Lever-inspired triboelectric respiration sensor for respiratory behavioral assessment and exhaled hydrogen sulfide detection

Abstract

Enhancing the flow sensitivity of the triboelectric respiration sensors (TRSs) is crucial in detecting shallow oral/nasal breath signal. The modulation of contact-separate distances between dielectrics is a simple and convenient tactic to enhance the output sensitivity of TRSs compared with the complex composite materials and microstructure design of the triboelectric dielectrics. Herein, a lever-inspired TRS with adjustable contact-separate distances between arms was designed for simultaneous respiratory behavioral assessment and exhaled hydrogen sulfide (H2S) detection. Results show that the TRS with the optimal length ratio of power arm to resistance arm (1:2) possesses excellent respiration sensing behaviors in measuring flow rate (0.5–8 L/min) and frequency (0.25–1 Hz), enabling the flow sensitivity under oral/nasal respiration. Meanwhile, an in-situ self-assembled Fe2+ doped polypyrrole (FPPy) sensing film was rationally selected as one of the back electrodes of triboelectric layers owing to the selective reaction between ferrous ions (Fe2+) and H2S. Under the optimal synthesis condition of FPPy film, the prepared TRS exhibits good H2S sensing performances, including a high response of 25.21% (10 ppm), good sensing repeatability (±0.46%), and low detection limit (1 ppm). Finally, a sensing mechanism on account of the impedance variations is proposed and verified based on the composition changes of the sensing materials unveiled by multiple analytical methods. This work proposes an effective way for building a flow-sensitive respiration monitoring device, and provides new insights into the impedance-induced sensing mechanism via establishing a linkage between interfacial gas chemisorption and output signals.