Rational design of Au NPs satellite nanostructure modified microelectrode for dual-mode detection of mercury ions in algal solution

Developing a microelectrode with in-situ multiple sensing modes will greatly expand the applicability and reliability of the analytical platform. Hence, a functional substrate with a satellite-like nanostructure was constructed on a gold microelectrode (Au ME). This structure not only amplifies the surface-enhanced Raman scattering (SERS) signal of the labeled molecule (4-nitrobenzenthiol, NBT) on the functionalized Au NPs, but also ensures the good electrical properties of the proposed functionalized microelectrode (Au ME/Au-AuNDNA). Based on this feature, the highly toxic heavy metal mercury ions (Hg2+) were used as a model to verify this dual modal analytical platform. Significantly, the proposed microelectrode has a satisfactory sensitivity to Hg2+and allows the simultaneous presentation of analytical results by dual-mode of SERS signal turn-off (LOD 2.7 x 10-11 M) and current signal turn-on (LOD 6.4 x 10-9 M), the detected concentration of Hg2+ is below the dangerous limit of World Health Organization (WHO) and the U.S. Environmental Protection Agency (EPA). This relies mainly on the formation of thymine-Hg2+-thymine (T-Hg2+-T) by the modified probe B ssDNA on the microelectrode to disrupt the satellite structure with AuNDNA, while the applied potential reduces the Hg2+ captured by T-Hg2+-T on the microelectrode surface. Such a fascinating analytical strategy was further evaluated in an environmental water sample simulated with algal solution and still showed a reliable analytical capability. Thus, the proposed dual-mode sensing concept not only opens new avenues for the coordinated application of novel electrochemical and SERS sensing techniques, but also provides a foundation for in-situ detection based on micro/nanoscale electrodes.