Comparative FT SERS, resonance Raman and SERRS studies of doxorubicin and its complex with DNA

Fourier transform surface enhanced Raman scattering (FT SERS) coupled with a microscope has been used as a probe to obtain information on the interaction of a drug and of its complex with DNA. Micro-FT SERS spectra of the antitumour agent doxorubicin (DOX) at 10(-5) M and of this complex with DNA have been recorded in aqueous silver hydrosol and compared with the corresponding resonance Raman (RR) and SERS spectra at concentrations of 5 x 10(-4) M and 5 x 10(-8) M, respectively. The interactions between the drug and calf thymus DNA induced identical effects in the RR and visible SERS spectra. The data show that the adsorption of the drug-DNA complex on the silver hydrosol does not induce detectable perturbations of the molecular interactions within the complex. Micro-FT SERS spectra were found to be partially different from those obtained in visible SERS spectra. These differences concern the relative enhancement of some vibrational modes which could hardly be observed when resonance excitation was used. The FT SERS approach enables further information to be obtained and additional details on the geometry of the drug-DNA interaction to be revealed. An analysis of the FT SERS spectra of the drug and of its complex with DNA not only confirms the model of interaction proposed using RR and SERS data in the visible, but brings about new information, especially on the vibrations of ring A of the molecule, which are usually masked by the vibrations of rings B and C dominant in the visible SERS spectra.