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Chemoresistive H₂S sensors using various oxide nanoparticles were prepared and heat-treated at 600 °C in an effort to define halitosis in human breath. WO₃, ZnO, and SnO₂ were tested as sensing materials, among which WO₃ showed the highest stability to H₂S. XPS analysis showed a metal sulfate peak on the surface of ZnO and SnO₂, which causes a recovery problem after 2 ppm H₂S exposure. On the contrary, the WO₃ sensor showed a stable signal in long-term operation in the presence of H₂S gas.

WO₃ gas sensors decorated with various catalytic metals were fabricated to investigate their sensing properties in the 0.2–5 ppm H₂S range with 80% relative humidity (RH). A 0.03 wt% Au-doped WO₃ sensor exhibited excellent H₂S sensitivity (R_air/R_gas = 12.40 at 2 ppm) toward H₂S, whereas pure WO₃ showed a sensitivity of 4.85 with negligible interference from the volatile organic compounds (VOCs).