Integrating Vacancies and Defect Levels in Heterojunctions to Synergistically Enhance the Performance of H₂S Chemiresistors for Periodontitis Diagnosis

Exhaled breath is considered an important source of samples and a reservoir of biomarkers, especially for disease diagnosis. In this study, we developed an ultrasensitive point-of-care gas sensor for the analysis of hydrogen sulfide (H₂S), which is a typical biomarker for periodontitis. A high-performance metal oxide semiconductor (MOS)-based chemiresistive H₂S sensor was developed by integrating Fe-doped MoO_3-x onto TiO₂ nanotube arrays. The substitution of Fe atoms into MoO_3-x not only induced oxygen vacancies, but also generated defect levels in the MoO_3-x/TiO₂ heterostructure, thus synergistically activating the gas sensing reaction at room temperature under ambient light. The resulting gas sensor exhibited ultrahigh sensitivity, fast response/recovery ability, and wide-range response to H₂S concentrations up to 400 ppm. Furthermore, the sensing device maintained more than 95% of its original response at 70% relative humidity. With a subparts-per-billion limit of detection (the LOD for H₂S was 0.34 ppb), the present sensor represents the most sensitive H₂S chemiresistor reported to date for room-temperature, real-time monitoring of H₂S concentration changes in the breath of healthy subjects, as well as for distinguishing breath samples of periodontitis patients and healthy individuals. This study utilizes the synergistic action of defects to provide an effective route for developing MOS-based ultrasensitive H₂S sensors for periodontitis diagnosis.