Integrated functional nucleic acids with 2D metal–organic framework composites as a label-free electrochemical sensor for trace Hg2+ sensing

In this study, a label-free functional nucleic acid electrochemical sensor was fabricated on the basis of a polyvinylpyrrolidone/graphene@Cu-based metal–organic framework (PVP/GNs@Cu-MOF). These PVP/GNs@Cu-MOF composites combine the advantages of the Cu-MOF (electrochemical redox properties, abundant functional groups on the surface, and porosity) and GNs (fast electron transfer rate and large specific surface area), achieving enhanced electrochemical performance. Mercury ions (Hg²⁺) can combine with thymine (T) rich nucleic acids through specific T–Hg²⁺–T coordination. Thus, a label-free functional nucleic acid electrochemical sensing platform for Hg²⁺ was proposed by modifying PVP/GNs@Cu-MOF composites and T rich functional nucleic acids on the surface of a glassy carbon electrode (GCE). Under optimized conditions, the as-proposed sensor exhibited a wide linear range of 5.0 fmol L⁻¹–1.0 pmol L⁻¹ with a low detection limit of 1.7 fmol L⁻¹ (S/N = 3) for Hg²⁺ detection. Furthermore, the strategy can also be used for the quantitative detection of Hg²⁺ in river water. The proposed sensing platform provides an alternative way for the determination of trace heavy metal ions (HMIs) in the environment.