Synthesis of water-soluble dopamine–melanin for ultrasensitive and ultrafast humidity sensor

Abstract

Natural melanin plays a vital role in living organisms, and is completely insoluble in almost all solvents. This article describes a simple method to synthesize water-soluble dopamine–melanin based on a new finding and the pH-dependent solubility of the dopamine–melanin. Use of the water-soluble dopamine–melanin in the humidity sensor system allows for the convenient and time-saving fabrication of dense and uniform films at the nanoscale, and features high device performance. The sensitivity of the thin-film humidity sensor made from such dopamine–melanin was evaluated as a more than five orders of magnitude change in resistance with relative humidity (RH) ranging from 100% to 0%. The dopamine–melanin sensor exhibited excellent response (0.42–0.47s) and recovery (0.43–0.49s) times under dynamic test, which are about one to two orders of magnitude faster than those of devices based on conventional inorganic materials.