Fluorescence optical fiber sensor for tetracycline

A new optical fiber sensor for monitoring tetracycline has been described, based on the fluorescence quenching of 1,4-bis(5,5'-dimethylbenzoxazole-1',3'-yl-2')benzene incorporated into a thin plasticized polymer film by tetracycline extracted from aqueous phase into film phase. The sensor is fully reversible and highly reproducible. Furthermore, the sensor exhibits a linear response to tetracycline in the range 6.98x10(-7)-8.73x10(-5) mol l(-1) with a detection limit of 1.06x10(-7) mol l(-1), and with the response time <30 s. The response is also selective to tetracycline, with some common pharmaceutical species, alkali and alkali-earth metal salts being highly discriminated, suggesting that the sensor can be used to monitor tetracycline in three pharmaceutical preparations. The recovery of tetracycline from commercial formulations is 95.3-98.3%.     

Anionic surfactant sensor based on a hetero-core structured optical fiber

A simple method of fiber optic spectrophotometric measurement for anionic surfactant is described. The probe was fabricated from hetero-core structured fiber optic that consisted of multi mode fibers and a short length of single mode fiber which was inserted in the multi mode fibers. The sensor surface was treated with octyltrimethoxysilane to adsorb the surfactant-methylene blue complex via hydrophobic interaction between the octyl group on the fiber surface and the hydrophobic group of the surfactant. Methylene blue—anionic surfactant complex adsorbed on the sensor surface caused propagating light loss because of evanescent wave interaction that was generated at the cladding. The propagating loss spectrum of the fiber showed a peak at around 610 nm. Absorbance increases with the concentration of the surfactant to reach an upper level at a concentration of 30?μm. The response time is within 30 min.     

多荧光光纤传感器及其在混合溶剂检测中的应用

微纳光纤与其他微纳结构的集成可以拓展荧光光纤传感器检测范围和集成度,是光纤传感领域的研究热点。目前,国际上关于荧光光纤传感器这一领域的研究还处于单一检测物荧光响应的阶段,对多检测物的多通道荧光响应仍存在很大挑战。本文结合微纳光纤的光波导性能以及有机荧光材料的光功能特性,制备了能够同时激发和收集多种荧光的微纳光纤,并将之应用于高性能荧光光纤传感器的制备。通过选用不同荧光波长的有机材料与凝胶掺杂,制备了多荧光发射的光纤涂层材料,可控构筑了多组分荧光检测剂掺杂凝胶涂层。利用荧光光谱结合色度图分析,确定检测物与色坐标的关系,实现了多检测物的多通道荧光响应,为实现多荧光光纤传感器的可控构筑提供了有益的借鉴和指导意义。     

Simplification and evaluation of a gold-deposited SPR optical fiber sensor.

The structure of the sensing element of a gold-deposited optical fiber sensor was simplified and quantitative analyses of various alcohols with the sensor showed improvement of the performance. The sensor uses surface plasmon resonance (SPR) at the interface of a sample solution and a thin (10 - 70 nm) gold film deposited on half of the exposed core of the optical fiber. The sensor with a film thickness of 45 nm can detect a small change of 5.6 x 10(-5) refractive index (RI) units in the refractivity. The response time is less than 0.5 min and the relative standard deviation for measurements is less than or equal to 1%. A straight line with a correlation coefficient of 0.9995 was obtained below 10%, v/v in the calibration curve for methanol solutions of benzyl alcohol. The minimum of the response curve due to the maximum excitation of SPR in the refractivity range from 1.33 to 1.44 RI units shifts to a lower refractivity as the film becomes thicker. The response curves of the sensors were calculated from SPR theoretical equations while considering of the distribution in the thickness of the deposited gold films. The improvement in the performance of the sensor is discussed.     

A hetero-core structured fiber optic pH sensor

Novel spectroscopic sensor based on a hetero-core structured fiber optic is described in this paper. The hetero-core structured fiber optic consists of multi mode fibers and a short piece of single mode fiber which was inserted in the multi mode fibers. Phenol red and/or cresol red as pH sensitive dyes were immobilized on the surface of the hetero-core portion by using sol-gel method, and the pH change detection was performed by immersing the hetero-core portion into the solution. In the case that the cresol-red immobilized fiber was immersed in the alkaline and/or acidic solution, the peak wavelength of the propagating loss spectra were about 575 and 545 nm, respectively. These propagating loss spectra were similar to that of the absorbance spectra of the dye solution. In the propagating loss spectra of phenol-red immobilized fiber, these spectra were similar to that of the dye solution. The colorimetric change of the dye in the support matrix was reversible, and the response time of the sensor was within 30 s.     

Synthesis of new metalloporphyrin triads: efficient and versatile tripod optical sensor for the detection of amines

Zinc and manganese complexes of porphyrin triads have been synthesized and are shown to be efficient as highly sensitive and selective tripod optical sensors for amines at the picomolar level.     

A novel optical sensor for uranium determination

A metal ion indicator, Alizarin Red S, was tested for its potential use in uranium selective optode membrane. The water-soluble indicator was lipophilized in the form of an ion pair with tetraoctylammonium bromide, and subsequently immobilized on a triacetyl cellulose membrane. The membrane responds to uranium ions, giving a color change from yellow to violet in acetate buffer pH 5. This optode has a linear range of (1.70-18.7) × 10⁻⁵ M of UO₂²⁺ ions with a limit of detection of 5 × 10⁻⁶ M. The response time of optode was within 6 min depending on the concentration of UO₂²⁺ ions. The sensor can readily be regenerated with hydrochloric acid solution (0.01 M). The optode is fully reversible.     

A new ion sensor based on fiber optics

A fluorimetric ion sensor based on fiber optics has been developed that employs Rhodamine 6G hydrophobically and electrostatically "trapped" on a Nafion film. The sensor is based on the measurement of quenching or enhancement of the Rhodamine 6G fluorescence by various ions. It was found that ions such as Co(2+), Cr(3+), Fe(2+), Fe(3+), Cu(2+), Ni(2+) and NH(+)(4) rapidly quench the Rhodamine 6G fluorescence at an initial rate that depends on the concentration of the ion. This quenching is then readily reversed by the addition of "reverser" ions such as H(+), Li(+), Na(+), K(+), Ba(2+), Ca(2+), Mn(2+), Zn(2+) and Mg(2+). Again, the initial rate for the attainment of the original fluorescence was found to depend on the concentration of the reverser ion. Therefore, by monitoring the quenching directly the concentration of quencher ions can be determined. In addition, by loading the film with quencher and monitoring the initial rate of return towards the original baseline signal, it is possible to determine non-quenching ions.     

Theoretical analysis of gold-deposited optical fiber sensor and characterization of the gold film.

Gold-deposited optical fiber sensors with film thicknesses from 30 to 60 nm were prepared, and the responses to a wide range of a refractivity (1.33-1.54 refractive index (RI) units) were investigated both experimentally and theoretically. The response curve of the sensor has two minima in the refractivity range from 1.33 to 1.44 and at 1.462 RI units. The former minimum is due to surface plasmon resonance (SPR) in the thin gold film, and shifts to a lower refractivity as the film becomes thicker. The response curves of the sensors with film thicknesses of 45 and 60 nm agreed well with those calculated from SPR theoretical equations. Morphology observations of the surfaces of deposited gold films on glass by atomic force microscopy (AFM) and a variation in resistance of the films with various thicknesses show the structure of the gold films. We concluded that the thin deposited gold films have many defects, and that the core of the gold-deposited optical fiber leaks light through the defects to the sample solution with the same refractivity (1.462 RI units) as that of the core.     

Planar and twisted lyotropic chromonic liquid crystal cells as optical compensators for twisted nematic displays

We have explored the use of lyotropic chromonic liquid crystals (LCLCs) as promising materials for optical compensators for liquid crystal displays. We used aqueous solutions of disodium cromoglycate in the range of concentrations that yield a chromonic N phase. The N phase is aligned by rubbed polyimide layers giving planar orientation. Two different types of LCLC-based elements are described: (a) a uniformly aligned planar N phase that forms an optically uniaxial plate with a negative birefringence; (b) twisted cells of LCLC obtained by doping the N phase with chiral amino acids. Both planar and twisted N* phase cells were used for compensation of the positive birefringence of twisted nematic (TN) displays; the TN devices were appreciably improved. We achieved achromatic dark state and contrast ratio up to 50:1 at all directions within a 40° cone of viewing angle.     

Planar and twisted lyotropic chromonic liquid crystal cells as optical compensators for twisted nematic displays

We have explored the use of lyotropic chromonic liquid crystals (LCLCs) as promising materials for optical compensators for liquid crystal displays. We used aqueous solutions of disodium cromoglycate in the range of concentrations that yield a chromonic N phase. The N phase is aligned by rubbed polyimide layers giving planar orientation. Two different types of LCLC-based elements are described: (a) a uniformly aligned planar N phase that forms an optically uniaxial plate with a negative birefringence; (b) twisted cells of LCLC obtained by doping the N phase with chiral amino acids. Both planar and twisted N* phase cells were used for compensation of the positive birefringence of twisted nematic (TN) displays; the TN devices were appreciably improved. We achieved achromatic dark state and contrast ratio up to 50:1 at all directions within a 40° cone of viewing angle.     

A high precision, fast response, and low power consumption in situ optical fiber chemical pCO2 sensor

A sensor system suitable for monitoring changes in partial pressure of carbon dioxide (pCO(2)) in surface seawater or in the atmosphere has been developed. Surface seawater samples are pumped into a PVC tube enclosing an inner Teflon AF tube, which served as a long pathlength gas-permeable liquid-core waveguide for spectrophotometry. The Teflon cell contains a pH-sensitive indicator-buffer solution consisting of bromothymol blue (BTB) and sodium carbonate. Carbon dioxide in the sample diffuses into the indicator-buffer solution to reach equilibrium, resulting in pH changes, which are detected by changes in the absorbance of BTB at wavelengths of 620 and 434 nm. The pCO(2) in the sample is then derived from the pH change. The sensor has a response time of 2 min at the 95% equilibrium value and a measurement precision of 0.26-0.37% in the range 200-800 microatm pCO(2). This chemical sensor takes advantage of a combination of long pathlength, multiple wavelength detection, indicator solution renewal, and in situ automatic control technology, and has the feature of low power consumption (the average being approximately 4 W with a peak of approximately 8 W).     

Photoresponsive ion-selective optical sensor

A novel concept of photoresponsive ion-selective optical sensor is described. Photochemical reactions can be utilized to generate and control ion fluxes in an ion-selective optode in the same manner as nonequilibrium electrochemical methods have been used in ion-selective electrodes. In contrast to their equilibrium counterparts, the photoresponsive pH-selective ion optodes are sensitive to both the buffer capacity of the sample and activity of hydrogen ions. Active optical probes are especially attractive for intracellular applications because they can be fabricated as submicron-sized beads. Common optical techniques, such as fluorescence microscopy and flow cytometry, can be combined with active ion probes with only minor modification of the existing experimental setup.     

A versatile amphiprotic cotton fiber for the removal of dyes and metal ions

Adsorption is an efficient method to combat the important issues of water pollution caused by dyes and metal ions. However, due to the surface charge diversity of pollutants, there is a pressing need to develop an all-round, efficient, cheap and environmentally friendly adsorbent. To this end, this work synthesized an amphiprotic adsorbent based on cotton fibers, which were chemically modified with a cationic monomer (3-chloro-2-hydroxypropyl trimethyl ammonium chloride) and anionic monomer (2-acrylamide-2-methyl propane sulfonic acid) respectively. The resultant amphiprotic cotton (AP-cotton) can cope with both of anionic and cationic pollutants. Its adsorption behavior as influenced by the pH value, adsorption time and initial concentration of various adsorbates was investigated. The results demonstrate that the adsorption equilibrium was reached within 4 h for Congo red (CR) and methylene blue (MB), 2 h for Cu²⁺ and 3 h for Pb²⁺, respectively. Adsorption kinetics showed that the adsorption rate was well fitted with the pseudo-second-order rate model, and the best adsorption isotherms fitted the Langmuir model. The Langmuir maximum adsorption capacities were 175.1 mg/g for CR, 113.1 mg/g for MB, 88.9 mg/g for Cu²⁺ and 70.6 mg/g for Pb²⁺, respectively, and the adsorption capacities could be maintained above 90 % after six regenerations. The all-round adsorption capacity and good regeneration performance of AP-cotton benefited from its hollow, flat-banded structure and amphiprotic characteristic. Therefore, AP-cotton exhibited a much better application potential compared with many other reported adsorbents based on natural materials.     

Controlled and scalable torsional actuation of twisted nylon 6 fiber

Large‐scale torsional actuation occurs in twisted fibers and yarns as a result of volume change induced electrochemically, thermally, photonically, and other means. A quantitative relationship between torsional actuation (stroke and torque) and volume change is here introduced. The analysis is based on experimental investigation of the effects of fiber diameter and inserted twist on the torsional stroke and torque measured when heating and cooling nylon 6 fibers over the temperature range of 26–62 °C. The results show that the torsional stroke depends only on the amount of twist inserted into the fiber and is independent of fiber diameter. The torque generated is larger in fibers with more inserted twist and with larger diameters. These results are successfully modeled using a single‐helix approximation of the twisted fiber structure. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1278–1286     

Vapor zone velocities measurement using a capillary optical fiber sensor with an application to gas chromatography

A fiber optic sensor has been used for real-time measurement of the migration rates of all the compounds in a mixture separated by gas chromatography. The sensor makes use of a coated capillary optical fiber as the column. This new type of waveguide consists in a polarization-maintaining optical core positioned close to the capillary edge along the entire fiber length. The optical detection is performed through the coupling of the two polarization modes of the waveguide and this coupling is detected by a polarimetric interferometry technique. Through some signal processing, the resulting interferogram provides the migration rates of the various compounds of a gas mixture flowing in the capillary. One of the major benefits of this optical migration rate sensing is that the detection of each velocity peak appears as soon as the analyte enters the capillary fiber and the peaks are constantly measured during the whole separation process. Carrier gas acceleration occurring in the column is plainly demonstrated. This paper presents a proof-of-concept on a qualitative basis. The experiments were done at 29 °C because the current opto-fluidic set-up cannot withstand a higher temperature.     

An optical calcium ion sensor

An optical fibre calcium ion sensor is described which utilises the chromogenic crown ether, (5-(4′-nitrophenylazo)-2-hydroxy-1,3-xylyl-18-crown-5), immobilised on a styrene/divinylbenzene copolymer at the tip of an optical fibre. The sensor is sensitive to calcium ions in the concentration range 5–50 mM.     

Non-enzymatic optical sensor for penicillins

We report on the first penicillin-sensitive fluorosensor not based on the use of an enzyme. Rather, the recognition process relies on the use of an anion carrier (which carries the penicillin anion from the aqueous sample into the membrane), a proton receptor (lipophilic nile blue which accepts the proton, thereby undergoing a change in fluorescence intensity), and a new lipophilic hydroxylic plasticizer material (which facilitates ion transport). All materials are contained in a dyed poly(vinyl chloride) membrane whose fluorescence is monitored. The optical sensor fully reversibly responds to penicillin V over the 0.01-10mM concentration range, and to penicillin G from 0.03 to 10mM. Potential interferences by about 20 other anions have been investigated. Nitrate, salicylate, and ascorbate were found to interfere significantly. These species are, however, usually not present in penicillin bioreactors or drug formulations where penicillin sensing is most important. The sensor does not respond to penicillins containing an aliphatic amino group (such as amoxicillin). The method has been applied for determination of penicillin G in pharmaceutical formulations.     

Photochemical modification of an optical fiber tip with a silver nanoparticle film: a SERS chemical sensor

We present a method of photochemical modification of an optical fiber tip with a silver nanoparticle film. The deposited silver nanoparticle film displays alternating light and dark circles, which are similar to a radial diffraction pattern. The modified optical fiber is examined as a chemical sensor for in situ detection. The modified fibers show excellent SERS activity, a low limit of detection (LOD), and good reproducibility. The maximum SERS activity of the sensor was achieved within 5.0 min of deposition. Thus, the method is also quite rapid.     

Trends in fiber optic sensor development

Fiber optic sensors continue to attract considerable attention and have been widely applied to diverse analytes. The current state of the art will be reviewed with the major focus on extrinsic fiber optic chemical sensors. Fiber optic characteristics, instrumentation and configurations will be described. Representative applications will be discussed from the clinical, industrial, and environmental areas. Advantages, limitations, and future directions will be discussed.