Development of a Paper-Based SERS Platform for On-Site Separation and Detection of Mercury Species in Aqueous Environments

Accurate identification of mercury species in aqueous environments is essential for assessing ecological and human health risks, given the distinct toxicity and bioaccumulation potential of different mercury forms. Herein, we present a paper-based analytical device that uses electrophoresis and surface-enhanced Raman scattering (SERS) for rapid and in situ detection of inorganic mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) in aqueous samples. Using a dumbbell-shaped paper microchannel and applying voltage to both ends of the channel, quickly separate Hg²⁺ and CH₃Hg⁺ due to their differential migration behaviors. The two mercury species were subsequently identified using AuNPs@β-cyclodextrin@4-mercaptophenylboronic acid (AuNPs@β-CD@4-MPBA) SERS tags, which enable distinct chemical recognition: electrophilic substitution by Hg²⁺ and Au-Hg amalgam formation with CH₃Hg⁺. The platform achieves sub μg L^-1 detection limits, completes the full workflow─from sample loading, mercury species separation, to spectra readout─in 5 min, and shows high specificity against common metal-ion interferents. Validation of mercury species in the seawater sample confirmed the robustness of the platform in complex matrices. This electrophoresis-assisted SERS platform provides a new strategy for online separation and identification of multiform toxic species.