Design and fabrication of a novel resisto-capacitive sensor for the detection of the freshness of fish

The development and fabrication process of a specialized resisto-capacitive sensor for the rapid determination of fish freshness is presented in this paper. The sensing is done by detecting volatile amine gases, specifically Ammonia ( \(\hbox {NH}_3\) ${\text{NH}}_3$ ), generated during fish spoilage. The proposed sensor offers the advantage of eliminating cross-selectivity, enhancing its accuracy and reliability. Designed as an Au patch electrode \(\hbox {Ag-SnO}_2/\hbox {SiO}_2/\hbox {Si}\) ${\text{Ag-SnO}}_2/{\text{SiO}}_2/\text{Si}$ MIS resisto-capacitive sensor, it is constructed on a silicon substrate with Ag-doped tin oxide ( \(\hbox {SnO}_2\) ${\text{SnO}}_2$ ) serving as the sensing material. The proper sensing layer preparation and its morphological study is verified using different material characterization techniques such as X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The sensor, incorporating 5 mol% Ag in \(\hbox {SnO}_2\) ${\text{SnO}}_2$ and integrated with a microcontroller, is evaluated in a gas-sensing experimental setup. It demonstrated excellent responsiveness to \(\hbox {NH}_3\) ${\text{NH}}_3$ gases, detecting concentrations ranging from parts per billion (ppb) to parts per million (ppm). Fish freshness is determined rapidly, with a sensor response time of approximately 69 s and a recovery time of around 135 s. The study established acceptance time limits for the safe consumption of fish stored at 25 \(^\circ \) $_{}^{\circ }$ C, 15 \(^\circ \) $_{}^{\circ }$ C, and 4 \(^\circ \) $_{}^{\circ }$ C using the proposed technique as 17 h, 48 h, and 105 h, respectively. The sensor’s unique architecture will make it more sensitive and selective.