Dual valence of Fe ions in ZnO nanofibers: Enabling rapid response and high selectivity for the listeria biomarker 3-hydroxy-2-butanone

Listeria monocytogenes is a life-threatening foodborne pathogen, and indirect detection via its specific metabolite 3-hydroxy-2-butanone has emerged as a validated strategy. However, reliable early monitoring of LM requires rapid response kinetics for real-time analysis and high selectivity against food-derived volatile organics, and achieving both simultaneously at the ppb level remains a significant challenge. Herein, we have synthesized Fe-doped ZnO nanofibers and the introduction of Fe induces the formation of a mixed Fe 2 + /Fe 3+ valence that facilitates dynamic redox cycling, thereby enhancing charge transfer efficiency and creating additional active sites to improve gas-sensing performance. Systematic gas-sensing evaluations showed that the 0.5% Fe-doped ZnO sensor exhibits an optimal response of 168.9–100 ppm 3H-2B at 170 °C, with a rapid response time of 2 s and a low detection of 110 ppb, significantly outperforming the undoped ZnO and higher Fe-doped counterparts. X-ray photoelectron spectroscopy confirmed the coexistence of Fe 2+ /Fe 3+ , whose dynamic redox cycles enhanced electron exchange between the nanofibers and 3H-2B, thereby boosting sensing performance. This study offers an economical method for 3H-2B detection and demonstrates variable-valence Fe is a potential dopant to tailor ZnO-based gas sensors toward food safety and environmental applications.