THE DESIGN OF DURABLE NA-SELECTIVE CHEMFETS BASED ON POLYSILOXANE MEMBRANES()

The design of durable sodium-selective CHEMFETs based on the covalent attachment of a sodium-selective ionophore and tetraphenylborate anion s to a polysiloxane membrane matrix is described. Simulations of the m embrane potential of such CHEMFETs using an extended version of the mo del developed previously in our group, revealed that a membrane with a reduced mobile ionophore and completely immobilized anionic sites sho uld give a sub-nernstain response owing to a counteracting diffusion p otential. CHEMFETs with all possible combinations of free and covalent ly bound ionophore and borate anions were prepared and the effect of c ovalent binding on the sensing behaviour was studied. The attachment o f both electroactive components to a polysiloxane membrane matrix resu lts in CHEMFETs that respond to Na+ activities in aqueous solution wit h good selectivity, and an almost nernstian slope (56.7 mV decade-1). The polarity of the membrane plays a crucial role. The durability is i mproved by the covalent attachment of the electroactive components (mo re than 90 days).