Evaluation of a biohybrid photoelectrochemical cell employing the purple bacterial reaction centre as a biosensor for herbicides

Abstract

The Rhodobacter sphaeroides reaction centre is a relatively robust and tractable membrane protein that has potential for exploitation in technological applications, including biohybrid devices for photovoltaics and biosensing. This report assessed the usefulness of the photocurrent generated by this reaction centre adhered to a small working electrode as the basis for a biosensor for classes of herbicides used extensively for the control of weeds in major agricultural crops. Photocurrent generation was inhibited in a concentration-dependent manner by the triazides atrazine and terbutryn, but not by nitrile or phenylurea herbicides. Measurements of the effects of these herbicides on the kinetics of charge recombination in photo-oxidised reaction centres in solution showed the same selectivity of response. Titrations of reaction centre photocurrents yielded half maximal inhibitory concentrations of 208 nM and 2.1 µM for terbutryn and atrazine, respectively, with limits of detection estimated at around 8 nM and 50 nM, respectively. Photocurrent attenuation provided a direct measure of herbicide concentration, with no need for model-dependent kinetic analysis of the signal used for detection or the use of prohibitively complex instrumentation, and prospects for the use of protein engineering to develop the sensitivity and selectivity of herbicide binding by the Rba. sphaeroides reaction centre are discussed.

Functional Nanohybrid Materials from Photosynthetic Reaction Center Proteins

“…The binding is effective and specific, so that the RC-based biohybrids can be used as active components of biosensor devices [63][64][65][66].…”

<strong>Evaluation of sensor performance for harmful compounds by using photo-induced electron transfer from photosynthetic membranes to electrodes</strong>

“…The geometric surface area of the electrode was 0.07 cm 2 . The amount of mediator was expressed as the fraction of mediator in the carbon paste mixture, (mediator)m% (w/w).…”

“…Rhodobacter sphaeroides (R. sphaeroides) is a typical purple bacterium, and the photocurrent generated in this organism's reaction center has been extensively investigated as a potential biosensor for classes of PSII-inhibiting herbicides [2]. R. sphaeroides are both simple and inexpensive to culture.…”

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

“…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].…”

“…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].…”