Electro-assembled Au NP array at liquid-liquid interface for dual-mode sensing of heavy metal ions

The self-assembly of gold nanoparticles (Au NPs) has attracted wide attention in the fields of sensing, catalysis and various optical devices. Compared with conventional self-assembly methods in the bulk solution or on the solid substrates, the liquid-liquid interface (LLI) provides a versatile plane with nanoscale flatness for addressable NP assembly. Here, we report a self-assembled Au NPs metasurface at the water-oil interface using a four-electrode electrochemical system that is stable, controllable, and enables dual-mode in-situ sensing. By building electrostatic energy well at LLI, a closely packed metasurface can be formed, which shows strong surface plasmon resonance (SPR) effect. In the presence of analytes, the metasurface generates significant changes in reflectance and surface-enhanced Raman scattering (SERS) spectra, which can be utilized as two sensing modes. Cu 2+ and Hg 2+ were targeted as two proof-of-concept analytes for the sensor. The limit of detection (LOD) can reach 0.147 nM and 0.421 nM, respectively, showing outstanding performance in heavy metal detection.