This work presents a study, analysis, design, and characterization of a localized surface plasmon resonance (LSPR) based ascorbic acid (AA) sensor with improved sensitivity compared to those already reported. Various multi-tapered (four, five, and eight tapered) optical fiber sensors (OFSs) have been developed and characterized in this study. Along with these, different nanomaterials (NMs), such as gold nanoparticles (AuNPs) and graphene oxide (GO), are immobilized over the bare probe. Further, NMs immobilized probes are functionalized with ascorbate oxidase. The AuNPs are well studied in the past with the variation in size, shape and surface functionalization and have been found to be well-suited NMs for biosensing applications. On the other hand, GO-based material is equally promising in the nanostructure-based optical sensing due to their broad surface area, high electrical conductivity, good chemical stability, and excellent mechanical behavior. The performance parameters of the proposed sensor, such as sensitivity (8.3 nm/mM), correlation correlator (0.9724), and limit of detection (51.94 µM) are greatly improved over the previous designs. A wide range of characterization and validation of NMs immobilized structures are reported here. It indicates a great potential in the practical implementation of LSPR based OFSs for routine diagnostics.

A novel periodically tapered structure-based gold nanoparticles and graphene oxide – Immobilized optical fiber sensor to detect ascorbic acid

This work proposed the simulation of a highly sensitive surface plasmon resonance (SPR) optical fibre sensor equipped with a hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ) layer coated with silver gratings on the surface of a D-shaped optical fibre. $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterial film was utilised as the sensing layer. Free electrons on the metal surface were stimulated via evanescent waves on the fibre surface to generate surface plasmon waves. The resonance absorption peaks were monitored to determine the changes in refractive index (RI). The SPR fibre sensor was optimised using the finite element method to analyse the structural parameters of the D-shaped optical fibre and silver gratings. This method was also applied to examine the effect of the thickness of the hematite sensing layer on sensor sensitivity (S). The hematite-coated silver gratings significantly enhanced the sensor as revealed by the simulation outcomes. In this work, the maximum response S of the sensor can reach $6.4~\mu \text{m}$ /RIU when the external RI was changed from 1.33 to 1.39 with 45 nm thick silver grating, 50 nm width air gaps and 12 nm thick hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ). The results suggest the high potential of $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterials in optical fibre-sensing applications.

Highly Sensitive D-Shaped Optical Fiber Surface Plasmon Resonance Refractive Index Sensor Based on Ag-α- Fe 2 O 3 Grating

A study of highly sensitive D-shaped optical fiber surface plasmon resonance based refractive index sensor using grating structures of Ag-TiO2 and Ag-SnO2

Sensitivity enhancement of surface plasmon resonance sensor based on wavelength and angular combined modulations

This work reports a simple optical fiber Surface Plasmon Resonance (SPR) sensor with ultra-high sensitivity for simultaneous measurement of the dual-parameter. The sensor is based on a D-shaped fiber with a nanolayer coating of Silver (Ag) and Hematite (α−Fe2O3). The Ag/α−Fe2O3 layer is deposited on the longitudinal surface of residual cladding, and a Fiber Bragg Grating (FBG) is inscribed on the single-mode fiber (SMF) for temperature compensation. The α−Fe2O3 layer protects the Ag layer from oxidation and effectively enhances the surface plasmon wave while interacting with free electrons. Finite Element Method (FEM) modeling is employed to investigate the refractive index (RI) and temperature response of the SPR sensor. The SPR sensor exhibits an ultra-high RI sensitivity of 8,518 nm/RIU (refractive index unit) in the RI range of 1.33 to 1.40, and a temperature sensitivity of −52 pm/°C in the temperature range of 20 °C to 60 °C. The SPR performance suggests that it is a potential candidate for various applications of dual-parameter sensing.

https://ieeexplore.ieee.org/ielx7/4563994/4814557/09875985.pdf

A Simple Optical Fiber SPR Sensor With Ultra-High Sensitivity for Dual-Parameter Measurement

In this paper, fiber-optic sensor based on surface plasmon resonance (SPR) is considered. The fiber-optic sensor is coated with thin nanoparticle metallic films. The nanoparticle metallic film consists of spherical metallic nanoparticles embedded in a host material. It is shown that sensitivity and absorption of sensor depends on number and type of films. It theoretically analyzed that the different states such as, fiber-optic sensor with a single thin layer of spherical gold or silver nanoparticle and a bimetallic arrangement of silver and gold nanoparticles. It also studied dependence of the sensitivity and absorption of sensor on the parameters such as gold particle size, film thickness, refractive index of host material, sensing region length, fiber core diameter, maximum absorption wavelength, half maximum width of the sensing medium and background refractive index of the sensing layer.

M. Salari

Papers

Theoretical investigation of absorption and sensitivity of nano-plasmonic fiber optic sensors