Electrochemical detection of adenine and guanine using a self-assembled copper(ii)–thiophenyl-azo-imidazole complex monolayer modified gold electrode

Abstract

Electrochemical detection of adenine (A) and guanine (G) using the self-assembled monolayer of copper(II)–thiophenyl-azo-imidazole modified gold electrode (Cu²⁺–IATP–Au) is reported. The self-assembled momolayer of 4-(2^′-imidazolylazo)thiophenol (IATP) on a gold electrode surface was prepared by covalent immobilization of imidazole onto a 4-aminothiophenol monolayer modified gold electrode by a diazotization-coupling reaction. The catalyst was formed by immobilizing Cu(II) ion on the IATP modified gold electrode. The modified gold electrode was characterised by Field emission scanning electron microscopy, Energy dispersive X-ray analysis, Infrared spectroscopy, Cyclic voltammetry and Electrochemical Impedance spectroscopic techniques. The Cu²⁺–IATP–Au electrode exhibits excellent electrocatalytic activity towards the oxidation of A and G. Without separation or pre-treatment, the modified electrode can detect A and G simultaneously in a mixture and DNA samples. In the presence of excess common interferents such as ascorbic acid, citric acid, cysteine, glucose, Na⁺, K⁺, Cl⁻, SO₄²⁻ had no effect on the peak current of A and G. In differential pulse voltammetry measurement, the oxidation current response of A and G was increased linearly in the concentration range 10–60 μM and the detection limit was found to be 0.06 μM and 0.01 μM (S/N = 3), respectively. The proposed method was applied to determine adenine and guanine in herring sperm DNA and the result was satisfactory.