High-Performance Ammonia Sensor Based on Bromocresol Green-Modified Visible Ag/PEEK Flexible Hollow Fiber: Theoretical Optimization, System Construction, and Breath Detection

The rapid detection of ammonia in human breath has significant research value in clinical diagnosis and health monitoring. In this study, we reported a bromocresol green (BCG)-modified silver-coated poly(ether ether ketone) hollow fiber (Ag/PEEK HF) ammonia gas sensor. The sensor cleverly utilizes flexible Ag/PEEK HF as a visible light transmission waveguide and gas chamber, with a BCG molecule layer deposited on its inner surface as the sensing medium. A theoretical optimization model for the sensor was developed based on geometric optics principles and the Beer–Lambert law. Sensitivity enhancement and system miniaturization were achieved through fiber bending, and experimental results agreed with theoretical predictions. The results indicate that the optimal BCG concentration for the system is 1 mg/mL. When the hollow fiber is bent at a 360° angle with a bending radius of 15 cm, the 120 cm-long BCG-Ag/PEEK HF sensor provides optimal sensing performance. The sensor demonstrates excellent reversibility and selectivity, achieving a detection limit as low as 50 ppb. The response and recovery times to human exhaled ammonia were 2 and 17 s, respectively. The sensor exhibited a relative standard deviation (RSD) of 6.82% and a measurement accuracy of 94.76%. With its miniaturized design and real-time monitoring capability, the sensor shows great potential for applications in noninvasive diagnosis of metabolic diseases, postoperative monitoring, and personalized healthcare.