A Sensor to Analyze Fish Freshness: A Virtual Sensor Array Based on an Electrochemical Chemotransistor.

The introduction of a quantitative definition of fish freshness enables the determination of the remaining storage time of raw fish materials. To measure this value, a virtual array of electrochemical chemotransistor-based chemical sensors was developed. The electrolyte used to electrically connect the four measurement electrodes and the reference electrode was optimized. To achieve the high stability, high electrochemical activity of chemosensitive material, and reversible potential of the silver/silver chloride reference electrode, a chloride-containing ionic liquid and polymeric acid mixture was used as the electrolyte. Polyaniline in different redox states was applied as the chemosensitive material with electrically controlled affinity. First, the sensor was evaluated for trimethylammonium detection, and then it was applied to fish samples. Unlike the response observed for trimethylammonium, the sensor's response to fish samples exhibited complex, non-exponential kinetics and a non-monotonic dependence on the storage duration of fish samples. To characterize these responses, a set of descriptors was introduced. The storage time was estimated by minimizing the Euclidean distance between the descriptors values obtained from fish samples and those determined during calibration. Based on the quantitative definition of freshness, this approach categorizes the current stage of fish products and predicts the remaining storage duration quantitatively.