Integration of PANI-SnO2 heterojunctions with portable optical microfibre for advanced operando ammonia gas sensing

In this work, we propose a synergistic framework between a p-n heterojunction and an optical microfibre for gas sensing, in which an n-type semiconductor, SnO 2 , and a p-type semiconductor, polyaniline (PANI), form on surface of the optical microfibre at room temperature. Owing to the strong interaction between evanescent waves and carriers of semiconductors, the device could detect ammonia gas with a high sensitivity of 3.98 pm/ppm and an extremely low theoretical limit of detection (LOD) of 15.2 ppm. Importantly, its ultrafast response time is experimentally achieved at 11 s with a recovery time of 7 s, which is lower than those of most reported ammonia gas sensing technologies. Based on the proposed innovative integration of optical fibre with a p-n heterojunction sensing strategy, this work could provide a new way to promote more high-performance hybrid optical and semiconductor sensing platforms.