Fast responding exhaled-breath sensors using WO₃ hemitubes functionalized by graphene-based electronic sensitizers for diagnosis of diseases

Diagnostic sensing device using exhaled breath of human have critical advantages due to the noninvasive diagnosis and high potential for portable device with simple analysis process. Here, we report ultrafast as well as highly sensitive bumpy WO₃ hemitube nanostructure assisted by O₂ plasma surface modification with functionalization of graphene-based material for the detection of acetone (CH₃COCH₃) and hydrogen sulfide (H₂S) which are biomarkers for the diagnosis of diabetes and halitosis, respectively. 0.1 wt % graphene oxide (GO)- and 0.1 wt % thin layered graphite (GR)- WO₃ hemitube composites showed response times of 11.5 ± 2.5 s and 13.5 ± 3.4 s to 1 ppm acetone as well as 12.5 ± 1.9 s and 10.0 ± 1.6 s to 1 ppm of H₂S, respectively. In addition, low limits of detection (LOD) of 100 ppb (R_air/R _gas = 1.7 for acetone and R_air/R_gas = 3.3 for H₂S at 300 °C) were achieved. The superior sensing properties were ascribed to the electronic sensitization of graphene based materials by modulating space charged layers at the interfaces between n-type WO₃ hemitubes and p-type graphene based materials, as identified by Kelvin Probe Force Microscopy (KPFM). Rapid response and superior sensitivity of the proposed sensing materials following cyclic thermal aging demonstrates good potential for real-time exhaled breath diagnosis of diseases.