Recent advances in bacteriorhodopsin-based energy harvesters and sensing devices

Highlights: • Bacteriorhodopsin is a purple membrane and light activated proton pumping protein. • Engineering of bR photocycle and its role are discussed with respect to proton pumping activity. • bR-based hybrid electrodes are efficient alternate for sensors, solar/fuel cells, and HER. • Future prospects of bR are addressed in energy, sensing, and information encryption. Bacteriorhodopsin (bR) is a trans-membrane photoactive protein commonly found in the purple membrane of Halobacterium salinarum. In light of the enhanced potential for light-activated proton pumping and color switching, this protein has been adopted favorably as platforms for versatile applications such as solar cells, fuel cells, biosensors, artificial retinas, optical devices, nanosensors, storage devices, camouflage, bio-defense, holographic memory, and security ink. This review is organized to highlight the photocycle of bR which can be modified through mutation. Because of high stability and proton-release characteristics, bR is regarded as an attractive platform for the production of hydrogen through the splitting of water to help maintain a sustainable economy based on renewable energy. In this review, recent advances in bR-based hybrid electrodes are summarized for their applications toward solar cells, water-splitting devices, and fuel cells. Further, emerging applications of bR in sensors and security inks are also discussed to apprise researchers of the potential and challenges in bR research.