Refractive Index Susceptibility of the Plasmonic Palladium Nanoparticle: Potential as the Third Plasmonic Sensing Material

Abstract

We demonstrate that Pd nanospheres exhibit much higher susceptibility of the localized surface plasmon resonance (LSPR) peak to medium refractive index changes than commonly used plasmonic sensing materials such as Au and Ag. The susceptibility of spherical Au nanoparticle-core/Pd-shell nanospheres (Au/PdNSs, ca. 73 nm in diameter) was found to be 4.9 and 2.5 times higher, respectively, than those of Au (AuNSs) and Ag nanospheres (AgNSs) having similar diameters. The experimental finding was theoretically substantiated using the Mie exact solution. We also showed from a quasi-static (QS) approximation framework that the high susceptibility of Pd LSPR originates from the smaller dispersion of the real part of its dielectric function than those of Au and Ag LSPR around the resonant wavelength. We conclude that the Pd nanoparticle is a promising candidate of "the third plasmonic sensing material" following Au and Ag to be used in ultrahigh-sensitive LSPR sensors.

Multi-Band High Refractive Index Susceptibility of Plasmonic Structures with Network-Type Metasurface

“…For the dip at λ 4 = 749 nm, strong dipolar plasmonic mode is also found. Notably, strong field intensity in the periodic dielectric layer and PMMA film can also be observed here, corresponding to the excitation of photonic mode and optical cavity mode [8,29]. The interaction between dipolar plasmonic mode, photonic mode, and optical cavity mode leads to the ultra-narrow reflection dip at λ 4 =749 nm.…”

“…Figure 3 shows snapshots of electric field intensity distributions for these six reflection dips. For the dip at λ 1 = 602 nm, butterfly-like distributions near the Au spacers between adjacent air nanoholes are observed, indicating the excited quadruple plasmonic mode with anti-parallel hybridized plasmons between adjacent Au spacers [8,32,33]. As a result, a Fano-type spectral line shape is obtained.…”

“…The coupling of light with surface plasmons can be controlled to obtain novel performances, e.g., enhanced optical transmission, strong field confinement, and Fano resonances [3][4][5][6][7]. These remarkable features endow plasmonic structures an extreme sensitivity to the refractive index (RI) change of surrounding mediums with the penetration depth of the evanescent field [5,[8][9][10][11]. Based on the susceptibility to the change in RI of surrounding mediums due to the spectral shift caused by the excited surface plasmons [10][11][12], a promising technology has been developed for simple, label-free, cost-effective, and real-time optical sensing [8,[13][14][15].…”

“…These remarkable features endow plasmonic structures an extreme sensitivity to the refractive index (RI) change of surrounding mediums with the penetration depth of the evanescent field [5,[8][9][10][11]. Based on the susceptibility to the change in RI of surrounding mediums due to the spectral shift caused by the excited surface plasmons [10][11][12], a promising technology has been developed for simple, label-free, cost-effective, and real-time optical sensing [8,[13][14][15]. So far, numerous sensors based on metallic nanostructures have been witnessed and widely employed for the detection of various analytes including cancer biomarkers, hazardous or toxic gases, DNA, and so on [15][16][17][18][19][20].…”

“…Metallic nanoparticles have been demonstrated with high susceptibility to the change in RI of surrounding mediums, and their RI sensitivity can be largely enhanced by optimizing the shapes, sizes, and arrangement of metallic nanoparticles [8][9][10][11]. Consequently, metallic nanoparticles have also been used to act as the sensor materials due to their inherent high susceptibility for the RI changes in environment.…”