Thin film and containment sensors with fluorosilicone as the matrix material for the ion-selective membrane are described, Potassium-, sodium- and calcium-selective sensors, with response characteristics similar to those of a conventional ISE using PVC-matrix membranes, have been realized, The notable features of the new membrane are a good adhesion and the improved mechanical strength compared with PVC matrix membranes, Furthermore, it has an optimal conductivity and a higher relative permittivity than 'conventional' silicones.