Dumbbell gold nanoparticle dimer antennas with advanced optical properties

Abstract

Plasmonic nanoantennas have found broad applications in the fields of photovoltaics, electroluminescence, non-linear optics and for plasmon enhanced spectroscopy and microscopy. Of particular interest are fundamental limitations beyond the dipolar approximation limit. We introduce asymmetric gold nanoparticle antennas (AuNPs) with improved optical near-field properties based on the formation of sub-nanometer size gaps, which are suitable for studying matter with high-resolution and single molecule sensitivity. These dumbbell antennas are characterized in regard to their far-field and near-field properties and are compared to similar dimer and trimer antennas with larger gap sizes. The tailoring of the gap size down to sub-nanometer length scales is based on the integration of rigid macrocyclic cucurbituril molecules. Stable dimer antennas are formed with an improved ratio of the electromagnetic field enhancement and confinement. This ratio, taken as a measure of the performance of an antenna, can even exceed that exhibited by trimer AuNP antennas composed of comparable building blocks with larger gap sizes. Fluctuations in the far-field and near-field properties are observed, which are likely caused by distinct deviations of the gap geometry arising from the faceted structure of the applied colloidal AuNPs.

Nanoscopy through a plasmonic nanolens

“…Theory and Simulations. Previous studies utilizing NPoMs [also known as particle-over-substrate, metal-insulator-metal waveguide, nanogap patch antenna (6) and equivalent to NP dimers, dumbbells (28), or homodimers (29)] suggest that light in the cavity is out-coupled through 1 of 2 antenna modes, either a transverse particle mode or a longer-wavelength, vertical-field gap mode (6,(30)(31)(32). Recent works show that emitters in the NPoM gap radiate dominantly through the gap mode, because of its stronger enhancement and radiative efficiency (33,34).…”

Correlation of surface-enhanced Raman scattering (SERS) with the surface density of gold nanoparticles: evaluation of the critical number of SERS tags for a detectable signal

“…Importantly, the AuNTs show several junctions between plasmonic nanoparticles, which are well known sites of electromagnetic enhancement, as required for SERS [49–54]. This corresponds to a constellation of electromagnetic hot spots inside each nanoaggregate, where the local field enhancement is achieved in order to amplify the Raman signal of the adsorbed molecules by several orders of magnitude.…”

Nanodiamonds and gold nanoparticles to obtain a hybrid nanostructure with potential applications in biomedicine

“…However, here, AuNPs are acting as fluorescence enhancers, without a typical donor-acceptor situation; showing a conduct like the one called the antenna effect [37]. According to the findings of Herrmann et al [38], in the case of high quantum yield emitters, the emission of fluorescence can be enhanced by an electric field associated to the excitation of localized plasmon modes in noble metal NPs. FITC is a high quantum yield emitter [39] and its interaction with gold from the hybrids could trigger an amplification of the emitted fluorescence similar to what occurs in the antenna effect, but to verify the real occurrence of this effect we need to perform experiments not included in this work.…”