Fiber-based Surface Plasmon Resonance Sensor for Lead Ion Detection in Aqueous Solution
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Fiber-based Surface Plasmon Resonance Sensor for Lead Ion Detection in Aqueous Solution F. H. Suhailin1,2 · A. A. Alwahib2,3 · Y. Mustapha Kamil4 · M. H. Abu Bakar2 · N. M. Huang5 · M. A. Mahdi2 Received: 22 December 2019 / Accepted: 22 March 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Maghemite/reduced graphene oxide nanocomposite has been successfully deposited onto the surface of a gold-coated Dshaped optical fiber. The synergetic combination of gold, graphene, and iron oxide nanoparticles has shown enhancement of the resonance field and sensitivity of the fiber-based plasmonic sensor. In particular, the sensor exhibited its capability to detect lead ions (Pb2+ ) in aqueous solution via monitoring the spectral response of the sensor probe to different concentrations of Pb2+ . A sensor sensitivity of 1.2 nm per μg/L was attained at the lowest detected Pb2+ concentration, which is 0.001 ppm (limit of detection). This robust, compact, and highly sensitive fiber-based plasmonic sensor will be of a great interest for an in situ and real-time water safety environmental monitoring. Keywords Nanocomposite · Graphene · Surface plasmon resonance sensor · Environmental monitoring 1 ω 2 (εs ) , c
Introduction
ks =
Surface plasmon resonance (SPR) is a collective oscillation of electrons usually excited at metallic surfaces by an electromagnetic field. The excitation depends on certain critical parameters including the phase matching between the wave vectors of incident light and plasmonic modes. The propagation constant of the plasmonic mode, ksp and light wave, ks in the dielectric medium are expressed as follows:
where εm and εs are the dielectric constants of metal and dielectric medium, respectively, ω is the frequency of incident angle and c is light velocity. For plasmonic modes excitation, the two wave vectors must be equal and since εm < 0 for metal and εs > 0 for dielectric medium the ksp can only be excited via evanescent wave [1]. The coupling between the evanescent wave and plasmonic modes will result in an energy transfer manifested by a sharp dip at reflected/transmitted spectrum of the incident wave. The plasmonic modes will propagate at the interface of metal and surrounding medium, exhibiting a high sensitivity to any changes in the surrounding medium, i.e., refractive index or concentration of analyte. The shift at the position of resonance dip from its initial position may form a basis for a real-time monitoring probe in SPR sensor. Over the past few decades, SPR sensors have become a central detection tool for physical, chemical, and biological quantities [2, 3]. A diverse range of sensor architectures such as the Kretschmann–Otto prism configuration [4], nano- or microarrays structures [5], and optical dielectric waveguides [6] have all been demonstrated. Recently, an alternative type of plasmonic sensor based on optical fiber has been attracting more attention due to the demand of simple, cost-effective, and miniaturized sensor architecture [7]. The flexibilit
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