Imperceptible and Disposable Humidity and Temperature Sensors with Low Environmental Footprint Enabled by Aerosol Jet Printing and Cellulose-Based Substrates.

The continuous growth of the electronics industry requires a reevaluation of traditional materials and manufacturing techniques to address the rising issue of electronic waste (e-waste). Environmental monitoring devices, which provide valuable insights into factors such as humidity and temperature, currently rely on non-degradable substrates and toxic metals, significantly contributing to plastic and electronic waste. Furthermore, conventional manufacturing techniques like screen printing, while effective, are limited in their ability to produce miniaturized, high-resolution features. Here, aerosol jet printing is used to fabricate devices for humidity and temperature monitoring, enabling minimal footprint (99.75% material reduction vs other printing methods), and precise patterning of features as small as 13 µm, even on biodegradable substrates. The resistive sensor is made of biocompatible conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) on a biodegradable cellulose substrate. It operates efficiently within a 10-80% RH range while maintaining a high optical transmittance of 91% in the visible spectrum. Additionally, by crosslinking PEDOT:PSS with (3 Glycidyloxypropyl)Trimethoxysilane (GOPS), the sensors effectively detects changes within a temperature range of 20-50 °C. This fully printed sensor on biodegradable substrates represents a step toward next-generation, eco-friendly, and metal-free solutions for environmental monitoring while minimizing ecological impact.