Permselectivities and ion-exchange properties of organically modified sol-gel electrodes

Sol-gel films prepared from organosilanes containing acidic/basic sites have been investigated as permselective and ion-exchange coatings for electroanalytical and bioanalytical investigations. When a glassy carbon electrode was modified with a sol-gel film fabricated from 3-aminopropyl-methyl-diethoxysilane (silane-NH2), excellent permselectivity and anion-exchange properties were obtained. For a pH 7.4, 1 mM potassium ferricyanide solution, an eight-fold increase in current was observed after the electrode was immersed in solution for 10 min whereas complete suppression of the electrochemical response for ruthenium hexaamine and methyl viologen was observed. Sol-gel films fabricated from trimethoxysilylpropyl ethylenediamine triacetic acid (silane-(COOH)(3)) exhibited nearly complementary behavior. An approximately 10-fold increase in current was observed for pH 7.4, 1 mM ruthenium hexaammine solutions and complete suppression of the potassium ferricyanide response was observed. These ion-exchange properties can be attributed to the strong electrostatic interactions between the acid/basic functional group in the matrix and the highly charged analyte molecules. When glassy carbon electrodes were modified with diethyl-(triethoxysilypropyl) malonate (silane-(COOEt)(2)), the films did not exhibit distinct ion-exchange properties but rather suppressed the reduction of potassium ferricyanide, The observed permselectivity results from the electron dense carbonyl group and/or hydrolyzed ester functionalities in the film.