In situ surface turbidity sensor based on localized light scattering from tilted fiber Bragg gratings.

We propose a compact fiber-optic sensor for in situ and continuous turbidity monitoring, based on surface optical scattering of polarized evanescent waves from targeted particles. The sensor is composed of a tilted fiber Bragg grating (TFBG) packaged inside a microfluidic capillary. The transmission spectrum of the TFBG provides a fine comb of narrow cladding resonances that are highly sensitive to the turbidity due to the localized light scattering of polarized evanescent waves from the microparticles near the fiber surface (as opposed to traditional bulk/volumetric turbidity measurement). We also propose a transmission spectral area interrogation method and quantify the repeatable correlation between the surface turbidity and the optical spectral area response. We show that the maximum sensitive turbidity response is achieved when the wavelength of the sensing cladding resonance matches the size of surrounding solid particles.

Selective detection of cadmium ions using plasmonic optical fiber gratings functionalized with bacteria.

Environmental monitoring and potable water control are key applications where optical fiber sensing solutions can outperform other technologies. In this work, we report a highly sensitive plasmonic fiber-optic probe that has been developed to determine the concentration of cadmium ions (Cd2+) in solution. This original sensor was fabricated by immobilizing the Acinetobacter sp. around gold-coated tilted fiber Bragg gratings (TFBGs). To this aim, the immobilization conditions of bacteria on the gold-coated optical fiber surface were first experimentally determined. Then, the coated sensors were tested in vitro. The relative intensity of the sensor response experienced a change of 1.1 dB for a Cd2+ concentration increase from 0.1 to 1000 ppb. According to our test procedure, we estimate the experimental limit of detection to be close to 1 ppb. Cadmium ions strongly bind to the sensing surface, so the sensor exhibits a much higher sensitivity to Cd2+ than to other heavy metal ions such as Pb2+, Zn2+ and CrO42- found in contaminated water, which ensures a good selectivity.

Palladium-coated plasmonic optical fiber gratings for hydrogen detection.

Surface plasmon resonance excitation with tilted fiber Bragg gratings has been typically studied using gold films to target biochemical sensing applications. However, surface plasmons can be excited on other metal coatings as well. In this work, plasmonic optical fiber grating platforms are developed using palladium films. Since the optical properties of this metal differ from the ones of gold, simulations are carried out to define the optimal thickness. Due to the phase transition of palladium in the presence of hydrogen, intensity changes in the optical transmission of the devices are produced. It is demonstrated that these platforms can be used for hydrogen detection at concentrations way below the lower explosive limit.

Effects of nonsteroidal anti-inflammatory drugs on serum proinflammatory cytokines in the treatment of ankylosing spondylitis.

OBJECTIVE: This study was conducted to investigate the correlation between serum levels of proinflammatory cytokines and the clinical efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) in patients with ankylosing spondylitis (AS). METHODS: A total of 148 patients with AS were selected and received NSAID treatment. ELISA was used to assess cytokine levels, and patients were assigned into the following groups: positively effective; effective; moderately effective; and ineffective. Spearman and Pearson correlation analyses were used for correlation analysis. RESULTS: The erythrocyte sedimentation rates (ESR), C-reactive protein (CRP) levels, and immunoglobulin A (IgA) levels of the case group after NSAID treatment were markedly lower than those before NSAID treatment. After treatment, the levels of interleukin (IL)-6, IL-17, and tumor necrosis factor (TNF)-α were markedly reduced, while IL-10 levels increased in the positively effective, effective, and moderately effective groups, and IL-12 levels decreased in the positively effective and effective groups. In addition, the levels of IL-6 and TNF-α were correlated with a greater number in the efficacy indexes and clinical parameters, followed by IL-10 levels, while the levels of IL-17 and IL-12 had relatively weaker correlations with these indexes and parameters. CONCLUSION: NSAIDs could promote the clinical efficacy of treatment for ankylosing spondylitis by regulating serum levels of proinflammatory cytokines.

Insight into the local near-infrared photothermal dynamics of graphene oxide functionalized polymers through optical microfibers.

Recently, although great attention has been paid to the design and exploitation of new classes of near-infrared (NIR) light-induced materials, the photothermal dynamics of these materials have not been fully explored. However, understanding the photothermal dynamics of NIR-light-responsive composites is of fundamental importance from the viewpoint of smart material design and processing at the nanoscale, and for the understanding of a number of related phenomena. Herein, an alternative approach to observe the dynamics of the photothermal process is developed, which relies on probing the local refractive index change in the nanocomposite matrix with a silica microfiber interferometer. In this approach, the light-induced morphological change of the polymer is captured by the microfiber because of the strong evanescent-field interaction, and is translated into a significant wavelength shift in the interferometric fringe. Therefore, probing the matrix to study the local photothermal dynamics is possible. The optical microfiber records various phase-transformation stages of the photothermal nanocomposites induced by different optothermal mechanisms, especially revealing the reconstruction process of Ag@reduced graphene oxide (Ag@G) nanosheets during the initial stage of the photothermal process. The feasibility of using optical fibers for studying the inner mechanism of material phase change is presented herein and it provides a new approach for fundamental investigations into smart material development at the nanoscales.

Improved detection sensitivity of γ-aminobutyric acid based on graphene oxide interface on an optical microfiber.

Interfacing bio-recognition elements to optical materials is a longstanding challenge to manufacture sensitive biosensors and inexpensive diagnostic devices. In this work, a graphene oxide (GO) interface has been constructed between silica microfiber and bio-recognition elements to develop an improved γ-aminobutyric acid (GABA) sensing approach. The GO interface, which was located at the site with the strongest evanescent field on the microfiber surface, improved the detection sensitivity by providing a larger platform for more bio-recognition element immobilization, and amplifying surface refractive index change caused by combination between bio-recognition elements and target molecules. Owing to the interface improvement, the microfiber has a three times improved sensitivity of 1.03 nm/log M for GABA detection, and hence a lowest limit of detection of 2.91 × 10-18 M, which is 7 orders of magnitude higher than that without the GO interface. Moreover, the micrometer-sized footprint and non-radioactive nature enable easy implantation in human brains for in vivo applications.

Transition-metal dichalcogenides heterostructure saturable absorbers for ultrafast photonics.

In this Letter, high-quality WS2 film and MoS2 film were vertically stacked on the tip of a single-mode fiber in turns to form heterostructure (WS2-MoS2-WS2)-based saturable absorbers with all-fiber integrated features. Their nonlinear saturable absorption properties were remarkable, such as a large modulation depth (∼16.99%) and a small saturable intensity (6.23 MW·cm-2). Stable pulses at 1.55 µm with duration as short as 296 fs and average power as high as 25 mW were obtained in an erbium-doped fiber laser system. The results demonstrate that the proposed heterostructures own remarkable nonlinear optical properties and offer a platform for adjusting nonlinear optical properties by stacking different transition-metal dichalcogenides or modifying the thickness of each layer, paving the way for engineering functional ultrafast photonics devices with desirable properties.

Plasmonic Optical Fiber-Grating Immunosensing: A Review.

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.

Electrochemical Surface Plasmon Resonance Fiber-Optic Sensor: In Situ Detection of Electroactive Biofilms.

Spectroelectrochemistry has been found to be an efficient technique for revealing extracellular electron transfer (EET) mechanism of electroactive biofilms (EABs). Herein, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor for monitoring EABs in situ. The sensor uses a tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber and coated with nanoscale gold film for high-efficiency SPR excitation. The wavelength shift of the surface plasmon resonance (SPR) over the fiber surface clearly identifies the electrochemical activity of the surface localized (adjacent to the electrode interface) bacterial cells in EABs, which differs from the "bulk" detections of the conventional electrochemical measurements. A close relationship between the variations of redox state of the EABs and the changes of the SPR under potentiostatic conditions has been achieved, pointing to a new way to study the EET mechanism of the EABs. Benefiting from its compact size, high sensitivity, and ease of use, together with remote operation ability, the proposed sensor opens up a multitude of opportunities for monitoring EABs in various hard-to-reach environments.

High-damage-resistant tungsten disulfide saturable absorber mirror for passively Q-switched fiber laser.

In this paper, we demonstrate a high-damage-resistant tungsten disulfide saturable absorber mirror (WS2-SAM) fabricated by magnetron sputtering technique. The WS2-SAM has an all-fiber-integrated configuration and high-damage-resistant merit because the WS2 layer is protected by gold film so as to avoid being oxidized and destroyed at high pump power. Employing the WS2-SAM in an Erbium-doped fiber laser (EDFL) with linear cavity, the stable Q-switching operation is achieved at central wavelength of 1560 nm, with the repetition rates ranging from 29.5 kHz to 367.8 kHz and the pulse duration ranging from 1.269 µs to 154.9 ns. For the condition of the maximum pump power of 600 mW, the WS2-SAM still works stably with an output power of 25.2 mW, pulse energy of 68.5 nJ, and signal-noise-ratio of 42 dB. The proposed WS2-SAM configuration provides a promising solution for advanced pulsed fiber lasers with the characteristics of high damage resistance, high output energy, and wide tunable frequency.

Mesoporous nanospheres functionalized optical microfiber biosensor for low concentration neurotransmitter detection.

A label-free and ultrasensitive microfiber interferometer biosensor has been demonstrated for detection of neurotransmitter molecule (5-HT). The surface morphology of the silicon dioxide nanospheres acting as molecule sieve provides an effective mean of gathering 5-HT molecules by designed mesoporous structure. The slight concentration change of 5-HT molecules is translated into a dramatic wavelength shift of the interferometric fringe pattern. The experimental results show that the biosensor has a linear response in concentration range from 100 fM to 1 µM and a detection limit as low as 84 fM.

Understanding the pH-dependent interaction between graphene oxide and single-stranded DNA through a fiber-optic interferometer.

A method based on a fiber-optic interferometer to study the pH-dependent interaction between graphene oxide and single-stranded DNA chains is carried out with the assistance of a scanning electron microscope and a confocal laser scanning microscope. The various wavelength shifts of the interferometric fringes of the transmission spectrum reveal the different strengths of interaction between graphene oxide and single-stranded DNA in various pH environments. The present work demonstrates the feasibility of optical fibers for studying the interaction between graphene oxide and biomolecules. It provides a potential means to understand the intermolecular interactions. This technique might effectively supplement the existing tools.

Evanescently coupled optical fiber refractometer based a tilted fiber Bragg grating and a D-shaped fiber.

A novel tip-reflective and power-referenced refractometer based on strong fiber-to-fiber optical coupling for a large range of surrounding refractive index (SRI) (from 1.33 to 1.45) is proposed and experimentally demonstrated. A short D-shaped fiber stub is placed in parallel and close contact to another standard circular fiber containing a weakly tilted Bragg grating (TFBG). The TFBG couples the light from the circular fiber's core into its cladding where it remains guided. Apart from the direct light coupling over the contact interface, the evanescent field from the guided cladding modes penetrates the surroundings and reaches the D-fiber core by tunneling across the medium into which the fiber pair is located. The amount of tunneling depends strongly on the SRI so that the total amount of light collected by the D-fiber provides a measure of the SRI. Sensitivities ranging from ~1000 to 13000 nW/RIU (Refractive Index Unit) have been obtained and the result is independent of temperature (within +/-10 nW of uncertainty). The measurement can be temperature-referenced through measurement of the TFBG spectrum if needed.

Resolution-improved in situ DNA hybridization detection based on microwave photonic interrogation.

In situ bio-sensing system based on microwave photonics filter (MPF) interrogation method with improved resolution is proposed and experimentally demonstrated. A microfiber Bragg grating (mFBG) is used as sensing probe for DNA hybridization detection. Different from the traditional wavelength monitoring technique, we use the frequency interrogation scheme for resolution-improved bio-sensing detection. Experimental results show that the frequency shift of MPF notch presents a linear response to the surrounding refractive index (SRI) change over the range of 1.33 to 1.38, with a SRI resolution up to 2.6 × 10(-5) RIU, which has been increased for almost two orders of magnitude compared with the traditional fundamental mode monitoring technique (~3.6 × 10(-3) RIU). Due to the high Q value (about 27), the whole process of DNA hybridization can be in situ monitored. The proposed MPF-based bio-sensing system provides a new interrogation method over the frequency domain with improved sensing resolution and rapid interrogation rate for biochemical and environmental measurement.

Review of plasmonic fiber optic biochemical sensors: improving the limit of detection.

This paper presents a brief overview of the technologies used to implement surface plasmon resonance (SPR) effects into fiber-optic sensors for chemical and biochemical applications and a survey of results reported over the last ten years. The performance indicators that are relevant for such systems, such as refractometric sensitivity, operating wavelength, and figure of merit (FOM), are discussed and listed in table form. A list of experimental results with reported limits of detection (LOD) for proteins, toxins, viruses, DNA, bacteria, glucose, and various chemicals is also provided for the same time period. Configurations discussed include fiber-optic analogues of the Kretschmann-Raether prism SPR platforms, made from geometry-modified multimode and single-mode optical fibers (unclad, side-polished, tapered, and U-shaped), long period fiber gratings (LPFG), tilted fiber Bragg gratings (TFBG), and specialty fibers (plastic or polymer, microstructured, and photonic crystal fibers). Configurations involving the excitation of surface plasmon polaritons (SPP) on continuous thin metal layers as well as those involving localized SPR (LSPR) phenomena in nanoparticle metal coatings of gold, silver, and other metals at visible and near-infrared wavelengths are described and compared quantitatively.

Polarimetric multi-mode tilted fiber grating sensors.

The polarimetric sensing characteristics of multi-mode-fiber based tilted fiber Bragg gratings (MMF-TFBG) have been analyzed and experimentally demonstrated. The larger diameter fiber core and graded index core/cladding profile enable the tilted gratings to excite multiple high-order core modes with significantly different polarization dependence and to form a well-defined "comb" of spectrally separated resonances at different wavelengths. Orientation-recognized twist/rotation measurements (-90° to 90°) have been achieved with sensitivity of 0.075 dB/deg by using intensity monitoring of two orthogonally polarized odd core-modes (LP11 and LP12). The proposed sensor is compact, works in reflection (a short section of MMF-TFBG spliced with a leading-in single mode fiber without any offset or tapering), is insensitive to temperature (intensity detection instead of wavelength monitoring) and is immune to unwanted intensity fluctuations (differential intensity measurement). Other TFBG sensing modalities, such as lateral pressure and surrounding refractive index are demonstrated separately with the same device configuration and interrogation principles.

Wideband-adjustable reflection-suppressed rejection filters using chirped and tilted fiber gratings.

Wideband-adjustable band-rejection filters based on chirped and tilted fiber Bragg gratings (CTFBG) are proposed and experimentally demonstrated. The flexible chirp-rate and wide tilt-angle provide the gratings with broadband filtering functions over a large range of bandwidths (from 10 nm to 150 nm), together with a low insertion loss (less than 1 dB) and a negligible back-reflection (lower than -20 dB). The slope profile of CTFBG in transmission can be easily tailored by adjusting the tilt angle, grating irradiation time and chirp rate-grating factor, and it is insensitive to the polarization state of the input light, as well as to temperature, axial strain and surrounding refractive index. Furthermore, by coating the CTFBG with a suitable polymer (whose refractive index is close to that of the cladding glass), the cladding modes no longer form weakly discrete resonances and leave a smoothly varying attenuation spectrum for high-quality band-rejection filters, edge filters and gain equalizers.

Orientation-dependent fiber-optic accelerometer based on grating inscription over fiber cladding.

An orientation-sensitive fiber-optic accelerometer based on grating inscription over fiber cladding has been demonstrated. The sensor probe comprises a compact structure in which a short section of thin-core fiber (TCF) stub containing a "cladding" fiber Bragg grating (FBG) is spliced to another single-mode fiber (SMF) without any lateral offset. A femtosecond laser side-illumination technique was utilized to ensure that the grating inscription remains close to the core-cladding interface of the TCF. The core mode and the cladding mode of the TCF are coupled at the core-mismatch junction, and two well-defined resonances in reflection appear from the downstream FBG, in which the cladding resonance exhibits a strong polarization and bending dependence due to the asymmetrical distribution of the cladding FBG along the fiber cross section. Strong orientation dependence of the vibration (acceleration) measurement has been achieved by power detection of the cladding resonance. Meanwhile, the unwanted power fluctuations and temperature perturbations can be referenced out by monitoring the fundamental core resonance.

UV exposure on a single-mode fiber within a multimode interference structure.

We experimentally study the effects of UV exposure on a single-mode fiber (SMF) with a fiber multimode interferometer (MMI) based on the singlemode-multimode-singlemode-multimode-singlemode (SMSMS) fiber structure. We observe a wavelength shift of over 33 nm when irradiating the central SMF in the SMSMS fiber structure with a 3-mm-width UV beam (the UV laser has a wavelength of 193 nm and pulse energy of 3 mJ). According to our numerical simulation, the SMSMS fiber structure can achieve a very high refractive-index (RI) sensitivity of 67670 nm/RIU with a very good linearity of R2≈0.9999. The structure can find potential application for high-sensitivity RI sensing by replacing the central SMF with a hollow-core optical fiber filled with the sample under test. The UV exposure technique can be used for tuning the characteristics of fiber MMI devices.

MALDI-TOF-MS serum protein profiling for developing diagnostic models and identifying serum markers for discogenic low back pain.

BACKGROUND: The identification of the cause of chronic low back pain (CLBP) represents a great challenge to orthopedists due to the controversy over the diagnosis of discogenic low back pain (DLBP) and the existence of a number of cases of CLBP of unknown origin. This study aimed to develop diagnostic models to distinguish DLBP from other forms of CLBP and to identify serum biomarkers for DLBP. METHODS: Serum samples were collected from patients with DLBP, chronic lumbar disc herniation (LDH), or CLBP of unknown origin, and healthy controls (N), and randomly divided into a training set (n = 30) and a blind test set (n = 30). Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed for protein profiling of these samples. After the discriminative ability of two most significantly differential peaks from each two groups was assessed using scatter plots, classification models were developed using differential peptide peaks to evaluate their diagnostic accuracy. The identity of peptides corresponding to three representative differential peaks was analyzed. RESULTS: The fewest statistically significant differential peaks were identified between DLBP and CLBP (3), followed by CLBP vs. N (5), DLBP vs. N (9), LDH vs. CLBP (20), DLBP vs. LDH (23), and LDH vs. N (43). The discriminative ability of two most significantly differential peaks was poor in classifying DLBP vs. CLBP but good in classifying DLBP vs. LDH. The accuracy of models for classification of DLBP vs. CLBP was not very high in the blind test (forecasting ability, 67.24%; sensitivity, 70%), although a higher accuracy was observed for classification of DLBP vs. LDH and LDH vs. N (forecasting abilities, ~90%; sensitivities, >90%). A further investigation of three representative differential peaks led to the identification of two peaks as peptides of complement C3, and one peak as a human fibrinogen peptide. CONCLUSIONS: Our findings benefit not only the diagnosis of CLBP but also the understanding of the differences between different forms of DLBP. The ability to distinguish between different causes of CLBP and the identification of serum biomarkers may be of great value to diagnose different causes of DLBP and predict treatment efficacy.