Target-Driven Z-Scheme Heterojunction Formation for ppb H₂S Detection from Exhaled Breath at Room Temperature

As a biomarker of periodontitis, sensitive and timely monitoring of hydrogen sulfide (H₂S) in exhaled breath at room temperature (RT) is important for the early intervention of oral diseases. However, the required high operation temperature to achieve high sensitivity is still a technical challenge for directly monitoring exhaled breath. In this study, by integrating metal-organic frameworks (MOFs) into self-aligned TiO₂ nanotube arrays (NTs), a chemiresistor gas sensor with outstanding sensitivity and selectivity was constructed for the detection of H₂S at RT. The precise regulation of a Co(III)-based MOF CoBDC-NH₂ (BDC-NH₂ = 2-aminoterephthalic acid) not only induced more active surface for the preconcentration of the target gas but also caused a buildup of Z-scheme heterojunctions in the H₂S atmosphere that induced an ultrahigh sensitivity at RT via 365 nm light-emitting diode irradiation. The response and recovery times decreased to ∼50 and ∼28%, respectively, when this system was exposed to UV light. The sensing chips based on the as-prepared TiO₂/CoBDC-NH₂ NTs exhibited the highest-ranking H₂S sensing performance, i.e., a limit of detection of 1.3 ppb and excellent selectivity even to 100 times high concentration of interference gases, owing to the synergistic chemical environment provided by NH₂-functionalized Co-MOFs and abundant photogenerated electrons provided by Z-scheme heterojunctions. This sensing chip was also used in a practical application for the timely monitoring of halitosis from direct exhaled breath. This study provides a reliable and sensitive design for clinically aiding the timely detection of H₂S in a complex oral environment.