Mixing thiols on the surface of silver nanoparticles: preserving antibacterial properties while introducing SERS activity
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Controlling the surface composition of self-assembled monolayers is one of the major experimental challenges in nanotechnology. Despite the significant interest of the scientific community and the considerable number of publications related to this topic, the potential in this field is still far from being fully exploited.We present in this study a versatile method to coat silver nanoparticles (AgNPs) having average diameter of 7 nm with mixed monolayers of two thiols, achieving a precise control of surface composition. Different combinations of thiols have been investigated, and the nanomaterials obtained have been characterized by complementary experimental techniques, addressing the composition of the mixed monolayer. The surface-enhanced Raman spectroscopy (SERS) effect on a Raman reporter (7-mercapto-4-methylcoumarine) introduced into the mixed monolayers has also been investigated. The antibacterial activity of the coated AgNPs was investigated, showing that the colloids were active against Escherichia coli and Staphilococcus aureus irrespective of the nature of the mixed monolayer. These materials are good candidates as SERS-tags for biological applications.
KeywordsSilver nanoparticles Mixed monolayers Self-assembled monolayers SERS Antibacterial activity Colloids
Funding for this research has been granted by Fondazione Cariplo (Bandi Ricerca Scientifica e Tecnologica sui Materiali Avanzati, 2010-0454), the Ministero dell’Istruzione, the Università e Ricerca (MIUR), the Almamater Foundation (Pavia) (project: Nanomedicine in ageing-associated prototypic diseases), and the Regione Lombardia (project SAL-45). The authors also want to thank Vittorio Necchi and Centro Grandi Strumenti, the University of Pavia; and Lucia Cucca, the Dipartimento di Chimica, the University of Pavia.
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