In the last few decays, the fiber-optic was employed in the field of sensing because of its benefits in contrast to other types of sensors such as small size, easy to fabricate, high response, and flexibility. In this study, unclad single mode fiber-optic sensor is proposed to operate at 650 nm wavelength. COMSOL Multiphysics 5.1 finite element method (FEM) is used to design the sensor and tested it theoretically. The middle portion of the fiber cladding is removed and replaced by gold nanoparticles (Au NPs) of 50 nm thickness. Analytic layer of 3 μm thickness was immersed in different liquids in range of refractive index (RI) from 1.000281 to 1.39. These liquids are NaCl Deionized (DI) water solution, sucrose-Deionized (DI) water solution, and glycerol solution Deionized (DI) water. It was found that the highest obtained sensitivity and resolution are for glycerol-DI water solution with value of 3157.98 (nm/RIU) and 3.16 × 10–5 (RIU), respectively. Furthermore, it is easy to fabricate and of low cost. In experiments, pulsed laser ablation (PLA) was used to prepare Au NPs. X-ray diffraction (XRD) shown that the peak of the intensity grew as the ablated energy increased as well as the structure crystallization. Transmission electron microscopy (TEM) revealed an average diameter of 30 nm at the three ablated energies, while X-ray spectroscopy (EDX) spectrum has indicated the presence of Au NPs in the prepared solution. The photoluminescence (PL) and ultraviolet–visible UV–Vis transmission were used to study the optical properties of the prepared Au NPs. An optical spectrum analyzer was used to obtain the sensor's output results. It has shown that best intensity was obtained for sucrose which confined with theoretical results.

This study proposed an unclad optical fiber biosensor based on the localized surface plasmon resonance phenomenon and operating at 650 nm using COMSOL Multiphysics 5.1 finite element method (FEM). Gold nanoparticles (50 nm thickness) were coated on the middle portion of the unclad fiber. Air, water, blood plasma, liver tissue, colon tissue, and pentanol (C5H11OH) were used as analytical layers with 3 µm. The sensor serves as a theoretical foundation for experimental research. The blood plasma had the highest sensitivity with a sensitivity of 10,638.297 nm/RIU and a resolution of 9.410-6RIU. The proposed sensor is a promising candidate for a low-cost, simple-geometry biochemical sensing solution.

This paper introduces a review of the use of gold nanoparticles (AuNPs) in the fabrication of optical fiber biosensors based on localized surface Plasmon resonance (LSPR) and Evanescent field absorption. The AuNPs have special properties, such as high surface/volume ratio, and intense light scattering/absorption, and stable structure. The main advantage of AuNPs in the application of the biosensor in the detection signal increasing, for especially low concentration analyses. Moreover, we illustrate some of the previous works in this field in the period from 2001-2021, which used optical fiber and AuNPs as a base in the development of various biosensors and all exhibited differently limits of detection, sensitivity, and good performances to its target detection.

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