Flexible Mo2CTx/MoSe2 Heterostructure Sensors for Ultrasensitive, Room-Temperature Detection of Exhaled H2S in Periodontitis Diagnosis.

Oral hydrogen sulfide (H2S) level is a critical biomarker for noninvasive periodontitis, making its sensitive and selective detection essential for early diagnosis and real-time monitoring. However, current sensing technologies still face significant limitations in achieving high sensitivity, selectivity, and stability within the complex oral environment. In this study, we report the development of an integrated heterostructure of two-dimensional Mo2CTx-modified MoSe2 (Mo2CTx/MoSe2 composite), tailored for room temperature H2S detection in periodontitis diagnosis. The composite synergistically combines the high electrical conductivity and abundant surface defects of Mo2CTx with the bandgap tunability and chemical specificity of MoSe2, yielding an outstanding gas-sensing performance. The optimized Mo2CTx/MoSe2 sensor (0.5 wt % Mo2CTx) demonstrated a high response (ΔR/R0 = 629% to 10 ppm of H2S), an ultralow detection limit (22 ppb), and superior selectivity (3.9-628 times against interfering gases). Moreover, it exhibited excellent long-term stability (<11% signal drift over 40 days) and mechanical robustness, underscoring its suitability for clinical deployment. Density functional theory simulations revealed that enhanced sensing performance arises from strong electronic coupling at the heterointerface, accelerated charge transfer, and efficient molecular activation of H2S. Real-time breath analysis confirmed the sensor's ability to dynamically track trace H2S levels, enabling effective discrimination between healthy individuals and periodontitis patients. This work presents a robust and scalable strategy for the early diagnostic screening of periodontitis and lays the groundwork for next-generation wearable or smart diagnostic platforms in oral healthcare.