Highly Responsive PEG/Gold Nanoparticle Thin Film Humidity Sensor via Inkjet Printing Technology.

In this study, a highly responsive humidity sensor is developed by printing gold nanoparticles (GNP) grafted with a hygroscopic polymer. These GNPs with are inkjet printed to form a uniform thin film over an interdigitated electrode with controllable thickness by adjusting the printing parameters. The resistance of the printed GNP thin film decreases significantly upon exposure to water vapor and exhibits a semi-log relationship with relative humidity (RH). The sensor can detect RH variations from 1.8% to 95% with large resistance changes up to 4 order of magnitudes with no hysteresis and small temperature dependence. In addition, with a thin thickness, the sensor can reach absorption equilibrium quickly with response and recovery times of ≤1.2 and ≤3 seconds, respectively. The fast response to humidity changes also allows the GNP thin film sensor to distinguish signals from intermittent humidification/dehumidification cycles with a frequency up to 2.5 Hz. The printed sensors on flexible substrates show little sensitivity to bending deformation and can be embedded in a mask for human respiratory detection. In summary, this study demonstrates the feasibility of applying printing technology for the fabrication of thin film humidity sensors, and the developed methodology can be further applied to fabricate many other types of nanoparticle based sensor devices.