The application of highly sensitive pH sensors manufactured in volume at low cost has great commercial interest due to an extensive array of potential applications. Such areas include industrial processing, biotechnology and medical diagnostics particularly in the development of point of care (POC) devices. A novel printable electrochemical pH sensor based on graphene and pigment melanin (PGM), was designed and produced by using a screen printing process that enables up scaling for potential commercial application. We demonstrate a highly sensitive pH sensor (62 mV pH⁻¹ ± 7) over a pH range from 5 to 8, with high stability and superior performance when compared with a number of existing devices and making it suitable for physiological applications.

Melanin is a generic term evoked for a broad class of indole/quinone-based natural pigments, mainly known for its primary role in photoprotection. Throughout the last couple of decades, melanin and melanin-like materials garnered a lot of attention as a soft biocompatible functional material for bioelectronic and optoelectronic devices due to their water-dependent conductivity and excellent biocompatibility. However, in the earlier days, the limited solubility and low electronic conductivity have hindered their progression in such technological helms. Currently, these issues have been overcome by different strategies. This review briefly updates the physical–chemical properties of melanin and melanin-inspired materials, and their technological problems and applications. We also emphasize some chemical tailoring procedures for synthesis and processing.

Optical and electrical properties of soluble melanin were discussed based on different chemical structures.