We describe combined AFM/SERS measurements on single nano-dumbbells, consisting of dibenzyl dithio-linked silver nanospheres (~30 nm). Moderate enhancement factors of ~ 107, which are readily accessible through plasmonically enhanced local fields, is sufficient to reach single molecule sensitivity (SMSERS). Given that Raman scattering is determined by a second rank tensor and the spatial heterogeneity of local fields at nano-junctions, relative intensities in SMSERS spectra can be used to locate molecules in 3-d space. The requirements are knowledge of the multipolar tensor of polarizability derivatives of the molecule, and the local field (and field gradients) of the nanostructure. Both can be reliably computed. We demonstrate the principles through illustrative SMSERS trajectories in which we track motions driven through light-induced forces, e.g., light driven fusion of the nanospheres.

SERS trajectories on a single nanodumbbell track single molecules in 3D space

244th National Meeting (2012)

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