THE SHORT-RANGE COMPONENT OF SERS : RESULTS OF BIOPOLYMERS

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Abstract
The short-range component of surface enhanced Raman scattering (SERS) is investigated using the biopolymers, DNA and poly-A. Both molecules form a double stranded helix (diameter about 20 Å). The chains are arranged with the sugar-phosphate backbone on the outside and the nucleic bases facing the center. At a positively charged silver surface (colloids, electrode) these biomolecules are adsorbed mainly trough the negatively charged sugar-phosphate backbone. Nucleic bases, located in the center of the helix do not exhibit any Raman signals. However after the destabilization of the double helical structure the nucleic bases interact directly with the surface and show strong SERS signals. These experimental observations indicate that the strong enhancement for DNA and poly-A on silver colloids and electrodes is caused by a short range mechanism for distances smaller than 5 Å from the surface

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