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 Fundamentals of Plasmonic CouplingThe coupling of plasmonics enhances the resonance intensity significantly and enables variable sensitive biosensors [1][2][3][4][5][6][7][8][9][10][11]. The factors that affect the coupling of nanoparticles include their particle size, coupling number, distance, direction, and shape [12][13][14][15][16][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 r core = 50 nm, r sat = 10 nm, and d sat = 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.