title: Structure-activity relationships in gold nanoparticle dimers and trimers for surface-enhanced Raman spectroscopy.
abstract: Understanding the detailed relationship between nanoparticle structure and activity remains a significant challenge for the field of surface-enhanced Raman spectroscopy. To this end, the structural and optical properties of individual plasmonic nanoantennas comprised of Au nanoparticle assemblies that are coated with organic reporter molecules and encapsulated by a SiO(2) shell have been determined using correlated transmission electron microscopy (TEM), dark-field Rayleigh scattering microscopy, surface-enhanced Raman scattering (SERS) microscopy, and finite element method (FEM) calculations. The distribution of SERS enhancement factors (EFs) for a structurally and optically diverse set of nanoantennas is remarkably narrow. For a collection of 30 individual nanoantennas ranging from dimers to heptamers, the EFs vary by less than 2 orders of magnitude. Furthermore, the EFs for the hot-spot-containing nanoparticles are uncorrelated to aggregation state and localized surface plasmon resonance (LSPR) wavelength but are crucially dependent on the size of the interparticle gap. This study demonstrates that the creation of hot spots, where two particles are in subnanometer proximity or have coalesced to form crevices, is paramount to achieving maximum SERS enhancements.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Kristin L
authors.initials: KL
authors.lastname: Wustholz
authors.forename: Anne-Isabelle
authors.initials: AI
authors.lastname: Henry
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: McMahon
authors.forename: R Griffith
authors.initials: RG
authors.lastname: Freeman
authors.forename: Nicholas
authors.initials: N
authors.lastname: Valley
authors.forename: Marcelo E
authors.initials: ME
authors.lastname: Piotti
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Natan
authors.forename: George C
authors.initials: GC
authors.lastname: Schatz
authors.forename: Richard P
authors.initials: RP
authors.lastname: Van Duyne
mesh_terms: D019281:Dimerization; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013059:Spectrum Analysis, Raman
chemical_list: D006046:Gold; D012822:Silicon Dioxide