Membrane support selection for ISFET as transducer for histamine detection

Histamine has been identified as chemical indicator to estimate the spoilage of food particularly in fish and fish products. Histamine produced in the fish muscle tissue by the action of bacterial decarboxylase enzyme on histidine, can cause poisoning if histamine content in spoilt fish exceeds the FDA safety limit of 100ppm. Ion Selective Field Effect Transistor (ISFET) was introduced by Bergveld in 1970 for the detection of H+ ions. Since then there has been a lot of progress on the applications of ISFET for the detection of other ions by applying a selective membrane on the gate insulator layer. In this report the ionophore-based sensor which employed potentiometry form of transduction made ISFET as a component for the detection of histamine. The selection of ISFET is done before the deposition of membrane on the gate insulator layer. Two types of polymers PVC and polyurethane were used for the membrane materials. These membranes were prepared by dissolving the polymer and the ionophore [Mn(TPP)Cl] in THF as the solvent. After depositing the membrane on the gate of the ISFET, it is left for the solvent to evaporate. A third membrane used was acrylate. In this case the membrane was photo-cured with a stream of nitrogen gas. From the sensitivity test it was found that PVC showed the highest sensitivity (36 mV/decade) followed by urethane (18.5 mV/decade) and acrylate (0.75 mV/decade). The modified ISFET is a promising device for detecting fish freshness. The advantage of ISFET being small and its ability to be integrated with electrochemical and silicon technology makes signal processing and on-site evaluation possible.