Noble Metal-Tailored Surface Engineering Enables Programmable Selectivity in MOS Gas Sensors via Catalytic Pathway Control

Gas sensors are critical for environmental monitoring, industrial safety, and healthcare; yet, achieving target-specific selectivity in complex gas mixtures remains a challenge. Metal oxide semiconductor sensors, though cost-effective, suffer from cross-sensitivity due to poorly understood surface reaction dynamics. While noble metal functionalization improves sensitivity, selectivity mechanisms are often ambiguously attributed to oxygen activation or spillover effects without direct molecular-level evidence. Here, we demonstrate that noble metal-tailored surface engineering of In₂O₃/ITO matrices (functionalized with Au, Pt, Pd, or Ag) enables programmable selectivity by controlling catalytic pathways, as revealed through time-resolved in situ Raman spectroscopy. Unlike conventional approaches, this strategy links selectivity to gas-specific intermediate formation (e.g., formate for HCHO, nitrate/nitrite for NO), providing direct spectroscopic validation of reaction mechanisms previously inferred only indirectly. A four-channel sensor array integrating these materials achieves real-time discrimination of HCHO, NH₃, H₂S, and NO at parts per billion levels, validated by principal component analysis. This work bridges surface chemistry with device design, offering a molecular-level blueprint for gas sensors that transcends trial-and-error methodologies. By elucidating catalytic pathways and enabling multicomponent detection in dynamic environments, the approach advances applications in air quality monitoring, industrial Internet of Things, and personalized healthcare, where precise analyte discrimination in complex matrices is paramount.