Diaminodurene as a Mediator of a Photocurrent Using Intact Cells of Cyanobacteria

Abstract

–A mediator for the measurement of a photocurrent generated by intact cells of cyanobacteria immobilized onto the working electrode in an electrochemical cell is described. The efficiency of diaminodurene (DAD) as an electron shuttle between the photosynthetic electron transport chain (PET) within the cells and the electrode was compared with ferrocyanide and p‐benzoquinone. A simple Synechococcus‐carbon‐paste electrode containing DAD as the mediator in the electrode material and the photosynthetic cells immobilized in a polymer matrix was constructed. The device required no addition of further reagents to the bulk solution for the generation of a photocurrent. Using cyclic voltammetry the second‐order rate constant for the reaction of DAD with the PET was determined. Diaminodurene compared favorably with p‐benzoquinone in that the overpotential was reduced to 0.2 V. The deterioration of the PET by the DAD was significantly decreased compared with p‐benzoquinone, resulting in a prolonged lifetime of the electrode. A possible mechanism for the reaction of DAD with the PET is discussed.

Characterization of the photoinduced electron transfer reaction from the photosynthetic system in Rhodobacter sphaeroides to an exogenous electron acceptor

“…To investigate how to effectively extract high-energy electrons generated by light excitation, several studies have examined photoelectrochemical anodic reactions using photosynthetic pigments [1][2][3][4][5][6][7][8][9]. In anodic reactions, light energy absorbed by pigments in plants and photosynthetic bacteria is transduced into reduced electron carrier molecules, which in turn exchange their electrons at a working electrode.…”

“…An exogenous electron acceptor can be used to mediate the transfer of electrons from the electron transport chain to the electrode because redox species in the photosynthetic organism do not react significantly at the working electrode. Addition of an exogenous electron acceptor greatly increases the magnitude of photocurrent [1][2][3]6,8,10]. Such a system can be employed for the detection of herbicides because they can disrupt photoinduced electron transfer [8,11,12].…”

A synthetic biology approach to engineering living photovoltaics

“…Different unicellular and filamentous strains have been incorporated in various setups. While early studies relied on artificial mediators for electron transfer between the cyanobacteria and electrodes, 14,16,17 more recent work has focused on the sole use of natural transfer mechanisms for electron transfer 15,18–20 . Theoretical calculations estimate the photocurrent generation capacity of cyanobacteria to be 700–7700 mW/m 2 7 , although most living photovoltaics do not exceed a few mW, with the best performing device achieving only around 100 mW in an optimized lab environment 21 .…”

“…Until recently, nearly all approaches to electrically link cells to electrodes have focused on the materials engineering of electrodes or synthetic redox mediators that abrogate these barriers to facilitate charge transfer. While the addition of artificial mediators can support electron transfer from cyanobacterial cells 16,24 , these mediators do not selectively accept electrons from only the charge carriers involved in photosynthesis. Rather, they accept electrons from any of the redox active molecules in the cell with an appropriate midpoint potential.…”

“…This limitation has been identified from multiple, experimental studies which, when taken together, identify membrane transport as the rate-limiting step: (1) rapid, increased photocurrent from isolated photosynthetic membrane fractions containing fewer photosynthetic complexes compared to whole-cell measurements 22 , (2) high currents obtained by inserting a nanoelectrode into the photosynthetic membranes of a chloroplast 67 , (3) improved electron transfer by engineering the electrode surfaces for improved interaction with the cell membrane 18,29,68 , (4) enhanced photocurrent extraction in the presence of membrane-permeable mediators 16,20,69 , and (5) comparative analysis calculating a lower charge extraction rate than predicted from oxygen evolution rates 70 .…”