Voltammetric study of the ion-exchange binding of non-electroactive metal cations to DNA-modified surfaces

Abstract

We describe a simple electrochemical protocol for studying the ion-exchange binding of non-electroactive ions, specifically mono- and divalent metal cations of biological relevance (Mg²⁺, Ca²⁺, and K⁺), to DNA-modified surfaces. After incubation in a dilute solution of multiply charged transition metal complex (5.0 µM [Ru(NH₃)₆]Cl₃), gold electrodes modified with thiolate–DNA monolayers respond to the presence of these non-electroactive metal cations by producing significant changes in the cyclic voltammograms (i.e., decrease of the integrated charge and shift of formal potential) of the surface-bound redox complex ([Ru(NH₃)₆]³⁺). The divalent cations (particularly Mg²⁺) can be detected at very low concentrations (<10 µM), while the on-set value for K⁺ is substantially higher (50 mM). The equilibrium binding constants for Mg²⁺ and Ca²⁺ to DNA-modified surfaces were calculated.