Abstract
We experimentally demonstrate that introduction of a dielectric film can prevent the surface plasmon resonance (SPR) curve from being shifted to a smaller angle, called negative shift, which occurs unpredictably when metallic nanostructures deposited on a metal film are exposed to an adsorption of binding analytes. From parylene coating experiments, we find that the proposed reflection-type SPR system with a low refractive index MgF2 film and gold nanorods can provide an enhanced sensitivity by more than 6 times as well as a reliable positive shift. It is due to the fact that use of a dielectric film can contribute to the compensation of an anomalous dispersion relation and the prevention of a destructive interaction of propagating surface plasmons with multiple localized plasmon modes. Our approach is intended to show the feasibility and extend the applicability of the proposed SPR system to diverse biomolecular reactions.
Highlights
Surface plasmons are transverse magnetic (TM) polarized waves trapped along a metaldielectric interface
For our experiment based on randomly distributed gold nanorods, damping-related back-bending of plasmon momentum kicks in, which induces the resonance momentum to be smaller with an increasing adsorption, in a way complicated by the presence of gold nanorods [15]
We proposed the surface plasmon resonance (SPR) substrates with MgF2 dielectric film between a gold film and gold nanorods to avoid an unpredictable behavior of negative shift in a sensitive plasmonic biosensor
Summary
Surface plasmons are transverse magnetic (TM) polarized waves trapped along a metaldielectric interface. Alternative SPR scheme with metallic nanogratings deposited on a metal film was proposed to improve the sensitivity while maintaining its intrinsic label-free detection [6,7] In principle, this approach could serve as an effective way to increase a surface reaction area and to generate a highly confined localized surface plasmon (LSP) modes, thereby increasing the field-matter interaction [8]. When an excitation of LSP mode becomes dominant, especially for extremely fine or densely packed gold nanogratings, the SPR curves are greatly distorted by multiple LSP excitations, often resulting in the negative shift It does not adversely affect the SPR sensing performance as long as the nature of the shift is a priori known, the negative shift is unpredictable and is generally accompanied by a notable degradation of SPR signal quality. This study will serve as the first step to demonstrate the possibility of guaranteeing a reliable and positive SPR signal amplification as well as the feasibility of improving field-matter interaction for recognizing biomolecular reactions of low molecular weights
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