Publications
Publications on Plasmon Resonant Nanoparticles from the plasmonics group at UCSDBelow are the titles and abstracts of our publications on the subject of Plasmon Resonant Nanoparticles. Updated on November 28, 2003.
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Local Refractive Index Dependence of Plasmon Resonance Spectra from Individual Nanoparticles
Jack J. Mock, David R. Smith, and Sheldon Schultz
Nanoletters, 3, 485 (2003)Abstract: We present an experimental optical darkfield microscope study of the dependence of the plasmon resonance spectrum of individual silver nanoparticles on the local index of refraction. We systematically characterize the position of the resonance peaks associated with the same set of individual silver nanoparticles embedded sequentially in index oils with increasing refractive index. This technique effectively allows the local refractive index to be stepped in increments of 0.04. As the local index is increased, the spectrum from each of the nanoparticles generally undergoes a very regular and reproducible red shift; however, we find that the amount of red shift per index increase varies depending on the shape of the nanoparticle and the mode of excitation. In particular, we find that the spectral peak that occurs in triangular nanoparticles exhibits a noticeably larger red shift than that associated with the dipole mode corresponding to spherical nanoparticles. Our results are consistent with experiments performed on ensembles of similar nanoparticles and suggest that individual nanoparticles may be utilized in biosensing applications where currently ensembles are being investigated.
Interparticle Coupling Effects on Plasmon Resonances of Nanogold Particles
K.-H. Su, Q.-H. Wei, X. Zhang, J.J. Mock, D. R. Smith, and S. Schultz
Nanoletters, 3, 1087 (2003).Abstract: The collaborative oscillation of conductive electrons in metal nanoparticles results in a surface plasmon resonance that makes them useful for various applications including biolabeling. We investigate the coupling between pairs of elliptical metal particles by simulations and experiments. The results demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling. It is also found that the shift decays approximately exponentially with increasing particle spacing and become negligible when the gap between the two particles exceeds about 2.5 times the particle short-axis length.
Composite Plasmon Resonant Nanowires
J.J. Mock, S.J. Oldenburg, D.R. Smith, D.A. Schultz, and S. Schultz
Nanoletters 2, 465 (2002)Abstract: We present an experimental study of the polarization dependent scattering of light from homogeneous and multisegment silver, gold, andnickel nanowires. The metallic nanowires are prepared within a polycarbonate membrane template by a combination of electroplating (gold and nickel) and electroless (silver) growth processes. The size range of the nanowire segments is such that surface plasmon resonances are supported, dominating the optical spectra. We characterize the light scattering properties of individual composite nanowires using an optical microscope configured for single particle spectroscopy. Because of the scattering efficiency associated with the plasmon resonance, very narrow (~30 nm diameter) nanowires can be readily observed under white-light illumination, with the spectral characteristics of each subsection easily distinguishable. Because of their compactness, these simply prepared multiisegment plasmon resonant nanowires are capable of hosting a large number of segment sequences over a comparatively small spatial range, suggesting their possible application as unique nanolabels in biological assays.
Single Crystal Silver Nanowires Prepared by the Metal Amplification Method
Mladen Barbic, Jack J. Mock, D.R. Smith, and S. Schultz
Journal of Applied Physics, 91, 9341(2002)Abstract: We present a method of fabricating single crystal silver nanowires based on the electroless deposition of silver into the pores of the polycarbonate membranes by the metal amplification process. A gold film on one side of the nanoporous membrane is used as the initiation layer for the silver crystal growth, while the pores of the membrane are used for guiding the growth of the silver crystal into a cylindrical nanostructure. Optical microscopy and spectroscopy of individual nanowires, transmission electron microscopy ~TEM!, and TEM diffraction crystallography were used to characterize the silver nanostructures. The metal amplification technique presents an electroless, simple, and inexpensive solution to the challenge of fabricating silver nanowires for electronic, optical, and biological applications.
Shape Effects in Plasmon Resonance of Individual Colloidal Silver Nanoparticles
J.J. Mock, M. Barbic, D. R. Smith, D.A. Schultz, and S. Schultz
Journal of Chemical Physics, 116, 6755 (2002)Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources covering the full range of wavelengths in the
visible spectrum.
Single-target Molecule Detection with Nonbleaching Multicolor Optical Immunolabels
Sheldon Schultz, David R. Smith, Jack J. Mock, and D.A. Schultz
PNAS, 97, 996 (2000).Abstract: We introduce and demonstrate the use of colloidal silver plasmonresonant particles (PRPs) as optical reporters in typical biological assays. PRPs are ultrabright, nanosized optical scatterers, which scatter light elastically and can be prepared with a scattering peak at any color in the visible spectrum. PRPs are readily observed individually with a microscope configured for dark-field microscopy, with white-light illumination of typical power. Here we illustrate the use of PRPs, surface coated with standard ligands, as target-specific labels in an in situ hybridization and an immunocytology assay. We propose that PRPs can replace or complement established labels, such as those based on radioactivity, fluorescence, chemiluminescence, or enzymaticycolorimetric detection that are used routinely in biochemistry, cell biology, and medical diagnostic applications. Moreover, because PRP labels are nonbleaching and bright enough to be rapidly identified and counted, an ultrasensitive assay format based on single-target molecule detection is now practical. We also present the results of a model sandwich immunoassay for goat anti-biotin antibody, in which the number of PRP labels counted in an image constitutes the measured signal.