Metal nanostructures are known to amplify the spontaneous emission of fluorescent molecules by resonant coupling to external electromagnetic fields. We have used spectroscopy to characterize the structural properties of emodin molecules, a natural anthraquinone dye, and bovine serum albumin, the most abundant protein in plasma, in the presence of silver nanoparticles. Aggregation of emodin at pH=10 and pH=6 gives rise to SERS and MEF effects in silver colloid. We have obtained MEF spectra at acidic pH=2.9 using two different silver nanostructures. We have also studied the change in the secondary structure of bovine serum albumin adsorbed on metal nanoparticles surface. Circular dichroism, fluorescence emission and fluorescence lifetime measurements indicate an increase in the alfa-helical content of the protein and a change in the environment of the tryptophan residues that bury in the interior of the biomolecule. This variation on the secondary structure could have further influence in the binding of the drug to form transport and regulatory complexes.

This work has been financially supported by projects: FIS2007-63065 from the Spanish Ministerio de Educación y Ciencia, S-0505/TIC/0190 from Comunidad Autónoma de Madrid and Research group 950247 from the UCM support. R. de Llanos acknowledges Ministerio de Ciencia e Innovación for a FPI fellowship.

5 páginas, 3 figuras, 1 tabla.-- Artículo presentado como póster al SPIE Photonics West 2010, "Plasmonics in Biology and Medicine VII" celebrado en San Francisco (USA) en enero de 2010.

Peer reviewed