Abstract
This study presents a flexible humidity sensor fabricated using a triacetyl cellulose (TAC) substrate coated with a rice powder thin film (RPTF) as an edible sensing layer via a simple drop-casting technique and demonstrates real-time breath rate monitoring. Unlikely other flexible substrates, TAC offers enhanced mechanical stability and flexibility, enabling robust and conformal device performance under repeated humidity cycling caused by breathing. The RPTF sensing layer exploits resistive variations induced by moisture absorption/desorption during breathing, achieving a sensitivity of ~8.8 nA/% RH. The sensor demonstrates rapid response/recovery behavior, with inhalation/exhalation times of 0.7/0.8 s and 0.8/0.8 s during nose and mouth breathing, which enables accurate real-time monitoring of respiratory cycles. Moreover, a real-time breath rate monitoring system was implemented to monitor different breath patterns of 15, 27, and 10 breaths per minute (bpm) under normal, fast, and slow breathing conditions, respectively, during physiological activity. These results establish that this nature-derived sensor is a sustainable and effective alternative for real-time breath rate monitoring, paving the way toward low-cost and user-friendly wearable sensors for personalized healthcare.