Immobilization of 1,2-naphthoquinone-4-sulfonic acid on gold electrode: application for cysteamine detection using Michael addition

Fabrication and electrochemical characterization of adsorbed 1,2-naphthoquinone-4-sulfonic acid sodium (Nq)-modified gold electrode is described in a wide pH range (3.00–9.00) in 0.1 M phosphate buffer solution using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and double-step potential chronoamperometry methods. The resulting Nq thin film-modified gold electrode (Nq/Au) was tested successfully to recognize cysteamine in an aqueous solution. It is found that cysteamine participates in Michael addition reaction with adsorbed Nq on gold electrode to form the corresponding thioquinone derivative. The reoxidation of the adduct at a potential of about 650 mV less positive than cysteamine at the surface of the bare Au electrode leads to an increase in the oxidative current, which is proportional to the concentration of cysteamine. The calibration plot for cysteamine was found to be linear in the ranges of 6.0 × 10⁻⁵–4.5 × 10⁻³ M and 8.0 × 10⁻⁶–5.5 × 10⁻⁴ by CV and DPV, respectively.