Development of an Adhesive Solution for a Modified ISFET with a Traditional Ion-selective PVC Membrane

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Abstract
Background: Ion-sensitive field-effect transistors (ISFETs) can measure the concentration of specific ions in solutions, by attaching ion-sensing membranes proposed for ion-selective electrodes (ISEs) to their gate surfaces. Numerous organic ion-sensing membranes for ISEs have been developed. However, the adhesion between the ion-sensing membranes and the gate surfaces is poor, therefore, adversely affecting the potential responses of ISFETs. Methods: New adhesive solutions to attach the ion-sensing polyvinyl chloride (PVC) membranes to the gate surfaces of ISFETs have been developed. The proposed adhesive solutions were made in tetrahydrofuran (THF) from polymer blends containing PVC and paraloid B-72 in different ratios. Results: It was found that the adhesive solution with a composition ratio of PVC: Paraloid B-72 = 10:90 provided particularly good adhesion and the best slope of the potential response to Na+-activity change. The best ion selectivity for the Na+ ion was exhibited by ISFET with the adhesive solution having a composition ratio of PVC: Paraloid B-72 = 20:80. Discussion:: The results of the tensile test indicated that the PVC components in the adhesive solutions may not be directly involved in adhesion to the gate surface of the ISEFTs. The adhesive solution consisting of only PVC content provided the worst slope of the potential response to Na+-activity change. Conclusion: The ion-sensing PVC membranes were stably attached using the proposed adhesive solutions on the gate surfaces of the ISFETs. By using the proposed adhesive solution, the ISFETs with the ion-sensing PVC membranes showed good potential responses.

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