Ultra-Fast Humidity Sensor for Breath Monitoring Using Cellulose Nanocrystal Film Derived from Banana Trunk

Cellulose nanocrystal (CNC) is synthesized from banana trunk due to their easy availability and high abundance. The cellulose nanocrystal is functionalized by amine to augment its optoelectronic properties. CNC film has been fabricated by solution casting method. In this letter, we report free-standing amine functionalized cellulose nanocrystal films as flexible sensors for organic Resistive Breath sensors. The structural characterizations reveal a high degree of crystallinity, 97% for amine-functionalized CNC with a diameter of about 17 nm. The response of the fabricated sensor to mouth breathing is examined under exhalation and inhalation at ambient conditions. Various breathing patterns of a healthy adult are identified, as slow breathing, normal breathing, and rapid breathing. The sensor exhibits an ultrafast response and recovery time of approximately 180 milliseconds, along with good repeatability. Additionally, the sensor achieves a high sensitivity of 10.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>A/%RH, confirming its suitability for humidity-based breath detection applications in wearable and health-monitoring systems.