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Photocatalytic optical fibers are promising for the degradation of gaseous and volatile pollutants in air due to their high specific surface area, high light utilization efficiency, easy regeneration, and sustainability. In particular, photocatalytic optical fibers have proven highly useful for the removal and conversion of different kinds of air pollutants in air. However, these fibers suffer from low photocatalytic degradation efficiencies. In this review, we have focused on introducing photocatalytic quartz optical fibers and photocatalytic plastic optical fibers for the degradation and transformation of gas-phase air pollutants. The principle of photocatalytic optical fibers and main methods for improving their photocatalytic and light utilization efficiencies based on semiconductor photocatalytic coatings are summarized. Moreover, the Langmuir-Hinshelwood kinetic rate equation was summarized to analyze the photocatalytic reduction of gaseous pollutants. Finally, an outlook on the future of photocatalytic optical fibers toward the removal and conversion of gaseous air pollutants is discussed.

We present a highly sensitive photocatalytic plastic optic-fiber (POF) sensor for the selective detection of phenol in aqueous solutions. To obtain high sensitivity and low limit of detection (LOD) of the sensor, part of the POF cladding was removed and replaced by a Canada balsam doped with GeO2 (CBG); a UV–vis-light-driven photocatalytic material, that is a CdS-sensitized Er3+YAlO3/SiO2/TiO2 (EYST) composite, was coated on the CBG film. To realize highly selective detection of phenol in water, a high phenol permselectivity and pH independence polymer membrane was fixed on the CdS-sensitized EYST-CBG-coated POF. Furthermore, a model was developed to show that the phenol concentration can be determined by measuring the change in transmitted light intensity of the POF sensor and the sensitivity of the sensors can be improved by employing the CdS-sensitized EYST film. The results showed that the proposed photocatalytic POF sensor has a high sensitivity of -0.39 (mg·mL−1)−1 and low LOD of 15 μg·L−1 for the selective detection of phenol in aqueous solutions with pH ranging from 2.0 to 14.0.

A novel immunosensor for detecting Newcastle disease virus (NDV) was developed using excessively tilted fiber grating (Ex-TFG) coated with gold nanospheres (AuNs). AuNs were coated on the Ex-TFG surface via Au–S bonds using 3-mercaptopropyltrimethoxysilane (MPTMS), and the activated staphylococcal protein A (SPA) was linked to AuNs by covalent bonds via cysteamine. AuNs greatly enhanced the impact of the analyte on the fiber cladding mode through the local surface Plasmon resonance (LSPR) effect, thus improving the detection limit and sensitivity of the immunosensor. Meanwhile, SPA enhanced the bioactivity of anti-NDV monoclonal antibodies (MAbs), thus promoting the effectiveness of specific binding events on the fiber surface. Immunoassays were performed by monitoring the resonance wavelength shift of the proposed sensor under NDV samples containing different particle amounts. Specificity was assessed, and clinical tests for NDV were performed by contrast experiments. Experimental results showed that the detection limit for NDV was about 5~10 times improved compared to that of reference Ex-TFG without AuN treatment. Moreover, the novel biosensor was reusable and could potentially be applied in clinic.

Using excessively tilted fiber grating (Ex-TFG) inscribed in standard single mode fiber, we developed a novel label-free immunoassay for specific detection of porcine circovirus type 2 (PCV2), which is a minim animal virus. Staphylococcal protein A (SPA) was used to modify the silanized fiber surface thus forming a SPA layer, which would greatly enhance the proportion of anti-PCV2 monoclonal antibody (MAb) bioactivity, thus improving the effectiveness of specific adsorption and binding events between anti-PCV2 MAbs and PCV2 antigens. Immunoassay experiments were carried out by monitoring the resonance wavelength shift of the proposed sensor under different PCV2 titer levels. Anti-PCV2 MAbs were thoroughly dissociated from the SPA layer by treatment with urea, and recombined to the SPA layer on the sensor surface for repeated immunoassay of PCV2. The specificity of the immunosensor was inspected by detecting porcine reproductive and respiratory syndrome virus (PRRSV) first, and PCV2 subsequently. The results showed a limit of detection (LOD) for the PCV2 immunosensor of ~9.371TCID50/mL, for a saturation value of ~4.801×10(3)TCID50/mL, with good repeatability and excellent specificity.

We present a refractive index (RI) distribution sensor based on an etched fiber Bragg grating (FBG). The FBG is etched by hydrofluoric acid solution until the residual diameter of its core is about 5.73 μm, and then it is installed in a micro-tube where the RI of the liquid medium decreases linearly along its axis. The reflection spectrum of the etched FBG changes from a single resonant peak into many micro-resonant peaks under the inhomogeneous liquid medium. The difference of the wavelengths between the maximum micro-resonant peak and the minimum one changes linearly with the RI gradient, and the average change of the wavelengths of them changes linearly with the average change of the RI as well. Experimental results show that the sensitivity of RI gradient and the average sensitivity of RI for this etched FBG sensor is about 336.2 nm mm/RIU and 49.44 nm/RIU, respectively, when the surrounding RI ranges from 1.330 to 1.3586. Associated with the sensitivity of the RI gradient and the average sensitivity of the RI, the linear RI distribution of inhomogeneous liquid medium surrounding the etched FBG can be obtained.

The complete energy matrix of 4f(1)/4f(13) electronic configuration has been established by using the complete (energy matrix) diagonalization method and superposition model. The calculated energy levels agree well with experimental findings. The structure parameters have been determined in the present work and given as follows: R-1 approximate to 0.23 nm, R-2 approximate to 0.24 nm, theta(1) approximate to 127.58, theta(2) approximate to 31.85. Comparing with the host crystal structure data, the varieties of bond lengths and angles are, respectively, Delta R-1 = Delta R-2 = 0.0004 nm, Delta theta(1) = 1.5 degrees and Delta theta(2) = -0.5%degrees. Thus, there is slightly tetragonal distortion. What is more, the intrinsic parameters are given in |(A) over bar (2)(R-0)| > |(A) over bar (4)(R-0)| > |(A) over bar (6)(R-0)| which are agreement with the results of many studies. (C) 2011 Elsevier GmbH. All rights reserved.