A note on distance dependence in surface enhanced Raman spectroscopy

It is appreciated that the surface enhanced Raman signal falls away rapidly from the substrate surface that provides the dominant electromagnetic enhancement. As many bio-molecules of interest are large, it is important to establish for any practical surface the usable distance from the surface at which molecules can still be detected. Using monolayer ssDNA arrays with three adenine bases close to the surface, or far from the surface, a two-point distance dependence for our toroidal shaped random array of silver structures has been performed. The results show enhancement at 30 nm out is definitely viable, making SERS and large bio-molecule compatible.