Investigation of Drift in Polyurethane Matrices for Salivary Nitrate Ion-selective Field-effect Transistors

Abstract

We systematically investigated the drift of ion-selective field-effect transistors (ISFETs) using a series of polyurethanes as a polymer matrix. Drift is one of the shortcomings of ISFETs that adopt a polymeric ion-selective membrane. The drift is caused by the pH change in the aqueous layer between the ion-selective membrane and the pH-sensitive gate of the ISFET. We previously reported NO3−-ISFETs with a novel polyurethane P7281-PU, which give specific stable values. This polyurethane showed less drift than conventional polyvinyl chloride. We considered that the urethane bonds in the ion-selective membrane might capture the diffused H+ or OH− ions that induce the drift. In this study, we investigate a polyurethane composed of an ion-selective membrane and consider how the condition and performance of the ion-selective membrane affect the drift. We selected eight types of polyurethane with almost the same composition as P7281-PU for comparison. We confirmed a narrower variation range of 4.5 mV/h from ISFETs with polyurethane P7293-PU than those of 33.7 mV/h from PVC and 5.0 mV/h from P7281-PU through drift tests using artificial saliva. From the tests, we also confirmed that the drift prevention effect might be caused by the ion-trapping sites generated with the hydrolysis of the urethane bonds.