Joint application of micro-Raman and surface-enhanced Raman spectroscopy to the interaction study of the antitumoral anthraquinone drugs danthron and quinizarin with albumins

We report on the joint application of surface-enhanced Raman scattering (SERS) and micro-Raman techniques to the study of danthron (DT) and quinizarin (QZ) and their complexes with human and bovine albumins. We propose a novel method based on the combination of SERS and micro-Raman spectroscopy by using immobilized Ag nanoparticles, which we have named micro-SERS, to improve the sensitivity of the SERS technique and that could be applied in recognition processes of drugs with large biomolecules. The micro-SERS technique demonstrated clear advantages over direct measurements in air: reproducibility, rapidity and high sensitivity due to a large coverage of the metal surface and good organization of the adsorbate on the surface. Furthermore, the chemical damage of the analyte induced by laser irradiation is substantially reduced. By means of this method, we were able to deduce important information concerning the binding properties of DT and QZ when interacting with human and bovine albumins. For instance, the interaction mechanism can be drastically modified when fatty acids are present in albumins, there are large differences between human and bovine albumins in the binding of the studied drugs related to changes in the amino-acid sequence of the binding pockets of these proteins and the interaction mechanism of the analysed drugs can be different depending on their structure. Copyright (C) 2004 John Wiley Sons, Ltd.