Unveiling the Doping Effect of Sub-4 nm Ultrathin SnO₂ Quantum Wires on Gas Sensors

The analysis of exhaled human breath has great significance for early noninvasive diagnosis. However, highly sensitive and selective detection against part-per-billion (ppb) biomarkers in exhaled human breath (RH ≥80%) at room temperature remains a challenge. SnO 2 quantum wires (QWs) consisting of a few hundreds to thousands of atoms are demonstrated to be promising for low-power consumption gas sensors to achieve an on-chip electronic nose. Here, we propose a low-temperature doping strategy in realizing the synthesis of the transition metal (Mn, Cr, V)-doped SnO 2 QWs. The doped SnO 2 QWs with sub-4 nm diameters as chemiresistive gas sensors enable us to improve the adsorption activities, achieving enhanced room-temperature sensing properties toward the trace biomarkers ( e.g., acetone, formaldehyde, and H 2 S) with the state-of-the-art limit of detection of 2.6, 1.5, and 1.3 ppb, respectively. These transition metal-doped SnO 2 QWs are then integrated as a sensor array, enabling gas identification at different relative humidities by using machine learning algorithms. Moreover, systematical characterizations combined with density functional theory (DFT) calculations are conducted to figure out the effect of doping on SnO 2 QW properties for the sensitive and selective ppb-level gas detection. The engineering of transition metal-doped SnO 2 QWs helps us to extend the library for the design of low-power consumption gas sensors in more broad applications.