Detection of Hg2+ in environmental water conditions by using a reusable SERS-based microfluidic chip with a high specificity and sensitivity

This work reported a surface-enhanced Raman spectroscopy (SERS)-based microfluidic chip that detects mercury ions (Hg²⁺) in water with high sensitivity and good reproducibility. Silver nanoparticles (AgNPs) are easily fabricated on a Si substrate using a thin, thermally treated Ag film. Cy3 functionalized single-stranded DNA (Cy3-ssDNA) serves as the probe, which is immobilized on the AgNPs (Cy3-ssDNA/AgNPs), generating a SERS-based sensing surface. Due to the strong interaction between thymine (T) bases and Hg²⁺, in the presence of these ions, the ssDNA forms a T-Hg²⁺-T hairpin structure, which enhances the SERS signal. This method exhibits a limit of detection (LOD) of 1 × 10⁻¹³ M. Furthermore, the proposed SERS chip demonstrates exceptional selectivity for mercury ions, as well as good reusability. The reusability of the SERS microfluidic chip was evaluated using the L-cysteine, which has a stronger affinity than T for Hg²⁺. By applying L-cysteine, the chip can be reused 10 times for the detection of Hg²⁺ at concentrations as low as 1 × 10⁻⁸ M. The method proposed in this study shows good sensitivity and holds good potential for application in the detection of Hg²⁺.