Bio-sourced, potentially biodegradable materials for fast response moisture sensors

Humidity is a very important physical parameter that plays an imperative role in technology and human activity. Researchers are paying more attention to develop moisture-responsive materials with outstanding characteristics such as high sensitivity, wide humidity detection range, fast response and short recovery times to keep pace with the on-going development in technology. Abundant, bio-sourced and biodegradable organic materials, such as melanin, are needed to enable the development of eco-designed technologies that alleviate the environmental footprint of the electronics sector. Melanin is a ubiquitous biomacromolecule with diverse functions including hydration dependent electrical response [1], photoresponse [2], antioxidant [3] , metal chelation [4], and free radical scavenging [5]. Melanin originates from the oxidative polymerization of (5,6)-dihydroxindole (DHI) and (5,6)-dihydroxindole 2-carboxyl acid (DHICA) building blocks [6]. DHI-melanin features ordered, conjugated structure with better electrical conductivity with respect to DHICA-melanin [5]. Herein, we investigate DHI-melanin and DHI-DHICA melanin thin films, spin coated and polymerized on technologically relevant and potentially biodegradable substrates, as active layers for fast response moisture sensors.