Aggregation of antitumoral drug emodin on Ag nanoparticles: SEF, SERS and fluorescence lifetime experiments.

We have studied the fluorescence and Raman emission of the anthraquinone drug emodin immobilized molecules on nanostructured silver surfaces, prepared through two different methods. Two different pHs (pH = 10 and pH = 6) have been used. The dye aggregation favors SEF at pH = 6, whereas quenching of fluorescence is observed at pH = 10, due to the short distance between emodin and Ag particles. Along with these results, SERS spectra have given us information about the different species present in the solution. We have used two different reducing agents to obtain the Ag nanoparticles: hydroxylamine hydrochloride and sodium citrate. In all the cases analysed, the enhancement of both SEF and SERS spectra, is larger for hydroxylamine hydrochloride than that for sodium citrate. We have also measured fluorescence lifetime, observing a shorter lifetime for emodin molecules near Ag nanoparticles than that for emodin solved in pure water, thus corroborating the results obtained in fluorescence emission spectra.