Electronic Transport in Porous Nanocrystals Enables Ultrasensitive Consistent Detection of Sulfur Dioxide under Variable Humidity

The growing release of gaseous pollutants, such as sulfur dioxide (SO2), underscores the need for widely distributed monitoring and reliable electronic sensing platforms capable of detecting trace concentrations of such contaminants under real-world conditions. However, achieving high sensitivity and selectivity, while maintaining stable, reproducible sensing performance with conductive materials, particularly under fluctuating humidity, remains a significant challenge. This work reports a highly crystalline, conductive tetrapyrazinoporphyrazine (TPz)-based metal-organic framework (MOF), DC-103, featuring cobalt-centered TPz ligands and copper bis(dioxolene) linkages. DC-103 exhibits rapid, robust, and humidity-resistant chemiresistive responses toward SO2 across diverse environments. Notably, DC-103 outperforms previously reported MOF-based SO2 sensors, achieving a limit of detection as low as 2.2 parts-per-billion (ppb) in air and maintaining consistent, reversible responses across 0-98% relative humidity levels. Furthermore, the sensor demonstrates excellent reusability in humid air, retaining consistent responses upon repeated exposures. Spectroscopic and computational analyses revealed distinct material-analyte interactions and redox changes of MOF components and sulfurous species under dry or humid nitrogen or air atmospheres. Collectively, these findings establish DC-103 as a robust chemiresistive sensor for SO2, with superior performance compared to structurally analogous or control structures, demonstrating applicability across diverse atmospheric conditions, and offering significant potential in occupational safety and environmental monitoring.