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.     

Capillary liquid chromatography of multiple peptides with on-line capillary electrophoresis immunoassay detection.

A competitive immunoassay for neuropeptide Y (NPY) based on capillary electrophoresis (CE) with laser-induced fluorescence detection was developed utilizing polyclonal antisera as the immunoreagent and fluorescein-labeled NPY as the tracer. The assay was performed with on-line mixing of reagents, automated injections, and a 3 s separation time. The assay had a detection limit of 850 pM. To detect NPY at lower concentrations, the assay was coupled on-line to reversed-phase capillary liquid chromatography (LC). In this arrangement, 5 microL samples were preconcentrated by capillary LC and eluted by a gradient of isopropanol-containing mobile phase. The resulting chromatographic peaks were monitored by the CE immunoassay. With preconcentration, the concentration detection limit was improved to 40 microM and NPY could be measured in push-pull perfusion samples collected from the paraventricular nucleus of freely moving rats. The technique was extended to simultaneous detection of NPY and glucagon secretion from islets of Langerhans.     

Multichannel homogeneous immunoassay for detection of 2,4,6-trinitrotoluene (TNT) using a microfabricated capillary array electrophoresis chip

A high-throughput homogeneous immunoassay for the sensitive detection of 2,4,6-trinitrotoluene (TNT) has been developed using radial capillary array electrophoresis microdevices. Samples consisting of equilibrium mixtures of anti-TNT antibody (Ab), fluorescein-labeled TNT, and various concentrations of unlabeled TNT were electrokinetically injected into 48 channels of a radial capillary array electrophoresis microchannel plate. The rapid electrophoretic separation allows us to analyze the equilibrium ratio formed by the competition between the labeled and the unlabeled TNT for Ab binding. The simultaneous parallel TNT separations facilitate determination of a calibration curve for the TNT assay, which has high sensitivity (LOD, 1 ng/mL) and a wide dynamic range (1-300 ng/mL).     

免疫亲和毛细管电泳的研究进展

免疫亲和毛细管电泳方法结合了免疫分析的高特异性和毛细管电泳分离的高效、快速、样品用量少等优点,是复杂样品中特定组分分析的重要方法之一。激光诱导荧光检测器的使用以及毛细管电泳分离前免疫预富集过程的引入,可以进一步提高分析测定的灵敏度,使其能够用于痕量物质的高灵敏测定。本文结合作者所在课题组的工作,对免疫亲和毛细管电泳的两种主要模式,即均相的毛细管电泳免疫分析(CEIA)和非均相的免疫亲和毛细管电泳(IACE)的研究进展进行了综述。     

毛细管电泳免疫化学发光高灵敏检测人血清中肿瘤标志物甲胎蛋白

本文首次报道了人血清免疫反应后直接进样并利用毛细管电泳分离化学发光灵敏检测AFP的新方法, 检测结果与医院使用的全自动微粒子化学发光仪检测结果吻合.     

Rapid chemiluminescence biosensing of microcystin-LR

A rapid immunoassay for sensitive detection of microcystin-LR using a portable chemiluminescence multichannel immunosensor (CL-MADAG) was developed. The sensor device is based on a capillary ELISA technique in combination with a miniaturized fluidics system and uses chemiluminescence as the detection principle. Minimum concentrations of at least 0.2 μg L⁻¹ microcystin-LR could be unambiguously measured in a spiked buffer system as well as in spiked real water samples. A single sample analysis for detection of microcystin-LR could be accomplished in just 13 min on the CL-MADAG. Besides providing a highly reproducible, fast and easy to perform test format, one major advantage of the newly established capillary immunoassay is represented by the feasibility of an internal retrospective quality control mechanism. Finally, simultaneous CL-MADAG measurements employing our inhibition immunoassay and a sandwich ELISA could be successfully demonstrated.     

Determination of methotrexate and its major metabolite, 7-hydroxymethotrexate, using capillary zone electrophoresis and laser-induced fluorescence detection

High-dosage methotrexate therapy requires careful monitoring of the drug in serum to ensure minimal toxic effects. A simple, rapid and sensitive method for the separation and quantitation of methotrexate and its major metabolite, 7-hydroxymethotrexate, using high-voltage capillary zone electrophoresis combined with laser-induced fluorescence detection is described. The detection limit for methotrexate is as low as 5.10(-10) M (signal-to-noise ratio = 3), while that for 7-hydroxymethotrexate is 2.10(-9) M. The linearity of the system extends over nearly four orders of magnitude for both methotrexate and 7-hydroxymethotrexate. The extraction efficiency for the drug and its metabolite from serum is 80-85% using a Sep-Pak C18 cartridge. Quantitation of methotrexate in serum was possible in the 10(-10) M range, nearly two orders of magnitude lower than that currently obtainable by existing methods. Good correlation (r = 0.99) for serum methotrexate concentrations was obtained with an enzyme-multiplied immunoassay technique. Comparison with an enzyme inhibition assay also provided similar results.     

Assay of protein drug substances present in solution mixtures by fluorescamine derivatization and capillary electrophoresis.

A method is described to enhance the resolution and detection sensitivity of proteins, peptides, and amino acids in capillary electrophoretic analysis of solution mixtures. The method consists of derivatizing the analytes with fluorescamine, which is normally used as a fluorogenic reagent for compounds containing a reactive primary amine functional group, and then using the derivative as an ultraviolet chromophore to enhance detection sensitivity (measured at 280 nm) in capillary electrophoresis. The results demonstrated a significant improvement in the separation and detection sensitivity of the derivatized analytes as compared to their underivatized counterparts. The use of chromophores, such as fluorescamine, in capillary electrophoresis facilitates the analysis of components of solution mixtures, such as pharmaceutical formulations, that could not be resolved and/or detected by conventional capillary electrophoresis procedures.     

Analysis of Follicle-Stimulating Hormone by CE with Chemiluminescence Detection Based on Competitive Immunoassay

A competitive immunoassay and capillary electrophoresis with enhanced chemiluminescence detection have been used for determination of follicle-stimulating hormone (FSH) in human serum. The method is based on the competitive immunochemical reaction of FSH and horseradish peroxidase (HRP)-labeled FSH with anti-FSH, CE separation of antibody-bound and free HRP-labeled FSH, then chemiluminescence detection. The detection limit depends on the stability of the immune complex, which depends on analysis time and detector design, and on the chemiluminescence enhancer used. A unique chemiluminescence detector without dead volume or diluent effects was therefore used, and sodium tetraphenylboron was selected as the optimum enhancer. As a result sensitivity was substantially improved. Free HRP-labeled FSH and the immune complex could be separated within 15 min in alkaline borate buffer by use of a potential of 15 kV. Under the optimum conditions a calibration plot for FSH was established in the concentration range 0–100 mIU mL⁻¹; the detection limit was 0.06 mIU mL⁻¹. The concentration sensitivity achieved was 30 times better than that of ELISA.     

Trace analysis of oxidized, nitrated, and chlorinated aromatic amino acids by capillary electrophoresis with electroosmotic flow modification allowing large-volume sample stacking

A capillary electrophoresis method has been developed for the simultaneous analysis of the oxidized, nitrated, and chlorinated aromatic amino acids, as well as their parent compounds. These modifications of the aromatic amino acids in proteins or free form are induced by the attack of reactive, mainly free radical species generated during cell stress, and these stable products may serve as biomarkers of cell damage. The analytes tyrosine, phenylalanine, dihydroxyphenylalanine, tryptophan, 3-nitrotyrosine, 3-chlorotyrosine, ortho-tyrosine, meta-tyrosine, 3-hydroxyphenylacetic acid (internal standard 1), and alpha-methyltyrosine (internal standard 2) were separated in their anionic forms in alkaline borate buffer. The polyamine spermine was used as electroosmotic flow (EOF) modifier. Adsorbing to the capillary wall, spermine can either suppress or even reverse the EOF depending on its concentration and the pH. The effects of the pH of the separation buffer, the spermine concentration, the temperature, and the applied field strength on the separation were examined. The modified aromatic amino acids are present in biological fluids in a much lower concentration than their parent compounds, thus high detection sensitivity of the analytical method is required. To achieve good detection sensitivity, field-amplified sample stacking of large injection volumes was applied. Omitting polyamine from the sample buffer allowed local reversal of the EOF, thus removal of the low conductivity sample buffer at the capillary inlet. In this way, 100% of the capillary to the detection window could be filled with the sample, and the detection limits achieved for the modified aromatic amino acids were in the range of 2.5-10 nM.     

Enhanced detection of seven glucoconjugated and hydroxylated porphyrins and chlorins by nonaqueous capillary electrophoresis combined with stacking

The nonaqueous capillary electrophoresis mode which includes a preconcentration step based on a transient pseudo-isotachophoresis to the simultaneous separation of seven glucoconjugated and hydroxylated porphyrins and chlorins, exhibiting very close structures, is reported. A high methanol content, of the buffer solution, was necessary in order to prevent self-assembly of the compounds and to enhance their solubility during separation. With the addition of 66% (v/v) methanol and 1% (w/v) NaCl in the aqueous sample solution, large volumes could be injected (44% capillary volume) without a loss in resolution. Sensitivity of detection was therefore improved by a 100-fold factor with regard to the method employing normal injection (2% capillary volume). Optimum electrophoretic conditions, in terms of sensitivity and performance, were obtained by using 20 mM phosphoric acid buffer, pH 2.2 and 50% methanol. The method was validated and applied to qualitative analysis of glucoconjugates in serum samples.     

Capillary electrophoresis immunoassay based on an on-column immunological reaction

An on-column immunological reaction was employed to achieve simple and rapid analysis in an immunoassay based on capillary electrophoresis using semiconductor laser-induced fluorescence detection. Human serum albumin (HSA) labeled with sulfoindocyanine succinimidyl ester (Cy5), a fluorescent compound with an absorption maximum at 649 nm, was used as a fluorescent probe for the immunoassay. In a binding assay, with anti-HSA as the analyte molecule, Cy5-HSA was injected in a capillary column followed by the injection of anti-HSA so as to form individual zones. By applying a potential, the anti-HSA reacted with Cy5-HSA at the boundary between Cy5-HSA and anti-HSA zones, since anti-HSA has a higher electrophoretic mobility than Cy5-HSA. Furthermore, the on-column method enhances the sensitivity by injecting a large volume of the sample. Free Cy5-HSA and its immunocomplex with anti-HSA were separated with less degradation in resolution than that predicted from the injection time of anti-HSA, even when the injection time for anti-HSA was increased. The ratio of the peak area of the complex to that of the total Cy5-HSA (free Cy5-HSA and the complex) increased in proportion to the injection time of anti-HSA. As a result, the detection limit was improved up to eight-fold (the concentration detection limit, 0.007 mg mL(-1), for an injection time of 240 s, compared to that obtained using an off-column sample preparation. Furthermore, the on-column reaction method was applicable to an immunoassay to determine native HSA, in which native HSA and Cy5-HSA react with anti-HSA stepwise. The detection limit in the stepwise reaction immunoassay was 0.005 mg mL(-1), which is 14 times lower than that in an off-column method, with the analysis time less than 10 min as the result of increasing the injection time of native HSA. In addition, the present on-column immunoassay was applied to the sample containing a high concentration of salts for investigating the effect of salts in the sample solution.     

Simultaneous analysis of plural samples in a CE-CL detector possessing micro-space area for reaction/detection.

Plural samples were simultaneously analyzed in a capillary electrophoresis (CE)-chemiluminescence (CL) detector system, taking advantage of a micro-space area for reaction/detection at the tip of the capillary. The CL reaction of 1,10-phenanthroline and hydrogen peroxide was adopted and a Cu(II) sample was used as a model. Three different length capillaries were inserted into a flow-type CL detection cell made of a Teflon tube. Three samples migrated in the corresponding capillaries at the same time and mixed with the CL reagent at the tip of capillary to produce CL. The simultaneous analysis of plural samples in the present system supported the possibility that a real sample could be determined more easily, rapidly, and precisely with the calibration curve.     

An ultrasensitive method for the determination of thiouracil and phenylthiouracil using capillary zone electrophoresis and laser-induced fluorescence detection

This paper reports the development of a method based on capillary electrophoresis with laser-induced fluorescence detection for the simultaneous determination of thiouracil (TU) and phenylthiouracil (PhTU) with high sensitivity (nanomolar range, i.e., attomoles detected). After derivatization with 5-iodoacetamidofluorescein, the analytes were separated by capillary zone electrophoresis using 20 mM phosphate buffer (pH 10.0) and quantified by fluorescence detection. The linearity range, precision, recovery, and detection limits were determined, and the method was shown to be applicable for the determination of TU and PhTU in spiked feed samples and urine.     

Capillary electrophoresis separation and permanganate chemiluminescence on-line detection of some alkaloids with beta-cyclodextrin as an additive.

Capillary electrophoresis has been used in combination with on-line permanganate chemiluminescence detection for the simultaneous determination of morphine, 6-monoacetylmorphine and heroin. It was found that beta-cyclodextrins could improve the separation efficiency and enhance the chemiluminescence signal. Improved sensitivity over capillary electrophoresis with UV detection was obtained. The procedure has detection limits of 23, 66 and 115 fmol for morphine, 6-monoacetylmorphine and heroin, respectively.     

Capillary electrophoresis separation of a mixture of chitin and chitosan oligosaccharides derivatized using a modified fluorophore conjugation procedure

A capillary electrophoresis (CE) method was developed for the simultaneous analysis of small chitin and chitosan oligosaccharides. For detection purposes, the oligomers were derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS), a well known fluorophore for oligosaccharides analysis. The detection was performed by laser-induced fluorescence (LIF) with an argon ion laser having an excitation wavelength of 488 nm and with emission monitored at 520 nm. Derivatization parameters such as reaction time and conditions were examined. Separation conditions were also varied by testing a range of buffer pHs and concentrations. The best conditions were found using an 80 mM borate buffer at pH 8.4. This CE-LIF optimized method was used for the analysis of an enzymatically produced oligo-chitosan sample composed of a complex mixture and having an average degree of polymerization of 3.7 monomer units and 80% deacetylation. The oligo-chitosan sample was treated with a chitin deacetylase-like enzyme, the products were derivatized with APTS, and then analyzed without purification. The goal was to determine whether the deacetylase-like enzyme could increase the extent of deacetylation of the oligo-chitosan sample.     

Rapid microvolume PCR of DNA confirmed by microchip electrophoresis.

PCR is an indispensable technique used in DNA analysis. However, with the traditional methods, the time spent on amplification and the subsequent analysis of PCR products is generally long. Therefore, it is essential to improve these two steps so that the whole procedure can be made faster. In the present work, with lambda-DNA as the control template, the amplification of 300-bp fragment could be completed within 37 s with capillary reaction chambers of LightCycler, and the following analysis of PCR products could be completed within 120 s with microchip electrophoresis as the detector. Since the high detection sensitivity of microchip electrophoresis, PCR products with template concentration as low as 5 fg/microL could be detected only after 435 s of amplification. In addition, based on additional optimized conditions simulated by CoventorWare, PCR microchips with distinct structure of the reaction chambers have been designed and successfully applied to the amplification of 300-bp fragment. By comparison, those chambers with ellipse and racket shapes were found to offer very high amplification efficiency. All of these results demonstrate the promise of integrating PCR and electrophoresis on microchip for developing easy-carrying instruments for the fast in situ detection of DNA.     

Capillary electrophoretic competitive immunoassay with laser-induced fluorescence detection for methionine-enkephalin

Immunoassays are commonly used in bioresearch for the detection and quantification of small proteins and macromolecules in biological fluids and other complex matrices. In this report, a competitive immunoassay using capillary electrophoresis (CE) with laser-induced fluorescence was developed for methionine-enkephalin (ME). The method is based on the competitive reaction between the ME and fluorescein conjugated ME (ME-F) with anti-ME antibody, capillary electrophoresis separation of the ME-antibody bound and free ME-F, followed by the laser-induced fluorescence detection of the fluorescent species. With the optimized separation conditions, it was possible to separate the antibody bound and free fluorescien conjugated ME by a capillary electrophoresis-laser-induced fluorescence (CE-LIF) analysis using an uncoated fused-silica capillaries. The results concluded that the assay specificity, selectivity and accuracy were excellent.     

Micro enzymatic assay coupled to capillary electrophoresis via liquid junction

Summary A system for capillary electrophoresis combined with enzymatic assay has been evaluated for the two enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Instrumentation included a post-column reactor coupled to the separation capillary by a liquid junction. A technique for generating a substrate solution flow into the reactor by utilizing two high voltage supplies is proposed. This method offers a high degree of freedom in optimizing the separation and enzymatic reaction conditions individually. Possibilities for improving the enzymatic assay sensitivity were also examined.     

Simultaneous determination of six toxic alkaloids in human plasma and urine using capillary zone electrophoresis coupled to time‐of‐flight mass spectrometry

A novel capillary zone electrophoresis separation coupled to electro spray ionization time‐of‐flight mass spectrometry method was developed for the simultaneous analysis of six toxic alkaloids: brucine, strychnine, atropine sulfate, anisodamine hydrobromide, scopolamine hydrobromide and anisodine hydrobromide in human plasma and urine. To obtain optimal sensitivity, a solid‐phase extraction method using Oasis MCX cartridges (1 mL, 30 mg; Waters, USA) for the pretreatment of samples was used. All compounds were separated by capillary zone electrophoresis at 25 kV within 12 min in an uncoated fused‐silica capillary of 75 μm id × 100 cm and were detected by time‐of‐flight mass spectrometry. This method was validated with regard to precision, accuracy, sensitivity, linear range, limit of detection (LOD), and limit of quantification (LOQ). In the plasma and urine samples, the linear calibration curves were obtained over the range of 0.50–100 ng/mL. The LOD and LOQ were 0.2–0.5 ng/mL and 0.5–1.0 ng/mL, respectively. The intra‐ and interday precision was better than 12% and 13%, respectively. Electrophoretic peaks could be identified by mass analysis.