Gold Nanoparticle Trimers Research Articles

A surface‐enhanced Raman‐spectroscopic study: Verification of the interparticle gap dependence of field enhancement by triangulation of spherical gold nanoparticle trimers

AbstractStrong electric field enhancement in the interparticle gap of resonators formed by two spherical Au nanoparticles occurs for polarization of the incoming light parallel to the dimer axis. This enhancement exhibits a strong dependence on gap width and is the basis of surface‐enhanced Raman scattering or tip‐enhanced Raman scattering. The enhancement factor as a function of gap width can be readily calculated solving Maxwellapos;s equations. However, the derived dependence is difficult to verify experimentally, in particular, because of the large uncertainty in determining the interparticle gap value, which is typically one or two orders of magnitude smaller than the diameters of the Au spherical nanoparticles forming the resonator. We demonstrate that a much more reliable verification of the predicted interparticle gap dependence of the electric field enhancement is possible using an approach analogous to triangulation in surveying and mapping.

Plasmonic Nanolenses: Electrostatic Self-Assembly of Hierarchical Nanoparticle Trimers and Their Response to Optical and Electron Beam Stimuli.

Asymmetric nanoparticle trimers composed of particles with increasing diameter act as "plasmonic lenses" and have been predicted to exhibit ultrahigh confinement of electromagnetic energy in the space between the two smallest particles. Here we present an electrostatic self-assembly approach for creating gold nanoparticle trimers with an assembly yield of over 60%. We demonstrate that the trimer assembly leads to characteristic red-shifts and show the localization of the relevant plasmon modes by means of cathodoluminescence and electron energy loss spectroscopy. The results are analyzed in terms of surface plasmon hybridization.

Multiple Resonances Induced by Plasmonic Coupling between Gold Nanoparticle Trimers and Hexagonal Assembly of Gold-Coated Polystyrene Microspheres.

Optical properties of a gold nanoparticle trimer assembly coupled with gold-coated hexagonally close-packed polystyrene microspheres were investigated by linear and nonlinear spectroscopy. The observed reflection spectrum shows multiple peaks from the visible to near-infrared spectral regions. The spectroscopic properties were also examined by a finite-difference time-domain simulation. We found that the optical response of plasmons excited in the gold nanoparticle trimers was significantly modulated by strong coupling of the plasmons and the photonic mode induced in the gold-coated polystyrene assembly. Two-photon induced photoluminescence and Raman scattering from the sample were investigated, and both signals were significantly enhanced at the gold nanoparticle assembly. The simulations reveal that the electric fields can be enhanced site-selectively, not only at the interstitial sites in the nanoparticle assembly but also at the gaps between the particle and the gold film due to plasmonic interactions, by tuning the wavelength and are responsible for the strong optical responses.

Optical properties and surface-enhanced Raman scattering activity of hexagonally arranged gold nanoparticle trimers

We studied optical properties of hexagonally arranged gold nanoparticle trimer assembly using optical microscopy. We found that the scattering spectrum showed multiple resonances in the visible region. We simulated the optical properties by assuming a pair of trimers as a model structure. The simulated spectrum reproduced the resonance features observed, and were assigned to plasmon-modes excited. Surface-enhanced Raman Scattering (SERS) activity of the assembly was found to be dependent on the excitation wavelength. The highest SERS enhancement was achieved with 633nm excitation, reaching 108. The wavelength-dependency of the activity indicates that plasmonic fields are responsible for the enhancement.

Nanoparticles: Modulation of Interparticle Distance in Discrete Gold Nanoparticle Dimers and Trimers by DNA Single‐Base Pairing (Small 26/2015)

The interparticle distance in gold nanoparticle trimers is modulated by T. Takarada and co-workers on page 3153. Each particle has one long DNA (green) and several short DNAs (orange). The long DNA serves to align the particles on a template DNA (purple). When the complementary DNA (blue) is hybridized to the short DNA, the interparticle distance is spontaneously decreased in the presence of salt (right front). However, no shrinkage occurs with the terminal-mismatched DNA (yellow) under the same conditions (left front).

Heavy Metal Detection: Triple Raman Label‐Encoded Gold Nanoparticle Trimers for Simultaneous Heavy Metal Ion Detection (Small 28/2015)

A stable and reliable SERS method for simutaneous Hg2+ and Ag2+ detection is demonstrated by H. Kuang and co-workers based on gold nanoparticle trimers, using T-Hg2+-T and C-Ag+-C mismatched base pairs. On page 3435, the LOD values are 1.69 for Hg2+ and 1.71 pg mL−1 for Ag+. Due to the significant enhancement of the electromagnetic field from gold nanoparticle trimers, this method is the most sensitive method so far for simultaneous heavy metal ion detection.