Magneto-Photoactivated Gold Plasmonic Nano-Islands and Quantum Dot Assemblies for ppt-Level NO₂ Detection

The intrinsic instability and limited chemical reactivity of metal nanoparticles have long restricted their direct integration in chemiresistive gas sensing. Here, we present a highly selective, tunable, ultra-stable, and ultra-sensitive NO₂ sensor derived from gold nano-islands (GNIs) and quantum dot (QD) assemblies anchored on a reactive sodium aluminophosphosilicate glass matrix (H1-glass). Thermal dewetting of sputtered Au films at 550°C under ambient conditions initiates a reactive glass-metal interaction (RGMI), leading to the formation of Au-rich core/semiconducting shell GNIs along with spatially dispersed QDs on the glass surface. Magnetometry and magnetic force microscopy reveal the emergence of room-temperature ferromagnetism across the GNI array. The resulting H1-Au sensor, featuring robustly embedded GNIs and QDs, demonstrates an exceptional chemiresistive response of 73.5% toward 40 ppm NO₂, with a remarkable detection limit of 50 ppb, and maintains full functionality at temperatures down to 0°C. Notably, the synergistic application of external magnetic fields and light irradiation further amplifies the sensor response to 11.67% at an ultralow concentration of 50 ppt NO₂, outperforming all previously reported chemiresistive gas sensing platforms. These findings establish RGMI-stabilized GNIs as a highly reliable and versatile platform for ultra-trace, low-temperature gas detection, with broad implications for chemical, environmental, and biomedical monitoring applications.