Optical fiber light-emitting diode-induced fluorescence detection for capillary electrophoresis

A highly sensitive optical fiber light-emitting diode (LED)-induced fluorescence detector for CE has been constructed and evaluated. In this detector, a violet or blue LED was used as the excitation source and an optical fiber with 40 microm OD was used to transmit the excitation light. The upper end of the fiber was inserted into the separation capillary and was situated right at the detection window. Fluorescence emission was collected by a 40 x microscope objective, focused on a spatial filter, and passed through a cutoff filter before reaching the photomultiplier tube. Output signals were recorded and processed with a computer using in-house written software. The present CE/fluorescence detector deploys a simple and inexpensive optical system that requires only an LED as the light source. Its utility was successfully demonstrated by the separation and determination of amino acids (AAs) labeled with naphthalene-2,3-dicarboxaldehyde (NDA) and FITC. Low detection limits were obtained ranging from 17 to 23 nM for NDA-tagged AAs and 8 to 12 nM for FITC-labeled AAs (S/N=3). By virtue of such valuable features as low cost, convenience, and miniaturization, the presented detection scheme was proven to be attractive for sensitive fluorescence detection in CE.     

Construction and performance of a drop cell for the nephelometric determination of sulfur dioxide

A nephelometric technique based on a liquid drop is described for the measurement of atmospheric sulfur dioxide. A 40-μl drop of barium chloride and hydrogen peroxide solution is suspended in a flowing-air sampling stream. The sulfur (IV) collected is oxidized to sulfur (VI) and finally precipitated as barium sulfate. Nephelometric detection of drop is achieved by an appropriate arrangement consisting of an optical fiber contacting the drop and a photodiode placed at 90° relative to the fiber. The design and characteristics of this drop-based gas sensor system are described. The analytical response, as photocurrent, is proportional to the product of the sampling period and the sulfur dioxide concentration. The detection limit is ca. 1.1 mg m⁻³ for a 10-min sampling time. The present technique is fairly rapid and simple, uses a small amount of reagent and is set up with low-cost equipment, making this system economically viable.     

Fiber optic sensors using novel substrates for hydrogen sulfide determination by solid surface fluorescence

Two different fiber optic sensors were developed for the determination of hydrogen sulfide at ppb concentration levels; a probe-type fiber optic sensor coated with polyethylene oxide containing 0.5 M CdCl(2) and a fiber optic sensor utilizing 0.5 M CdCl(2)-pretreated filter paper as solid substrate. In the first type, CdCl(2)-polyethyleneoxide (PEO) mixture was coated onto the tip of a fiber optic probe and the probe was exposed to H(2)S. The methodology is based on the measurement of CdS fluorescence on the surface. Detection limit (3s) of the PEO-coated fiber optic system was 36.0 ppb for H(2)S and precision at the 0.552 ppm level was 29% R.S.D. For the fiber optic system utilizing CdCl(2)-pretreated filter paper, two different configurations were devised and evaluated; a bifurcated fiber optic sensor and a single fiber optic sensor. Similar figures were obtained with these two systems; the detection limit (3s) was 4.0 ppb for the bifurcated fiber optic sensor and 4.3 ppb for the single fiber optic sensor, and both sensors had linear responses in the range 0.032-1.0 ppm. Their precisions at 0.299 ppm level were also very similar, 10 and 11% R.S.D., respectively, for the bifurcated and single fiber systems. In addition to the fiber optic sensors developed, various surfactants (sodiumdodecylsulfate (SDS), Aerosol OT, Aerosol A102, Aerosol 501), some cellulosic substances (sodium carboxymethylcellulose (CMC), ethylcellulose, hydroxypropylmethylcellulose, ethylhydroxyethylcellulose, alpha-cellulose) and several water-soluble polymers (polyacrylicacid polyethleneoxide (PEO), polyvinylalcohol (PVA)) were dissolved in proper solvents and after mixing with 0.5 M CdCl(2), were spread over glass slides. These novel solid substrates were exposed to H(2)S and fluorescence signal on the surfaces of the glass slides was measured with a luminescence spectrometer. The new substrates were shown to be good alternatives to filter paper for the determination of H(2)S by room temperature solid surface fluorescence spectrometry.     

Selective interactions of concanavalin A at lipid membranes on the surface of an optical fiber

An optical configuration was developed for sampling fluorescence coupled into an optical fiber from evanescent wave excitation of fluorescent materials at a lipid membrane on a quartz fiber surface. Selective interactions of pyrene-labelled concanavalin A located on a phosphatidyl choline-cholesterol lipid membrane with fluorescein isothiocyanate-labelled dextran in bulk aqueous solution were monitored by the intrinsic fluorescence sensing configuration. Monosialoganglioside, G(M1), was employed as a receptor in a phospholipid membrane on an optical fiber for selective measurement of pyrene-labelled concanavalin A in solution. Quantitative measurement was hindered by non-selective adsorption of cancanavalin A, but the potential for use of a lipid membrane in a fluorometric biosensor was established.     

Calibration of an optical condensate measurement technique using indirect static headspace gas chromatography.

Researchers in the Department of Mechanical Engineering seek to obtain a means to measure less than 3 mg of H2O that adheres to a metal surface as condensate. The objective is to calibrate optical reflectance measurements of an aluminum surface as a function of the condensate thickness present. Collaboration with the Hazardous Substance Research Center at Michigan State University results in the development of an indirect static headspace gas chromatographic technique capable of measuring H2O in low-milligram quantities. The technique utilizes manual headspace sampling, a megabore capillary column, and a flame ionization detector. A correlation of r2 = 0.999 is obtained for the calibration of the indirect measurement technique. The calibration of the analytical instrument demonstrates adequate precision (< +/- 50 microg at a 95% confidence interval) for such a heterogeneous sample. The calibration samples consist of a strip of aluminum metal, H2O, and pulverized calcium carbide to convert the H2O to acetylene. A scaled calibration technique is used to simplify handling trace water volumes. The surface reflectance measurements are found to correlate well (r2 = 0.935) with measurements of the condensate mass. This result facilitates the development of an optical mass-transfer measurement technique. This study focuses on the analytical method and its relationship with engineering research.     

Application of laser-induced optical fiber fluorimetry to the analysis of ultralow level of uranium

A laser-induced optical fiber fluorimetry has been reported for the analysis of ultralow level of uranium. The fluorescence spectrometer includes five major components: a pulsed nitrogen laser, optical fibers, an optrode, a detector, and a boxcar. The fluorescence intensity of uranyl ions is linear with respect to the concentration of uranium. The detection limit of uranium in 1M phosphoric acid is 24 ppb. This technique can be used for the remote, on-line measurement of low level uranium.     

Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 microL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7% and differed only by 0.2% from the expected value.     

Sample preparation including sol-gel immunoaffinity chromatography for determination of bisphenol A in canned beverages, fruits and vegetables

The paper describes the development of a very simple method to prepare samples of canned food (beverages, fruits and vegetables) for the determination of bisphenol A by isocratic HPLC with fluorescence detection. The new sample preparation method makes use of the selectivity of bisphenol A antibodies immobilized in a silica matrix by an inexpensive and simple sol-gel technique. In spite of applying highly complex food matrices, immunoaffinity columns could be used for clean-up of at least 15 real samples. Limits of detection (S/N=3) ranged from 0.1 ng/ml for beverages to 4.3 ng/g for vegetables.     

Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 μL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7 % and differed only by 0.2 % from the expected value. Received: 19 January 2000 / Revised: 28 February 2000 / Accepted: 3 March 2000     

Design and evaluation of capillary coupled with optical fiber light‐emitting diode induced fluorescence detection for capillary electrophoresis

A new detector, capillary coupled with optical fiber LED‐induced fluorescence detector (CCOF‐LED‐IFD, using CCOF for short), is introduced for CE. The strategy of the present work was that the optical fiber and separation capillary were, in the parallel direction, fastened in a fixation capillary with larger inner diameter. By employing larger inner diameter, the fixation capillary allowed the large diameter of the optical fiber to be inserted into it. By transmitting an enhanced excitation light through the optical fiber, the detection sensitivity was improved. The advantages of the CCOF‐CE system were validated by the detection of riboflavin, and the results were compared to those obtained by the in‐capillary common optical fiber LED‐induced fluorescence detector (IC‐COF‐LED‐IFD, using COF for short). The LODs of CCOF‐CE and COF‐CE were 0.29 nM and 11.0 nM (S/N = 3), respectively. The intraday (n = 6) repeatability and interday (n = 6) reproducibility of migration time and corresponding peak area for both types of CE were all less than 1.10 and 3.30%, respectively. The accuracy of the proposed method was judged by employing standard addition method, and recoveries obtained were in the range of 98.0–102.4%. The results indicated that the sensitivity of the proposed system was largely improved, and that its reproducibility and accuracy were satisfactory. The proposed system was successfully applied to separate and determine riboflavin in real sample.     

Electrochemical modulation of remote fluorescence imaging at an ordered opto-electrochemical nanoaperture array.

An array of nanometer-sized apertures capable of electrochemically modulating the fluorescence of a model analyte is presented. The device, which combines near-field optical methods and ultramicroelectrode properties in an array format, is based on an etched coherent optical fiber bundle. Indeed, the fabrication steps produced an ordered array where each optical nanoaperture is surrounded by a ring-shaped gold nanoelectrode. The chronoamperometric behavior of the array shows stable diffusion-limited quasi-steady-state response. The model analyte, tris(2,2'-bipyridine) ruthenium, emits fluorescence in the Ru(II) state, but not in the oxidized Ru(III) state. Fluorescence is excited by visible light exiting from each nanoaperture since light is confined to the tip apex by the gold coating. A fraction of the isotropically emitted luminescence is collected by the same nanoaperture, transmitted by the corresponding fiber core and eventually detected by a charge-coupled device (CCD) camera. The array format provides a fluorescence image resolved at the nanometric scale which covers a large micrometric area. Therefore the high-density array plays a bridging role between these two fundamental scales. We established that the opto-electrochemical nanoapertures are optically independent. Fluorescence of the sample collected by each nanoaperture is modulated by changing the potential of the nanoring electrodes. Reversible electrochemical switching of remote fluorescence imaging is performed through the opto-electrochemical nanoaperture array itself. Eventually this ordered structure of nanometer light sources which are electrochemically manipulated provides promising photonic or electro-optical devices for various future applications. For example, such an array has potential in the development of a combined SNOM-electrochemical nanoprobe array to image a real sample concomitantly at the nanometer and micrometer scale.     

A simple,low-cost,remote fiber-optic micro volume fluorescence flowcell for capillary flow-injection analysis

A small volume flowcell for fluorescence detection in capillary flow injection (CFI) analysis has been created by using a low cost, commercially available fluidic device. Fluorescence detection is achieved using an optical fiber to deliver excitation light to the sample flowing through the device and another optical fiber to collect fluorescence emission. The flowcell is a standard fluidic cross with a swept volume of 721 nL. Optical fibers were oriented at right angles using standard sleeves and ferrules to set their position near the cross intersection. Multiple excitation sources were used including a low power UV laser and blue and UV light emitting diodes (LED). The full emission spectrum detection limits, using the laser, for fluorescein and bovine serum albumin (BSA) were 0.30 ppb and 2.1 x 10(-4)% (w/w), respectively. Two fluidic crosses were used in series for multi-wavelength fluorescence excitation using fiber-optically coupled LED.     

一种新的基于折射率变化的光纤化学传感器

在光纤化学传感器中,基于样品折射率变化的传感器是其中的重要分支,并获得了广泛的实际应用^[1].根据敏感部件的不同可将其分为两大类:一类的敏感部件是裸光纤,这类传感器已用于检测苯、甲醇和丙酮^[2],测定血样中葡萄糖浓度^[3],鉴定燃油质量.     

Use of the original silicone cladding of an optical fiber as a reagent-immobilization medium for intrinsic chemical sensors

It is demonstrated that extended-length sensors can be fabricated by the direct immobilization of suitable reagents into the original cladding of a plastic-clad silica (PCS) optical fiber. This cladding, a copolymer of vinyl-terminated poly(dimethylsiloxane) and poly(dimethylmethylhydrosiloxane), is an attractive immobilization matrix for a wide variety of reagents and opens up new avenues of sensor design. Unlike fibers with custom-drawn cladding, the new approach offers greater photo- and thermal stability and permits immobilization of several reagents in adjacent sections of a single fiber. Further, compared to room-termperature vulcanizable (RTV) silicone films used often in optical point sensors, the silicone cladding of a PCS optical fiber offers a number of advantages, including a dynamic fluorescence quenching constant for an immobilized fluorophore that is up to 3.4 times higher, tolerance to aggressive environments (e.g. highly alkaline solutions), lower rates of indicator leaching, high uniformity, and applicability to extended-length sensing. The homogeneity of the microenvironment of the fiber cladding, its resistance to aggressive alkaline solutions, and its ability to transport water vapor were probed by introducing a variety of reagents into the cladding, including a fluorescent ruthenium complex and acid-base and solvatochromic indicators. The new sensor-fabrication approach should find wide application, including detection of neutral species in gases and dissolved in water, and for spatial analyte mapping over extended, remote areas.     

微孔板发光二极管诱导荧光-表面活性剂增敏法测定盐酸小檗碱

研制了微孔板发光二极管诱导荧光分析仪,以发光二极管为激发光源,Y形光纤束传导激发光和荧光,采用平面型光敏二极管接收荧光.采用二维定位器移动微孔板,可实现对多个样品快速连续的测定.利用弱碱性介质中阴离子表面活性剂十二烷基苯磺酸钠(SDBS)对盐酸小檗碱荧光的增敏作用,在pH 9.0的Britton-Robinson缓冲溶...     

A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis

A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y‐style optical fiber was used to transmit the excitation light and a four‐branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low‐cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis.     

Synthesis of a Novel m-Substituted Poly(phenoxy-imine) and Investigation of its Fluorescence and Some Properties

Oxidative polycondensation of 3-((2-phenylhydrazono)methyl)phenol (3-PHMP), a new m-substituted poly(phenoxy-imine), was studied using oxidants such as sodium hypochlorite, air (O₂) and hydrogen peroxide in an aqueous alkaline medium under various polymerization conditions. The macromolecular structure and optical properties of the polymer were characterized with elemental analysis, Size Exclusion Chromatography (SEC), Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR), absorption and fluorescence spectroscopy techniques. As a result of fluorescence measurement, the fluorescence lifetime of poly(3-PHMP) in DMF was calculated as 2.88 ns (χ²= 1.12). An electrochemical property the monomer and polymer were also studied using Cyclic Voltammetry (CV) technology. According to the CV measurements, the electrochemical band gaps (E_g′) of 3-PHMP and poly(3-PHMP) were found to be 2.64 and 1.94 eV, respectively. Electrical conductivity of the polymer was measured by the four-point probe technique. The electrical conductivity of poly(3-PHMP) was found to be ～3.2 × 10^?2S/cm. Thermo Gravimetric Analysis (TGA) revealed poly(3-PHMP) to be stable against thermo-oxidative decomposition. In addition, the in vitro antimicrobial activities of the synthesized compounds were tested on various microorganisms.     

Determination of heavy metals and rare earth elements in environmental samples by ICP-MS after solid phase preconcentration with chelating resin fibers and anion exchanger filters.

A solid phase collection/concentration method using anion exchanger filters and a small syringe packed with chelating resin fibers is adopted as a preconcentration tool for trace elements and a separation tool for matrices in aqueous samples prior to the measurement by inductively coupled plasma-mass spectrometry (ICP-MS). The effects of fiber volume, sample volume, eluent volume, and sample flow rate on metal recoveries were investigated in detail to obtain optimum pretreatment conditions. Several heavy metals (HMs) such as, V, Mn, Co, Ni, Cu, Zn, Ga, Cd, Pb, Th and U, as well as 14 rare earth elements (REEs) in sample solutions at pH 6 were quantitatively collected on the solid phase. These adsorbed elements were completely recovered by eluting with 2 ml of 1.0 M nitric acid. At pH 6, more than 99% of alkali and alkaline earth metals in sample solutions were eliminated. The proposed method was evaluated by analyzing two standard reference materials (SRM): peach leaves (NIST 1547) and pond sediment (NIES No. 2). The solid samples were decomposed by microwave-heating and pressurizing acid digestion technique, and then treated by the proposed syringe-type pretreatment method, followed by the ICP-MS measurement. The analytical results for HMs in the SRMs obtained by the present method agreed well with the certified values.     

Sensitivity enhancement of fluorescence detection in CE by coupling and conducting excitation light with tapered optical fiber

This paper reports the enhancement of sensitivity of detection for in‐column fiber optic‐induced fluorescence detection system in CE by tapered optical fiber (TOF). Two types of optical fiber, TOF and conventional cylindrical optical fiber (COF), were employed to construct the CE (TOF‐CE and COF‐CE) and were compared for sensitivity to riboflavin (RF). The fluorescence intensities from a RF sample with excitation light sources and fibers at various coupling angles were investigated. The fluorescence signal from TOF‐CE was ca. ten times that of COF‐CE. In addition, the detection performance of four excitation light source‐fiber configurations including Laser‐TOF, Laser‐COF, LED‐TOF, and LED‐COF were compared. The LODs for RF were 0.21, 0.82, 0.80, and 7.5 nM, respectively, for the four excitation light source–fiber configurations. The results demonstrate that the sensitivity obtained by LED‐TOF is close to that of Laser‐COF. Both Laser‐TOF and LED‐TOF can greatly improve the sensitivity of detection in CE. TOF has the major attribute of collecting and focusing the excitation light intensity. Thus, the sensitivity obtained by LED‐TOF without focusing lens is just same as that of LED‐COF with a focusing lens. This demonstrates that the CE system can be further simplified by eliminating the focusing lens for excitation light. LED‐TOF‐CE and LED‐COF‐CE system were applied to the separation and determination of RF in real sample (green tea), respectively. The tapered fiber optic‐induced fluorescence detection system in CE is an ideal tool for trace analysis.     

A portable sensor for the rapid detection of naphthalene acetic acid in fruits and vegetables using stabilized in air lipid films with incorporated auxin-binding protein 1 receptor

The present technique describes the development of a simple sensitive spot optical test and the construction of a portable biosensor for the rapid one-shot detection of naphthalene acetic acid (NAA) using stabilized lipid films supported on a methacrylate polymer on a glass fiber filter with incorporated auxin-binding protein 1 receptor. The lipid films without the receptor provided fluorescence under a UV lamp. The use of the receptor in these films quenched this fluorescence and the colour became similar to that of the filters without the lipid films. A drop of aqueous solution of naphthalene acetic acid provided a “switching on” of the fluorescence which allows the rapid detection of this stimulant at the levels of 10⁻⁹ M concentrations. It was also possible to have quantitative data based on a calibration graph. The effect of potent interferences included a wide range of compounds. The results showed no interferences from these compounds in concentration levels usually found in real samples. The method was applied for the determination of NAA in fruits and vegetables and the reproducibility of the method was checked in about 50 samples. A quantitative method for the detection of NAA in crops that can be complimentary to HPLC methods is provided in the present paper. These lipid films can be used as portable biosensors for the rapid one-shot detection of NAA in fruits and vegetables by non-skilled personnel in the field.