Uniform monolayer of branched silver nanoplates-assembled nanoparticles for sensitive and reproducible SERS detection of harmful molecules

Surface-enhanced Raman scattering (SERS) technique can offer the fingerprint information of trace substances, and thus has wide potential applications in many fields. There is still a requirement to develop new and effective methods to construct high-performance SERS substrates. Here, a facile electrodeposition method is presented for fabricating large-scale uniform films assembled by branched silver (Ag) nanoplates. The morphology and structure of such film are highly uniform over a large area, which can ensure good spectral uniformity and reproducibility. There are dense sub-10 nm gaps between neighboring Ag nanoplates and between neighboring branches, forming plenty of hot spots. Therefore, the branched Ag nanoparticle monolayer exhibits high SERS activity along with excellent spectral repeatability. It is found that the limit of detection (LOD) towards rhodamine 6G and 4-aminothiophenol can reach 0.387 pM and 49.0 pM, respectively, showing high sensitivity of the designed SERS substrate. The enhancement factor of the prepared roughened Ag nanoparticle monolayer is computed to be as large as 2.37 × 108. Then, the highly roughened nanoparticle monolayer is used to detect cationic dye and fungicide (methylene blue, MB) and a synthetic cytokinin (6-benzylaminopurine, 6-BAP), and the corresponding LODs are determined down to 1.1 nM and 28.8 pM, respectively. Such LODs are much lower than the tolerance for MB and 6-BAP residues established by some authoritative regulations. Sensitive monitoring of 6-BAP residue on vegetables and fruits can also be achieved using such SERS substrate, indicating its promising application in environment monitoring and food safety supervision.