A Comprehensive Review: Materials for the Fabrication of Optical Fiber Refractometers Based on Lossy Mode Resonance

Recent Trends in Chemical Sensors for Detecting Toxic Materials

Industrial development has led to the widespread production of toxic materials, including carcinogenic, mutagenic, and toxic chemicals. Even with strict management and control measures, such materials still pose threats to human health. Therefore, convenient chemical sensors are required for toxic chemical monitoring, such as optical, electrochemical, nanomaterial-based, and biological-system-based sensors. Many existing and new chemical sensors have been developed, as well as new methods based on novel technologies for detecting toxic materials. The emergence of material sciences and advanced technologies for fabrication and signal-transducing processes has led to substantial improvements in the sensing elements for target recognition and signal-transducing elements for reporting interactions between targets and sensing elements. Many excellent reviews have effectively summarized the general principles and applications of different types of chemical sensors. Therefore, this review focuses on chemical sensor advancements in terms of the sensing and signal-transducing elements, as well as more recent achievements in chemical sensors for toxic material detection. We also discuss recent trends in biosensors for the detection of toxic materials.

Soft molecularly imprinted nanoparticles with simultaneous lossy mode and surface plasmon multi-resonances for femtomolar sensing of serum transferrin protein

The simultaneous interrogation of both lossy mode (LMR) and surface plasmon (SPR) resonances was herein exploited for the first time to devise a sensor in combination with soft molecularly imprinting of nanoparticles (nanoMIPs), specifically entailed of the selectivity towards the protein biomarker human serum transferrin (HTR). Two distinct metal-oxide bilayers, i.e. TiO₂-ZrO₂ and ZrO₂-TiO₂, were used in the SPR-LMR sensing platforms. The responses to binding of the target protein HTR of both sensing configurations (TiO₂-ZrO₂-Au-nanoMIPs, ZrO₂-TiO₂-Au-nanoMIPs) showed femtomolar HTR detection, LODs of tens of fM and K_Dapp ~ 30 fM. Selectivity for HTR was demonstrated. The SPR interrogation was more efficient for the ZrO₂-TiO₂-Au-nanoMIPs configuration (sensitivity at low concentrations, S = 0.108 nm/fM) than for the TiO₂-ZrO₂-Au-nanoMIPs one (S = 0.061 nm/fM); while LMR was more efficient for TiO₂-ZrO₂-Au-nanoMIPs (S = 0.396 nm/fM) than for ZrO₂-TiO₂-Au-nanoMIPs (S = 0.177 nm/fM). The simultaneous resonance monitoring is advantageous for point of care determinations, both in terms of measurement's redundancy, that enables the cross-control of the measure and the optimization of the detection, by exploiting the individual characteristics of each resonance.

An All-Fiber Fabry-Pérot Sensor for Emulsion Concentration Measurements

This paper describes a Fabry-Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under real industrial conditions, and enables temperature-compensated online measurement of emulsion concentration with a high resolution of 0.03 Brix. The measuring system was equipped with filtering of the emulsion and automatic cleaning of the sensor, which proved to be essential for successful implementation of a fiber optic RI sensor in machining emulsion monitoring applications.

Lossy mode resonance fiber-optic sensor based on ZnO particles fabricated by chemical bath deposition

We present a lossy mode resonance (LMR) sensor fabricated by chemical bath deposition (CBD) using a U-shaped optical fiber with an exposed core. The ZnO particles that generate LMR were prepared by a very costly method in three steps via permanganate activation and the deposition of ZnO on the fiber core using CBD. The process of deposition was monitored in real time through the optical fiber, and a clear absorption spectrum with an LMR peak was obtained. The surface of the sensor with absorbance reaching 1.0 was covered with nano- to submicron particles of ZnO. The refractive index (RI) sensitivity of the sensor was measured using sucrose solution and was found to increase as the amounts of ZnO on the sensor increased, reaching 23 Abs/RI unit (RIU). The RI resolutions of the sensors with absorbance reaching 0.40, 0.65, and 1.0 during CBD were determined as ΔRI = 0.000060, 0.00017, and 0.00018, respectively, with a 99.7% confidence interval for the RI. Pretreatment during CBD was found to dramatically affect the fabrication of LMR sensors owing to their size and occupancy of deposited ZnO particles, the effects of which can be observed in real time using fiber optics.

A Study of the Lossy Mode Resonances during the Synthesis Process of Zinc Telluride Films

Films of zinc telluride (ZnTe) were deposited on the surface of a chemically thinned section of an optical fiber by metalorganic chemical vapor deposition. The boundary values of temperatures and the concentration ratios of the initial tellurium and zinc precursors at which the synthesis of ZnTe coatings is possible are determined. The influence of the position of the thinned part of the optical fiber in the reactor on the growth rate of films on the side surface of the fiber was studied, on the basis of which, the parameters of the deposition zone were determined. By placing a section of an optical fiber with an etched cladding in the center of this zone, sensitive elements for refractometers were created. The principle of their operation is based on the dependence of the spectral position of the lossy mode resonance (LMR) maximum on the refractive index (RI) of the external medium. It has been found that even thin films deposited on a light guide in a continuous process have cracks. It is shown that the interruption of the deposition process makes it possible to avoid the appearance of defects in the zinc telluride layers even with the repeated deposition of the sensor. The sensitivity of the spectral position of the LMR to changes in the RI of aqueous sodium chloride solutions in the range from 1.33 to 1.35 for the first transverse electric and transverse magnetic LMRs was 6656 and 6240 nm per refractive index unit, respectively.

Semiconductor Multimaterial Optical Fibers for Biomedical Applications

Integrated sensors and transmitters of a wide variety of human physiological indicators have recently emerged in the form of multimaterial optical fibers. The methods utilized in the manufacture of optical fibers facilitate the use of a wide range of functional elements in microscale optical fibers with an extensive variety of structures. This article presents an overview and review of semiconductor multimaterial optical fibers, their fabrication and postprocessing techniques, different geometries, and integration in devices that can be further utilized in biomedical applications. Semiconductor optical fiber sensors and fiber lasers for body temperature regulation, in vivo detection, volatile organic compound detection, and medical surgery will be discussed.

Optical fiber thermo-refractometer

This work presents the implementation of a thermo-refractometer, which integrates the measurement of both refractive index and temperature in a single optical fiber structure. To this purpose, a lossy mode resonance (LMR)-based refractometer is obtained by means of the deposition of a titanium dioxide (TiO₂) thin film onto a side-polished (D-shaped) single mode fiber. Measurement and subsequent temperature compensation are achieved by means of a fiber Bragg grating (FBG) inscribed in the core of the D-shaped region. The LMR wavelength shift is monitored in transmission while the FBG (FBG peak at 1533 nm) displacement is observed in reflection. The LMR is sensitive to both the surrounding refractive index (SRI), with a sensitivity of 3725.2 nm/RIU in the 1.3324-1.3479 range, and the temperature (- 0.186 nm/°C); while the FBG is only affected by the temperature (32.6 pm/°C in the 25°C - 45°C range). With these values, it is possible to recover the SRI and temperature variations from the wavelength shifts of the LMR and the FBG, constituting a thermo-refractometer, where it is suppressed the effect of the temperature over the refractometer operation, which could cause errors in the fourth or even third decimal of the measured SRI value.

Using lossy mode resonance for in situ measurement of the refractive index of a layer deposited on an optical fiber lateral surface

We demonstrate an approach that allows for measurement of the real part of the refractive index (RI) and the thickness of the coating deposited on the cylindrical surface of a thinned optical fiber using a tin dioxide (SnO₂) film as an example. While the layer is being synthesized, lossy mode resonances (LMRs) are observed in the transmission spectra of the fiber light guide at any particular wavelength at regular intervals. It is shown that there are at least two functions by which the RI of a film can be calculated from the obtained spectra.

Sensing performance of surface waveguide modes excited in long-period fiber grating with gold-silicon nanocoatings

We carry out a very early theoretical study on surface waveguide modes excited in a long-period fiber grating (LPFG) coated with gold-silicon thin films for refractive index sensing. The surface waveguide modes originate from the intermode transition of EH cladding modes and present a very strong evanescent field penetrating into the surrounding medium, which makes them ultrasensitive to external changes. By tracking the dual resonances of surface waveguide modes, ultrahigh sensitivity up to 7267.7nm/RIU around 1.315 is obtained, which is 76-/4-fold higher than the case of bare LPFG/LPFG-assisted surface plasmon resonance, together with the capability of self-referenced measurement. This new, to the best of our knowledge, concept is expected to find wide applications based on refractive index sensing.

Ultracompact Chip-Scale Refractometer Based on an InGaN-Based Monolithic Photonic Chip

Optical refractometer constitutes the core element for many applications, from determining the purity and concentration of pharmaceutical ingredients to measuring the sugar content in food and beverages, and the analysis of petroleum. Here, we demonstrated the monolithic integration of light-emitting diodes (LEDs) and photodetectors (PDs) to fabricate ultracompact refractometers with a chip size of 475 × 320 μm². The light emission and photodetection properties of the devices containing the same InGaN/GaN multi-quantum wells have been characterized, confirming that the PD can respond to the emission of the LED. The flip-chip assembly of the chip enables the exposed sapphire substrate to be in direct contact with the solution, and the refractive index sensing capability governed by the change of critical angle and Fresnel reflection at the sapphire/solution interface has been investigated. The processing of the optically smooth surface of sapphire and the integration of high-reflectance distributed Bragg reflector beneath the devices facilitate the amount of light received by the PD. The monolithic chip is capable of detecting solutions with a refractive index ranging from 1.3325 to 1.5148 RIU and exhibits a sensitivity of 7.77 μA/RIU and a resolution of 6.4 × 10^-6 RIU at the LED current of 10 mA. Rapid real-time responses of 33.9 ms for rise time and 34.7 ms for fall time are obtained in the detected photocurrent, thereby verifying the feasibility of the chip-scale refractometer.

Optical Biosensors for the Detection of Rheumatoid Arthritis (RA) Biomarkers: A Comprehensive Review

A comprehensive review of optical biosensors for the detection of biomarkers associated with rheumatoid arthritis (RA) is presented here, including microRNAs (miRNAs), C-reactive protein (CRP), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), interleukin-6 (IL-6) and histidine, which are biomarkers that enable RA detection and/or monitoring. An overview of the different optical biosensors (based on fluorescence, plasmon resonances, interferometry, surface-enhanced Raman spectroscopy (SERS) among other optical techniques) used to detect these biomarkers is given, describing their performance and main characteristics (limit of detection (LOD) and dynamic range), as well as the connection between the respective biomarker and rheumatoid arthritis. It has been observed that the relationship between the corresponding biomarker and rheumatoid arthritis tends to be obviated most of the time when explaining the mechanism of the optical biosensor, which forces the researcher to look for further information about the biomarker. This review work attempts to establish a clear association between optical sensors and rheumatoid arthritis biomarkers as well as to be an easy-to-use tool for the researchers working in this field.