title: Catalytic effects of silver plasmonic nanoparticles on the redox reaction leading to ABTS˙+formation studied using UV-visible and Raman spectroscopy.
abstract: ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) is a compound extensively employed to evaluate the free radical trapping capacity of antioxidant agents and complex mixtures such as biological fluids or foods. This evaluation is usually performed by using a colourimetric experiment, where preformed ABTS radical cation (ABTS˙+) molecules are reduced in the presence of an antioxidant causing an intensity decrease of the specific ABTS˙+UV-visible absorption bands. In this work we report a strong effect of silver plasmonic nanoparticles (Ag NPs) on ABTS leading to the formation of ABTS˙+. The reaction of ABTS with Ag NPs has been found to be dependent on the interfacial and plasmonic properties of NPs. Specifically, this reaction is pronounced in the presence of spherical nanoparticles prepared by the reduction of silver nitrate with hydroxylamine (AgH) and in the case of star-shaped silver nanoparticles (AgNS). On the other hand, spherical nanoparticles prepared by the reduction of silver nitrate with citrate apparently do not react with ABTS. Additionally, the formation of ABTS˙+is investigated by surface-enhanced Raman scattering (SERS) and the assignment of the most intense vibrational bands of this compound is performed. The SERS technique enables us to detect this radical cation at very low concentrations of ABTS (∼2 μM). Altogether, these findings allow us to suggest the use of ABTS/Ag NPs-systems as reliable and easy going substrates to test the antioxidant capacity of various compounds, even at concentrations much lower than those usually used in the spectrophotometric assays. Moreover, we have suggested that ABTS could be employed as a suitable agent to investigate the interfacial and plasmonic properties of the metal nanoparticles and, thus, to characterize the nanoparticle metal systems employed for various purposes.
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Garcia-Leis
authors.affiliation: Department of Biophysics, Faculty of Science, P.J. Safarik University in Kosice, Jesenna 5, 041 54 Kosice, Slovak Republic. zuzana.jurasekova@upjs.sk and Center for Interdisciplinary Biosciences, Faculty of Science, P.J. Safarik University in Kosice, Jesenna 5, 041 54 Kosice, Slovak Republic.
authors.forename: D
authors.initials: D
authors.lastname: Jancura
authors.affiliation: Institute of Experimental Physics, SAS, Watsonova 47, 041 01 Kosice, Slovak Republic and Department of Biochemistry, Faculty of Science, P.J. Safarik University in Kosice, Srobarova 2, 040 01 Kosice, Slovak Republic.
authors.forename: M
authors.initials: M
authors.lastname: Antalik
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid, Spain.
authors.forename: J V
authors.initials: JV
authors.lastname: Garcia-Ramos
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, 28006 Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Sanchez-Cortes
authors.affiliation: Department of Biophysics, Faculty of Science, P.J. Safarik University in Kosice, Jesenna 5, 041 54 Kosice, Slovak Republic. zuzana.jurasekova@upjs.sk and Center for Interdisciplinary Biosciences, Faculty of Science, P.J. Safarik University in Kosice, Jesenna 5, 041 54 Kosice, Slovak Republic.
authors.forename: Z
authors.initials: Z
authors.lastname: Jurasekova