Development of a new matrix based on a silicone ladder polymer for ion-sensing membranes

A silicone ladder-type polymer was successfully utilized for a matrix of an ion sensing membrane to fabricate an ion-sensitive field-effect transistor. An ion sensing membrane was readily fabricated by mixing a silicone ladder-type oligomer with a quaternary ammonium salt, casting onto the gate of the field-effect transistor, and polymerizing with heating. Since no acid catalysts were needed to prepare the ion sensing membrane, it was possible to keep the quaternary ammonium salt in the matrix without decomposition. The ion-sensitive field-effect transistor based on the silicone ladder-type polymer and the quaternary ammonium salt showed a linear response with a slope of -58.1 mV decade(-1) very close to the theoretical Nernstian response over an NO3- range between 3.0 x 10(-6) and 1.0 x 10(-1) M. The time required to reach 90% total response was within 5 s, when the NO3- concentration was changed from 1.0 x 10(-3) to 3.0 x 10(-3) M. The newly fabricated ion-sensitive field-effect transistors have kept their original sensitivity for more than half a year.