Plasmonic refractive index sensing using strongly coupled metal nanoantennas: nonlocal limitations

Abstract

Localized surface plasmon resonance based on coupled metallic nanoparticles has been extensively studied in the refractive index sensing and the detection of molecules. The amount of resonance peak-shift depends on the refractive index of surrounding medium and the geometry/symmetry of plasmonic oligomers. It has recently been found that as the feature size or the gap distance of plasmonic nanostructures approaches several nanometers, quantum effects can change the plasmon coupling in nanoparticles. However, most of the research on plasmonic sensing has been done based on classical local calculations even for the interparticle gap below ~3 nm, in which the nonlocal screening plays an important role. Here, we theoretically investigate the nonlocal effect on the evolution of various plasmon resonance modes in strongly coupled nanoparticle dimer and trimer antennas with the gap down to 1 nm. Then, the refractive index sensing in these nonlocal systems is evaluated and compared with the results in classical calculations. We find that in the nonlocal regime, both refractive index sensibility factor and figure of merit are actually smaller than their classical counterparts mainly due to the saturation of plasmon shifts. These results would be beneficial for the understanding of interaction between light and nonlocal plasmonic nanostructures and the development of plasmonic devices such as nanosensors and nanoantennas.

Influence of the CTAB surfactant layer on optical properties of single metallic nanospheres

“…The confinement of electric field of nanoparticles deposited on a substrate is usually concentrated near the surface for dipolar mode. Moreover, an electron cloud oscillating in higher refractive index of substrate than superstrate (air) result in a redshift of plasmonic modes due to reduction of polarization charges, therefore the restoring force and the frequency [35,36]. This reduction of polarization charges depends on the intersection of the nanoparticle-surface interfaces.…”

Plasmonics of regular shape particles, a simple group theory approach

“…At these points, light is confined in subwavelength distances (< 20 nm) and field amplitudes are large [2,3]. The ability to produce and control hot spots offers great promises for many applications, including sensing [4][5][6], heating [7,8], photosynthesis [9,10], oncology [11][12][13], imaging [14,15], computer science [16] and many others. In view of the technological applications envisaged, it is necessary to develop simple methods to investigate this phenomenon.…”

Formation of anisotropic gold nanoparticles on indium tin oxide substrates as a plasmonic sensing material

“…The most commonly used are isotropic NPs, namely nanospheres, due to their simple and easy preparation and synthesizing method. 20,22 However, the application of metal nanospheres in plasmonic sensing is limited due to their weak and size-dependent absorption strength. Nanostructures of larger diameters also have the effect of producing broader spectra, yielding lower sensitivity.…”

“…Metal NPs have a unique optical properties obtained from the interaction of light and electron on the surface called localized surface plasmon resonance (LSPR). 14 The characteristics of LSPR adsorption are highly dependent on the particle size, 15 shape, 16 composition 17 and the dielectric constant 18,19 of the surrounding medium 20,21 and have a potential in plasmonic sensing applications. The most commonly used are isotropic NPs, namely nanospheres, due to their simple and easy preparation and synthesizing method.…”