Fig 1. Scanning electron micrographs of electroless deposition of Au particles on TNA, showing a wide range of particle sizes (a)-(c). EDS mapping of Au deposits are shown in green on the micrographs (a’)-(c’). The XPS of the Au-TNA electrode shows deposition of metallic Au, attributed to the distinct 4f5/2 and 4f7/2 peaks (d).

Fig. 2. (a) X-ray diffraction pattern of Au-TNA showing anatase phase (A) of titania as well as rutile phase titania (R). Au crystal phase and Ti crystal phases are also identified. (b) Residual plot of Rietveld refinement simulation.

Fig. 3. Raman spectra of (a) TNA shows the peaks at 147, 196, 399, 415, 515, 640 cm-1 (b) Au-TNA multiply by a factor of 10 showing the peaks at 147, 243, 435, 614 cm-1.

Fig. 4. (a) Diffuse-Reflectance spectra of TNA and Au-TNA. The surface plasmon resonance band in the Au-TNA electrode is evident from the excitation band ~490 nm. (a’) The inset plot shows the absorption of Au particles alone. (b) The Tauc plots for indirect band gap transitions (n = 2) for TNA and Au-TNA where used to estimate the bad gap of the materials.

Fig. 5. Amperometeric detection of four volatile organic biomarkers. Graphs (a)-(d) (solid line) depict the Au-TNA sensor response when exposed to light, while the graphs (a')-(d') (dashed line) show the sensor response without exposure to light. A clear enhancement in the signal strength is observed when the Au-TNA sensor electrode is irradiated.

Fig. 6. Schematics depicting proposed Au-TNA sensor response mechanisms. Two mechanisms are proposed to explain the enhanced sensor responses. The first (Scheme 1) is based on band theory, and explains operation without irradiation. The second mechanism (Scheme 2) is based on a cascade charge transfer via size quantization effect of irradiated Au particles.