A pH-based bio-rheostat: A proof-of-concept

Biological matter is attracting increasing attention because it shows innovative features that have found several applications in technology, from highly sensitive sensors for medical treatments to devices for energy harvesting. Furthermore, most of its phenomenology remains unclear thus giving hints for speculative investigations. In this letter, we explore the possibility to use a well-known photosensitive protein, the Reaction Center of Rhodobacter Sphaeroides, to build up an electrical pH sensor, i.e., a device able to change its resistance depending on the pH of the solution in which it crystalizes. By using a microscopic model previously tested on analogue proteins, we investigate the electrical response of the Reaction Center single protein under different conditions of applied bias, showing the feasibility of the bio-rheostat hypothesis. As a matter of facts, the calculated resistance of this protein grows of about 100% when going from a pH = 10 to a pH = 6.5. Moreover, calculations of the current voltage characteristics well agree with available experiments performed with a current atomic force microscopy under neutral conditions. All findings are in qualitative agreement with the known role of pH in biochemical activities of Reaction Center and similar proteins, therefore supporting a proof-of-concept for the development of innovative electron devices based on biomaterials.