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)

Flow cell for strain- and temperature-compensated refractive index measurements by means of cascaded optical fibre long period and Bragg gratings

An optical fibre sensing system based on a hybrid cascaded long period grating (LPG) and fibre Bragg grating configuration and a thermo-stabilized flow cell for refractometric measurements is proposed. The system makes it possible to measure, and thus to cancel, the LPG cross-sensitivities to strain, temperature and fibre bending. The experimental results show that the proposed system provides satisfactory performances as far as the refractive index sensitivity and resolution are concerned. The maximum sensor sensitivity and resolution are 3120 nm/RIU and 2 × 10 -5 RIU, respectively. The whole system with its flow cell and the gratings fabrication are extensively described, together with the acquisition and data processing. The stability of the sensor for several hours was also tested. We believe that the proposed system can be successfully used for label-free chemical/biochemical sensing

A complete optical sensor system based on a POF-SPR platform and a thermo-stabilized flow cell for biochemical applications

An optical sensor platform based on surface plasmon resonance (SPR) in a plastic optical fiber (POF) integrated into a thermo-stabilized flow cell for biochemical sensing applications is proposed. This device has been realized and experimentally tested by using a classic receptor-analyte assay. For this purpose, the gold surface of the POF was chemically modified through the formation of a self-assembling monolayer. The surface robustness of the POF-SPR platform has been tested for the first time thanks to the flow cell. The experimental results show that the proposed device can be successfully used for label-free biochemical sensing. The final goal of this work is to achieve a complete, small-size, simple to use and low cost optical sensor system. The whole system with the flow cell and the optical sensor are extensively described, together with the experimental results obtained with an immunoglobulin G (IgG)/anti-IgG assay

Long period and fiber Bragg gratings written within the same fiber for sensing purposes

Long period gratings (LPGs) have been recently proposed as sensing elements of chemical/biological compounds, exploiting their sensitivity to the refractive index changes in the surrounding environment. One of the difficulties of their utilization for this purpose is their strong dependence also to strain and temperature effects. An intrinsic optical feedback able to eliminate these effects was developed by manufacturing on the same fiber the LPG and a fiber Bragg grating (FBG) which is immune from external refractive index changes and is influenced by strain and temperature. An accurate temperature measurement system is utilised to eliminate or in any case to reduce to a minimum the interferences coming from temperature changes. A KrF excimer laser is used to write both the gratings into the same photosensitive fiber. The period of the LPG and FBG gratings are 615 μm and 530 nm, respectively and the attenuation at their resonance wavelengths (1570 nm for LPG and 1534 nm for FBG) was of the order of 15-20 dB. The same source, a broadband superluminescent diode with emission peak at 1550 nm, is used to interrogate both the gratings. The transmission spectra is acquired by means of an optical spectrum analyzer (OSA) controlled by a PC and an in-house software identifies the attenuation band in the FBG and LPG transmission spectra and calculates the minimum values. A suitable thermo-stabilized flow cell with a volume of 50 μL containing the fiber with the two gratings, has been developed and characterized

Comparative assessment of the performance of long period fiber grating-based biosensors

Evanescent wave-based optical fiber biosensors consisting of long period grating (LPG) are presented. A chemical or a biochemical interaction taking place on a conveniently treated surface causes a refractive index (RI) change that can be evaluated using optical approaches. By implementing the same antibody/antigen (IgG/anti-IgG) assay protocol in the same experimental conditions, a comparative assessment of the biosensor performance was carried out by using different types of LPGs (standard, turn-around point and coated) in which the coupling occurred with different cladding modes. These sensors were firstly characterized in terms of volume (or bulk) RI sensitivity, which just provides an indication of the biosensor performance, and then of detection limit (LOD), which in turn represents a real and effective analytical parameter of biosensors extrapolated from their calibration curves. LODs of the order of μg L-1 (10-11 M) were achieved for turn-around point and coated LPGs both in buffer and in serum as real and complex matrix, thus also proving the biosensor specificity

Real-Time Study of the Adsorption and Grafting Process of Biomolecules by Means of Bloch Surface Wave Biosensors

A combined label-free and fluorescence surface optical technique was used to quantify the mass deposited in binary biomolecular coatings. These coatings were constituted by fibronectin (FN), to stimulate endothelialization, and phosphorylcholine (PRC), for its hemocompatibility, which are two properties of relevance for cardiovascular applications. One-dimensional photonic crystals sustaining a Bloch surface wave were used to characterize different FN/PRC coatings deposited by a combination of adsorption and grafting processes. In particular, the label-free results permitted to quantitatively assess the mass deposited in FN adsorbed (185 ng/cm2) and grafted (160 ng/cm2). PRC binding to grafted FN coatings was also quantified, showing a coverage as low as 10 and 12 ng/cm2 for adsorbed and grafted PRC, respectively. Moreover, desorption of FN deposited by adsorption was detected and quantified upon the addition of PRC. The data obtained by the surface optical technique were complemented by water contact angle and X-ray photoelectron spectroscopy (XPS) analyses. The results were in accordance with those obtained previously by qualitative and semiquantitative techniques (XPS, time-of-flight secondary ion mass spectrometry) on several substrates (PTFE and stainless steel), confirming that grafted FN coatings show higher stability than those obtained by FN adsorption