Comparison of polysiloxane films substituted by undecenyl-cyclam and by naphthyl-cyclam for the design of ISFET devices sensitive to Fe3+ ions

Abstract

The synthesis and properties of new silicone-based functional materials having attached cyclam macrocycles have been assessed with regard to their application as ion-sensitive membranes of chemical sensors. The preparation process of thin films of the sensitive materials has been designed so that each chemical compound is attached by means of chemical bonds: the macrocyclic ionophore was chemically bound to the silicone polymer and the polymer material was attached to the sensitive surface of the electrochemical devices by means of chemical grafting. The properties of such materials have been evaluated for detection of iron(III) species in water using ion-sensitive field-effect transistor (ISFET) and electrolyte–insulator–semiconductor (EIS) structures, both sensitized by a coating with the functional polymer materials. Two types of cyclam derivatives and two types of synthesis processes have been compared with that respect. The first material, “PDMS-Cyclam”, was prepared by grafting N-10-undecenyl-cyclam to poly(methylhydrosiloxane) (PMHS). The cyclam ionophore of the second material, “PDMS-Naphthyl-Cyclam”, bore a naphthyl pendent group that enhanced the complexing properties for Fe3+ ions. Linear response with respect to the pFe(III)=−Log[Fe3+] was observed over three decades (EIS) or two decades (ISFET) of concentration. A Nernstian response toward Fe3+ ions was observed for the “PDMS-Naphthyl-Cyclam” membrane. These devices exhibit good chemical stability and a long lifetime in aqueous medium.