multilayers of Photosystem i Proteins in Dry Hybrid Bio-Solid Devices

The use of dry functional protein films on solid-state platforms is essential in a variety of optoelectronic devices where aqueous environment is not favorable. The photoactive photosynthetic protein photosystem I (PS I) is a good choice to be used as an active component in optoelectronic devices as it was shown to be photoactive in dry environment. Gerster, D.; Reichert, J.; Bi, H.; Barth, J. V.; Kaniber, S. M.; Holleitner, A. W.; Visoly-Fisher, I.; Sergani, S.; Carmeli, I. Photocurrent of a single photosynthetic protein. Nat. Nanotechnol. 2012, 7, 673-676. Although the extinction coefficient of PS I is high, the absorption cross section of oriented monolayer of PS I proteins attached to solid surfaces is limited by the 10 nm thickness of the layer. This limits the efficiency and potential use of the PS I for practical applications. In this work, the absorption cross section and photovoltage were enhanced by fabrication of serially oriented multilayers. This was achieved by cross-linking free amine residues located on the surface of PS I monolayer to thiols located at the oxidizing side of successive PS I cysteine mutants. The process repeated in a successive manner to obtain the desired multilayer thickness. The films were characterized by various methods, such as absorption measurements, ellipsometry, atomic force microscopy, and Kelvin probe spectroscopy, to determine the thickness, absorption coefficient, plasmonic effects, and photopotential of the films. The multilayers demonstrated an enhanced photovoltage caused by the increase of absorption cross section and the serial arrangement of the photosynthetic proteins. The technique developed here for the formation of oriented dry multilayers can be utilized in hybrid bio-solid-state electronic devices, in which an enhancement in single-monolayer parameters, such as absorption cross section and photovoltage, is required.