Atomically Precise Nanoclusters as SERS Probes

Atomically precise nanoclusters (NCs) exhibit molecule-like fingerprints, yet their Raman response is usually buried under intense luminescence. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) to probe the molecular nature of the stable eight-electron silver NC, [Ag₁₇(o₁-carboranethiolate)₁₂]^3- (abbreviated as Ag₁₇), by integrating it with plasmonic gold nanotriangles (Au NTs), forming an Ag₁₇@Au NT nanohybrid. This is the first demonstration of an atomically precise NC functioning as a stable next-generation Raman probe under harsh laser conditions. Synergistic electromagnetic (EM) and chemical enhancement (CE) mechanisms yield an overall enhancement factor of up to ∼6 × 10⁵, with ∼2 × 10² attributed to CE, consistent with time-dependent density functional theory (TDDFT) calculations. TDDFT reproduces the observed spectra and reveals low-lying hybrid charge-transfer excited states, underpinning the CE pathway. Plasmonic confinement and charge transfer cooperatively amplify the Raman scattering of the Ag-Ag bonds and carborane framework at the nanoscale junctions of the Ag₁₇@Au NT nanohybrid.