Surface‐enhanced Raman spectroscopy of biomolecules. Part III.—Determination of the local destabilization regions in the double helix

Surface‐enhanced Raman (SER) spectra of nucleotides, calf thymus DNA and plasmid pAO 3 in the supercoiled and relaxed conformations adsorbed on colloidal silver were analysed. Two different techniques were used for the preparation of the silver hydrosol. All the compounds were adsorbed on the standard hydrosol with very low specificity with respect to the chemical nature of the adsorbate. ‘Activation’ of the standard hydrosol by Cl⁻ ions induced adsorption sites highly specific to the adenine nucleotides. It was demonstrated that recording of highresolution SER spectra of nucleic acids and their components at 10⁻¹³ g is possible and that ‘activation’ of the silver hydrosol permits the selective detection of the sites of destabilization of double‐stranded helices and identification of the nucleotides in these sites.