Ultrasensitive and Wide-Range-Detectable Flexible Breath Sensor Based on Silver Vanadate Nanowires

Breath sensors capable of integrating with the soft, curvilinear surfaces of human skin in an intimate, noninvasive fashion can offer many opportunities for diagnosing and treating respiratory-related disease such as breathlessness, bronchial asthma, and central sleep apnea. For such applications, highly sensitive and wide-range-detectable humidity sensors that can overlie the skin under the nose conformably for continuous and real-time breathing monitoring are highly desirable. Here, we propose an ultrasensitive flexible breath sensor based on silver vanadate nanowires (AgVO₃ NWs). The AgVO₃ NWs synthesized by a hydrothermal method are active semiconductors featuring a large specific surface area, which are highly sensitive to humidified air and can detect 20% relative humidity (RH) to 90% RH at room temperature. By merging the AgVO₃ NWs with a Au interdigitated electrode on a polyimide (PI) substrate, we prepared a flexible AgVO₃-NW-based breath sensor that exhibited about a 1 order of magnitude of resistance variation with a response time of 0.6 s and a recovery time of 1.2 s during exhaling and inhaling. The cyclic experiment results demonstrate that the sensor has excellent consistency and repeatability to follow human breath with different breathing rates, indicating that it can be used for long-term, ambulatory respiratory monitoring. Also, the sensor can be applied for prewarning of sleep apnea syndrome in a facile way when combined with an apnea alarm module built by microprogrammed control unit (MCU) circuitry.