Protein fingerprinting of Staphylococcus species by capillary electrophoresis with on-capillary derivatization and laser-induced fluorescence detection

Capillary electrophoresis (CE) coupled with laser-induced fluorescence detection (LIF) has allowed to obtain protein fingerprints, which have demonstrated to be useful in microorganisms characterization. In this work, protein fingerprints of two species of Staphylococcus grown in different culture media and submitted to temperature and nitrosative stress were studied by CE-LIF. After the growth of the bacteria, protein extracts were obtained by cell lysis using sonication. The water-soluble fraction of these lysates was derivatized on-capillary with a fluorogenic dye, 3-(2-furoyl)quinoline-2-carboxaldehyde. The fluorescent products were analyzed by CE using phosphate buffer containing submicellar concentrations of sodium pentanesulfate and detected by LIF. Different protein fingerprints were obtained depending on the bacterial specie studied, indicating the usefulness of this method for the identification of different species of the same bacterial genus. It was also demonstrated that the CE protein fingerprints were dependent on the culture conditions, such as growth medium, or on stressing conditions, such as heat shock or nitrosative stress.     

Analysis of trace amounts of bovine beta-lactoglobulin in infant formulas by capillary electrophoresis with on-capillary derivatization and laser-induced fluorescence detection

Bovine beta-lactoglobulin (betaLG) has been described by several authors as the main allergen present in cow's milk. It can induce allergic reactions even at the low concentration existing in hypoallergenic formulas based on hydrolyzed cow's milk proteins (generally lower than microM). In this paper, the usefulness of a capillary electrophoresis method with on-capillary derivatization and laser-induced fluorescence detection for the analysis of trace amounts of betaLG in a commercial hypoallergenic formula has been demonstrated. To confirm the identity of the peak of betaLG based on migration time, an immunorecognition step employing an anti-betaLG antibody was performed. BetaLG was quantitated in the whey and casein fractions of the hypoallergenic formula. The concentration of betaLG in the whey fraction of the formula was about 3 orders of magnitude lower than the average value present in cow's milk. In the casein fraction of the formula, the concentration of betaLG was about 1 order of magnitude lower than in the whey fraction. The method developed was also used for the quality control of three cereal-based infant foods formulated without milk to test the presence or absence of betaLG as an indicator of milk contamination during the fabrication process. BetaLG in a concentration of 10(-7) M or higher was not observed in any of the cereal-based infant formulas analyzed.     

Inverse-flow derivatization for capillary electrophoresis of DNA fragments with laser-induced fluorescence detection

A novel method is presented to detect DNA fragments separated by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection using inverse-flow derivatization. In electrophoresis, the intercalating dye, thiazol orange was only added to the separation buffer at the positive polarity. The negatively charged DNA fragments migrated from the negative polarity to the positive polarity, while the positively charged dye migrated in the opposite direction. When DNA fragments met with dye ions, the DNA–dye complexes were formed. The complexes continued migrating to the positive end, due to their net negative charges. When the complexes passed through the detection window, the fluorescent signals were generated. Importantly, DNA fragments migrated as their native state before DNA–dye complexes were formed. This procedure was used to detect double stranded DNA (dsDNA) and single stranded DNA (ssDNA) fragments, and polymerase chain reaction (PCR) products. The excellent resolution and good reproducibility of DNA fragments were achieved in non-gel sieving medium. This procedure may be useful in genetic mutation/polymorphism detections.     

Separation and determination of carnosine-related peptides using capillary electrophoresis with laser-induced fluorescence detection

A capillary electrophoresis (CE) method with laser-induced fluorescence (LIF) detection was developed for the separation and detection of carnosine-related peptides (carnosine, anserine, and homocarnosine). A sensitive and fluorogenic regent, 3-(4-carboxybenzoyl) quinoline-2-carboxaldehyde (CBQCA) was selected as a precapillary labeling reagent for imidazole dipeptides to form isoindole derivatives. The optimized molar ratio between CBQCA and peptide was found to be 75:1, and 50 mmol/L borate buffer (pH 9.2) was used for the derivatization in order to achieve good efficiency. Three imidazole dipeptides were baseline-separated within 20 min by using 112 mmol/L sodium borate (pH 10.4-10.8) as running buffer. Concentration detection limits (signal-to-noise ratios) for carnosine, anserine, and homocarnosine were 4.73, 4.37, and 3.94 nmol/L, respectively. This method has been applied to the analysis of human cerebrospinal fluid (CSF) and meat dry powder of pig and sheep. Recoveries were in the range of 82.9-104.8% for homocarnosine in CSF. For carnosine and anserine, the recoveries are 98.3% and 80.2% in meat dry powder of pig and 111.2% and 112.8% in meat dry powder of sheep, respectively.     

Rapid and sensitive determination of phosphoamino acids in phosvitin by N-hydroxysuccinimidyl fluorescein-O-acetate derivatization and capillary zone electrophoresis with laser-induced fluorescence detection

A method was developed for the determination of phosphoamino acids by capillary zone electrophoresis-laser-induced fluorescence detection (argon ion laser, excitation at 488 nm and emission at 520 nm) using derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA). Different variables affecting the derivatization (SIFA concentration, derivatization pH, reaction temperature and reaction time) and the separation (type, pH and concentration of buffer, applied voltage and injection mode) were investigated in detail. The optimized separation conditions were 40 mM boric acid buffer (pH 9.2) for background electrolyte, 25 kV for the separation voltage, 25 degrees C for the capillary temperature and 5 s at 0.5 psi for the sample injection. Under the optimal conditions, the SIFA-labeled phosphoamino acids were fully separated within 7 min. The detection limits ranged from 0.1 to 0.3 nM, which are the lowest values reported for capillary electrophoresis (CE) methods. The proposed methodology allowed the rapid, sensitive and selective determination of phosphoamino acids in hen egg yolk phosvitin by the standard addition method. The recovery of these compounds in real sample was 94.0-103.5%. The developed method surpasses previously published CE methods in terms of detection limit, separation time, stability and simplicity of the electrophoretic procedure.     

Development of a method for quantitative analysis of the major whey proteins by capillary electrophoresis with on-capillary derivatization and laser-induced fluorescence detection

The main whey proteins have been derivatized on-capillary with 3-(2-furoyl)quinoline-2-carboxaldehyde (FQ) and analyzed using a laboratory-made capillary electrophoresis apparatus provided with a laser-induced fluorescence detector. Several parameters controlling on-capillary derivatization of proteins, including pH, mixing time, reaction time, concentration of the reagents (potassium cyanide and FQ), and reaction temperature, were optimized. Coefficient variations were lower than 1% for migration time and 7% for peak height. Assay detection limits for the different proteins were in the range 5 nM to 10 nM. The method developed was applied to the separation of the major whey proteins in a laboratory-made cheese whey and in an infant food formulated with milk. In addition, the beta-LG content of these samples was quantitated. The results showed good agreement with those given by an RP-HPLC method and with those reported in the literature.     

毛细管电泳-激光诱导荧光检测法测定抗癫痫药加巴喷丁

建立了毛细管电泳-激光诱导荧光(CE-LIF)测定抗癫痫药加巴喷丁的方法。加巴喷丁经4-氯-7-硝基苯并-2-氧杂-1,3-二唑(NBD-Cl)衍生化后,采用10 mmol/L硼砂-10 mmol/L十二烷基硫酸钠(pH 9.75)的缓冲体系,加巴喷丁在6 min内实现高效基线分离。方法的线性范围为0.01～10 mg/L(r=0.9997),检出限为2 μg/L,定量限为10 μg/L。方法的平均回收率为100.2%～103.1%,相对标准偏差为0.15%～1.00%(n=3)。该方法灵敏、快速、准确和可靠,已用于加巴喷丁药物制剂的质量控制。     

Single cell determination of nitric oxide release using capillary electrophoresis with laser-induced fluorescence detection

Measurements of nitric oxide (NO) release at single cell level are fundamental to understand the diverse physiological functions of this remarkable molecule. To achieve this purpose, capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was originally described for the sensitive determination of NO release in individual neuron and mammalian cell after 8-(3,4-diaminophenyl)-2,6-bis(2-carboxyethyl)-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (DAMBO-P(H)) was chosen as the fluorescent probe. Various parameters affecting NO trapping in vivo and CE separation were systematically studied. Under the optimal conditions, complete and fast separation of the resulted targeted high-fluorescent triazole (DAMBO-P(H)-T) was achieved in about 3 min (2.89 min), and the relative standard deviations (RSDs) values of migration time and peak area were less than 5% and 9% for intra-day and inter-day assays, respectively. The detection limit was 42 amol (at a signal-to-noise ratio of 3). The feasibility of application of the developed method was validated by successfully applied to the measurements of NO release from four single cell study models. This original application of this method in diverse samples represents a powerful tool to study the kinetics of NO release by neuronal cells during neurotransmission, as well as for the understanding of the pathobiological and therapeutic basis of this molecule for cardiovascular diseases and under oxidative stress.     

Competitive immunoassay for vancomycin using capillary electrophoresis with laser-induced fluorescence detection

A competitive immunoassay using capillary electrophoresis with laser-induced fluorescence was developed for vancomycin. Capillary electrophoresis using a Tris-glycine running buffer provided adequate separation of the antibody-bound from the unbound fluorescent probe (tracer) in less than 4 min. Laser-induced fluorescence polarization (LIFP) provided high sensitivity detection and simultaneous monitoring of fluorescence intensity and polarization. A fluorescence polarization value of 0.30 confirmed the formation of the antibody-tracer complex. Calibration curves showed a working linear range of 2-3 orders of magnitude with a minimum detectable concentration of 0.98 ng mL(-1) (or 1.1 fg vancomycin). Clinical samples obtained from patients undergoing vancomycin treatment were analyzed for vancomycin and the results correlated well with a standard immunoassay based on latex particle detection that was routinely used by a hospital laboratory. Only 1/10 of the reagents were needed as compared with the standard immunoassay.     

Detection of recombinant hirudin using capillary electrophoresis with laser-induced fluorescence detection

Hirudin, a thrombin inhibitor, is a polypeptide of 65 amino acids. To check purity levels and perform pharmacokinetic studies of recombinant hirudin (r-hirudin), a specific and reproducible analysis method is required. Capillary electrophoresis (CE) is rapidly becoming an important procedure for the analysis of biological molecules. Recently, CE combined with immunoassay has emerged as a new analytical technique. CE-based immunoassay (CEIA) is a sensitive and specific method combining laser-induced fluorescence (LIF) and immunoassay. Therefore, in this study, we specifically investigated fluorescence labeling and determination of r-hirudin by CEIA with a LIF detector using labeled r-hirudin and polyclonal antibody. r-Hirudin was labeled with fluorescein isothiocyanate (FITC). FITC-labeled r-hirudin was purified using high-performance liquid chromatography (HPLC). The method is based on preincubation of r-hirudin and antibody for 20 min, followed by CE analysis using an uncoated capillary. Free and bound r-hirudin were separated within 5 min using CE with high reproducibility. This study demonstrated that the CEIA method could be applied to quantitative analysis of r-hirudin in biological fluids.     

Sensitive determination of ephedrine and pseudoephedrine by capillary electrophoresis with laser-induced fluorescence detection

A CE-LIF method was developed for the separation and sensitive detection of ephedrine and pseudoephedrine after derivatization by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol (NBD-C1). The derivatization and separation conditions were investigated in detail and the optimum conditions were obtained. Under the optimum experiment conditions, good linearity relationships (correlation coefficients: 0.9942 for ephedrine and 0.9970 for pseudoephedrine) between the peak heights and concentrations of the analytes were obtained (0.7-140 microM). The detection limits were 0.16 microM for ephedrine and 0.17 microM for pseudoephedrine, which indicated that the sensitivities were at least ten times improved over those reported in the literature obtained by UV detection. The method was applied to the analysis of ephedrine and pseudoephedrine in ephedra herb plants and preparations with good results.     

Analysis of amino acids in individual human erythrocytes by capillary electrophoresis with electroporation for intracellular derivatization and laser-induced fluorescence detection

A method for monitoring amino acids in single erythrocytes is described. For intracellular derivatization, reagent fluorescein isothiocyanate (FITC) was introduced into living cells by electroporation. For an 8 microm erythrocyte, the analytes were diluted by a factor of only 1.6. After completion of the derivatization reaction, a single cell was injected into the separation capillary tip and lysed there. The derivatized amino acids were separated by capillary electrophoresis, followed by laser-induced fluorescence detection. Nine amino acids were quantitatively determined, with amounts of amino acids ranging from 3.8-32 amol/single cell.     

Near-infrared laser-induced fluorescence detection in capillary electrophoresis

As capillary electrophoresis continues to focus on miniaturization, either through reducing column dimensions or situating entire electrophoresis systems on planar chips, advances in detection become necessary to meet the challenges posed by these electrophoresis platforms. The challenges result from the fact that miniaturization requires smaller load volumes, demanding highly sensitive detection. In addition, many times multiple targets must be analyzed simultaneously (multiplexed applications), further complicating detection. Near-infrared (NIR) fluorescence offers an attractive alternative to visible fluorescence for critical applications in capillary electrophoresis due to the impressive limits of detection that can be generated, in part resulting from the low background levels that are observed in the NIR. Advances in instrumentation and fluorogenic labels appropriate for NIR monitoring have led to a growing number of examples of the use of NIR fluorescence in capillary electrophoresis. In this review, we will cover instrumental components used to construct ultrasensitive NIR fluorescence detectors, including light sources and photon transducers. In addition, we will discuss various types of labeling dyes appropriate for NIR fluorescence and finally, we will present several applications that have used NIR fluorescence in capillary electrophoresis, especially for DNA sequencing and fragment analysis.     

Sensitive determination of erythrosine and other red food colorants using capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was applied to separation and sensitive determination of red food colorants. Diode pumped frequency-doubled Nd:YAG laser (532 nm) was used as an excitation source in a laboratory-built CE-LIF system. For highly fluorescent erythrosine B (E127), an extrapolated limit of detection (LOD) of 0.4 ng mL(-1) (S/N=3) was achieved. Extrapolated LODs of other tested red additives, such as carmoisine, E122 (0.5 microg mL(-1)); amaranth, E123 (0.2 microg mL(-1)); ponceau 4R, E124 (0.3 microg mL(-1)) and red 2G, E128 (0.3 microg mL(-1)) were about one-order lower compared to results obtained with CE with absorbance detection in UV/vis (CE-UV/vis). The main advantages of using CE-LIF for analysis of food samples are high selectivity and minimization of matrix effect. To our knowledge, this is the first use of CE-LIF for determination of red food colorants.     

In-capillary derivatization and analysis of amino acids,amino phosphonic acid-herbicides and biogenic amines by capillary electrophoresis with laser-induced fluorescence detection

This paper describes a general approach for the in-capillary derivatization of amino compounds and the subsequent sensitive determination of the derivatives by micellar electrokinetic chromatography (MEKC) or capillary zone electrophoresis (CZE) with laser-induced fluorescence (LIF) detection. Amino acids, biogenic amines and amino phosphonic acid-herbicides were chosen as model analytes to evaluate the analytical potential of this approach. Fulfilment of the in-capillary reaction of the analytes using LIF detection hinged on the excellent labeling chemistry of 5-(4,6-dichloro-s-triazin-2-ylamino)fluorescein (DTAF) and the good resolution achieved in the separation of derivatized analytes. Careful optimization of the electrophoretic conditions in the mixing step of this protocol allowed the determination of amino acids, biogenic amines and phosphorus-containing amino acid-herbicides with concentration limits of detection at the nug/L level and relative standard deviations from 3.5 to 5.8%. The whole analysis is carried out within 20 min, resulting in a very simple, fast and practical approach for the fully automated analysis of amino acids and related compounds in low-volume and low-concentration samples.     

Competitive immunoassay for recombinant hirudin using capillary electrophoresis with laser-induced fluorescence detection

A competitive immunoassay based on capillary electrophoresis (CE) with laser-induced fluorescence (LIF) has been developed for the determination of recombinant hirudin (r-hirudin) in biological mixtures. Hirudin, a thrombin inhibitor, is a polypeptide of 65 amino acids. To check purity levels and perform pharmacokinetic studies of (r-hirudin), specific and reproducible analysis methods are demanded. The work involved the development of separation conditions allowing for routine analysis of plasma samples. In this study, r-hirudin was labeled with fluorescein isothiocyanate (FITC), and FITC-labeled r-hirudin was purified using high-performance liquid chromatography. The purified product was then mixed with the sample followed with the addition of anti-hirudin antibody. Free, antibody-bound, and tagged r-hirudin could be separated within 5 min by CE analysis using uncoated fused-silica capillary with high reproducibility. The developed method can be used to determine r-hirudin with good precision and a detection limit lower than 20 nM. This result demonstrates the feasibility of the CE-LIF immunoassay method for the determination of r-hirudin in plasma samples.     

Multiplexed microRNA detection by capillary electrophoresis with laser-induced fluorescence

In this study, we developed a novel assay that simultaneously detects multiple miRNAs (microRNAs) within a single capillary by combining a tandem adenosine-tailed DNA bridge-assisted splinted ligation with denaturing capillary gel electrophoresis with laser-induced fluorescence. This proposed method not only represents a significant improvement in resolution but also allows for the detection of multiple miRNAs within a single capillary based on the length differences of specified target bridge DNA. The assay's linear range covers three orders of magnitude (1.0 nM to 1.0 pM) with a limit of detection (S/N=3) as low as 190 fM (2.5 zmol). Five miRNAs of Epstein-Barr virus (EBV) were also detected in EBV-infected nasopharyngeal carcinoma cells, while they did not appear in non-virus infected cells. Moreover, the electropherogram indicated that the screening of isomiRs (isomer of miRNA) of BART2 by CE-LIF is feasible by our proposed method. The developed electrophoresis-based method for miRNA detection is fast, amplification-free, multiplexed and cost-effective, making it potentially applicable to large-scale screening of isomiRs.     

Use of capillary electrophoresis and laser-induced fluorescence for attomole detection of amino acids

A capillary electrophoresis and laser-induced fluorescence (CE-LIF) method was developed to identify and quantitate at amol (10(-18)) concentration. Amino acids were derivatized with 3-(4-carboxybenzoyl)-2-quinoline-carboxaldehyde prior to CE-LIF analysis. The assay was developed by varying the sodium borate concentration, buffer pH, operating voltage, and operating temperature. A run buffer system containing 6.25 mM borate, 150 mM sodium dodecyl sulfate, and 10 mM tetrahydrofuran (pH 9.66) at 25 degrees C, and 24 kV provided analysis conditions for a high-resolution, sensitive, and repeatable assay of amino acids. The rate of derivatization, stability of the labeled amino acids, and amino acid quantitation varied for each amino acid. Amino acids were detected with greater efficiency by this method than automated HPLC amino acid analysis. The repeatability of the assay ranged from 0.3 to 0.9% within a day and 0.7 to 1.5% between analysis days. Bacterial amino acid utilization in a chemically defined medium was successfully monitored using this method. This work defines a sensitive and repeatable method for the detection of amino acids during bacterial metabolism.     

Fast analysis of amino acids in wine by capillary electrophoresis with laser-induced fluorescence detection

A fast analytical method has been developed for the determination of nine amino acids, together with serotonin, in wine samples of different origin and vintage. The method is based on capillary electrophoresis coupled to laser-induced fluorescence detection. Separation was obtained by using a fused-silica capillary (75?μm id, 74.0?cm total length, 60.0?cm length to detector) and a background electrolyte composed of carbonate buffer (20?mM, pH 9.2), applying a 20?kV voltage. Direct hydrodynamic injection of wine samples was made after an original microwave-assisted derivatisation step with 5-(4,6-dichlorotriazinyl)aminofluorescein. Fluorescence was induced by an Ar-Ion laser, exciting at 488?nm. Good linearity (r(2) >0.9990) was obtained for all considered analytes and sensitivity was also good, with limits of detection in the 7-50?ng/mL range. The method was successfully applied for the analysis of commercial Italian wines and thus seems to be suitable for the determination of the relevant amino acids and serotonin, providing good results in terms of accuracy and precision, together with the advantage of a very fast, microwave-assisted derivatisation procedure. Future applications of the method are planned to check for wine adulterations and commercial frauds.