Mechanism-Informed Design Framework of Nanocrystalline Semiconductor Chemiresistors Enabling Room-Temperature, ppb-Level, Dual-Redox Gas Sensing.

Wearable breath and environmental monitoring require room‑temperature gas sensors that detect oxidizing pollutants and reducing biomarkers at trace levels. Most nanocrystalline chemiresistive sensors are still optimized by an isolated strategy, which struggles to account for the complex interplay of material parameters and their ambiguous individual contributions. Therefore, this trial-and-error approach is inefficient for enhancing the coupled gas-adsorption and charge-transfer steps, particularly when aiming for multiple gases with opposite redox characteristics. Here, we establish a mechanism‑informed design framework for semiconductor chemiresistors based on the PbS nanocrystal (NC) thin films. The framework synergistically tunes materials and device parameters (surface chemistry, NC size and facets, film thickness, carrier density, and band edges) and couples them to a parameterized COMSOL model to predict and elucidate gas-sensing performance. For oxidative NO2, the framework identifies Cd‑enriched surfaces, 5.3 nm particle sizes, and three-layer films as the optimal parameters, yielding a room‑temperature response of ∼1936 at 1 ppm. Extending the framework to acetone, a reducing volatile organic compound scarcely explored with NC-based sensors, leads to S‑surface-enriched 3.3 nm diameter NCs and bilayer films, enabling an ultralow room‑temperature limit of detection (LOD) of 0.23 ppm. Finally, the pixelated sensor is designed to realize dual‑redox gas sensing, maintaining low LODs and producing distinct signatures for gas mixtures. This work provides a generalizable, simulation‑assisted platform for the rational design and integration of high‑performance, low‑power chemiresistive gas sensors.