Online phototransformation–flow injection chemiluminescence determination of triclosan

A highly selective and sensitive chemiluminescence method for the determination of triclosan is proposed. The method is based on the phototransformation of triclosan to a light-emitting precursor in the presence of fluorescein in alkaline medium and the chemiluminescence reaction is then triggered by strong base or oxidants such as N-bromosuccinimide. Based on this reaction an online phototransformation–flow injection manifold was developed, in which the photoreactor comprises a 150-cm-long × 0.8-mm-i.d. piece of PTFE tubing coiled around a 25-W fluorescent lamp, and the phototransformed products were then injected into a carrier stream of borate buffer. After mixing with the oxidant stream the produced light was detected by a photomultiplier. A wide calibration range from 8.0 × 10⁻⁸ to 1.0 × 10⁻⁴ mol L⁻¹ was obtained under the optimized conditions, and the detection limit was as low as 5.0 × 10⁻⁸ mol L⁻¹. The whole process of analysis, including the online phototransformation and subsequent chemiluminescence detection, could be completed in 6 min. Most of the foreign substances tested showed high tolerance levels, and the proposed method was directly applied to the determination of triclosan in toothpaste samples without any pre-separation procedure. Figure Schematic representation of the phototransformation of triclosan and subsequent chemiluminescence reaction     

Capacitive biosensor for detection of endotoxin

A capacitive biosensor for the detection of bacterial endotoxin has been developed. Endotoxin-neutralizing protein derived from American horseshoe crab was immobilized to a self-assembled thiol layer on a biosensor transducer (Au). Upon injection of a sample containing endotoxin, a decrease in the observed capacitive signal was registered. Endotoxin could be determined under optimum conditions with a detection limit of 1.0 × 10⁻¹³ M and linearity ranging from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹⁰ M. Good agreement was achieved when applying endotoxin preparations purified from an Escherichia coli cultivation to the capacitive biosensor system, utilizing the conventional method for quantitative endotoxin determination, the Limulus amebocyte lysate test as a reference. The capacitive biosensor method was statistically tested with the Wilcoxon signed rank test, which proved the system is acceptable for the quantitative analysis of bacterial endotoxin (P < 0.05). Figure The flow-injection capacitive biosensor system and the capacitive properties of the transducer surface, where C_SAM is the capacitance change of the self-assembled thiol monolayer, C_P is the capacitance change of the protein layer, C_a is the capacitance change of the analyte layer and C_Total is the total capacitance change measured at the working electrode/solution interface (modified from Limbut et al., 2006. Biosens Bioelectron 22: 233-240)     

Catechol determination in compost bioremediation using a laccase sensor and artificial neural networks

An electrochemical biosensor based on the immobilization of laccase on magnetic core-shell (Fe₃O₄–SiO₂) nanoparticles was combined with artificial neural networks (ANNs) for the determination of catechol concentration in compost bioremediation of municipal solid waste. The immobilization matrix provided a good microenvironment for retaining laccase bioactivity, and the combination with ANNs offered a good chemometric tool for data analysis in respect to the dynamic, nonlinear, and uncertain characteristics of the complex composting system. Catechol concentrations in compost samples were determined by using both the laccase sensor and HPLC for calibration. The detection range varied from 7.5 × 10^–7 to 4.4 × 10^–4 M, and the amperometric response current reached 95% of the steady-state current within about 70 s. The performance of the ANN model was compared with the linear regression model in respect to simulation accuracy, adaptability to uncertainty, etc. All the results showed that the combination of amperometric enzyme sensor and artificial neural networks was a rapid, sensitive, and robust method in the quantitative study of the composting system. Figure Structure of the magnetic carbon paste electrode used in the electrochemical biosensor     

Optical sensing in microfluidic lab-on-a-chip by femtosecond-laser-written waveguides

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica capillary electrophoresis chip. High-quality waveguides crossing the microfluidic channels are fabricated and used to optically address, with high spatial selectivity, their content. Fluorescence from the optically excited volume is efficiently collected at a 90° angle by a high numerical aperture fiber, resulting in a highly compact and portable device. To test the platform we performed electrophoresis and detection of a 23-mer oligonucleotide plug. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs fabricated with standard techniques. Figure Femtosecond laser written waveguides can selectively excite fluorescence in a microfluidic channel of a commercial lab-on-a-chip. A compact scheme for on-chip detection by laser induced fluorescence is applied to capillary electrophoresis of a 23-mer Cy3-labeled oligonucleotide     

Aptamer-based label-free method for hemin recognition and DNA assay by capillary electrophoresis with chemiluminescence detection

An aptamer-based label-free approach to hemin recognition and DNA assay using capillary electrophoresis with chemiluminescence detection is introduced here. Two guanine-rich DNA aptamers were used as the recognition element and target DNA, respectively. In the presence of potassium ions, the two aptamers folded into the G-quartet structures, binding hemin with high specificity and affinity. Based on the G-quartet–hemin interactions, the ligand molecule was specifically recognized with a K _d ≈ 73 nM, and the target DNA could be detected at 0.1 μM. In phosphate buffer of pH 11.0, hemin catalyzed the H₂O₂-mediated oxidation of luminol to generate strong chemiluminescence signal; thus the target molecule itself served as an indicator for the molecule–aptamer interaction, which made the labeling and/or modification of aptamers or target molecules unnecessary. This label-free method for molecular recognition and DNA detection is therefore simple, easy, and effective. Figure A label-free approach to aptamer-based hemin recognition and DNA detection is introduced, which gives great potential for using a small molecule itself as the indicator for molecular recognition and DNA detection thereby avoiding any labeling or modification step     

Photofragmentation of nitro-based explosives with chemiluminescence detection

A simple, fast, reliable, sensitive and potentially portable explosive detection device was developed employing laser photofragmentation (PF) followed by heterogeneous chemiluminescence (CL) detection. The PF process involves the release of NO_{x(x = 1,2)} moieties from explosive compounds such as TNT, RDX, and PETN through a stepwise excitation–dissociation process using a 193 nm ArF laser. The NO_{x(x = 1,2)} produced upon PF is subsequently detected by its CL reaction with basic luminol solution. The intensity of the CL signal was detected by a thermoelectrically cooled photomultiplier tube with high quantum efficiency and negligible dark current counts. The system was able to detect trace amounts of explosives in various forms in real time under ambient conditions. Detection limits of 3 ppbv for PETN, 2 ppbv for RDX, and 34 ppbv for TNT were obtained. It was also demonstrated that the presence of PETN residue within the range of 61 to 186 ng/cm² can be detected at a given signal-to-background ratio of 10 using a few microjoules of laser energy. The technique also demonstrated its potential for the direct analysis of trace explosive in soil. An LOD range of 0.5–4.3 ppm for PETN was established, which is comparable to currently available techniques. Figure Photofragmentation–chemiluminescence detector     

Chemiluminescent imaging analysis of interferon alpha in serum samples

Enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase (HRP)-catalyzed fluorescent reaction, and oxalate chemiluminescence imaging analysis have been combined to develop a sensitive, simple, and rapid method for analysis of interferon alpha (α-IFN) in human serum samples. A typical “sandwich type” immunoassay was used. Reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H₂O₂), catalyzed by HRP, produced 2,3-diaminophenazine (PDA), which was detected by chemiluminescence imaging analysis with the bis(2,4,6-trichlorophenyl)oxalate (TCPO)–H₂O₂–glyoxaline–PDA chemiluminescent system. The TCPO chemiluminescent imaging system is more sensitive and the chemiluminescence quantum yield is at least five times higher than for the luminol–H₂O₂–HRP–PIP (p-iodophenol) chemiluminescent imaging system. The results showed there was a very good linear correlation between response and amount of α-IFN in the range 1.3–156.0 pg mL⁻¹ (R = 0.9991) and the detection limit was 0.8 pg mL⁻¹ (S/N=3). The relative standard deviation (n = 9) was 4.7%. The proposed method has been used for successful analysis of the amount of α-IFN in human serum. The results obtained compared well with those obtained by conventional colorimetric ELISA and luminol chemiluminescent ELISA. Figure Procedures of the proposed method     

Flow-injection solid surface lanthanide-sensitized luminescence sensor for determination of <Emphasis Type="Italic">p</Emphasis>-aminobenzoic acid

A single optosensing device based on lanthanide-sensitized luminescence was developed for determination of p-aminobenzoic acid (PABA). The method is based on the formation of a complex between PABA and Tb(III) immobilized on the solid phase (QAE A-25 resin) placed inside the flow cell. NaCl (1 M) was used as carrier solution and HCl (0.05 M) as eluent. The sample solutions of PABA (100 μL) containing Tb(III) and buffered at pH = 6.0 were injected into the carrier stream and the luminescence was measured at λ _ex = 290 nm and λ _em = 546 nm. The method shows a linear range from 0.2 to 6.0 μg mL⁻¹ with an RSD of 1.2% (n = 10) and a sampling frequency of 22 h⁻¹. A remarkable characteristic of the method is its high selectivity which allows it to be satisfactorily applied to the analysis of PABA in pharmaceutical samples without prior treatment. Figure Typical emission bands of Tb(III) in a solid-phase PABA–Tb(III) luminescence spectrum     

Electrochemistry meets enzymes: instrumental on-line simulation of oxidative and conjugative metabolism reactions of toremifene

The metabolism of the selective estrogen receptor modulator toremifene was simulated in an on-line electrochemistry/enzyme reactor/liquid chromatography/mass spectrometry system. To simulate the oxidative phase I metabolism, toremifene was oxidized in an electrochemical (EC) flow-through cell at 1,500 mV vs. Pd/H₂ to its phase I metabolites, some of which are reactive quinoid species. In the presence of glutathione-S-transferase (GST), these quinoid compounds react with glutathione, which is also the common detoxification mechanism in the body. While reacting with glutathione, the chlorine atom is eliminated from the toremifene moiety. Due to higher conversion rates, GST supplied in continuous flow proved to be more efficient than using immobilized GST on magnetic microparticles. In the absence of GST, not all GSH adducts are formed, proving the necessity of a phase II enzyme to simulate the complete metabolic pathway of xenobiotics in an on-line EC/LC/MS system. Figure Mass voltammogram of toremifene     

Sequential preconcentration by coupling of field amplified sample injection with pseudo isotachophoresis–acid stacking for analysis of alkaloids in capillary electrophoresis

A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced by acetonitrile and pseudo isotachophoresis (ITP)–acid stacking is developed for simply but efficiently concentrating alkaloid cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent in the succeeding pseudo ITP. After sample injection had been completed, a plug of H⁺ was injected electrokinetically and a neutralization reaction between H⁺ and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3–600 ng/mL for myosmine and 4.9–900 ng/mL for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples. Figure Sequential preconcentration processes: a sample injection; b introduction of HCl; c capillary zone electrophoresis separation. A ⁻ tartrate, white circles acetonitrile, black circles Na⁺, sample zone, myosmine, anabasine     

Flow injection chemiluminescence immunoassay for 17β-estradiol using an immunoaffinity column

A new flow injection chemiluminescent immunoassay was developed for the detection of 17β-estradiol (E₂). The method uses p–iodophenol (PIP) as enhancer and is based on a solid-phase immunoassay format in which an E₂–OVA immobilized immunoaffinity column inserted in the flow system is used to trap unbound horseradish peroxidase (HRP)-labeled anti-E₂ antibody after an off-line incubation of E₂ with HRP-labeled anti-E₂ antibody. The trapped enzyme conjugate was detected by injecting substrates to produce an enhanced chemiluminescence (CL) response. The linear range for E₂ was 10.0–1,000.0 ng mL⁻¹ with a correlation coefficient of 0.996 and a detection limit of 3.0 ng mL⁻¹. The sampling and chemiluminescence detection time for one sample was 400 s after a pre-incubation procedure of 30 min. Serum samples detected by this method were in good agreement with the results obtained by EIA with E₂–biotin.      

Chemiluminescence assay for quinones based on generation of reactive oxygen species through the redox cycle of quinone

A sensitive and selective chemiluminescence assay for the determination of quinones was developed. The method was based on generation of reactive oxygen species through the redox reaction between quinone and dithiothreitol as reductant, and then the generated reactive oxygen was detected by luminol chemiluminescence. The chemiluminescence was intense, long-lived, and proportional to quinone concentration. It is concluded that superoxide anion was involved in the proposed chemiluminescence reaction because the chemiluminescence intensity was decreased only in the presence of superoxide dismutase. Among the tested quinones, the chemiluminescence was observed from 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 1,4-naphthoquinone, whereas it was not observed from 9,10-anthraquinone and 1,4-benzoquinone. The chemiluminescence property was greatly different according to the structure of quinones. The chemiluminescence was also observed for biologically important quinones such as ubiquinone. Therefore, a simple and rapid assay for ubiquinone in pharmaceutical preparation was developed based on the proposed chemiluminescence reaction. The detection limit (blank + 3SD) of ubiquinone was 0.05 μM (9 ng/assay) with an analysis time of 30 s per sample. The developed assay allowed the direct determination of ubiquinone in pharmaceutical preparation without any purification procedure. Figure Chemiluminescence generated through the redox cycle of quinone     

Highly efficient analysis of underivatized carbohydrates using monolithic-silica-based capillary hydrophilic interaction (HILIC) HPLC

A polyacrylamide (PAAm)-modified monolithic silica capillary column of increased phase ratio, 200T-PAAm, for hydrophilic interaction liquid chromatography (HILIC) was prepared. The column showed high separation efficiency, with a theoretical plate height H = 7–20 μm at a linear velocity, u = 1–7 mm/s. From a kinetic plot analysis, it was expected that the monolithic column could provide three times faster separation than particle-packed HILIC columns under a pressure limit at 20 MPa. HILIC coupled with electrospray ionization (ESI)–mass spectrometry (HILIC-ESI-MS) using the 200T-PAAm column was employed for the analysis of underivatized carbohydrates to achieve fast and efficient separations of mixtures containing mono-, di-, and trisaccharides within 5 min. Under single MS full scan mode, 200 pg of oligosaccharides was detected by the system. The limit of detection (LOD) of the LC-ESI-MS/MS system was determined using selected reaction monitoring (SRM) to be as low as 3.2 ng/mL (attomol level) for nonreducing saccharides. The system was successfully applied to the detection of disaccharides in extracts of plant, such as corn, soybean, and Arabidopsis thaliana. Figure HILIC-ESI-MS provides a high-efficiency separation and sensitive detection of underivatized carbohydrate oligomers, e.g., the homologs of glucose (1) up to maltoheptaose (7)     

Certification and uncertainty evaluation of the certified reference materials of poly(ethylene glycol) for molecular mass fractions by using supercritical fluid chromatography

Poly(ethylene glycol) (PEG) is a useful water-soluble polymer that has attracted considerable interest in medical and biological science applications as well as in polymer physics. Through the use of a well-calibrated evaporative light-scattering detector coupled with high performance supercritical fluid chromatography, we are able to determine exactly not only the average mass but also all of the molecular mass fractions of PEG samples needed for certified reference materials issued by the National Metrology Institute of Japan. In addition, experimental uncertainty was determined in accordance with the Guide to the expression of uncertainty in measurement (GUM). This reference material can be used to calibrate measuring instruments, to control measurement precision, and to confirm the validity of measurement methods when determining molecular mass distributions and average molecular masses. Especially, it is suitable for calibration against both masses and intensities for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Figure Comparison between the molecular mass fractions of PEG 1000 before calibration (si) (○) and after calibration (wi) (⧫). The error bar shows the expanded uncertainty of k = 2 of each mass fraction     

A mild and expedient one-pot synthesis of substituted benzimidazoles in water using a phase-transfer catalyst

Abstract  1-Alkyl/phenyl-2-arylbenzimidazoles have been synthesized in very good to excellent yields by a one-pot condensation of N-alkyl/phenyl-o-phenylenediamines with aryl aldehydes in water at room temperature using cetylpyridinium bromide as a cheap and eco-friendly catalyst. Graphical abstract        

Development of a multichannel flow-through chemiluminescence microarray chip for parallel calibration and detection of pathogenic bacteria

Pathogen detection is important for health and safety reasons. Several outbreaks all over the world have shown the need for rapid, qualitative, quantitative, and, particularly, multianalyte detection systems. Hence, a multichannel flow-through chemiluminescence microarray chip for parallel detection of pathogenic bacteria was developed. The disposable chip made of acrylonitrile–butadiene–styrene (ABS) copolymer was devised as a support for a multiplexed sandwich immunoassay. Calibration and measurement was possible in one experiment, because the developed chip contains six parallel flow-through microchannels. Polyclonal antibodies against the pathogenic bacteria Escherichia coli O157:H7, Salmonella typhimurium, and Legionella pneumophila were immobilized on the chip by microcontact printing in order to use them as specific receptors. Detection of the captured bacteria was carried out by use of specific detection antibodies labelled with biotin and horseradish peroxidase (HRP)–streptavidine conjugates. The enzyme HRP generates chemiluminescence after adding luminol and hydrogen peroxide. This signal was observed by use of a sensitive CCD camera. The limits of detection are 1.8 × 10⁴ cells mL⁻¹ for E. coli O157:H7, 7.9 × 10⁴ cells mL⁻¹ for L. pneumophila, and 2.0 × 10⁷ cells mL⁻¹ for S. typhimurium. The overall assay time for measurement and calibration is 18 min, enabling very fast analysis.      

Headspace mass spectrometry methodology: application to oil spill identification in soils

In the present work we report the results obtained with a methodology based on direct coupling of a headspace generator to a mass spectrometer for the identification of different types of petroleum crudes in polluted soils. With no prior treatment, the samples are subjected to the headspace generation process and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of volatiles in the sample analysed. The mass spectrum corresponding to the mass/charge ratios (m/z) contains the information related to the composition of the headspace and is used as the analytical signal for the characterization of the samples. The signals obtained for the different samples were treated by chemometric techniques to obtain the desired information. The main advantage of the proposed methodology is that no prior chromatographic separation and no sample manipulation are required. The method is rapid, simple and, in view of the results, highly promising for the implementation of a new approach for oil spill identification in soils. Figure PCA score plots illustrate clear discrimination of types of crude oil in polluted soil samples (e.g. results are shown for vertisol)     

One-step regioselective green synthesis of 2,3-mannoepoxy-β-cyclodextrin under aqueous conditions

Abstract  A simple method for the straightforward regioselective synthesis of 2,3-mannoepoxy-β-cyclodextrin, which is a valuable precursor for further functionalization of β-cyclodextrin, is achieved under aqueous conditions without any organic solvents at a moderate yield. Graphical abstract        

Analysis of biosensors by chemically specific optical techniques. Chemiluminescence-imaging and infrared spectroscopic mapping ellipsometry

The standard methods currently used to read out microarrays are fluorescent and chemiluminesent imaging techniques. These methods require labeling of a component with a marker and, usually, only the concentration of the marker molecule is detected. A label-free imaging method that also enables quantitative spectroscopic analysis of the composition and component interaction would be of great advantage. In this article it is shown for the first time that IR mapping ellipsometry enables label-free imaging of a biochip before and after incubation with peptide solution. The measurements prove that IR ellipsometry is a sensitive tool for laterally resolved identification of the different materials and determination of the composition of a biochip. The lateral resolution required was achieved by using radiation from an infrared synchrotron beamline.      

Study on an on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography for separation and determination of trace estrone in environment

Estrone is one of the important potential endocrine-disrupting compounds, and the sensitive and reliable analytical methods for the determination of estrone are required for the assurance of human health. In this paper, using estrone as template molecule, 3-aminopropyltriethoxysilane as function monomer, and tetraethoxysilicane as cross-linker, a highly selective molecularly imprinted microsphere was synthesized by surface molecular imprinting technique combined with a sol–gel process. The imprinted material was characterized by the Fourier transform infrared and static adsorption experiments, and the results showed that it exhibited good recognition and selective ability for estrone. A novel method for separation and determination of trace estrone in environmental sample was developed using on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography. With a sample loading flow rate of 2.6 mL min⁻¹ for a 9.6-min extraction, the enrichment factor obtained by the slopes of the linear portion in comparison with the direct injection of 10 μL standard sample solution was 1,045. The detection limit (S/N = 3) was 5.7 ng L⁻¹, and the relative standard deviations for nine replicate extractions of 5.0 μg L⁻¹ estrone was less than 10.0%. This method was evaluated for quantitative determination of estrone in well and lake water samples spiked at two levels (0.5 and 1.0 μg L⁻¹) with recoveries ranging from 86% to 95%.