Metal-Organic Framework Induced Prenucleation to Construct Solid Solution Semiconductor Metal Oxides With Synergistic Enhancement of Moisture Resistance and Gas Response.

Accurately resolving trace acetone against the highly humid background of exhaled breath remains a central obstacle to non-invasive diabetes diagnosis. Here we develop a metal-organic framework (MOF)-conversion-induced prenucleation strategy for the controlled construction of Fe2TiO5-δ (FTO) solid solutions. During the topological transformation of MIL-125(Ti), Ti-derived oxide nuclei form within the pores of a daughter Fe-based MOF, enabling the generation of FTO enriched with mixed-valence Fe3+/Fe2+ and Ti4+/Ti3+ centres and abundant oxygen vacancies. The optimized FTO-3.49 sensor selectively detects acetone across 30-90% relative humidity, reaches a detection limit of 100 ppb and distinguishes ppb-level acetone concentrations in simulated exhaled breath. This performance is underpinned by mixed-valence centres that limit water-induced hydroxyl accumulation and oxygen vacancies that create additional adsorption sites and strengthen acetone binding, as supported by spectroscopic and computational evidence. This defect-valence synergy enables stable acetone sensing under highly humid conditions and provides a materials-design route towards humidity-resilient metal-oxide sensors for breath-acetone analysis.