RESEARCH PAPER Human serum albumin as protecting agent of silver nanoparticles: role of the protein conformation and amine groups in the nanoparticle stabilization Emilio I. Alarcon • Carlos J. Bueno-Alejo • Christopher W. Noel • Kevin G. Stamplecoskie • Natalia L. Pacioni • Horacio Poblete • J. C. Scaiano Received: 13 July 2012 / Accepted: 12 December 2012 Ó Springer Science+Business Media Dordrecht 2012 Abstract Thermally denatured human serum albu- min interacts with *3.0 nm spherical AgNP enhanc- ing the fluorescence of Trp-214 at large protein/ nanoparticle ratios. However, using native HSA, no changes in the emission were observed. The observa- tion is likely due to differences between native and denatured protein packing resulting from protein corona formation. We have also found that NH 2 blocking of the protein strongly affects the ability of the protein to protect AgNP from different salts/ions such as NaCl, PBS, Hank’s buffer, Tris–HCl, MES, and DMEM. Additionally, AgNP can be readily prepared in aqueous solutions by a photochemical approach employing HSA as an in situ protecting agent. The role of the protein in this case is beyond that of protecting agent; thus, Ag ? ions and I-2959 complexation within the protein structure also affects the efficiency of AgNP formation. Blocking NH 2 in HSA modified the AgNP growth profile, surface plasmon band shape, and long-term stability suggest- ing that amine groups are directly involved in the formation and post-stabilization of AgNP. In particu- lar, AgNP size and shape are extensively influenced by NH 2 blocking, leading primarily to cubes and plates with sizes around 5–15 nm; in contrast, spherical monodisperse 4.0 nm AgNP are observed for native HSA. The nanoparticles prepared by this protocol are non-toxic in primary cells and have remarkable antibacterial properties. Finally, surface plasmon excitation of native HSA@AgNP promoted loss of protein conformation in just 5 min, suggesting that plasmon heating causes protein denaturation using continuous light sources such as commercial LED. Keywords Silver nanoparticles Á Human serum albumin Á Lysine residues Á Plasmon mediated protein denaturation Introduction Over the last two decades, metal nanoparticles have attracted a great deal of interest for biomedical Electronic supplementary material The online version of this article (doi:10.1007/s11051-012-1374-7) contains supplementary material, which is available to authorized users. E. I. Alarcon Á C. J. Bueno-Alejo Á C.W. Noel Á K. G. Stamplecoskie Á N. L. Pacioni Á J. C. Scaiano (&) Department of Chemistry, Centre for Catalysis Research and Innovation, University of Ottawa, 10 Marie Curie, Ottawa, ON K1N 6N5, Canada e-mail: tito@photo.chem.uottawa.ca Present Address: N. L. Pacioni INFIQC, Departamento de Quı ´mica Orga ´nica, Facultad de Ciencias Quı ´micas, Universidad Nacional de Co ´rdoba, Ciudad Universitaria, 5000 Cordoba, Argentina H. Poblete Center for Bioinformatics and Molecular Simulations, Universidad de Talca, 2 Norte 685, Casilla 721, Talca, Chile 123 J Nanopart Res (2013) 15:1374 DOI 10.1007/s11051-012-1374-7