<p>Achieving reliable chemiresistive gas sensing under breath-like, high-humidity conditions remains a critical challenge due to water-induced charge screening and disrupted surface redox reactions. In this work, we report a 0D/2D Ti₃C₂T_x quantum dot–decorated V₂CT_x MXene hybrid synthesized via a single-step, HF-free in-situ method that simultaneously delaminates the MAX phase and constructs robust Ti–O–V chemical bonds at the interface, which regulate both charge transport and molecular recognition. These engineered linkages provide abundant active sites for H₂S adsorption while enabling efficient charge transport across the heterojunction. Quantum-confined Ti₃C₂T_x QDs act as photocarrier generators, and the metallic V₂CT_x sheets serve as high-mobility electron channels, enabling fast and sensitive signal transduction under low-power UV light (365&#xa0;nm). Crucially, Ti–O–V interfacial motifs and surface –OH terminations create high-affinity adsorption sites that enable proton-assisted H₂S transport through hydration layers, conferring strong selectivity over common interferents (NO₂, SO₂, NH₃, acetone, ethanol) even at high relative humidity. The sensor exhibits linear H₂S responses from 50 ppb to 90 ppm, a low detection limit of ~ 31 ppb, and rapid response/recovery times (8 and 9&#xa0;s, respectively), while maintaining stable operation at 90% relative humidity. In a qualitative breath test, the sensor detected a distinguishable signal increase after garlic consumption, corresponding approximately to a rise from ~ 50 ppb to ~ 180 ppb, based on calibration with standard H₂S concentrations. This study highlights interfacial chemical bonding as a powerful design strategy for next-generation, humidity-tolerant MXene gas sensors with practical applicability in non-invasive diagnostics and environmental monitoring.</p> Graphical abstract <p></p>