Photoactive Electrodes Incorporating Electrosprayed Bacterial Reaction Centers

Abstract

Highly effi cient light absorption and charge separation within the photosystem and reaction center (RC) complexes of photosynthetic plants and bacteria are of great interest for solar cell and photo detector applications, since they offer almost unity quantum yield and expected ultimate power conversion effi ciencies of more than 18% and 12%, respectively. In addition, the charge separated states created by these protein complexes are very long lived compared to conventional semiconductor solar cells. In this work, a novel technique is presented for the deposition of photosynthetic protein complexes, by electrospraying RCs of Rhodobacter sphaeroides onto highly ordered pyrolytic graphite (HOPG) electrodes. Remarkably, it is shown that the RCs not only survive exposure to the high electric fi elds but also yield peak photocurrent densities of up to 7 µA cm −2 , which is equal to the highest value reported to date.

Plasmon‐Enhanced Photocurrent of Photosynthetic Pigment Proteins on Nanoporous Silver

“…Correcting for a measured 2.4-fold greater loading, RC-LH1 complexes generated a 2.5-fold larger peak current on RS compared with SS (Table 1) transfer of charge between the working and counter electrodes, producing potential differences that dissipate in the initial dark period. [28,29] To characterize this transient photocurrent further, measurements were made with a rotating RS|RC-LH1 electrode to establish a forced convection of oxidized and reduced quinone mediator through the bulk solution. At a rotation speed of 500 rpm there was a dramatic increase in the level of the stable photocurrent up to values that were almost identical to the initial peak transient current,…”

On the mechanism of ubiquinone mediated photocurrent generation by a reaction center based photocathode

“…This provides sufficient time for diffusional processes to remove electrons from the "negative terminal" of the RC and donate electrons to the "positive terminal", resetting the RC for the next turnover. Developments in our understanding of RC mechanism have influenced the design of new synthetic materials for solar energy conversion, and there is interest in the hybridization of both natural and engineered RC proteins with man-made materials for applications in photovoltaics [4][5][6][7][8][9], biosensing [10,11] and molecular electronics [12,13].…”

“…Particular attention has been paid to the Photosystem I complex from oxygenic phototrophs [15][16][17] and both the RC and RC/light harvesting complexes from anoxygenic purple photosynthetic bacteria such as Rhodobacter (Rba.) sphaeroides [4][5][6][7][8]10,[18][19][20][21][22][23]. Major preoccupations of this work have been the development of strategies for effective interfacing of the positive and negative terminals of the photovoltaic protein to the working and counter electrode, either through direct binding or the use of diffusional mediators [4][5][6][7][8][16][17][18][19][20][21][22][23][24][25][26][27].…”

“…sphaeroides [4][5][6][7][8]10,[18][19][20][21][22][23]. Major preoccupations of this work have been the development of strategies for effective interfacing of the positive and negative terminals of the photovoltaic protein to the working and counter electrode, either through direct binding or the use of diffusional mediators [4][5][6][7][8][16][17][18][19][20][21][22][23][24][25][26][27]. In the case of RC's from purple bacteria a particularly effective strategy has been to use analogues of the natural electron donor and electron acceptor, cytochrome (cyt) c2 and ubiquinone-10 (UQ10), to connect the photovoltaic protein to the two electrodes [18,20,22,[27][28][29].…”

“…We do so by measuring the photocurrents generated by electrode-bound RCs with mutations that block specific quinone-mediated electron or proton transfer steps within the RC, and by examining how isoprenoid "tail" length affects the capacity of ubiquinone to mediate diffusional charge transfer between electrodes. With recent large gains in 5 photocurrent magnitude [4,5,7] and mounting interest in this field, this work provides insight into design principles for the development of more effective biophotovoltaic cells and biosensors.…”