Ultrasensitive Organic Humidity Sensor with High Specificity for Healthcare Applications

Abstract

Humidity sensors have gained immense importance as non-invasive, wearable healthcare devices for personal care as well as disease diagnostics. However, non-specificity, poor stability at extreme conditions, and low sensitivity of the humidity sensor inhibit its usage as a health monitoring device. In the present study, N−F containing organic molecule, SelectfluorTM (F-TEDA) based humidity sensors with ∼1–2 mm long needle-shaped crystals is fabricated on interdigitated electrodes resulting in excellent performance. The unidirectional growth of crystals led to the formation of a conduction pathway for water molecules across the crystal, which otherwise are non-conducting. The as-fabricated humidity sensor at an operational voltage of 0.8 V displays a sensitivity of six orders in magnitude, best reported so far. The sensor does not exhibit any response upon exposure to various volatile organic compounds and reactive gases, indicating remarkable specificity. The sensor is tolerant to high moisture of 95 % for prolonged hours followed by monitoring over several days and degrades to 50 % of its original sensitivity only after continuous exposure for several days. Electrochemical impedance spectroscopy (EIS) shows reversal from resistive to capacitive behavior with increasing humidity levels. The fabricated humidity sensor acts as a healthcare device for breath rate monitoring and touch-free examination of skin moisture.