a polyimide matrix is employed to form a substance - sensitive membrane which is particularly suited for installation on a solid state sensor . polyimide , dissolved in a solvent , such as n , n - dimethylformamide , or n - methyl - 2 - pyrrolidone , is combined with an ionophore , plasticizer , and a lipophilic additive . the ionophore may be a calcium ionophore , an ammonium ionophore , or any other ionophore . the membrane may also incorporate , or may be covered by , a bioactive agent , such as an enzyme , an immunochemical , bacteria , antibody , virus , or antigen . the plasticizer is one or both of dimethyl phthalate and diethylene glycol dibenzoate . the lipophilic additive may be potassium tetrakisborate . the resulting substance - sensitive membrane has electrochemical properties which compare favorably to those of conventional pvc membranes , and exhibit significantly greater adhesion to glasses and semiconductor substrate materials . the improved adhesion may prolong the life of the sensors and prevent the formation of electrolyte shunts which have been known to render solid state sensors inoperative .