Surface-Enhancement Raman Scattering Sensing Strategy for Discriminating Trace Mercuric Ion (II) from Real Water Samples in Sensitive, Specific, Recyclable, and Reproducible Manners

It is of essential importance to precisely probe mercury­(II) (Hg²⁺) ions for environment-protection analysis and detection. To date, there still remain major challenges for accurate, specific, and reliable detection of Hg²⁺ ions at subppt level. We herein employ gold nanoparticles (AuNPs) decorated silicon nanowire array (SiNWAr) as active surface-enhanced Raman scattering (SERS) substrates to construct a high-performance sensing platform assisted by DNA technology, enabling ultrasensitive detection of trace Hg²⁺ in ∼64 min and with low sample consumption (∼30 μL). Typically, strong SERS signals could be detected when the single-stranded DNA structure converts to the hairpin structure in the presence of Hg²⁺ ions, due to the formation of thymine (T)-Hg²⁺-T. As a result, Hg²⁺ ions with a low concentration of 1 pM (0.2 ppt) can be readily discriminated, much lower than those (∼nM) reported for conventional analytical strategies. Water samples spiked with various Hg²⁺ concentrations are further tested, exhibiting a good linear relationship between the normalized Raman intensities and the logarithmic concentrations of Hg²⁺ ranging from 1 pM to 100 nM, with a correlation coefficient of R² = 0.998. In addition, such SERS sensor features excellent selectivity, facilely distinguishing Hg²⁺ ions from various interfering substances. Moreover, this presented SERS sensor possesses good recyclability, preserving adaptable reproducibility during 5-time cyclic detection of Hg²⁺. Furthermore, unknown Hg²⁺ concentration in river water can be readily determined through our sensing strategy in accurate and reliable manners, with the RSD value of ∼9%.