Hexaferrocenium tri[hexa(isothiocyanato)iron(III)] trihydroxonium complex as a new DNA intercalator for electrochemical DNA biosensor

Abstract

Ferrocene or ferrocenium has been widely studied in the field of organometallic complexes because of its stable thermodynamic, kinetic and redox properties. Novel hexaferrocenium tri[hexa(isothiocyanato)iron(III)]trihydroxonium (HexaFc) complex was the product from the reaction of ferrocene, maleic acid and ammonium thiocyanate and was confirmed by elemental analysis CHNS, FTIR and single crystal X-ray crystallography. In this study, HexaFc was used for the first time as an electroactive indicator for porcine DNA biosensor. The UV–Vis DNA titrations with this compound showed hypochromism and redshift at 250 nm with increasing DNA concentrations. The binding constant (K_b) for HexaFc complex towards CT-DNA (calf-thymus DNA) was 3.1 × 10⁴ M⁻¹, indicated intercalator behaviour of the complex. To test the usefulness of this complex for DNA biosensor application, a porcine DNA biosensor was constructed. The recognition probes were covalently immobilised onto silica nanospheres (SiNSs) via glutaraldehyde linker on a screen-printed electrode (SPE). After intercalation with the HexaFc complex, the response of the biosensor to the complementary porcine DNA was measured using differential pulse voltammetry. The DNA biosensor demonstrated a linear response range to the complementary porcine DNA from 1 × 10⁻⁶ to 1 × 10⁻³ µM (R² = 0.9642) with a limit detection of 4.83 × 10⁻⁸ µM and the response was stable up to 23 days of storage at 4 °C with 86% of its initial response. The results indicated that HexaFc complex is a feasible indicator for the DNA hybridisation without the use of a chemical label for the detection of porcine DNA.