One-Step In Situ Inkjet Printing Fabrication of Au-Decorated Polyaniline on MEMS Platforms for Sensitive Ammonia Sensing at ppb-Level.

High-performance ammonia (NH3) sensors play a critical role in environmental protection and noninvasive medical diagnosis. This work reports a new NH3 sensor based on Au-microsphere-decorated polyaniline (PANI) manufactured by a precise in situ inkjet printing method on a MEMS micro-hotplate. The in situ oxidative polymerization of aniline was performed directly on the MEMS platform using AuCl3 as a bifunctional oxidant and precursor, with a hierarchical morphology of microspheres (~750 nm) and nanorods (~250 nm). Reduced from Au3+ in the polymerization reaction, Au microparticles achieve substantial catalytic promotion by virtue of chemical sensitization and spillover effect. The optimized Au-PANI MEMS sensor exhibits a superlative response of 201% toward 1 ppm NH3 at room temperature, with an ultra-low theoretical limit of detection (LOD) of 0.42 ppb. Furthermore, the device demonstrates rapid response/recovery kinetics (76 s/72 s), exceptional selectivity against common interfering gases (SO2, CO, H2, etc.), and robust long-term stability with high response retention over two months. This research provides a scalable, cost-effective strategy for the mass production of miniaturized, high-sensitivity gas sensors for industrial and healthcare applications.