Fabrication of Microsensor for Detection of Low-Concentration Formaldehyde Gas in Formalin-Treated Fish

Here, an ultrafast direct laser patterning technique to fabricate a low-cost microsensor and its application for formaldehyde detection are reported. The patterns of microheater and interdigitated electrodes (IDEs) were realized using laser micromachining techniques by ablation of gold thin film on alumina substrate. The thin film of gold microheater showed good stability up to 300 °C with a fast response time of 80 s and temperature coefficient of resistance (TCR) was calculated as $1.37\times 10^{-{3}}/^{\circ }\text{C}$. Moreover, gold microheater exhibited long-term reliability under self-heating mode with a negligible resistance drift < 0.5% over a period of 330 h at 250 °C through consuming low power with a heating efficiency of 0.23 °C/mW. Thermal imaging camera revealed the uniform temperature distribution with negligible heat gradient profile over the whole microsensor platform. To state-of-the-art gas sensing application of this coplanar sensing platform, a nanostructured SnO2 was deposited on IDE, which exhibited high sensitivity (13.96% ppm $^{-{1}}$ ) to formaldehyde even to detect sub-ppm concentrations with fast response (32 s) and recovery kinetics (72 s). Moreover, the microsensor was also used on-site rapid screening for the detection and quantification of formaldehyde concentration in formalin-treated fish sample.