Graphene quantum dots as a novel sensing material for low-cost resistive and fast-response humidity sensors

A room temperature graphene quantum dots (GQDs) based sensing material for relative humidity monitoring is presented. GQDs are synthesized by pyrolysis of citric acid and are deposited on a metallic interdigitated microelectrodes by drop-casting technology. GQDs are nanosheets around 20nm in average lateral size and an average height of 2.7±0.9nm. The response time is around few seconds and the sensitivity shows an exponential relation between 15 and 80% of RH, in resistive configuration device working at room temperature. The electrical changes as a function of the RH are related to the capillary condensation produced on the surface of the GQDs. Due to this physical behavior, a resistive path is formed between the microelectrodes and the condensed water vapor, and the resistivity of the system diminishes as the RH increases. A comparison on real time between the sensor developed and a commercial device corroborates the potential application of the novel sensor presented in this work.