Design and Fabrication of a Capacitive Sensor for the Detection of Formaldehyde in Fish at Room Temperature

Traders and suppliers have been artificially extending the shelf life of raw fish using formaldehyde (HCHO). This practice leads to significant health risks, including renal injury, nasopharyngeal cancer, and severe abdominal pain after consuming cooked fish contaminated with formaldehyde. Consequently, detecting formaldehyde in fish has become a critical area of research. A portable metal-insulator-semiconductor (MIS) capacitive sensor ( $20\times 20$ mm) with a silver (Ag) metal patch electrode has been fabricated for rapid detection of formaldehyde from formalin-treated raw fish. Here, reduced graphene oxide (rGO) is used as a sensing material deposited on $\text {SiO}_{{2}}/\text {Si}$ wafer to increase the effective sensing interaction area. An Ag-spot electrode was printed on top of the sensing layer using a thermal deposition technique using a hard mask. The sensor calibration was carried out using known concentrations of volatile formaldehyde. The sensor stands out with its innovative capacitive design, elevating sensitivity beyond conventional approaches. The sensor has shown a sensitivity of 142.1 pf/ppm and response of 120% at 0.5 ppm with a limit of detection (LoD) of 0.5 ppm. This unique design not only simplifies fabrication but also guarantees both high sensitivity and reliability. The results of the study indicate that the sensor system effectively and rapidly (85 s) detects formalin-treated fish at room temperature (300 K). The portable and cost-effective nature of the device assures on-site measurement of formalin in fresh raw fish.