Fiber Optic Sensing with Lossy Mode Resonances: Applications and Perspectives

This review focuses on the recent advances in lossy more resonance (LMR) fiber optic sensors. LMR sensors present many interesting features also in comparison with surface plasmon resonance (SPR), the most widespread resonance-based sensing platform. Two key parameters determine the performance of LMR sensors: geometrical configuration and material supporting the LMR. After reviewing those aspects and some fundamentals of the theory, the review focuses on the sensing mechanisms, mainly based on refractometry, and their possible applications. Many examples from the literature are reported ranging from electric field to pressure sensors and from gas detection to biosensors. Such vibrant activity on LMR sensors confirms the potentiality of this technology making it a very promising platform for sensor development

Lossy mode resonance enabling ultra-low detection limit for fibre-optic biosensors (INVITED)

The combination of optical fibre-based biosensors with nanotechnologies is providing the opportunity for the development of in situ, portable, lightweight, versatile and high-sensitivity optical sensing platforms. We report on the generation of lossy mode resonances (LMRs) by means of the deposition of nm-thick SnO2 film on optical fibres. This allows measuring precisely and accurately the changes in refractive index of the fibre-surrounding medium with very high sensitivity compared to other optical technology platforms, such as long period grating or surface plasmon resonance. This approach, mixed with the use of specialty fiber structures such as Dshaped fibres, allows improving the light-matter interaction in strong way. Different imaging systems, i.e. SEM and TEM along with X-EDS tool, have been used to study the optical features of the fiber coating. The shift of the LMR has been monitored in real-time thanks to conventional wavelength interrogation system and ad hoc developed microfluidics. A big leap in performance has been attained by detecting femtomolar concentrations in human serum. The biosensor reusability has been also tested by using a solution of sodium dodecyl sulphate.This work was supported by the National Research Council of Italy (CNR) for the Short Term Mobility program 2017, by the Government of Navarra (project no. 72/2015) and by the Spanish Agencia Estatal de Investigacion (AEI) and European Regional Development Fund (FEDER) (TEC2016-78047-R,TEC2016-79367-C2-2-R)

Lossy mode resonance sensors based on tungsten oxide thin films

Tungsten oxide (WO3) thin-films fabricated on glass slides have been proven to generate lossy mode resonances (LMRs) in the visible region. Obtained devices were characterized in transmission by lateral incidence of light on the edge of glass slides. Resonances at both TE and TM polarizations were analyzed for different thicknesses and in different deposition conditions. Moreover, it was successfully proved that WO3 coated glass slides present a high sensitivity to refractive index, which opens the path to the application of this structure in the domain of optical sensors.This work was supported in part by the Spanish Agencia Estatal de Investigación (AEI) through project PID2019-106231RB-I00 and by Italian Ministry of University and Research (MIUR) through the University Research Project 2017 (prot. RG11715C8213BD81)

Biosensing with optical fiber gratings

AbstractOptical fiber gratings (OFGs), especially long-period gratings (LPGs) and etched or tilted fiber Bragg gratings (FBGs), are playing an increasing role in the chemical and biochemical sensing based on the measurement of a surface refractive index (RI) change through a label-free configuration. In these devices, the electric field evanescent wave at the fiber/surrounding medium interface changes its optical properties (i.e. intensity and wavelength) as a result of the RI variation due to the interaction between a biological recognition layer deposited over the fiber and the analyte under investigation. The use of OFG-based technology platforms takes the advantages of optical fiber peculiarities, which are hardly offered by the other sensing systems, such as compactness, lightness, high compatibility with optoelectronic devices (both sources and detectors), and multiplexing and remote measurement capability as the signal is spectrally modulated. During the last decade, the growing request in practical applications pushed the technology behind the OFG-based sensors over its limits by means of the deposition of thin film overlays, nanocoatings, and nanostructures, in general. Here, we review efforts toward utilizing these nanomaterials as coatings for high-performance and low-detection limit devices. Moreover, we review the recent development in OFG-based biosensing and identify some of the key challenges for practical applications. While high-performance metrics are starting to be achieved experimentally, there are still open questions pertaining to an effective and reliable detection of small molecules, possibly up to single molecule, sensing in vivo and multi-target detection using OFG-based technology platforms

Nanocoated fiber label-free biosensing for perfluorooctanoic acid detection by lossy mode resonance

The determination of per- and polyfluoroalkyl substances (PFAS) in environmental samples, such as drinking waters, requires the design of high performing and versatile sensing strategies. Label-free biosensing platforms based on specialty fiber optics are a valid option to face this challenge. Among them, lossy mode resonance (LMR) fiber optic biosensors are showing remarkable performance in terms of detection limit, selectivity, and reproducibility. The detection of small molecules, such as perfluorooctanoic acid (PFOA), can be achieved with the help of well-designed biological recognition layers. In this study, the biosensing potentialities of a label-free LMR-assisted optical platform based on nanocoated fibers are investigated. Delipidated human serum albumin (hSA) was used as biological recognition layer for PFOA in aqueous solution. Different fiber functionalization protocols based on the covalent immobilization of hSA were tested. The conformational changes related to the formation of hSA/PFOA complex were followed via optical monitoring of LMR spectral shift, showing a trend that can be modeled with Langmuir adsorption isotherm. These results confirmed the potentiality of LMR-based fiber biosensors for the detection of small molecules, such as PFOA, in synthetic samples