Enzyme-linked flow-injection immunoassay using immobilized secondary antibodies

A fast, non-equilibrium enzyme-linked flow-injection immunoassay (FIIA) system using an immobilized secondary-antibody reactor is described. The assay method is based on the competition between the enzyme-labeled antigen and analyte (unlabeled antigen) for a limited amount of soluble primary-antibody binding sites. This mixture is then introduced via flow-injection into the secondaryantibody reactor. The reactor bound enzyme activity, as measured by flowing an appropriate substrate solution through the reactor, is inversely proportional to the concentration of free analyte in the sample. By using non-equilibrium conditions, a single assay takes a total time of 13 min or less including regeneration of the reactor. To illustrate the application of this system, theophylline and insulin were chosen as model hapten and macromolecule analytes, respectively. Preliminary studies suggest that the new FIIA system is suitable for determining theophylline in serum with acceptable accuracy and precision.     

Separation-free amperometric enzyme immunoassay

A new technique for conducting a separation-free amperometric enzyme immunoassay is described using DNP-aminocaproic acid as the analyte. The technique is based on the combined use of a recently described separation-free enzyme immunoassay (19) and an electrode system that senses H₂O₂. Oxidation of glucose to gluconate and H₂O₂ by the enzyme reconstituted from DNP-conjugate apoglucose oxidase (DPN-CAGO) and FAD was continuously measured amperometrically. The reconstitution was inhibited by preincubation with anti-DNP antibody before adding FAD. This antibody-induced inhibition of the reconstituting of the holoenzyme was reversed by adding DNP-amino caproic acid to DNP-CAGO before adding the antibody to DNP-CAGO. Based on (a) the antibody-induced inhibition of holoenzyme reconstitution, (b) a specific ligand-induced reversal of the inhibition, and (c) an electrochemical system that measures H₂O₂, we developed a separation-free (homogeneous) amperometric enzyme immunoassay.     

Flow injection electrochemical enzyme immunoassay based on the use of an immunoelectrode strip integrate immunosorbent layer and a screen-printed carbon electrode

A flow injection amperometric immunoassay system based on the use of screen-printed carbon electrode for the detection of mouse IgG was developed. An immunoelectrode strip, on which an immunosorbent layer and screen-printed carbon electrode were integrated, and a proposed flow cell have been fabricated. The characterization of the flow immunoassay system and parameters affecting the performance of the immunoassay system were studied and optimized. Amperometric detection at 0.0 V (versus Ag/AgCl) resulted in a linear detection range of 30-700 ng ml⁻¹, with a detection limit of 3 ng ml⁻¹. The signal variation among electrode strips prepared from variant batch did not exceed 8.5% (n=7) by measuring 0.5 μg ml⁻¹ antigen standard solution.     

Electrochemical studies of 1,5-dihydroxynaphthalene as substrate for voltammetric enzyme immunoassay

Immunoassay is one of the biochemical analytical techniques using the specific antigen antibody com-plexation for analytical purposes. It has extensive ap-plication in clinical diagnostics, prevention and cure of diseases, and virus diagnostics. The presentation and progress of immunoassay methodology are one of the greatest achievements of bioanalytical chemistry. It is estimated that several-hundred millions of immuno-analytical determinations are carried out every year all over the world. E…     

Micro-plate chemiluminescence enzyme immunoassay for aflatoxin B1 in agricultural products

In this work, a micro-plate chemiluminescence enzyme immunoassay by antibody-coated for the determination of aflatoxin B1 (AFB1) in agricultural products has been established. Aflatoxin B1 antibody (AFB1-Ab) was adsorbed physically on polystyrene micro-plate hole as solid phase antibody, which took place immunity-reaction between antigen and antibody with AFB1 standard solution or samples by direct competition. Luminol-hydrogen peroxide chemiluminescence system catalyzed by horseradish peroxidase (HRP) with p-iodophenol enhancement was used as signal detecting system. The effects of several factors, including composition and pH of coating solution, dilution ratio and amount of antibody and enzyme labeled antigen, time of antibody-coating, incubation and chemiluminescence reaction, and other relevant variables upon the immunoasaay were studied and optimized. The linear range of proposed method for AFB1 was 0.05-10.0 ng g⁻¹ with a correlative coefficient of −0.9997. The sensitivity of the proposed method was 0.01 ng g⁻¹. The RSDs of intra- and inter-assay were less than 12.2% and 10.0%, respectively. This method has been successfully applied to the evaluation of AFB1 in agricultural products with recoveries of 79.8%, 101.9% and 115.4% for low, middle and high concentration samples, respectively. It shows a good correlation with the commercial available ELISA kit for AFB1 with correlative coefficient of 0.9098 indicating that the established CLEIA method can be used to determine AFB1 in real samples.     

Rapid Determination of Fluoride in Potable Waters by Potentiometric Flow Injection Analysis

Abstract

A potentiometric flow injection analysis system is described, enabling tap water and other fluoride-bearing matrices of low interferent level to be determined at the rate of 360 samples per hour using an electrode polished with slurried alumina. Important parameters, such as carrier stream composition, sample volume and detector cell design are discussed with respect to this system, Fluoride electrodes regenerated with silver fluoride and silver epoxy are evaluated in flow injection mode, both before and after polishing.     

Investigation of several parameters influencing signal generation in flow-through membrane-based enzyme immunoassay

Rapid-response analytical tests that can be performed at the point of sampling are based on a visual detection system. The influence of different factors on the signal generation in a membrane-based enzyme immunoassay was investigated. The research was applied to a flow-through immunoassay for the detection of ochratoxin A (OTA). This assay format is a very convenient, simple and fast qualitative screening tool. Conjugates of OTA with horseradish peroxidase (HRP) and alkaline phosphatase (AP) were used as enzyme tracers. A new conjugate OTA-AP has been synthesized in our laboratory and its performance in the assay was compared with that of OTA-HRP. Different substrate systems for HRP and AP were compared. Several reagents, including polymers and surfactants, were tested for their possible effect on signal generation with the use of OTA-HRP conjugate. Polymers such as poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) 6000 exerted a favourable effect on signal amplification, whereas surfactants negatively affected assay performance. The highest signal amplification (30–70% compared to the standard assay procedure) was achieved using 0.5% PVA in tetramethylbenzidine (TMB) Colorburst substrate solution and phosphate-buffered saline (PBS) for the washing step. It allowed more reliable visual estimation of the results from OTA-HRP assay. Exclusion of the detergent (Tween 20) from the washing solution exerted a favourable effect on assay performance using both enzyme tracers. The assay using OTA-HRP was more susceptible to matrix interferences than the assay with OTA-AP. Signal development in the matrix was better for the OTA-AP assay and visual estimation of the results was easier to perform in this case. For the analysis of spiked wheat samples, OTA-AP conjugate gave a more sensitive, stable and reproducible assay with a cut-off level of 4 μg kg⁻¹ for OTA. The application of the new OTA-AP conjugate resulted in improved assay performance for the food samples.     

基于抗原包被的微孔板式化学发光酶免疫分析法测定人尿中的雌三醇

将雌三醇-6-(O-羧甲基)肟(E3-6-CMO)与牛血清白蛋白(BSA)形成的偶联物E3-6-CMO-BSA物理吸附于聚苯乙烯微孔板孔内作为固相抗原,与雌三醇(E3)标准溶液或者水解尿样中待测E3通过竞争法进行免疫反应.以对碘苯酚增强的辣根过氧化物酶(HRP)催化鲁米诺-过氧化氢化学发光体系作为信号检测系统,建立了一种高通量、简便快速、灵敏稳定的化学发光酶免疫分析方法用于测定人尿中E3的含量.考察和优化了包被液的酸碱性、抗原包被浓度、酶标抗体稀释比例及用量、温育时间、化学发光底物用量及化学发光反应时间的影响.在最优实验条件下,方法的灵敏度为0.20ng/mL,批内和批间变异系数均在15%之内,低、中、高浓度加标水解尿样的平均回收率分别为107.9%、100.9%和91.2%.使用抗原包被法和抗体包被法同时对10份水解尿样进行测定,结果显示相关性良好,相关系数为0.9984,表明本方法可以满足临床检测的要求.     

Amperometric measurements with ion-selective electrode membranes in a flow system

Calcium and salicylate sensitive electrode membranes based on plasticized PVC were used for selective amperometric detection in a flow injection system. The peak current was found to depend linearly on concentration and the working range extended well below the potentiometric detection limit.Dedicated to Professor W. Simon on the occasion of his 60th birthday     

Immobilization of L-glutamate oxidase and peroxidase for glutamate determination in flow injection analysis system

Streptomyces SP.N 14, isolated from soil samples, produced extracellular L-glutamate oxidase (GOD) in liquid culture. After a two-step ammonium sulfate purification and dextran G-150 chromatography, the specific activity was reached at 28.2 U/mg. The partial purified enzyme and horseradish peroxidase (HRP) were covalently coupled to alkylamine controlled pore glass (CPG) by means of glutaraldehyde. About 200–300 U/g of immobilized GOD and 300–400 U/g of immobilized HRP were obtained. The immobilized enzymes were packed into a teflon tube and used in flow injection analysis (FIA) for glutamate in broth. A good linear range was observed for this immobilized enzyme system at 0.1–2.0 mM, and the precision was 2.8% (n = 25). More than 80 samples were measured within an hour. One enzyme column with about 4 U of immobilized GOD and 5 U of immobilized HRP, applied for 50 assays/d, has been used for more than 50 d. The concentration of L-glutamate remaining lower than 2.0 mM, the determination of glutamate in this system was not affected by pH and temperature within the range of 6.0–7.0 and 25–35‡C, respectively. The system was applied to determine L-glutamate in broth samples during L-glutamate fermentation, and good correlation was achieved between results obtained with the system and with the Warburg’s method.     

Stopped-flow injection analysis. The influence of diffusion on dispersion of normal and reverse flow injection

A relationship is derived to enable the comparison of the dispersion heights of normal and reverse flow injection analysis (FIA). A single channel flow system is employed in the absence of a chemical reaction. The stopped-flow injection method is used to probe the influence of molecular diffusion on the overall dispersion of normal and reverse FIA, which appeared to demonstrate fundamentally different diffusion behaviors. Small discrepancies are observed between the dispersion heights, which are enhanced by the stopped-flow period, especially when unmatched matrix ionic compositions of the indicator and counter solutions were involved. For these conditions, the diffusion flux rate is enhanced considerably, displaying a peak, in addition to the transient, for both methods. The influence of diffusion on the dispersion characteristics of normal and reverse FIA is discussed theoretically. Diffusion in the proposed model is postulated to oppose dispersion by convection. The latter initiates concentration gradients in the injection zone and propagates it with flow time over the dispersion zone profile. The diffusion flux then reacts in order to confine the indicator dispersion for normal FIA and to enhance it for reverse FIA. This model is consistent with the experimental results and accounts for most of the phenomena encountered. Probably owing to the influence of secondary flow phenomena, the use of coiled tubes has suppressed the effects of diffusion on the overall dispersion behavior.Part of the experimental work was performed at IMI Institute for Research and Development, Haifa, Israel.     

Development of a flow manifold for Fe(III) ion determination with a fluoride ion-selective electrode

Continuous-flow (CF) and flow-injection (FI) analysis using the fluoride ion-selective electrode (FISE) as detector have been investigated. The measurements were performed in a home-made cell under appropriate flow conditions (2.86 or 3.45 ml min⁻¹, 0.2 ml samples, 10⁻⁶ M sodium fluoride). The calibration graph was obtained by plotting the signal height versus concentration of iron in the range of Fe(III) concentration from 10⁻⁵ to 10⁻¹ M in acetate buffer (pH 2.8 or 3.4). In all described procedures, the range of linear response extends to the Fe(III) concentration from 1×10⁻³ to 1×10⁻¹ M, with detection limit 9×10⁻⁵ M. The effect of double-line, two-line flow manifold and CF was investigated and discussed.     

Development of an electrochemical flow injection immunoassay (FIIA) for the real-time monitoring of biospecific interactions

Not only are sensors a revolution in analysis; they themselves are also experiencing a revolution brought about by parallel developments in sensor fabrication techniques and materials, polymer chemistry, signal processing methodologies, the increased use of biomolecular processes as a means of analyte detection, and the coupling of sensors to other techniques such as flow injection analysis. Many of these developments have been incorporated into the present study, which we are undertaking in the development of our immunosensor technology. The system described here utilises screen-printed electrodes which are low-cost, disposable devices that are simple to fabricate. Incorporated into our sensor is the electroactive polymer, polyaniline, which brings about mediatorless redox coupling between the electrode and biomolecular components attached to the polymer surface. This system also utilises enzyme-labelled antibodies as the biomolecular recognition component for the analysis of the test analyte, biotin. The system has also been integrated into a flow injection system. This has led to the monitoring of real-time antibody-antigen interactions using electrochemical methods and foreshadows the development of single-step immunosensors.     

A Tissue-Based Electrode for Peroxidase Assay: Preliminary Results in Hormone Determination by EIA

Abstract

A liver tissue based electrochemical sensor for hydrogen peroxide has been realized for determination of peroxidase activity in solution. Its behaviour is based on the oxygen electrode and an enzyme catalase largely present in liver tissue. The competition between the two enzymatic reactions based on catalase and peroxidase results in a probe for peroxidase activity determination in the range 5 · 10^?3 ? 2.5 · 10^?1 U/mL.

Digoxin and Insulin, have been determined in standard solution by the living-tissue probe, by using immunoreactions with peroxidase labelled hormones and antibodies fixed on vial wall of a commercial test kit.     

Flow injection immunoassays: A review

This review covers the application of flow injection analysis to immunoassays (FIA-IA). The advantages and limitations of this approach are discussed. Future directions, particularly those involving microfluidic systems are highlighted.     

Sensitive and rapid chemiluminescence enzyme immunoassay for microcystin-LR in water samples

A highly sensitive, specific, simple, and rapid chemiluminescence enzyme immunoassay (CLEIA) was developed for the determination of microcystin-LR (MC-LR). Several physicochemical parameters such as the chemiluminescent assay mediums, the dilution ratio of MC-LR-OVA conjugate, monoclonal antibody concentration, and peroxidase labeled antibody concentration were studied and optimized. Under optimum conditions, calibration curve obtained for MC-LR had detection limits of 0.032 ± 0.003 μg L⁻¹, the 50% inhibition concentration (IC₅₀) was 0.20 ± 0.02 μg L⁻¹ and the quantitative detection range was 0.062-0.65 μg L⁻¹. The proposed methods was successfully applied to the monitoring of MC-LR in spiked water samples without significant effect of the matrix, and the recovery of MC-LR added to water samples at different concentrations ranged from 80% to 115% with the coefficients of variation (CVs) less than 9%. The LOD attained from the calibration curves and the results obtained for the real samples demonstrate the potential use of CLEIA as a screening tool for the analysis of MC-LR in environmental samples.     

Membrane sensors for batch and flow injection potentiometric determination of ethamsylate (cyclonamine) in pharmaceutical preparations

The lipophilic nickel(II) and iron(II) bathophenanthroline derivatives of ethamsylate are used as ion-exchangers with high selectivity characteristics for ethamsylate. Poly(vinyl chloride) membrane sensors incorporating these electroactive materials display fast linear response for 1 × 10^–1–1 × 10^–4 M ethamsylate under static and hydrodynamic modes of operation. In an acetate buffer of pH 4, the calibration slope is 51–53 mV/concentration decade and the lower limit of detection is 5.3 g/ml. Except for salicylate and nitrate, most common anions, organic sulfonates, carboxylates, phenolates and various pharmaceutical excipients and diluents do not interfere. Determination of ethamsylate in various dosage forms shows an average recovery of 98.9% of the nominal and a mean standard deviation of 0.7%.     

Development of a sensitive micro-magnetic chemiluminescence enzyme immunoassay for the determination of carcinoembryonic antigen

A micro-magnetic chemiluminescence (CL) enzyme immunoassay with high sensitivity, selectivity, and reproducibility was developed for the determination of the tumor marker, carcinoembryonic antigen (CEA) in human serum. A sandwich scheme assay has been utilized with fluorescein isothiocyanate antibody (FITC)-labeled anti-CEA antibody and alkaline phosphate (ALP)-labeled anti-CEA antibody being used in the CL detection. The CL signal produced by the emission of photons from 4-methoxy-4-(3-phosphate-phenyl)-spiro-(1,2-dioxetane-3,2′-adamantane) (AMPPD) was directly proportional to the amount of analyte present in a sample solution. The influences of the reaction time of antigen with antibody, the reaction time of substrate with label, the dilution ratio of ALP-labeled anti-CEA antibody, the concentration of FITC-labeled anti-CEA antibody, and other relevant variables upon the CL signal were examined and optimized. The CL responses depended linearly on the CEA concentration over the range from 2 to 162 ng mL⁻¹ in a logarithmic plot. Assay sensitivity as low as 0.69 ng mL⁻¹ was achieved. A coefficient of variance of less than 13% was obtained for intra- and inter-assay precision. This method has been successfully applied to the analysis of CEA in human serum. According to the procedure based on spiked standards, the recoveries obtained were 80–110%. Comparison experiments were carried out with the commercially available CEA chemiluminescence immunoassay. Satisfactory results were obtained according to a paired t-test method (t value < t _critical at the 95% confidence level).     

Electrochemical enzyme immunoassay using model labels

Enzyme immunoassays (EIAs) based on electrochemical detection offer several potential advantages and have been applied in clinical, medical, biotechnological, food and environmental analysis. Among the enzyme labels employed, horseradish peroxidase (HRP), alkaline phosphatase (ALP) and glucose oxidase (GOx) are the most common. This brief review reflects recent advances, challenges, and trends of electrochemical EIAs focusing on HRP, ALP or GOx as labels over the past five years. We especially emphasize current development of EIAs combined with other developments, including nanotechnology and miniaturization.     

Enzyme-catalyzed reaction of OPD-H_2O_2-HRP voltammetric enzyme-linked immunoassay system

Ｈｏｒｓｅｒａｄｉｓｈｐｅｒｏｘｉｄａｓｅ(ＨＲＰ)ｃａｎｓｔｒｏｎｇｌｙｃａｔａｌｙｚｅｔｈｅｒｅａｃｔｉｏｎｏｆＨ2Ｏ2ｏｘｉｄｉｚｉｎｇｏｐｈｅｎｙｌｅｎｅｄｉａｍｉｎｅ(ＯＰＤ),ｔｈｅｃｈｒｏｍａｔｉｃｐｒｏｄｕｃｔｏｆｗｈｉｃｈｃａｎｂｅｄｅｔｅｃｔｅｄｉｎｅｎｚｙｍｅｌｉｎｋｅｄｉｍｍｕｎｏｓｏｒｂｅｎｔａｓｓａｙ(ＥＬＩＳＡ)ｗｉｔｈｓｐｅｃｔｒｏｐｈｏｔｏｍｅｔｒｙ[1].Ｉｎｖｏｌｔａｍｍｅｔｒｉｃｅｎｚｙｍｅｌｉｎｋｅｄｉｍｍｕｎｏａｓｓａｙ[2—4],ＯＰＤＨ2Ｏ2ＨＲＰｓｙｓｔｅｍｈａｓｆ…