Surface-enhanced Raman scattering (SERS) intensities for individual Au nanospheres, nanoshells, and nanosphere and nanoshell dimers coated with nonresonant molecules are measured, where the precise nanoscale geometry of each monomer and dimer is identified through in situ atomic force microscopy. The observed intensities correlate with the integrated quartic local electromagnetic field calculated for each specific nanostructure geometry. In this study, we find that suitably fabricated nanoshells can provide SERS enhancements comparable to nanosphere dimers.

Au and Ag nanoshells are investigated as substrates for surfaceenhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 ؋ 10 10 on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.nanoparticles ͉ nanoshells ͉ plasmons ͉ spectroscopy S ince the initial discovery of surface-enhanced Raman scattering (SERS) (1-4), understanding how the local electromagnetic environment enhances the substrate-adsorbate complex's spectral response has been of central importance. It has become increasingly evident that plasmon resonances of the metallic substrate provide intense, local optical-frequency fields responsible for the electromagnetic contribution to SERS (5-7).The lack of reliable techniques for controlling the properties of the local field at the metal surface has been a major experimental limitation in the quantification and understanding of SERS. A striking example of this is the series of experiments reporting enormous SERS enhancements of 10 12 to 10 15 for dye molecules adsorbed on surfaces of aggregated Au and Ag colloid films (6,8,9). The SERS enhancements reported in these experiments have been attributed to localized plasmons, or ''hot spots,'' occurring randomly across this film that fortuitously provide the appropriate electromagnetic nanoenvironment for large SERS enhancements (10). More recent studies have shown that localized plasmons giving rise to very large field enhancements can be formed at the junctions between adjacent nanoparticles (11,12). These plasmons can be described within the plasmon hybridization picture as dimer resonances (13-15). Likewise, self-similar geometries also provide a means for developing large field enhancements (10, 16).Several experimentally realizable geometries, such as triangles (17), nanorings (18), and nanoshells (19), support well defined plasmon resonances whose frequencies can be controlled by judicious modification of the geometry of the nanoparticle. Each of these nanostructured geometries offers its own unique nearfield properties: plasmon resonant frequency, spatial distribution of the near-field amplitude across the surface of the nanostructure, orientation dependence on polarization of the incident light wave, and spatial extent of the near field. The near-field properties of metallic nanoparticles can be calculated very precisely by a variety of methods, such as analytic Mie scattering theory for high-symmetry geometries, and numerical methods such as the discrete dipole approximation (DDA) (20) and the finite difference time domain (21) methods for nanoscale objects of reduced symmetry. Thus, we can approac...

A rapid immunoassay capable of detecting analyte within complex biological media without any sample preparation is described. This was accomplished using gold nanoshells, layered dielectric-metal nanoparticles whose optical resonance is a function of the relative size of its constituent layers. Aggregation of antibody/nanoshell conjugates with extinction spectra in the near-infrared was monitored spectroscopically in the presence of analyte. Successful detection of immunoglobulins was achieved in saline, serum, and whole blood. This system constitutes a simple immunoassay capable of detecting sub-nanogram-per-milliliter quantities of various analytes in different media within 10-30 min.

Gold nanoshells, nanoparticles consisting of a silica core coated with a thin gold shell, exhibit a strong optical resonance that depends sensitively on their core radius and shell thickness. Gold nanoshells have been fabricated with a peak optical extinction that can be varied across the near-infrared region of the spectrum (800 nm–2.2 μm). Multipolar plasmon resonances are clearly resolvable in the extinction spectra and agree well with electromagnetic theory. Additional resonances due to particle aggregation are also observed. The frequency agile infrared properties of these nanoparticles make them particularly attractive for a range of technologically important applications.

This paper describes the functionalization of the surfaces of gold nanoshells, which consist of silica nanoparticles coated with a continuous thin layer of gold. Previous studies have shown that gold nanoshells exhibit optical properties similar to those of metal colloids (e.g., strong optical absorptions and large third-order nonlinear optical polarizabilities). In contrast to metal colloids, however, the plasmon resonance of the nanoshells can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum by adjusting the relative size of the dielectric core and the thickness of the gold overlayer. In efforts to develop new strategies for protecting and manipulating these nanoparticles, this paper describes the functionalization of the surfaces of gold nanoshells with self-assembled monolayers derived from the adsorption of a series of alkanethiols. The nanoshells are characterized by transmission electron microscopy, UV−vis spectroscopy, FTIR spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy and by examining their relative solubility in a variety of organic solvents.

Systematic variation of the internal geometry of a dielectric core-metal shell nanoparticle allows the local electromagnetic field at the nanoparticle surface to be precisely controlled. The strength of the field as a function of core and shell dimension is measured by monitoring the surface enhanced Raman scattering (SERS) response of nonresonant molecular adsorbates (para-mercaptoaniline) bound to the nanoparticle surface. The SERS enhancement appears to be directly and exclusively due to nanoparticle geometry. Effective SERS enhancements of 106 are observable in aqueous solution, which correspond to absolute enhancements of 1012 when reabsorption of Raman emission by nearby nanoparticles is taken into account.

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Metal nanoshells are nanoscale optical components that allow for the controllable redirection of electromagnetic radiation via careful engineering of their multilayer structures. By varying the core size and shell thickness of these nanoparticles, nanoscale “antennas” are constructed that can be selectively driven into a dipolar or quadrupolar oscillation pattern. With scattering cross sections many times larger than their physical cross section, these antennas efficiently couple to the incident electromagnetic wave. These structures can focus, redirect, or split the incident light with subwavelength precision, and may find useful applications in the remote coupling of electromagnetic signals into nanoscale machines or devices.