Room-Temperature NH₃ Gas Surface Acoustic Wave (SAW) Sensors Based on Graphene/PPy Composite Films Decorated by Au Nanoparticles with ppb Detection Ability

Exhaled human breath analysis has great potential for the diagnosis of diseases in non-invasive way. The C-13-Urea breath test for the diagnosis of Helicobacter pylori infection indicates the ammonia concentration of 50-400 ppb in the breath. This work successfully developed a surface acoustic wave (SAW) resonator based on graphene/polypyrrole composite films decorated by gold nanoparticles (AuNPs-G/PPy) with sensitivity and selectivity to detect ammonia in parts-per-billion concentrations, which is promising for the accurate diagnosis of H. pylori infection. XRD, EDS, and SEM characterized the AuNPs-G/PPy nanocomposites, providing comprehensive insights into their structural, compositional, and morphological properties. The gas-sensing capabilities of the fabricated SAW sensors were extensively investigated, focusing on their response to NH3 gas at ambient temperature. The concentration of ammonia gas was effectively quantified by monitoring the frequency shift of the SAW device. Notably, our developed SAW sensor demonstrated outstanding sensitivity, selectivity, repeatability, and reproducibility for 50-1000 ppb NH3 in dry air. The excellent sensing performance of the AuNPs-G/PPy hybrid composite film can be attributed to the synergistic effects of graphene's superior conductivity, the catalytic properties of gold nanoparticles, and the conductivity sensitization facilitated by electron-hole recombination on the polypyrrole surface.