Application of iron bathophenanthroline complex as a redox mediating agent for imaging surface immobilized DNA using scanning electrochemical microscopy

A new approach for imaging DNA immobilized on gold and carbon paste surfaces was described using scanning electrochemical microscopy (SECM). The new approach is based on the application of iron (II)-4,7-diphenyl-1,10- phenanthroline as a redox mediating agent. Gold surfaces were activated prior to DNA immobilization using thioctic acid and 2-aminoethanethiol. Carbon paste surfaces were modified using the iron (II) complex. The influence of applied potential onto the gold substrate, on the assembly of immobilized DNA was evaluated. Cyclic voltammetry of the iron complex gave one reduction peak at +0.55 and one oxidation peak at +1.20 V versus saturated calomel reference electrode. Generation of current signals during SECM imaging of immobilized DNA was attributed to the oxidation of Fe(bathophen) ²⁺ ₃ under the tip of the capillary electrode. Generated Fe(bathophen) ₃ ³⁺ species was assumed to diffuse into the immobilized DNA and subsequently oxidize the guanine residue in DNA. A redox electrolyte consisted of 10 ^?4 M Fe(bathophen) ²⁺ ₃ in 0.1 M KCl-Tris buffer pH 7, was used for imaging DNA immobilized on modified gold surfaces. A 10 ^?3 M Fe(CN) ^4? ₆ in 0.1 M KCl electrolyte solution was used for imaging immobilized DNA on carbon paste modified with 5% Fe(bathophen) ²⁺ ₃ . Complementary information on surface coverage and its uniformity on gold surfaces were obtained by imaging the same samples using atomic force microscopy (AFM).