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

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)

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

Recent Development of Resonance-Based Optical Sensors and Biosensors

n/

Manufacturing and Spectral Features of Different Types of Long Period Fiber Gratings: Phase-Shifted, Turn-Around Point, Internally Tilted, and Pseudo-Random

The manufacturing and spectral features of different types of long period fiber gratings (LPFGs), ranging from phase-shifted, turn-around point, and internally tilted gratings, to pseudo-random gratings, are described and discussed in detail. LPFGs were manufactured on boron-germanium co-doped photosensitive optical fibers with the point-by-point technique using an excimer KrF laser operating at 248 nm. The developed experimental setup to manufacture high-quality LPFGs was designed to totally customize any type of gratings with the possibility of setting different parameters, such as the grating period (or pitch), the number of grating planes, the number of laser shots for each plane, etc. Some important spectral features of the LPFGs’ spectra were taken into account. This allows realizing homemade devices useful in several fiber-based applications, such as optical filtering, coupling systems, random lasers, physical and chemical sensing, and biosensing

Towards a Uniform Metrological Assessment of Grating-Based Optical Fiber Sensors: From Refractometers to Biosensors

A metrological assessment of grating-based optical fiber sensors is proposed with the aim of providing an objective evaluation of the performance of this sensor category. Attention was focused on the most common parameters, used to describe the performance of both optical refractometers and biosensors, which encompassed sensitivity, with a distinction between volume or bulk sensitivity and surface sensitivity, resolution, response time, limit of detection, specificity (or selectivity), reusability (or regenerability) and some other parameters of generic interest, such as measurement uncertainty, accuracy, precision, stability, drift, repeatability and reproducibility. Clearly, the concepts discussed here can also be applied to any resonance-based sensor, thus providing the basis for an easier and direct performance comparison of a great number of sensors published in the literature up to now. In addition, common mistakes present in the literature made for the evaluation of sensor performance are highlighted, and lastly a uniform performance assessment is discussed and provided. Finally, some design strategies will be proposed to develop a grating-based optical fiber sensing scheme with improved performance