Abstract
The use of nanoparticles (NPs) in scientific applications has attracted the attention of many researchers in the last few years. The use of NPs can help researchers to tune the physical characteristics of the sensing coating (thickness, roughness, specific area, refractive index, etc.) leading to enhanced sensors with response time or sensitivity better than traditional sensing coatings. Additionally, NPs also offer other special properties that depend on their nanometric size, and this is also a source of new sensing applications. This review focuses on the current status of research in the use of NPs within coatings in optical fiber sensing. Most used sensing principles in fiber optics are briefly described and classified into several groups: absorbance-based sensors, interferometric sensors, fluorescence-based sensors, fiber grating sensors, and resonance-based sensors, among others. For each sensor group, specific examples of the utilization of NP-embedded coatings in their sensing structure are reported.
Highlights
For the last few decades optical fiber sensors have experimented an important growth and relevance in sensing technologies field
The absorption mechanisms are described by the Lambert-Beer Law, where the transmission of the light through an analyte, material, or sensitive region (T, called transmittance) represents the relation between the light intensity before (Io) and that after (I) passing through this sensitive region, expressed by the following equation: T = I = 10−αL = 10εCL, Io where L is the length of interaction within the absorbing region and α is the absorption coefficient which can be denoted as the product of the molar absorptivity (ε) and the concentration (C) of the target
photonic crystal fibers (PCFs) and microstructured optical fibers (MOFs) are recently used in the development of new sensors with metallic NPs based on metal-enhanced fluorescence (MEF) or surface-enhanced Raman scattering (SERS)
Summary
For the last few decades optical fiber sensors have experimented an important growth and relevance in sensing technologies field. Nanostructured thin films and nanocoatings have been applied to the diverse optical fiber configurations for the fabrication of new sensors Thanks to these combinations, many devices have been developed obtaining the detection and monitoring of multiple parameters such as a wide range of gases [3, 4], pH [5], temperature [6], humidity [7, 8], ions [9], and biomolecules [10, 11]. It has been demonstrated that selected NP-embedded coatings enhance some parameters of previous devices, for example, sensitivity [12, 13], dynamic range, robustness, and lifetime On one hand, these improvements are due to the fact that NPs can provide additional special properties in coatings (mesoporosity, higher roughness, antibacterial behavior, etc.). Intensity-based sensors, interferometric sensors, fluorescence-based sensors, fiber grating sensors, and resonance-based sensors are the most typical ones
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