Noninvasive and Wearable Respiration Sensor Based on Organic Semiconductor Film with Strong Electron Affinity

Interventional medical detection techniques require expensive devices and cause inconvenience and discomfort to the human body, which restricts their application to the frequency and duration of measurements. A noninvasive respiration test is urgently required for the next-generation medical technologies in early disease warning and postoperative monitoring. This article describes a noninvasive and wearable sensing device that shows high sensitivity toward acetone in respiratory gases with excellent stability, low energy consumption, and reliable flexibility. To obtain such a sensor, the organic semiconductor compound La(TBPP)(TBNc) (TBPP = tetrakis(4-tert-butylphenyl)porphyrin; TBNc = tetrakis(4-tert-butylphenyl)naphthalocyanine) was synthesized and further self-assembled into a highly ordered flexible film via a simple solution-vapor annealing method. The fabricated flexible film was deposited on an interdigitated electrode with poly(ethylene terephthalate) substrate and employed as an electrical identification component for a respiration sensor. Thanks to the attractive electron-transfer properties of highly ordered films and strong electron affinity of La(TBPP)(TBNc) molecules, the as-prepared sensor shows a low detection limit (200 ppb) and acceptable selectivity. The wrinkled/rippled structure of films endows the fabricated sensors with the ability of mechanical flexibility. More importantly, the experimental results suggest the potential application of acetone identification in real respiratory gases and provide a new concept for the development of noninvasive and wearable medical diagnostic devices.