Label-free electrochemical sensing of Hg2+ using a Bi2WO6–DNA nanocomposite interface

Abstract

Heavy metal ion detection is important for ensuring public health and protecting the environment. In this work, DNA-mediated bismuth tungstate (BW) was developed towards the electrochemical detection of mercury ions (Hg²⁺). In the composite, Bi³⁺ interacts with the oxygen atoms of the tungstate anion WO₄²⁻, while sugar and the phosphate groups of DNA are attracted to the positively charged Bi³⁺ ions in BW. The BW–DNA composite is significant because it combines the high electron transfer ability of BW with the selective binding ability of DNA toward Hg²⁺ (via T–Hg²⁺–T coordination). This synergy provides excellent sensitivity and eco-friendly detection of mercury in water, making it a promising platform for human health and real-time environmental monitoring. The BW–DNA-modified electrode surface demonstrates excellent electrochemical oxidation of mercury ions with good reaction kinetics in a diffusion-controlled process. The Hg²⁺ ions selectively bind to these thymine bases of DNA, such as the thymine–Hg²⁺–thymine base pair, a metal-mediated mismatch formation instead of the standard Watson–Crick base pair formation. By combining the high affinity of DNA for Hg²⁺ with the catalytic and conductive properties of BW, the sensor achieves selective, sensitive and reliable electrochemical detection. This approach not only enhances the interaction between the electrode surface and target ions but also minimizes interference from other metals. The successful detection of Hg²⁺ in real water samples ensures the practical utility of the sensor for environmental surveillance and public health protection. Overall, this work contributes to a cost-effective, stable and biocompatible sensing platform for heavy-metal monitoring in complex aqueous systems. The BW–DNA demonstrates a high electroactive surface area of 4.57 × 10⁻³ m² with an efficient current density of 4.31 × 10⁻³ A m⁻², which is strongly utilized for the electrochemical detection of Hg²⁺ ions. The proposed BW–DNA composite exhibits an excellent linear Hg²⁺ concentration detection of 10 µM–1 mM, with an LOD of 1.3 µM. Finally, this sensing approach has been effectively applied in real time analysis of Hg²⁺ ions in tap and lake water, with acceptable recovery results.