Water Soluble Flexible Substrate-Based Humidity Sensor for Transient Sensing

Advancements in smart sensing technologies for biomedical, agriculture, pharmaceuticals, and the Internet of Things (IoT) have driven a growing demand for large-scale sensor production. Many such applications require limited operational lifetimes, making biodegradable transient sensors a promising route toward sustainable, eco-friendly systems. In this work, we present a humidity sensor in which the chitosan-polyvinyl alcohol (PVA) substrate not only provides mechanical support but also serves as the sensing layer with MXene as conducting interdigitated electrodes. The film dissolves completely in water within one day, enabling transient operation, while the MXene-based electrodes can be recovered and reused. The sensor exhibits a clear response to relative humidity in the range of 18-68% Relative Humidity (RH), with a sensitivity of 528% at 68% RH. Additionally, breath monitoring experiments demonstrate its potential for biosensing applications. Biodegradability tests confirm complete degradation of the substrate in soil, water, and acidified water, along with successful recycling of the MXene electrodes. This study demonstrates a sustainable strategy for transient, recyclable, and eco-friendly humidity sensors with practical applications in smart and green electronics.