Homogeneous Fluorescence Resonance Energy Transfer Immunoassay for the Determination of Zearalenone

This study demonstrates the use of antigen-antibody binding for the detection of zearalenone. Based on the principle of the fluorescence resonance energy transfer (FRET) phenomenon between antibody and antigen, an immunoassay, in which zearalenone coupled with the anti-zearalenone antibody, was developed, optimized, and applied. Owing to intrinsic fluorescence properties in basic pH conditions with the optimal cationic surfactant, anti-zearalenone and zearalenone played roles as the respective donor and acceptor in the FRET immunoassay. As the concentration of analyte increased, the antigen/antibody emission intensity ratio (I _430 nm/I _350 nm) was enhanced due to larger amounts of zearalenone/anti-zearalenone complexes. This assay, based on the ratio of intensities (I _430 nm/I _350 nm), displayed high specificity and sensitivity with a detection limit of 0.8 ng mL^?1 for zearalenone. The results obtained from analysis of spiked wheat grain samples were found to be in good agreement with those obtained by employing a direct competitive enzyme-linked immunosorbent assay. The label-free, noncompetitive, and homogeneous FRET immunoassay strategy served as a powerful tool for the simple, rapid, and sensitive quantitative determination of zearalenone in food and feed matrices.     

A Magnetic Particle-Based Competitive Enzyme Immunoassay for Rapid Determination of Ciprofloxacin: A Potential Method for the General Detection of Fluoroquinolones

Fluoroquinolones are effective antimicrobial agents, but their residues in food may cause serious health issues. Hence, it is necessary to develop a rapid and simple assay for fluoroquinolones. In this study, monoclonal antibodies against ciprofloxacin with broad specificity to fluoroquinolones were prepared. The newly developed magnetic particle-based competitive enzyme immunoassay was performed in a homogeneous sample, and ciprofloxacin was quantitatively detected in the range of 0.3–24.3 ng mL^?1. The IC₅₀ and LOD values of the method were 2.27 ng mL^?1 and 0.25 ng mL^?1. In chicken muscle, the recoveries of spiked ciprofloxacin at 8, 20, and 40 ng mL^?1 were all higher than 79%. Additionally, the performance of the developed magnetic particle-based immunoassay exhibited an excellent correlation with commercial ELISA kits (r = 0.997). The anti-ciprofloxacin monoclonal antibodies provided high cross-reactivity with eight fluoroquinolones analogues: enrofloxacin (110.1%), sarafloxacin (99.7%), difloxacin (90.2%), danofloxacin (89.8%), norfloxacin (110.3%), lomefloxacin (65.2%), ofloxacin (75.1%), and flumequine (45.0%). This protocol provides an alternative immunoassay for ciprofloxacin with the advantages of simple separation, a homogeneous reaction, rapid detection (within 30 min), and stable results. Furthermore, it may be employed for the rapid general determination of fluoroquinolones in animal products.     

Multi-Analyte Immunoassay for Pesticides: A Review

The current trend of pesticide immunoassay is developing multi-analyte immunoassays, that is, more than one target can be detected per test. In this mini-review, the strategies to achieve multi-analyte immunoassays, which include multi-antibody strategy, broad-specificity antibody strategy, and others, are briefly introduced. In addition, the recent developments of multi-analyte immunoassays for pesticides were summarized. At last, we give a future outlook of this area, which includes rational design generic hapten with the assist of computer-assisted molecular modeling (CAMM), further improving the properties of broad-specificity antibody by recombinant antibody (rAb) technology and developing a noncompetitive immunoassay format.     

微板式化学发光酶免疫分析法临床测定人血清中孕酮

将抗兔IgG(即二抗)物理吸附于聚苯乙烯微孔板上作为通用固相,通过免疫反应制备固相抗体。采用辣根过氧化物酶催化鲁米诺-过氧化氢化学发光体系,建立了一种高通量、简便、快速的化学发光酶免疫分析方法用于临床测定人血清中的孕酮。对各种影响因素如免疫试剂的稀释度、发光底物选择、发光反应时间及温育条件等进行了考察和优化,最终选定的实验条件:孕酮抗体和HRP标记物的最佳稀释度分别为1∶100000和1∶15000;选用Ⅱ号发光底物,发光反应10min后测定;37℃水浴条件下温育1h。对建立的方法进行了评价。该方法的灵敏度为0.08μg/L;批内和批间相对标准偏差均在15%之内;低、中、高3个不同浓度值样品的平均回收率分别为101%、101%和94.4%(在87.8%～108%之间)。使用本方法和经典的放射免疫法同时对36份人血清样品进行测定,结果显示,本方法与放射免疫分析方法相关性良好,其相关系数为0.9502。     

Voltammetric Immunoassay for the Detection of Protein Biomarkers

A strategy for a fast (ca. 20 min), specific, electrochemical immunoassay for the cardiac biomarker creatine kinase (CK) and the human cytokine interleukin 10 (IL10) has been developed in this paper. The polyaniline modified gold surface formed from electrochemical reduction of diazonium salt supplies a solid substrate to link the activated carboxylic acid groups from the antibodies, which were labelled with ferrocene. The direct electrochemistry of ferrocene allows the analysis of protein markers with good sensitivity. The creatine kinase sensor demonstrates limit of detection of 0.5 pg mL^?1 in a physiological Krebs‐Henseleit solution. The anti‐IL10 antibody retained fluorescence activity after further coupling to ferrocene and covalent immobilization on to a gold electrode, showing a linear detection range for IL‐10 from 0.001 ng mL^?1 to 50 ng mL^?1 in PBS. We attribute the high sensitivity to the well‐controlled modified surface which results in end–on antibodies that can specifically capture the antigen with ease.     

SPR免疫竞争法研究小分子吗啡与其抗体间作用的动力学特征

表面等离子体共振技术(SPR)主要应用于生物大分子相互作用的研究,本文采用溶液竞争法,测定了小分子吗啡与其抗体作用的结合常数K₁,并计算了吗啡抗体与吗啡化牛血清白蛋白的结合常数K₂.证明了多抗对抗原的亲和力较单抗大,并表明大分子蛋白质的存在对抗体与待测物的结合有阻碍作用.     

Heterogeneous and Homogeneous Aptamer‐Based Electrochemical Sensors for Thrombin

Nanomolar concentrations of thrombin were electrochemically monitored using heterogeneous switch‐on and homogeneous switch‐off approaches that incorporated ferrocenyl aptamers. For the first time, the heterogeneous approach was coupled to a glucose/glucose oxidase (GOx) amplification‐regeneration system which increased its sensitivity by 2 folds with detection limits of 4.3 nM and 2.5 nM in the absence and presence of glucose/GOx, respectively. We also present a new homogeneous system involving the ferrocenyl aptamer binding thrombin in solution causing a significant decrease in its diffusion coefficient. Thus the ferrocene anodic current decreased at an unmodified gold electrode with detection limit of 3.9 nM and 12 times larger linear range than the heterogeneous method.     

Substituted Ferrocenylboranes – Potential Ligand Precursors for ansa‐ Metallocenes,Constrained Geometry Complexes and ansa‐Diamido Complexes

A wide range of potential ligand precursors and related compounds have been synthesized from ferrocenyldibromoborane and ferrocenylenebis(dibromoborane) via salt elimination reactions. These comprise ligand precursors suitable for the preparation of (i) ansa‐metallocenes such as [FcB(η¹‐C₅H₅)₂] ( 2 ), [FcB(1‐C₉H₇)₂] ( 3 ), [FcB(3‐C₉H₇)₂] ( 4 ) and [1,1′‐fc{B(3‐C₉H₇)₂}₂] ( 11 ), (ii) constrained geometry complexes such as [FcB(1‐C₉H₇)N(H)Ph] ( 7 ) and [FcB(3‐C₉H₇)N(H)Ph] ( 8 ), (iii) ansa‐diamido complexes such as [FcB(N(H)Ph)₂] ( 9 ) as well as (iv) the related compounds [FcB(Br)N(H)tBu] ( 5 ), [FcB(Br)N(H)Ph] ( 6 ), [1,1′‐fc{B(Br)N(SiMe₃)₂}₂] ( 12 ) and [1,1′‐fc{B(Br)NiPr₂}₂] ( 13 ) (Fc = ferrocenyl, fc = ferrocenylene, C₅H₅ = cyclopentadienyl, C₉H₇ = indenyl). All new compounds have been characterised by multinuclear NMR spectroscopic techniques and in the case of 7 and 12 by X‐ray diffraction methods.     

增强化学发光酶免疫分析法测定血清中的铁蛋白

本文采用对碘苯酚增强的Ｌｕｍｉｎｏｌ－Ｈ２Ｏ２－ＨＲＰ化学发光反应体系作为免疫分析的最终检测手段，建立了一种新的铁蛋白的免疫分析方法，与酶联免疫分析法相比，该方法具有灵敏度高，线性范围宽等特点。方法的相对标准偏差３．７％，标准曲线线性范围为０．１２－２０００ｎｇ／ｍｌ，用该方法对血清中的铁蛋白进行了测定，其结果与ＥＬＩＳＡ法所得结果一致。     

4-Amino-1-naphthylphosphate as a substrate for the amperometric detection of alkaline phosphatase activity and its application for immunoassay

Immunosensors and biochemical array detection systems based on electrochemical transducers have many advantages such as low detection limit, fast response, simple design and ease of miniaturization. However, further development of such sensors will depend on the availability of suitable substrates that can be converted by a labeling enzyme to an electrochemically active product. Here, we report the synthesis of 4-amino-1-naphthylphosphate and it’s application as a new substrate for alkaline phosphatase. The electrochemical and enzymatic properties of this compound were investigated and compared with the properties of other aromatic 1,4-dihydroxy and 1,4-hydroxy-amine derivatives. The product of the enzyme reaction was 4-aminonaphthol, which was rapidly converted in the presences of air to 1,4-iminonaphthoquinone. This compound could then be detected in an amperometric flow injection assay (AFIA) with −200 mV versus Ag/AgCl potential application. The analytical range for mouse IgG, in an alkaline phosphatase amplified sandwich immuoassay with amperometric detection, was 0.01-100 μg ml⁻¹.     

Optimization of a Direct Competitive Enzyme-Linked Immunoassay for Carbofuran and Application to Water Samples

Abstract

A direct competitive enzyme-linked immunosorbent assay (ELISA) for carbofuran was developed, which was based on the anti-BFNB IgG monoclonal antibody (McAb) and a homologous enzyme tracer (BFNB-HRP). The influence of several physicochemical factors (salt, pH, detergent, and solvent) on the immunoassay was studied. For the standard curve, an I₅₀ of 2.98 µg/l and a limit of detection (I₁₀) of 0.27 µg/l was obtained in a high salt concentration buffer (0.08 M PBS, pH 7.0) with 0.03% BSA. A common challenge for immunoassay, time-dependent drift, was effectively circumvented in our study. The optimized ELISA has been used to quantify carbofuran in water samples spiked at different amounts. The excellent recoveries (71% to 130%) achieved confirmed the potential of the immunoassay for monitoring of carbofuran in waters without purification steps.     

A novel π-donor–π-acceptor system: 1-(4,5-dimethyl-1,3-dithiol-2-ylidene)-1-ferrocenyl-3,3-dicyanopropene

The title compound was prepared by reacting the anion of malononitrile with the corresponding ethanal, and characterised by UV–vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography. Attachment of an additional ferrocenyl donor group to the π-donor–π-acceptor system does not enhance intramolecular charge transfer, because its bulk distorts the planarity of the conjugated chain.     

The Bioluminescence Resonance Energy Transfer from Firefly Luciferase to a Synthetic Dye and its Application for the Rapid Homogeneous Immunoassay of Progesterone

The sensitive BRET system for the homogeneous immunoassay of a low‐molecular weight antigen was developed using progesterone as an example. Two thermostable mutants of the Luciola mingrelica firefly luciferase (Luc)—the “red” mutant with λ_max.em = 590 nm (RedLuc) and the “green” mutant with λ_max.em = 550 nm (GreenLuc)—were tested as the donors. The water‐soluble Alexa Fluor 610× (AF) dye was selected as the acceptor because its two absorption maxima, located at 550 and 610 nm, are close to the bioluminescence maxima of the GreenLuc and RedLuc, respectively. The methods for the synthesis of the luciferase–progesterone (Luc–Pg) conjugate and the conjugate of the dye and the polyclonal antiprogesterone antibody (AF–Ab) were developed. Both conjugates retained their functional properties, had high antigen–antibody binding activity, and demonstrated a high BRET signal. The homogeneous immunoassay system based on the BRET from the firefly luciferase to the synthetic dye was established to assay progesterone as a model antigen. Optimization of the assay conditions, the composition of the reaction mixture, and the concentrations of the donor and the acceptor made it possible to reach the minimum detectable progesterone concentration of 0.5 ng mL^?1.     

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene: A Redox‐Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene ( 1 ) acts as molecular electrochemical sensor for magnesium, calcium, zinc, and cadmium ions in acetonitrile solution. The new redox peak, anodically shifted by ca. 0.40 V, which appears in the cyclic voltammogram of 1 in the presence of even small amounts (10 mol %) of these ions, is unaffected by an excess of alkali metal ions. Metal complexation is accompanied by a batho‐ and hyper‐chromic shift of the band in the visible region of the UV‐Vis spectrum of 1 . A detailed study of the behaviour of 1 towards zinc chloride in acetonitrile solution has revealed that 1 is able to accommodate a maximum of two zinc ions. Oxidation of zinc‐coordinated 1 leads to partial decomplexation. The N‐methyl and N‐benzyl species 1 Me⁺, 1 Me₂²⁺, 1 Bzl⁺ and 1 Bzl₂²⁺ have been synthesized and the former two structurally investigated by X‐ray diffraction. Alkylation causes an anodic shift of the redox potential of the ferrocene nucleus, which is linearly dependent on the number of alkyl groups introduced. Octamethyl‐1, 1′‐di(2‐thiophenyl)ferrocene ( 2 ) has also been synthesized and structurally characterized by X‐ray diffraction. Cyclic voltammetry has revealed that, in contrast to 1 , 2 does not respond to the divalent metal ions studied.     

Self‐Assembled Redox System for Bioelectrocatalytic Assay of L‐Ascorbylphosphate and Alkaline Phosphatase Activity

Ferrocene‐terminated self‐assembled monolayer (Fc‐SAM) on gold was used as an electron‐transfer mediator in the electrochemical assay of L ‐ascorbic acid 2‐phosphate (AAP). The assay is based on the enzymatic action of alkaline phosphatase (ALP), which triggers the release of vitamin C (L ‐ascorbic acid, AA) from AAP. The latter is easily oxidized on the Fc‐SAM under the diffusion limiting conditions that favors quantitative measurement of the AA concentration on a rotating disk electrode. We demonstrate the utility of the electrochemically active Fc‐SAM to probe the mechanism and to determine the kinetic parameters of an enzymatic reaction. The electrochemical technique was compared to a conventional spectrophotometric method of ALP activity detection using p‐nitrophenylphosphate (p‐NPP) as a substrate. We demonstrate that our new technique is also suitable for the analytical determination of ALP activity. The detection limits for both AAP and ALP were found to be 13 μM and 2 pM, respectively.     

Electrochemically assisted injection – a new approach for hyphenation of electrochemistry with capillary-based separation systems

A new concept based on the electrochemical conversion of analyte species during the injection into capillary flow systems is presented. This approach is termed electrochemically assisted injection (EAI). In a specially designed injection cell containing the analyte solution a conversion efficiency of about 83% can be achieved. Potassium octacyanotungstate(IV) served as a model compound for the analytical characterisation of EAI applying capillary flow injection analysis with double-pulse amperometric detection. Capillary electrophoresis experiments were performed using EAI to study the electrochemical oxidation of various ferrocene derivatives in acetonitrile solution. The electropherograms recorded with UV detection show separated signals for the ferrocene compounds and their oxidation products. The migration behaviour and the stability of ferrocenium cations and other reaction products were investigated.     

基于酶催化沉积放大的电化学阻抗法用于人免疫球蛋白M的检测

提出了一种基于酶催化沉积放大的电化学免疫分析方法。先通过免疫夹心反应,将酶标抗体(羊抗人IgM-HRP)固定到电极表面。通过HRP催化双氧水氧化3,3′-二氨基联苯胺在电极表面形成不溶性沉积物,从而放大电化学检测信号。实验通过蛋白A实现抗体的定向固定。考察了包被抗体的浓度和包被溶液的pH对抗体固定的影响,以及酶标抗体的用量和沉积时间对免疫分析的影响。传感器信号响应与人免疫球蛋白M(IgM)浓度在2.1~670μg/L范围内具有良好的线性关系;检出限达0.08μg/L。     

Self‐Assembling of Redox‐Active Atrazine Poly(ethylenimine) Conjugates – Interfacial Electrochemical and Spectroscopic Characterization

Thin films of polymers tethered with both atrazine haptens and ferrocenyl (Fc) probes were formed on polycrystalline gold electrodes by taking advantage of the facile formation of self‐assembled monolayers (SAMs) of thiolates. These films were characterized by polarization modulation Fourier transform infrared reflection–absorption spectrometry (PM‐IRRAS), X‐ray photoelectron spectroscopy (XPS) and cyclic voltammetry. The combination of these techniques gave a full insight into the structure and the binding mode of the polymers and provided useful quantitative information about both Fc entity and atrazine hapten surface density. This may open the way to a new type of immunosensor for atrazine monitoring.