Detection of Explosive Vapors: The Roles of Exciton and Molecular Diffusion in Real‐Time Sensing

Time‐resolved quartz crystal microbalance with in situ fluorescence measurements are used to monitor the sorption of the nitroaromatic (explosive) vapor, 2,4‐dinitrotoluene (DNT) into a porous pentiptycene‐containing poly(phenyleneethynylene) sensing film. Correlation of the nitroaromatic mass uptake with fluorescence quenching shows that the analyte diffusion follows the Case‐II transport model, a film‐swelling‐limited process, in which a sharp diffusional front propagates at a constant velocity through the film. At a low vapor pressure of DNT of ≈16 ppb, the analyte concentration in the front is sufficiently high to give an average fluorophore–analyte separation of ≈1.5 nm. Hence, a long exciton diffusion length is not required for real‐time sensing in the solid state. Rather the diffusion behavior of the analyte and the strength of the binding interaction between the analyte and the polymer play first‐order roles in the fluorescence quenching process.     

Simple and sensitive method for spectrofluorimetric determination of dodecyl benzene sulfonic acid sodium

The interaction of poly(diallyldimethyl ammonium chloride) (PDDA) with dodecyl benzene sulfonic acid sodium (DBS) has been studied by fluorescence spectra. The fluorescence of DBS can be greatly enhanced by addition of PDDA, owing to the interaction between PDDA and DBS. The enhancement intensity of fluorescence was proportional to the concentration of DBS over the range 2.5x10(-7) to 9.6x10(-5)molL(-1). Its detection limit is 3.5x10(-7)molL(-1). The method has high sensitivity and selectivity and was applied to the determination of trace amounts of DBS in water samples with satisfactory result.     

Proton "off-on" behaviour of methylpiperazinyl derivative of naphthalimide: a pH sensor based on fluorescence enhancement

In a search for new type pH sensing fluorophores, the possibility of using the proton "off-on" switch behaviour of naphthalimide derivatives for optical pH sensor preparation has been explored. A new compound, N-allyl-4-(4[prime or minute]-methyl-piperazinyl)-1,8-naphthalimide (AMPN), was synthesized. The enhancement of fluorescence of AMPN with the increase of hydrogen ion concentration is based on arresting photo-induced electron transfer to the naphthalimide fluorophore from aliphatic amine group after its protonation. The Stokes Shift of the proposed type of pH sensing fluorophore is significantly larger than that of the fluorescein counterparts. To avoid the leakage of the fluorophore, AMPN was photo-copolymerized with 2-hydroxyethyl methacrylate and acrylamide on the glass surface. The fluorescence intensity of membrane contacted with a pH 3.50 buffer is 4.7 times of that for pH 12.00 buffer solutions. The proposed pH sensor is not susceptible to ionic strength and shows good selectivity, repeatability and short response time. The membrane shows a good stability with a lifetime over two months. The sensor can be used for the determination of pH in the range of pH 4.5-9.0, without interference of most commonly co-existing inorganic ions and some organic species. The sensor has been applied to the analysis of urine samples.     

A fluorescent probe for zinc ions based on N-methyltetraphenylporphine with high selectivity

N-methyl-alpha,beta,gamma,delta-tetraphenylporphine (NMTPPH) has been used to detect trace amount of zinc ions in ethanol-water solution by fluorescence spectroscopy. The fluorescent probe undergoes a fluorescent emission intensity enhancement upon binding to zinc ions in EtOH/H(2)O (1:1, v/v) solution. The fluorescence enhancement of NMTPPH is attributed to the 1:1 complex formation between NMTPPH and Zn(II) which has been utilized as the basis for the selective detection of Zn(II). The linear response range covers a concentration range of Zn(II) from 5.0x10(-7) to 1.0x10(-5)mol/L and the detection limit is 1.5x10(-7)mol/L. The fluorescent probe exhibits high selectivity over other common metal ions except for Cu(II).     

Fluorescence Reaction of 5- (p-Methoxyphenylazo)-8-(p-tolylsulfonamido)quinoline with Cobalt(II) and Its Analytical Application

Abstract

5-(p-Methoxyphenylazo)-8-(p-tolylsulfonamido) quinoline(MTAQ) has been synthesized. The product was checked by IR, theroograviae-try, NMR and elemental analysis. A highly sensitive spectrofluorim-etric method has been developed for the determination of cobalt(II) based on the formation of a complex with MTAQ in slightly basic medium aqueous solution and In the presence of nonionic surfactant, tween-80. The complex shows two excitation maxima at 304 nm and 338 nm, its emission maximum is centred at 402 nm. The fluorescence intensity is proportional to cobalt(II) concentration in the range of 0-85 ppb. The method has good selectivity and has been applied to the direct fluorimetric determination of trace cobalt(II) in pig's liver, Dianchi shrimp and celery.     

Determination of ultra trace levels of 1,2-dichloroethane in air by sample enrichment micromachined gas chromatography-differential mobility detection

A novel analytical procedure has been developed for the analysis of ultra trace levels of 1,2-dichloroethane (EDC) in air using sample enrichment in combination with micromachined gas chromatography (GC) and differential mobility detection (DMD). When compared to other contemporary GC techniques, such as GC-flame ionization detection, GC-electron capture detection, or GC-electrolytic conductivity detection, the employment of a DMD in combination with a preconcentrator provided better sensitivity and markedly improved selectivity. The increase in sensitivity reduces false-negative results, while the improvement in selectivity decreases the potential for false-positive results. Using the technique described, a complete analysis can be conducted in less than 10 min, with a detection limit of 0.7 ppb (v/v) of EDC and a short term precision of less than 6%. A correlation coefficient of 0.9988 was obtained over an EDC concentration range from 0.7 ppb to 36.4 ppb (v/v). The analytical system also has an on-board microTCD in series with the DMD, allowing both detector outputs to be monitored simultaneously. With the pre-concentration technique, the microTCD can detect EDC as low as 15 ppb (v/v) with a substantially enhanced linear dynamic range in addition to providing a confirmation means for the presence of EDC at the level cited.     

CEA fluorescence biosensor based on the FRET between polymer dots and Au nanoparticles

Polymer dots were employed as luminophors to design a fluorescence biosensor for carcinoembryonic antigen (CEA) with high sensitivity and selectivity; the increased fluorescence intensity is proportional to CEA concentration in the range of 0.1-10 ng mL(-1).     

DNAzyme-based fluorescent microarray for highly selective and sensitive detection of lead(II)

A facile microarray-based fluorescent sensor for the detection of lead (II) was developed based on the catalytic cleavages of the substrates by a DNAzyme upon its binding to Pb(2+). The release of the fluorophore labelled substrates resulted in the decrease of fluorescence intensity. The sensor had a quantifiable detection range from 1 nM to 1 μM and a selectivity of >20 fold for Pb(2+) over other metal ions.     

Modular aptameric sensors

We report the first examples of modular aptameric sensors, which transduce recognition events into fluorescence changes through allosteric regulation of noncovalent interactions with a fluorophore. These sensors consist of: (a) a reporting domain, which signals the binding event of an analyte through binding to a fluorophore; (b) a recognition domain, which binds the analyte; and (c) a communication module, which serves as a conduit between recognition and signaling domains. We tested recognition regions specific for ATP, FMN, and theophylline in combinations with malachite green binding aptamer as a signaling domain. In each case, we were able to obtain a functional sensor capable of responding to an increase in analyte concentration with an increase in fluorescence. Similar constructs that consist only of natural RNA could be expressed in cells and used as sensors for intracellular imaging.     

A fluorescence chemosensor based on peptidase for detecting nickel(II) with high selectivity and high sensitivity

We report herein a new class of metal ion chemosensors and give the first example of a metal-dependent peptidase chemosensor for metal ions. The chemosensor contains the basic specific Ni(II)-dependent peptide bond hydrolysis sequence (Gly-Ala-Ser-Arg-His-Trp-Lys-Phe-Lys). The substrate was labeled with a fluorophore at the N-terminal and a quencher at the C-terminal Lys side chain. Initially, the MOCAc ((7-methoxycoumarin-4-yl)acetyl-) emission was quenched by the nearby quencher. In the presence of Ni(II), the substrate was irreversibly cleaved at the cleavage site, leading to a 20-fold increase in fluorescence intensity. The chemosensor combines the high selectivity of a peptidase (at least greater than tenfold for Ni(II) over other metal ions) with the high sensitivity of fluorescence detection limit of 50 nM and can be applied for the quantitative detection of Ni(II) over a concentration range of three orders of magnitude. Given this degree of selectivity and sensitivity, our molecular engineering design may prove useful in the future development of other peptidase-based probes for different metal ions in toxicological and environmental monitoring.     

On-line monitoring of electroosmotic flow for capillary electrophoretic separations

A recently developed technique for monitoring electroosmotic flow (EOF) in capillary electrophoresis by periodic photobleaching of a neutral fluorophore added to the running buffer has been further characterized and optimized and then applied to monitoring EOF during a typical capillary electrophoresis separation. The concentration of neutral fluorophore (rhodamine B) added to the running buffer for monitoring EOF has been decreased by one order of magnitude. The rate at which EOF can be measured has been increased from 0.2 to 1.0 Hz by decreasing the distance between the bleaching beam and the laser-induced fluorescence detector from 6.13 to 0.635 mm. The precision of the measured EOF ranges from 0.2 to 1.8%. Under typical experimental conditions, the dynamic range for flow measurements is 0.066 to 0.73 cm s(-1). Experimental factors affecting precision, signal-to-noise (S/N) ratio and dynamic range for EOF monitoring have been examined. This technique has been applied to measure EOF during a separation of phenolic acids with analyte detection by UV/VIS absorbance. The EOF monitoring method has been shown not to interfere with UV/VIS absorbance detection of analytes.     

The application of trimesic acid to the determination of terbium by spectrofluorimetry

A sensitive, direct spectrofluorimetric method for the trace determination of terbium with use of trimesic acid (TMA) has been developed. The reaction conditions for the fluorescence system of terbium with TMA were studied. The terbium ion can form a stable binary chelate with TMA, having a ratio of 1:1 in the pH range 3.5-6.5. The maximum excitation and emission wavelengths are 260 nm and 545 nm for the terbium chelate, respectively. The reaction is instantaneous and the fluorescence intensity of the terbium chelate remains stable from 0.25 to 4 h. Under the optimal experimental conditions the fluorescence intensity is a linear function of concentration in the range 0.0248-6.35 mug ml(-1) of terbium. The relative standard deviation is still within +/-4% in the presence of one-thousandfold amounts of the other lanthanide ions, and common foreign ions hardly interfere in the determination. The method can be employed for the determination of trace amounts of terbium in rare earth ores or oxides because of its high sensitivity and selectivity with good reproducibility and accuracy.     

Synthesis of 1,8-naphthalimide-based fluorescent nano-probes and their application in pH detection

Fluorescent nano-probes with particle sizes of 20 nm, 120 nm and 300 nm for proton were prepared through click reaction. The photophysical properties of the nano-probes were mainly affected by the particle size.     

Fluorimetric Analysis of Aluminum in Diluted Hemodialysis Solutions by Using a Novel Schiff Base

A spectrofluorimetric method has been developed for trace amount of aluminum(III) by using a novel Schiff base, N,N′-bis(salicylidene)-1,4-diaminobuthane (BUTAS), and 4-methyl-2-aminophenol (OAP). Since the aluminum complexes are generally fluorescent, aluminum(III) increases the fluorescence intensity of BUTAS-OAP by formation of Al-BUTAS-OAP complex. The fluorescence of the complex is measured at an excitation wavelength of 410 nm with an emission at 526 nm. Aluminum(III) can be detected within a concentration limit of 0.11–1.62 ppb and the lowest detection limit being 0.07 ppb. The proposed method was applied to diluted hemodialysis solution and spectrofluorimetric data was compared with data of standard pharmacopoeia method.     

Rapid Fluorometric Screening of Antibiotics in Seafood

Simple and rapid fluorometric screening methods have been developed based on the competitive binding between the target and an intercalating fluorophore dye to double-stranded-DNA (dsDNA). In this study, the long-wavelength fluorescente dye TOTO-3 was employed as the indicator. Compounds that interact with dsDNA will affect the binding of TOTO-3 to the nucleic acid thereby changing the fluorescence intensity. The analyte concentration is indirectly determined by the decrease in fluorescence intensity. A fiber optic fluorescence screening system was developed for rapid and convenient sample processing. Lambda DNA (48.5 kb) was chosen as a suitable sensing nucleic acid material. Detection of sulfathiazole and chloramphenicol in shrimps using this method was studied in the range of 0.5–25 ng mL⁻¹ of sulfathiazole and of 1–50 ng mL⁻¹ of chloramphenicol. Detection limits of 0.5 ng mL⁻¹ of sulfathiazole and 1 ng mL⁻¹ of chloramphenicol were achieved. This approach is useful as a routine test in the monitoring of antibiotics in the environment or aquaculture products. The easy operation and the rapid and sensitive detection make this a potential high-throughput screening method.     

Capillary Electrophoresis Immunoassay for 2, 4-Dichlorophenoxyacetic Acid

ABSTRACT

A capillary electrophoresis (CE) immunoassay format for 2, 4-dichlorophenoxyacetic acid (2, 4-D) is demonstrated. A fluorescent labeled 2, 4-D analog competes with the analyte of interest for a finite number of binding sites provided by anti-2, 4-D monoclonal antibodies. CE then provides a means of separating and measuring both the free and antibody-bound fluorescent tracer using laser-induced fluorescence detection. For this assay format, the amount of free tracer is a sensitive indicator for the concentration of analyte present in the sample. A sequential injection format allows the rapid analysis of a small number of samples. The dynamic concentration range for 2, 4-D in either buffer or river water is 5 ppb to 1000 ppb.     

Spectrofluorimetric method for determination of aluminium with chromotropic acid and its application to water samples

A rapid and sensitive method for the trace level determination of aluminium based on the formation of a 1:1 complex with chromotropic acid (1,8-dihydroxynaphthlene-3,6-disulfonic acid) in an methanol medium is reported. The fluorescence intensity of the system was 50 times greater than that of the system without aluminium. This method is very sensitive and selective for the direct determination of aluminium ion. The fluorescence is excited at 346 nm and measured at 370 nm. The optimum conditions are a chromotropic acid concentration of 5.0 ml (1.0x10(-4) M) and pH 4.0+/-0.5 (acetic acid-sodium acetate buffer). The fluorescence intensity is a linear function of the concentration of Al(III) in the range 2-100 ng ml(-1) and the detection limit is 1.0 ng ml(-1). The method has been applied successfully to the determination of trace amount of Al(III) in tap, river and sea-water samples.     

Determination of polychlorinated biphenyls by liquid chromatography–atmospheric pressure photoionization–mass spectrometry

This study presents the atmospheric pressure photoionization (APPI) of high‐chlorinated (five or more chlorine atoms) polychlorinated biphenyls (PCBs) using toluene as dopant, after liquid chromatographic separation. Mass spectra of PCB 101, 118, 138, 153, 180, 199, 206 and 209 were recorded by using liquid chromatography‐APPI‐tandem mass spectrometry (LC‐APPI‐MS/MS) in negative ion full scan mode. Intense peaks appeared at m/z that correspond to [M ? Cl + O]^? ions, where M is the analyte molecule. Furthermore, a detailed strategy, which includes designs of experiments, for the development and optimization of LC‐APPI‐MS/MS methods is described. Following this strategy, a sensitive and accurate method with low instrumental limits of detection, ranging from 0.29 pg for PCB 209 to 8.3 pg for PCB 101 on column, was developed. For the separation of the analytes, a Waters XSELECT HSS T3 (100 mm × 2.1 mm, 2.5 µm) column was used with methanol/water as elution system. This method was applied for the determination of the above PCBs in water samples (surface water, tap water and treated wastewater). For the extraction of PCBs from water samples, a simple liquid–liquid extraction with dichloromethane was used. Method limits of quantification, ranged from 4.8 ng l^?1, for PCB 199, to 9.4 ng l^?1, for PCB 180, and the recoveries ranged from 73%, for PCB 101, to 96%, for PCB 199. The estimated analytical figures were appropriate for trace analysis of high‐chlorinated PCBs in real samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Fiber-optic sensor for iodine based on a covalently immobilized aminobenzanthrone Schiff base.

An aminobenzanthrone Schiff base has been synthesized as a new fluorescence carrier for the preparation of an optical chemical sensor for iodine. The response of the sensor is based on fluorescence quenching of the aminobenzanthrone Schiff base by iodine. The sensor shows a linear response toward iodine in the range of 1.0 x 10(-5) to 1.0 x 10(-3) mol l(-1), with a detection limit of 6.0 x 10(-6) mol l(-1) at pH 8.0. Leaching of the fluorophore from the membrane is effectively hindered by covalent immobilization, resulting in an enhanced sensor lifetime. In addition to satisfactory reproducibility and reversibility, the prepared sensor exhibits sufficient selectivity toward iodine with respect to other coexisting ions. The sensor has been applied to the determination of iodine in common salt samples.