Atomically Precise Silver Clusters as New SERS Substrates

An atomically precise silver cluster, Ag-152 protected with thiolate ligands, was used as a surface-enhanced Raman scattering (SERS) substrate. The cluster shows intense enhancement of Raman signals of crystal violet with an enhancement factor of 1.58 x 10(9). Adaptability of the substrate for a wide range of systems starting from dyes to biomolecules is demonstrated. Solid-state drop casting method was used here, and SERS signals were localized on the Ag-152 crystallites, confirmed from Raman images. Excellent periodicity of clusters, their plasmonic nature, and absence of visible luminescence are the main reasons for this kind of large enhancement. SEAS was compared with smaller clusters and larger nanoparticles, and the size regime of Ag-152 was found to be optimum. Several control experiments were done to understand the SERS activity in detail. The method has wide adaptability as the cluster can be easily drop-casted on any surface like paper, cotton, and so forth to produce effective SERS media. The work suggests that atomically precise clusters, in general, can show SERS activity.