Abstract
In this work, an optical fiber sensor based on the localized surface plasmon resonance (LSPR) phenomenon has been designed for the detection of two different chemical species (mercury and hydrogen peroxide) by using Layer-by-Layer Embedding (LbL-E) as a nanofabrication technique. In the first step, silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) have been synthesized by using a chemical protocol as a function of the strict control of three main parameters, which were polyelectrolyte concentration, a loading agent, and a reducing agent. In the second step, their incorporation into nanometric thin films have been demonstrated as a function of the number of bilayers, which shows two well-located absorption peaks associated to their LSPR in the visible region at 420 nm (AgNPs) and 530 nm (AuNPs). Finally, both plasmonic peaks provide a stable real-time reference measurement, which can be extracted from the spectral response of the optical fiber sensor, which shows a specific sensing mechanism as a function of the analyte of study.
Highlights
Mercury presents a risk in the pollution of water bodies, affecting human health and the ecosystem
The experimental results corroborate the possibility of the stable detection of two different parameters with a different sensing mechanism, which is based on the wavelength displacement of the localized surface plasmon resonance (LSPR) associated to the strong affinity of the mercury towards AuNPs or to the reduction in the LSPR associated with the oxidation process of the absorbance change related to silver nanoparticles (AgNPs) due to the action of hydrogen peroxide
The mercury detection substance was obtained from mercury (II) chloride (HgCl2 ), and an aqueous solution of 30 wt% of H2 O2 was used in order to obtain the hydrogen peroxide samples
Summary
Mercury presents a risk in the pollution of water bodies, affecting human health and the ecosystem. The interaction Au-Hg makes the chemical modification of the surface nanoparticles possible, which shows an alteration in the resultant size and shape of the nanoparticles [9] This issue enables a maximum absorbance wavelength shift of the nanoparticles’ longitudinal plasmon mode, which is a reliable sensing signal in the optical fiber device [31]. The employed nanofabrication bottom-up process is the Layer-by-Layer (LbL) nanoassembly technique This deposition method makes the fabrication of ultra-thin films (sensitive region) on optical fiber cores possible by using oppositely charged polyelectrolytes, which act as effective capping agents of the metallic nanoparticles [33,34,35]. The experimental results corroborate the possibility of the stable detection of two different parameters with a different sensing mechanism, which is based on the wavelength displacement of the LSPR associated to the strong affinity of the mercury towards AuNPs or to the reduction in the LSPR associated with the oxidation process of the AgNPs due to the action of hydrogen peroxide
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