Highly Sensitive and Selective NiO/WO3 Composite Nanoparticles in Detecting H2S Biomarker of Halitosis.

Indirectly monitoring halitosis via the detection of hydrogen sulfide (H2S) biomarkers using gas sensors is a newly emerging technique. However, such H2S sensors are required with critically high selectivity and sensitivity, as well as a ppb-level detection limit, which remains technologically challenging. To address such issues, here, we have developed highly sensitive and selective H2S sensors with NiO/WO3 nanoparticles (NPs), which have been synthesized by firstly hydrolyzing WO3 NPs and subsequently decorating with NiO NPs in a hydrothermal process. Theoretically, the NiO/WO3 NPs assist in forming a thicker electron depletion layer, adsorbing more oxygen species O2- to oxidize H2S and finally release more electrons. Beneficially, 2.1 wt % NiO/WO3 NPs show high sensitivity to H2S (Ra/Rg = 15031 ± 1370 @ 10 ppm, 100 °C), which is 42.6-fold higher than that of the pristine WO3 NPs (Ra/Rg = 353 ± 5.6 @ 10 ppm, 100 °C). Further, the H2S sensor shows ppb-level detection limit (Ra/Rg = 4.95 ± 2.9 @ 0.05 ppm, 100 °C) and high selectivity. Practically, NiO/WO3 NP sensor prototype has been employed to detect the simulated exhaled halitosis compared with that of gas chromatography, revealing a close concentration of H2S. Our investigation offers an experimental base in future intelligent medical applications.