Effect of Surface Coverage of Gold Nanoparticles on the Refractive Index Sensitivity in Fiber-Optic Nanoplasmonic Sensing.

Wei-Te Wu,Chang-Yue Chiang,Chien-Hsing Chen,Lai-Kwan Chau

doi:10.3390/s18061759

Abstract

A simple theoretical model was developed to analyze the extinction spectrum of gold nanoparticles (AuNPs) on the fiber core and glass surfaces in order to aid the determination of the surface coverage and surface distribution of the AuNPs on the fiber core surface for sensitivity optimization of the fiber optic particle plasmon resonance (FOPPR) sensor. The extinction spectrum of AuNPs comprises of the interband absorption of AuNPs, non-interacting plasmon resonance (PR) band due to isolated AuNPs, and coupled PR band of interacting AuNPs. When the surface coverage is smaller than 12.2%, the plasmon coupling effect can almost be ignored. This method is also applied to understand the refractive index sensitivity of the FOPPR sensor with respect to the non-interacting PR band and the coupled PR band. In terms of wavelength sensitivity at a surface coverage of 18.6%, the refractive index sensitivity of the coupled PR band (205.5 nm/RIU) is greater than that of the non-interacting PR band (349.1 nm/RIU). In terms of extinction sensitivity, refractive index sensitivity of the coupled PR band (−3.86/RIU) is similar to that of the non-interacting PR band (−3.93/RIU). Both maximum wavelength and extinction sensitivities were found at a surface coverage of 15.2%.

Highlights

Gold nanoparticles (AuNP) have been used over a wide range of fields in chemical and biochemical analyses such as clinical analysis [1,2,3,4,5,6], molecular diagnostics [7,8] bio-interaction analysis and drug discovery [9], agricultural diagnostics [10,11], environmental monitoring [12], and food safety analysis [13,14,15]
The energy density of an analyze the extinction spectrum of gold nanoparticles (AuNPs) varies with particle size [16] and shape [17,18], leading to a special absorption band of AuNP known as the plasmon resonance (PR) band [19]
Is the imaginary part of the dielectric function of the spherical metal nanoparticle, R is the radius of the spherical metal nanoparticle; λ is the wavelength of the incident light; εm is the dielectric constant of the external environment, which can be expressed as εm = nm 2 ; nm is the refractive index of the external environment

Summary

Introduction

Gold nanoparticles (AuNP) have been used over a wide range of fields in chemical and biochemical analyses such as clinical analysis [1,2,3,4,5,6], molecular diagnostics [7,8] bio-interaction analysis and drug discovery [9], agricultural diagnostics [10,11], environmental monitoring [12], and food safety analysis [13,14,15]. The energy density of an AuNP varies with particle size [16] and shape [17,18], leading to a special absorption band of AuNP known as the plasmon resonance (PR) band [19]. This absorption band results when the frequency of an incident light is resonant with the collective dipole oscillation of the conduction electron in the AuNP and is known as particle plasmon resonance (PPR), known as localized surface plasmon resonance (LSPR). Various forms of assays based on AuNPs have been developed, such as solution-phase-based [4,12,14], slide-based [3,11,15,22], and optical fiber-based [1,2,5,6,10,23,24,25,26,27,28,29,30]

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