Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 2. Demonstration of Selectivity in the Presence of Direct Interferences

Abstract

Three modes of selectivity based on charge-selective partitioning, electrolysis potential, and spectral absorption wavelength were demonstrated simultaneously in a new type of spectroelectrochemical sensor. Operation and performance of the three modes of selectivity for detection of analytes in the presence of direct interferences were investigated using binary mixture systems. These binary mixtures consisted of Fe(CN)₆^3- and Ru(bpy)₃²⁺ and of Fe(CN)₆^4- and Ru(CN)₆^4- in aqueous solutions. Results on the Fe(CN)₆^3-/Ru(bpy)₃²⁺ binary mixture showed that an anion-exchange coating consisting of PDMDAAC-SiO₂ [where PDMDAAC is poly(dimethyldiallylammonium chloride)] and a cation-exchange coating consisting of Nafion-SiO₂ can trap and preconcentrate analytes with charge selection. At the same time, such coatings exclude interferences carrying the same type of charge as that of the exchange sites in the sensor coating. Using the Fe(CN)₆^4-/Ru(CN)₆^4- binary mixture, the Fe(CN)₆^4- component can be selectively detected by restricting the modulation potential cycled to a range specific to the redox-active Fe(CN)₆^4- component and simultaneously monitoring the optical response at the overlapping wavelength of 420 nm. It was also shown that, when the wavelength for optical monitoring was chosen as 500 nm, which is specific to the Ru(CN)₆^4- component, interference from the Fe(CN)₆^4- component for spectroelectrochemical detection of Ru(CN)₆^4- was significantly suppressed, even though the cyclic modulation potential encompassed the redox range for the Fe(CN)₆^4- component.