Beyond band diagrams: Quantum-dot-engineered heterointerfaces for low-temperature chemiresistive gas sensing-mechanisms, operando evidence, and reliability

Quantum-dot (QD)-engineered heterointerfaces offer a versatile route to low-temperature chemiresistive gas sensing through tunable electronic structure, large surface-to-volume ratio, short charge-transfer distances, and interface-sensitive transport. Yet QD incorporation simultaneously changes particle size, accessible area, defect and ligand chemistry, porosity, carrier transport, and network connectivity. Enhanced response therefore does not, by itself, demonstrate quantum confinement or heterojunction-controlled transduction. This critical review evaluates metal-oxide, chalcogenide, carbon-based, two-dimensional, and multicomponent QD sensors operating from room temperature to approximately 150 °C. It distinguishes quantum confinement from classical full-volume depletion; classifies architectures by gas access and current path; and examines competing contributions from interfacial barriers, defects, catalytic sensitization, phase conversion, ligands, and diffusion. Particular emphasis is placed on evidence capable of testing mechanism claims, including size-controlled comparisons, measured energy levels, work-function and impedance analysis, operando vibrational and photoelectron spectroscopy, isotope experiments, product analysis, and experimentally constrained computation. Humidity, mixed gases, incomplete recovery, baseline drift, QD oxidation or coalescence, interface reconstruction, manufacturing variability, and measurement-system artefacts are treated as parts of sensor function rather than secondary complications. The review consolidates practical validation, reporting, and design rules that connect material response to mechanistic confidence, reliability, and application fitness. Its central conclusion is that trustworthy QD gas sensors require orthogonal evidence under realistic conditions and optimization of the complete sensing system, not response maximization alone.