Solar-converting nanosystems using biomaterial resources carry great potential for developing sustainable technologies to ameliorate climate change and minimize reliance on fossil fuels. By mimicking natural photosynthesis, diverse proof-of-concept biosolar systems have been used to produce green electricity, fuels and chemicals. Although increasingly efficient devices have been reported, notably those with 3D nanostructured electrodes for improved biocatalyst loading and light absorption, the best-performing systems keep employing freely-diffusing toxic mediators and mass transfer processes, precluding a large-scale implementation. To overcome these limitations, a key factor is to ensure efficient electronic communication between biocatalysts and the electrode together with the appropriate orientation of (photo)electroactive protein to achieve the highest possible charge transfer efficiency and minimize wasteful back reactions.
Here, we present a strategy developed in our laboratory to optimize the abiotic/biotic interface by rationally engineering a covalent molecular interface. The metalorganic interface, compatible with various transparent conducting oxide (TCO) and graphenoids, is terminated with nitrilotriacetic acid (NTA) metal complexes. This universal molecular anchors serves to immobilize in an oriented manner His6-tagged proteins, such as biophotocatalysts and other redox-active proteins. The photoelectrochemical properties of the modified TCOs shown that the covalent functionalization induces a p-doping of the electron-rich surfaces, resulting in an enhanced unidirectional cathodic photocurrent up to 1 μA·cm-2.
The engineered interface was furher employed for the construction of biophotovoltaic devices incorporating His6-tagged cytochrome c (a natural electron relay) and photosystem I. In the resulting biophotocathodes, we identified a controllable effect at the abiotic/biotic interfaces essential for achieving more effective vectorial electron transfer. The (bio)nanoarchitectures with a boosted interface depict much-higher photocurrent outputs and faster electron transfer kinetics compared to the unboosted analogs, even in presence of freely-diffusive mediators. These results open a new avenue for efficiently interfacing biomachineries, providing a benchmark design advancement in the quest for viable biohybrid technologies.