Gold-Nanoparticle-Based Flexible Humidity Sensor for Breath Monitoring and Smart Irrigation Systems

In the realm of the Internet of Things, humidity monitoring is imperative for the progressive evolution of intelligent technology within the domains of healthcare, agriculture, and industry. Herein, a resistive-type, multifunctional, and highly sensitive gold-nanoparticle-based humidity sensor was developed, which has a whopping ∼5 orders of resistance change in response to humidity variation from 40%RH to 95%RH. The sensor exhibits excellent sensitivity (28.6 MΩ/%RH), high thermal stability (in the usual working temperature range 25–50 °C), high flexibility (under different bending radii from 18 to 24 mm), prolonged shelf life (∼190 days), and short response/recovery time (∼206/∼280 ms toward respiration monitoring). Owing to these merits, the fabricated sensor has been illustrated for applications like respiration monitoring, non-contact sensing, and soil moisture monitoring. Furthermore, we have designed and demonstrated a smart irrigation system by integrating the gold-nanoparticle-based non-contact humidity sensor for the first time with an Arduino microcontroller. This device is designed to continually observe the soil moisture level using a calibration algorithm that monitors the humidity and supplies water to the crop plant according to a preset threshold. This helps in intelligent assessment and response to the moisture content of the soil in real time.