title: Direct Cross-Linking of Au/Ag Alloy Nanoparticles into Monolithic Aerogels for Application in Surface-Enhanced Raman Scattering.
abstract: The direct cross-linking of Au/Ag alloy nanoparticles (NPs) into high surface area, mesoporous Au/Ag aerogels via chemical oxidation of the surface ligands is reported. The precursor alloy NPs with composition-tunable morphologies were produced by galvanic replacement of the preformed Ag hollow NPs. The effect of Au:Ag molar ratio on the NP morphology and surface plasmon resonance has been thoroughly investigated and resulted in smaller Au/Ag alloy NPs (4-8 nm), larger Au/Ag alloy hollow NPs (40-45 nm), and Au/Ag alloy hollow particles decorated with smaller Au NPs (2-5 nm). The oxidative removal of surfactant ligands, followed by supercritical drying, is utilized to construct large (centimeter to millimeter) self-supported Au/Ag alloy aerogels. The resultant assemblies exhibit high surface areas (67-73 m(2)/g), extremely low densities (0.051-0.055 g/cm(3)), and interconnected mesoporous (2-50 nm) networks, making them of great interest for a number of new technologies. The influence of mesoporous gel morphology on surface-enhanced Raman scattering (SERS) has been studied using Rhodamine 101 (Rd 101) as the probe molecule. The alloy aerogels exhibit SERS signal intensities that are 10-42 times higher than those achieved from the precursor Au/Ag alloy NPs. The Au/Ag alloy aerogel III exhibits SERS sensing capability down to 1 nM level. The increased signal intensities attained for alloy aerogels are attributed to highly porous gel morphology and enhanced surface roughness that can potentially generate a large number of plasmonic hot spots, creating efficient SERS substrates for future applications.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Gao
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Richard J Alan
authors.initials: RJ
authors.lastname: Esteves
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Lamia
authors.initials: L
authors.lastname: Nahar
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Jordan
authors.initials: J
authors.lastname: Nowaczyk
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284-2006, United States.
authors.forename: Indika U
authors.initials: IU
authors.lastname: Arachchige
keywords: Au/Ag alloy nanoparticles; direct cross-linking; nanoparticle assembly; sol−gel method; surface-enhanced Raman spectroscopy