Effect of monovalent cations (Li+, Na+, K+, Cs+) on self-assembly of thiol-modified double-stranded and single-stranded DNA on gold electrode

Abstract

In this article we investigate the effect of monovalent cations (Li⁺, Na⁺, K⁺, Cs⁺) on self-assembly of thiol-modified double-stranded DNA (ds-DNA) and single-stranded DNA (ss-DNA) on gold electrodes. Electrochemical characteristics (surface coverage, ion penetration and charge transfer) of ds-DNA and ss-DNA self-assembled monolayers (SAMs) formed with different monovalent cations are inspected based on six important interfacial parameters including surface coverage (Γ_m), interfacial capacitance (C), phase angle (Φ_1 Hz), ion transfer resistance (R_it*), current density difference (Δj) and charge transfer resistance (R_ct) from chronocoulometry (CC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three sections are included: (1) Investigation of the relationships of parameters (Γ_m, C, Φ_1 Hz, R_it*, Δj and R_ct) for ds-DNA-SAMs and ss-DNA-SAMs with cation types and concentrations; (2) confirmation and explanation of our experimental results combined with our recently proposed simple DNA model and literature reports; (3) exploration of the mechanism for the orders of monovalent cations (Li⁺, Na⁺, K⁺, Cs⁺) on availing the adsorption of ds-DNA and ss-DNA molecules on gold based on their physicochemical parameters (ion size, solvation free energy and enthalpy, ion-water bond length and water exchange rate) and possible binding modes with DNA molecules. This work might provide a useful reference for understanding interactional mechanism of cations with DNA molecules.