Silver nanosheets self-assembled on polystyrene microspheres to form "hot spots" with different nanogap distances for...

Herein, we reported a facile method to control the nanogap distance of silver (Ag) nanosheets to obtain high sensitive plasmonic Surface-enhanced Raman scattering (SERS) substrates. The sulfonated polystyrene (SPS) microspheres with different diameters were first fabricated using micro-emulsion synthesis, and then the SPS microspheres were coated with Ag nanosheets through chemical synthesis with citric acid/ascorbic acid to form Ag nanosheets@SPS (Ag@SPS) substrates with different nanogap distances. The results showed that the nanogap distance of Ag nanosheets self-assembled on SPS microspheres reduced from 80-150 nm to 28-68 nm when the diameter of SPS microspheres increased from 0.9 to 3.5 μm, and the enhancement factor (EF) increased from 10⁵ to 10⁷, the limit of detection of rhodamine 6G (R6G) for the Ag@SPS microspheres reduced from 10^-10 to 10^-13 mol/L. It confirmed that the Ag nanosheets coated on the surface of SPS microspheres could achieve ultra trace detection of analyte. Furthermore, the low concentration detection limit for melamine with the Ag@SPS microspheres substrate was about 10^-8 mg/L, which is lower than the standard legislated by the European Union and the Food & Drug Administration. In addition, the SERS spectrum of 3-mercaptopropionic acid (3-MPA) could be also detected when its concentration was 10^-8 mol/L. The prepared substrate offered a promising opportunity for SERS practical applications.