Surface Plasmon Effects on the Binding of Antitumoral Drug Emodin to Bovine Serum Albumin

Nanoparticles are used to carry and deliver drugs to disease tissues. They constitute an alternative to classical protein-ligand complexes. Metal nanoparticles also display interesting optical properties based on localized surface plasmons. We have studied the influence of silver nanoparticle-BSA and silver nanoparticle-BSA-emodin interactions over the protein structure as well in the protein-drug binding using circular dichroism as well as time-resolved and steady-state fluorescence. The metal was found to induce structural changes on the protein and to influence the drug binding. In particular, secondary structure diminishes, and complexes formed in the presence of nanoparticles are less stable than in water solution, while the amount of drug molecules interacting with the protein is higher when the metal is present. Energy transfer experiments between the protein and the drug in presence of nanoparticles indicate a decrease in the energy transfer efficiency. The results presented here will help to further understand the nanoparticles-protein-drug interactions and the role that silver nanoparticles may play in biomedical and pharmacological applications.