Photoelectrochemistry of Photosystem I Bound in Nafion

Abstract

Developing a solid state Photosystem I (PSI) modified electrode is attractive for photoelectrochemical applications because of the quantum yield of PSI, which approaches unity in the visible spectrum. Electrodes are constructed using a Nafion film to encapsulate PSI as well as the hole-scavenging redox mediator Os(bpy)2Cl2. The photoactive electrodes generate photocurrents of 4 μA/cm(2) when illuminated with 1.4 mW/cm(2) of 676 nm band-pass filtered light. Methyl viologen (MV(2+)) is present in the electrolyte to scavenge photoelectrons from PSI in the Nafion film and transport charges to the counter electrode. Because MV(2+) is positively charged in both reduced and oxidized states, it is able to diffuse through the cation permeable channels of Nafion. Photocurrent is produced when the working electrode is set to voltages negative of the Os(3+)/Os(2+) redox potential. Charge transfer through the Nafion film and photohole scavenging at the PSI luminal surface by Os(bpy)2Cl2 depends on the reduction of Os redox centers to Os(2+) via hole scavenging from PSI. The optimal film densities of Nafion (10 μg/cm(2) Nafion) and PSI (100 μg/cm(2) PSI) are determined to provide the highest photocurrents. These optimal film densities force films to be thin to allow the majority of PSI to have productive electrical contact with the backing electrode.

Design of an Os Complex‐Modified Hydrogel with Optimized Redox Potential for Biosensors and Biofuel Cells

“…Wiring of enzymes to electrode surfaces by means of redox hydrogels is of particular interest for the design of biosensors, enzymatic biofuel cells or biophotovoltaic devices . The electron transport between the electrode and the prosthetic group of the enzyme within these bioactive films is mediated by redox relays that are attached to the hydrogel backbone.…”

“…Wiring of enzymes to electrode surfaces by means of redox hydrogels [1] is of particulari nterestf or the design of biosensors, [2][3][4] enzymatic biofuel cells [5][6][7] or biophotovoltaicd evices. [8][9][10] The electron transport between the electrode and the prostheticg roup of the enzyme within these bioactive films is mediated by redox relays that are attached to the hydrogel backbone. Osmiumc omplexes of the type[ Os(bpy) 2 L x ]( bpy = 2,2'-bipyridine, L = chloro ligando rl igand bearing al inker group for the attachment to the polymer backbone; x = 1, 2) are widely used as redoxm ediators in hydrogels because of the fast electron transferr ates they exhibit between the Os centers and the prosthetic groups in variouse nzymes,f or example,a mong others glucose oxidase, [11][12][13] PQQ-dependent glucosed ehydrogenase (PQQ-sGDH, PQQ = pyrroloquinoline quinone), [14,15] cellobiose dehydrogenase( CDH), [16,17] pyranose dehydrogenase [18] or laccase.…”

Enhanced photocurrent from Photosystem I upon in vitro truncation of the antennae chlorophyll

“…Electrodes were cut from the Au-coated slides into 2.5 9 0.8 cm chips. A 20 ll drop of a mixture containing 0.1 wt% Nafion, 32 lM Os(bpy) 2 Cl 2 , 47.5 mM Na-phosphate buffer pH 7, 0.024 wt% Triton, and PSI was dropped onto the Au electrode and allowed to air dry in the dark at room temperature (Baker et al 2014b). PSI concentrations were adjusted between samples to maintain 1.9 lg Chl per electrode unless otherwise stated.…”

“…. Samples were under an applied potential of -0.2 V versus Ag/AgCl, which was applied for 5 min before testing to equilibrate the system prior to the experiment, and this wait period also allows the Nafion film to fully hydrate (Baker et al 2014b). Photocurrent measurements consisted of a 1-min illumination period followed by 2 min in the dark.…”

“…. Isolated PSI has been employed in a wide range of applications from using proteoliposomes in order to photosensitize mammalian cells to suspending PSI particles in a Nafion film in solid-state photovoltaics (Baker et al 2014b;Kuritz et al 2005).…”