title: Gold Nanopyramids Assembled into High-Order Stacks Exhibit Increased SERS Response.
abstract: This Letter describes how gold pyramidal nanoshells (nanopyramids) can be assembled into low- and high-order structures by varying the rate of solvent evaporation and surface wettability. Single-particle and individual-cluster dark field scattering spectra on isolated, dimers and trimers of nanopyramids were compared. We found that the short wavelength resonances blue-shifted as the particles assembled; the magnitude of this shift was greater for high-order structures. To test which assembled architecture supported a larger Raman-active volume, we compared their surface enhanced Raman scattering (SERS) response of the resonant Raman molecule methylene blue (λ(ex) = 633 nm). We discovered that high-order structures exhibited more Raman scattering compared to low-order assemblies. Finite-difference time-domain modeling of nanopyramid assemblies revealed that the highest electromagnetic field intensities were localized between adjacent particle faces, a result that was consistent with the SERS observations. Thus, the local spatial arrangement of the same number of nanoparticles in assembled clusters is an important design parameter for optimizing nanoparticle-based SERS sensors.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113.
authors.forename: Kelsey A
authors.initials: KA
authors.lastname: Stoerzinger
authors.forename: Warefta
authors.initials: W
authors.lastname: Hasan
authors.forename: Julia Y
authors.initials: JY
authors.lastname: Lin
authors.forename: Alex
authors.initials: A
authors.lastname: Robles
authors.forename: Teri W
authors.initials: TW
authors.lastname: Odom