High sensitivity surface-enhanced raman scattering in solution using engineered silver nanosphere dimers

We describe Raman spectroscopy measurements of distyrylbenzene (DSB) molecules equipped with plasmonic antennae in the form of silver dumbbells in aqueous solution under ambient conditions. A synthetic strategy in which the dithiolated molecule is used as the linker between silver nanospheres ensures that the molecules are attached at the intersphere gap where local fields are maximally enhanced. The measured and calculated enhancement factors are in excellent agreement. The reported method has sufficient sensitivity to also allow for the detection of molecules tethered to single spheres, with 100-1000-fold weaker enhancement. Spectral analysis allows assignment of structures and reveals that in addition to the normal Raman active modes IR active transitions appear in the Raman spectra where field gradients dominate.