Single Atoms Couple Molecular Coordination to Near-Resonant Charge Transfer in Surface-Enhanced Raman Scattering.

Chemical enhancement in surface-enhanced Raman scattering (SERS) is generally attributed to interfacial charge transfer, yet how atomically defined coordination converts molecular binding into enhanced vibrational polarizability remains unresolved. Here we show that Au-coordinated Pt single atoms function as charge-transfer bridges within a TiOx nanocavity/Au nanoparticle architecture, coupling molecular coordination to near-resonant Raman enhancement. The Pt single atoms serve three interdependent roles: binding target molecules, modulating interfacial electronic states, and mediating charge transfer. Together with photonic confinement and plasmonic hotspots, this atomically defined pathway produces an apparent SERS enhancement factor of 3.6 × 1011 and enables measurements within a statistically defined single-molecule occupancy regime. We term this cooperative process Spatial-Plasmonic Atomic Coupling Enhancement (SPACE), which connects atomic-scale coordination and energy-level alignment with macroscopic Raman amplification. As a proof of analytical utility, cysteamine functionalization couples benzaldehyde capture through Schiff-base formation to the single-atom-mediated enhancement pathway, enabling gas-phase detection down to 0.3 ppbv. These findings establish single-atom coordination as a general design principle for transforming interfacial molecular binding into near-resonant vibrational amplification.