Joseph B. Jackson

INFRARED EXTINCTION PROPERTIES OF GOLD NANOSHELLS

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.

Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates

Au and Ag nanoshells are investigated as substrates for surface-enhanced 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 × 1010 on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.

CONTROLLING THE SURFACE ENHANCED RAMAN EFFECT VIA THE NANOSHELL GEOMETRY

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.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.

Light scattering from dipole and quadrupole nanoshell antennas

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.

Enhancing the active lifetime of luminescent semiconducting polymers via doping with metal nanoshells

We report a dramatic, concentration-dependent decrease in the rate of photo-oxidation of semiconducting polymers due to the addition of small amounts of metal nanoshells to the polymer. In each case, the nanoshell resonances are tuned to the triplet exciton-ground state energy of the polymer. The nanoshell dopants slow the oxidation rate yet do not affect the photoluminescent properties of the polymers to which they have been added.

A rapid, whole blood immunoassay using metal nanoshells

Using metal nanoshells as an immunoassay substrate, we describe an immunoassay capable of detecting blood borne analyte on the order of minutes. Near infrared resonant gold nanoshells were labeled with antibodies specific to rabbit IgG analyte. The antibody-nanoshell conjugates were detectable via near infrared photometry in solution with saline, serum, and whole blood. Addition of analyte induced aggregation of antibody-nanoshell conjugates, causing a decrease in the original nanoshell near infrared resonance. Aggregation proceeded in a concentration dependent fasion in all three mediums (saline, serum, whole blood), permitting quantitative detection of analyte within 10-30 minutes and sensitivities <1 ng/mL.

Plasmon-plasmon interaction between gold nanoshells and gold surfaces

Summary form only given. Gold nanoshells are colloidal particles with a dielectric core covered by a gold shell. The plasmon resonance of the nanoshells can be tuned by varying the ratio of the core/shell radii. An enhancement in the electromagnetic energy can be found, at resonance, in the region close to the nanoshell known as the near field. It has been shown theoretically and experimentally that if the evanescent near fields of a surface plasmon polariton and a particle plasmon overlap, an efficient exchange of energy from the freely propagating electromagnetic waves into surface plasmons can be achieved. Previous experiments used particles that lacked the extraordinary tunability of nanoshells. We give our sample geometry. After evaporating a layer of gold onto a glass slide, we deposit self-assembled monolayers (SAMs) of a polymer (PDDA) and Hectorite (a synthetic clay), to control the spacing between the gold surface and the nanoshells.

Multipole resonant light scattering properties of gold nanoshells

Summary form only given. Metal nanoshells, spherical dielectric nanoparticles coated with an ultrathin, homogeneous metallic layer, provide a concentric sphere scattering geometry which is ideal for the selective excitation of multipole plasmon resonances in metal nanostructures. In the metal nanoshell geometry, the plasmon resonance frequency is a sensitive function of the relative dimensions of the core and shell, and can be shifted hundreds of nanometers in wavelength from the plasmon resonance of the corresponding solid metal nanoparticle.