Three-Dimensional Conductive Conjugated Polyelectrolyte Gels Facilitate Interfacial Electron Transfer for Improved Biophotovoltaic Performance

Living biophotovoltaics represents a potentially green and sustainable method to generate bio-electricity through rewiring of photosynthetic electron transport chains (P-ETCs) to interconnect photosynthetic bacteria to electrodes. However, barriers to electron transfer across the abiotic/biotic interface hinders solar-to-electricity conversion efficiencies. Herein, we report on a facile method to improve interfacial electron transfer by combining the photosynthetic cyanobacterium Synechococcus elongatus PCC 7942 (Syne) with a conjugated polyelectrolyte (CPE) atop indium tin oxide (ITO) charge-collecting electrodes. By self-assembly of the CPE with Syne, soft and semitransparent Syne/CPE biocomposites are formed with three-dimensional conductive networks that exhibit mixed ionic-electronic conduction. These specific structures rewire an artificial P-ETC from bacteria to electrodes, allowing for improved and sustained photocurrent output compared to the performance of bacteria alone. Electrochemical studies confirmed the enhanced interfacial electron transport efficiency via the artificial P-ETC. Furthermore, microscopic photocurrent mapping for the biocomposites down to the single-cell level revealed a ~0.2 nanoampere output per cell, which translates to a 10-fold improvement relative to that of bare Syne, corroborating highly efficient long-range electron transport from Syne to the electrode via the three-dimensional CPE structure. This synergistic combination of biotic and abiotic materials underpins the significantly improved performance of biophotovoltaic devices, providing broader insights into the electron transfer mechanisms in a variety of bio-hybrid systems within semi-artificial photosynthesis and bioelectronic devices.