Interparticle Coupling-Enhanced Detection
When the distances between two or more plasmonic nanoparticles are very small, the plasmon resonance scattering spectra are greatly enhanced and distinct colour changes occur due to the coupling of the particles. Similar to fluorescence resonance energy t
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Interparticle Coupling-Enhanced Detection
Abstract When the distances between two or more plasmonic nanoparticles are very small, the plasmon resonance scattering spectra are greatly enhanced and distinct colour changes occur due to the coupling of the particles. Similar to fluorescence resonance energy transfer, plasmonic coupling is also distance dependent. Thus, researchers have fabricated colorimetric sensors by modulating the distance between nanoparticles, which have been used in a wide variety of applications, including DNA hybridisation, heavy-metal-ion detection, and protein binding. In this chapter, we primarily focus on the coupling of single particles, which enables the single-molecule detection through enhanced sensitivity. Keywords Interparticle coupling • Chains of metal nanoparticles • Biosensors • Biomolecular detection • Cell imaging • Plasmonic nanopores
5.1 Fundamentals of Plasmonic Coupling The coupling of plasmonics enhances the resonance intensity significantly and enables variable sensitive biosensors [1–11]. The factors that affect the coupling of nanoparticles include their particle size, coupling number, distance, direction, and shape [12–17]. Lee calculated the influence of particle size, number, composition, and distance using the generalised multiparticle Mie formalism [18]. The satellites in this work were made of gold with a relative permeability μ = 1. Cores composed of either gold or glass were considered. The surrounding medium was assumed to be free space with a permittivity ε = μ = 1. The permittivity of the glass core was 2.25. As shown in Fig. 5.1a, as the satellite number increased, the scattering peak wavelength exhibited a nearly linear redshift. For rcore = 50 nm, rsat = 10 nm, and dsat = 2 nm, the redshift was approximately 1 nm per satellite. Although these calculations may not accurately reflect absolute quantities, they reveal the trends in the peak wavelength as the number of satellites increases.
Y.-T. Long and C. Jing, Localized Surface Plasmon Resonance Based Nanobiosensors, SpringerBriefs in Molecular Science, DOI: 10.1007/978-3-642-54795-9_5, © The Author(s) 2014
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5 Interparticle Coupling-Enhanced Detection
Fig. 5.1 Effect of varying satellite number, size and core size, satellite distance; normalised scattering cross section and peak shift Δλ of core-satellite nanoassemblies for a, b increasing satellite number (rcore = 50 nm, rsat = 10 nm, and dsat = 2 nm); c increasing satellite radius (rcore = 50 nm, nsat = 5, and dsat = 2 nm); d, e increasing core radius (rsat = 10 nm, nsat = 10, and dsat = 2 nm); and f increasing satellite distance (rcore = 50 nm, rsat = 30 nm, and nsat = 5); solid line is shown as a guide, and error bars represent standard deviation from ten randomly generated core-satellite assemblies. Reprinted with permission from Ref. [18]. Copyright (2009) AIP Publishing LLC
Meanwhile, the plasmon resonance bandwidth decreased with an increasing number of satellites because of local plasmonic coupling. The small na
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