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

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 (0.42-0.47 s) and recovery (0.43-0.49 s) times under dynamic test, which are about one to two orders of magnitude faster than those of devices based on conventional inorganic materials. (C) 2015 Elsevier B.V. All rights reserved.