Development of a direct competitive enzyme-linked immunoassay for carbofuran in vegetables

Three ELISA formats, antigen coated, antibody coated and the second antibody coated for the determination of carbofuran were investigated with conjugations including hapten–BSA, hapten–OVA, hapten–HRP and anticarbofuran IgG–HRP. Results showed that the second antibody-coated method of ELISA had a better performance in the establishment of standard curves and detection of carbofuran residue in vegetables samples. The sensitivity for detection, the I₅₀ value was 36.1 ng/ml at a practical working concentration range from 3.44 to 380.1 ng/ml and the limit of detection for carbofuran was 3.44 ng/ml. The average recoveries of determination for carbofuran spiked in cabbage, lettuce, carrot, winter fragrant-flowered garlic, bamboo shoot and green soy bean were 85.24%, 101.8%, 103.6%, 90.52%, 106.9% and 94.08%, respectively. Additional analyses confirmed that the results given by the ELISA method was in agreement with those of the gas chromatography (GC) method.     

Development of a sensitive ELISA for the analysis of the organophosphorous insecticide fenthion in fruit samples

Two fenthion haptens, 4-(4-(dimethoxyphosphorothioyloxy)-2-methylphenylamino)-4-oxobutanoic acid (H1) and 6-(methoxy(4-(methylthio)phenoxy)phosphorothioylamino)hexanoic acid (H2), were synthesized. H1 was conjugated with bovine serum albumin (BSA) and H2 with ovalbumin (OVA) by the active ester method. Then H2-OVA conjugate was used as coating antigen, while H2-BSA conjugate was used to produce polyclonal antibodies. After optimization, an effective competitive indirect enzyme-linked immunosorbent assay (ELISA) for determination of fenthion was established with the new combination of antibody/antigen, I₅₀ of which was 0.01 ng/ml, and there was only cross reactivity (CR) with fenitrothion (4.5%), and CRs with other tested pesticides were all below 0.1%. The recoveries obtained by standard fenthion addition to the different fruit samples such as grape, peach, pear and tomato were all from 79.8% to 106.0%. Therefore, the optimized ELISA may become a new convenient and satisfied analytical tool for monitoring fenthion residues in agricultural samples.     

Identification of tetrodotoxin antigens and a monoclonal antibody

Two kinds of antigens for tetrodotoxin (TTX) were made, using carrier protein ovalbumin (OVA) and bovine serum albumin (BSA), by the formaldehyde method. Nondenaturing gel electrophoresis, gel filtration and ultraviolet spectrophotometry were employed to analyze the coupling of TTX to carrier proteins. The results indicate that nondenaturing gel electrophoresis and gel filtration can be employed to analyze the coupling of TTX to BSA and OVA qualitatively, and ultraviolet spectrophotometry can be employed to analyze the molecular coupling ratio of TTX to BSA and OVA quantitatively. Spleen cells from Balb/C mice immunized with an artificial TTX-formaldehyde-ovalbumin conjugate were fused with SP2/0 myeloma cells. A hybridoma cell line (4D5), which secreted IgG₁ subclass monoclonal antibody against TTX, was produced by “limiting dilution” cloning. The molecular weight, the affinity constant and the titre of the monoclonal antibody (mAb) secreted by 4D5 were 183.69 kDa, 0.98 × 10⁸ M⁻¹ and 3.6 × 10⁵, respectively. The number of the hybridoma chromosome was 88–104.     

Development of an indirect competitive immunoassay for parathion in vegetables

An indirect competitive immunoassay for the insecticide parathion has been optimized and characterized. This assay is based on a monoclonal antibody (2H₉) produced from an immunogen, a bovine thyroglobulin (BTG) conjugate wherein the reduced form of parathion was multiply bound to the carrier protein via diazo bonds. Assay was performed in the parathion-HSA coated (0.25 μg/ml) ELISA format in which antibody was diluted 1:2000. Several physicochemical factors (pH, ionic strength, BSA concentrations and organic solvent) that influence assay performance were studied and optimized. Finally, the assay was applied to the analysis of parathion in spiked vegetable samples. The sensitivity, estimated as the IC₅₀ value, was 360 ng/ml, with a practical working range between 47 and 6000 ng/ml, a limit of detection of 26 ng/ml, and inter-assay and intra-assay variations less than 10%. The average recovery of parathion added to potato, celery and Chinese cabbage were 173 ± 34%, 108 ± 15% and 98 ± 6%, respectively.     

Development of competitive indirect ELISA for the detection of tetrodotoxin and a survey of the distribution of tetrodotoxin in the tissues of wild puffer fish in the waters of south-east China

A monoclonal antibody against tetrodotoxin (TTX) was produced from the hybridoma cell line T6D9, which was established by the fusion of Sp2/0 myeloma cells with spleen cells isolated from a Balb/c mouse immunized with the TTX–keyhole limpet hemocyanin (KLH) conjugate. This monoclonal antibody belongs to the IgG1 subclass; the affinity constant of the antibody is 2.4 × 10^?8 mol l^?1. The relative cross-reactivity of the antibody with TTX was 100%, but with saxitoxin, KLH and bovine serum albumin (BSA) it was less than 1%, respectively. The titre of the antibody in ascites was 6.4 × 10⁶; the reference working concentration was 1:1.2 × 10⁵. By using this monoclonal antibody, a competitive indirect enzyme-linked immunoabsorbant assay (ELISA) for the analysis of TTX was developed. The linear portion of the dose–response curve of TTX concentration was in range 5–500 ng ml^?1. The limit of detection was 5 ng ml^?1 according 10% inhibition with TTX to anti-TTX monoclonal antibody. The concentration of TTX inhibiting 50% of antibody binding was about 50 ng ml^?1. The recoveries from TTX spiked samples were 79.5–109.5%. In addition, the toxicity of some wild puffer fish specimens captured from south-east China and the Yangzi River in Jiangsu province was determined. The results indicate that the toxicity and toxin tissue distribution vary in different species of wild puffer fish.     

Development of a highly sensitive and specific monoclonal antibody-based enzyme-linked immunosorbent assay for determination of doxycycline in chicken muscle,liver and egg

A modified indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) method was developed using a highly sensitive and specific monoclonal antibody (McAb) to determine doxycycline (DC) residues in chicken tissues and egg. The McAb against DC was produced by hybridoma technique and a modified ic-ELISA was characterised in terms of sensitivity, specificity, precision and accuracy. At optimal experimental conditions, the standard curve was constructed at concentrations ranged from 0.01 to 100 ng/ml. The IC₅₀ value was 1.32 ± 0.18 ng/ml. The limit of detection was 0.14 ± 0.02 ng/g. The recoveries of DC from spiked chicken liver, muscle, and egg at levels of 50–600 ng/g were 84.6–85.5%, 88.2–89.1%, and 84.4–89.3%, respectively. The coefficient variations (CVs) were 5.1–9.3%, 3.7–11.3%, and 4.7–9.8%, respectively. Linear regression analysis showed good correlation, with r² values 0.9909 for chicken liver and 0.9916 for chicken muscle.     

2,4-二氯苯氧乙酸人工抗原合成及鼠源多克隆抗血清的制备

采用碳化二亚胺法(EDC法)将2,4-D与牛血清白蛋白(BSA)及卵清蛋白(OVA)偶联,合成免疫原2,4-D-BSA和包被原2,4-D-OVA,采用紫外扫描(UV)和聚丙烯酰胺凝胶电泳(SDS-PAGE)法进行鉴定;用2,4-D人工免疫抗原(2,4-D-BSA)免疫BALB/c纯系小鼠,采用间接ELISA测定多抗血清效价、阻断ELISA鉴定其抑制。结果表明:BSA与2,4-D偶联后,波峰出现右移,表明偶联成功;SDS-PAGE电泳中BSA的泳动速度大于2,4-D-BSA,表明2,4-D已与BSA成功偶联;6只小鼠血清效价均达到了1:1.28×104,且1号小鼠多抗血清敏感性最好,半数抑制IC50为72.48ng/mL,表明成功获得了高效价、特异性好、亲和力较高的鼠源抗2,4-D多克隆抗体血清,为2,4-D残留免疫学检测方法的建立奠定了良好的基础。     

Development of polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay for sodium saccharin residue in food samples

A sensitive and specific polyclonal antibody (PcAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) for sodium saccharin is described. 6-Amino saccharin was coupled to carrier protein for artificial antigen by diazotisation. New Zealand white rabbits were immunised to obtain anti-sodium saccharin PcAb and then icELISA was developed. The assay showed high sensitivity and specificity to sodium saccharin, with the 50% inhibition value (IC₅₀) of 0.243 μg mL⁻¹, workable range (IC₃₀–IC₇₀) of 0.050–12.8 μg mL⁻¹ and limit of detection (LOD, IC₂₀) of 0.021 μg mL⁻¹. The average recoveries of sodium saccharin in spiked food samples were estimated ranging from 70.7% to 98.8%. A statistically significant correlation of results was obtained between this new ELISA and previously established HPLC approaches with the food-relevant sodium saccharin concentration range 0–320 μg mL⁻¹ (R² = 0.9887–0.9975). These results indicated that the established ELISA was a potential and useful analytical tool for rapid determination of sodium saccharin residue in food samples.     

Detection of alkaline phosphatase by competitive indirect ELISA using immunoglobulin in yolk (IgY) specific against bovine milk alkaline phosphatase

Immunoglobulin in yolk (IgY) (with a titer of 1.3 × 10⁶) specific against bovine milk (BM) alkaline phosphatase (ALP) was obtained by intramuscularly immunizing hens on the thigh and was used as the primary antibody to conduct competitive indirect enzyme-linked immunosorbent assay (CI-ELISA) to determine BMALP in ALPs from BM and Escherichia coli sources. A relationship between the ELISA value and the BMALP level (0.01–10 μg/mL) in whole milk (R² = 0.9019) or in skimmed milk (R² = 0.9402) was observed. The maximal inhibition (%) of BMALP on the microtiter plate by free BMALP at 10 μg/mL whole milk (3.89 mU/μg BMALP) was about 50%, while no inhibition (%) of BMALP by free E. coli ALP at concentrations between 0.01 to 10 μg/mL (60 mU/μg E. coli ALP) was determined. At BMALP levels higher than 0.1 μg/mL, CI-ELISA was proved to be effective in differentiating between BMALP and E. coli ALP and quantifying BMALP in whole milk or skimmed milk in the presence of E. coli ALP with an activity of 0.6 U/mL. Higher inhibition (about 70%) of BMALP on the microtiter plate by free BMALP in diluted (10¹–10⁴ fold) milk samples was observed. The optimal conditions for CI-ELISA in determining BMALP (0.1–10 μg/mL) from ALPs in milk samples were using 10³-fold diluted crude IgY specific against BMALP as primary antibody and 10³-fold diluted goat anti-chicken IgG–ALP conjugate as the secondary antibody.     

1-芘丁酸人工抗原的制备及鉴定

为制备及鉴定1-芘丁酸（1-pyrenebutyric acid）人工抗原。采用碳化二亚胺（EDC）法将1-芘丁酸与牛血清白蛋白（BSA）和鸡卵清白蛋白（OVA）进行偶联,合成人工免疫原PBA-BSA和人工检测抗原PBA-OVA;紫外扫描及SDS-聚丙烯凝胶电泳（SDS-PAGE）结果显示抗原制备成功;鼠源多抗血清的效价均已超过1 000,IC₅₀=14.31 ng/mL;与多环芳烃1-芘甲醇、1-芘甲醛、芘的交叉反应率小于14.40%,与菲、萘、苯并芘、BSA以及OVA交叉反应率均小于0.05%。作者成功制备出了PBA-BSA抗原,并且得到了敏感性良好的鼠源多抗血清,为后期单克隆抗体的制备及免疫学快速检测方法的建立奠定基础。     

孔雀石绿人工抗原的合成及多克隆抗体的制备

通过研究孔雀石绿(MG)抗原的合成和多克隆抗体的制备,探索研究食品中孔雀石绿残留的检测方法。本实验先合成含有羧基的孔雀石绿半抗原(CMG),并用液-质联用法进行分析鉴定。半抗原经重氮化法处理后分别偶联两种载体蛋白BSA和OVA,并通过紫外分光光度法进行鉴定。与CMG标准品和两种载体蛋白的紫外吸收光谱相比,偶联物的吸收峰发生了明显的偏移,计算得免疫原的偶联比为10.6:1,说明偶联成功。通过免疫制备多克隆抗体,并通过间接ELISA法对CMG抗血清的效价进行检测,并进一步检测抗体的特异性,两只兔子的IC50值分别为8.1ng/mL和4.6ng/mL。     

Development of an enzyme-linked immunoassay for the detection of gentamicin in swine tissues

We developed an enzyme-linked immunoassay that provides rapid and sensitive detection of gentamicin in swine tissues. Rabbit was immunized with gentamicin-BSA conjugate and antiserum was collected after the fifth immunization. After optimizing the concentration of immunoreagents, competitive indirect ELISA (ciELISA) gave an IC₅₀ value of 0.98 ng/ml, while competitive direct ELISA (cdELISA) exhibited lower IC₅₀ value of 0.92 ng/ml, thus cdELISA was further optimized under various pH values and ionic strengths of assay buffer, different coating methods and incubation time. The optimized ELISA can be completed within 45 min and it showed negligible cross-reactivity with other aminoglycosides. The recoveries of gentamicin from spiked swine tissues at levels of 25–200 μg/kg ranged from 64.7% to 101.2% with CVs of 4.5–12.1%, and the detection limits were 6.2 μg/kg in muscle, 3.6 μg/kg in liver and 2.7 μg/kg in kidney, respectively.     

环丙氨嗪完全抗原的合成及免疫原性鉴定

目的合成并鉴定环丙氨嗪(cyromazine,CA)人工抗原。方法采用碳二亚胺法(1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride,EDC)将环丙氨嗪与牛血清蛋白(bovine serum albumin,BSA)和鸡卵清蛋白(ovalbumin,OVA)分别偶联;采用紫外分光光度法(ultraviolet spectrophotometry,UV)、聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate polyacrylamide gel electrophoresis,SDS-PAGE)和动物免疫对人工抗原进行鉴定。经过4次免疫,间接ELISA测定小鼠血清抗体效价,间接竞争ELISA测定血清灵敏性。结果 UV法和SDS-PAGE法结果初步显示半抗原环丙氨嗪和载体蛋白偶联成功;小鼠血清效价均在1:6400以上,2号小鼠多抗血清半数抑制浓度IC_(50)为27.5 ng/mL。结论本研究成功合成了环丙氨嗪的人工抗原,为环丙氨嗪单克隆抗体制备奠定基础。     

Folic acid complexes with human and bovine serum albumins

The interaction of folic acid with human serum (HSA) and bovine serum albumins (BSA) at physiological conditions, using constant protein concentration and various folic acid contents was investigated. FTIR, UV–visible and fluorescence spectroscopic methods as well as molecular modelling were used to analyse folic acid binding sites, the binding constant and the effect on HSA and BSA stability and conformations. Structural analysis showed that folic acid binds HSA and BSA via both hydrophilic and hydrophobic contacts with overall binding constants of K_{folic acid–HSA} = 8.1 (±0.5) × 10⁴ M⁻¹ and K_{folic acid–BSA} = 1.0 (±0.3) × 10⁵ M⁻¹. The number of bound acid molecules per protein was 1.7 (±0.4) for HSA and 1.5 (±0.3) for BSA complexes. Molecular modelling showed participation of several amino acids in folic acid–protein complexes stabilised by hydrogen bonding network. Folic acid complexation altered protein secondary structure by major reduction of α-helix from 59% (free HSA) to 35% (acid-complex) and 62% (free BSA) to 25% (acid-complex) with an increase in random coil, turn and β-sheet structures indicating protein unfolding. The results suggest that serum albumins might act as carrier proteins for folic acid in delivering it to target molecules.     

莱克多巴胺人工抗原及抗体的制备

莱克多巴胺是一种禁用β-兴奋剂,建立莱克多巴胺药残的快速检测方法是实现对其进行有力监控的有效途径,而莱克多巴胺抗体是快速免疫检测法的基本试剂。本实验用全新的方法研究了莱克多巴胺免疫原的合成,采用对氨基苯甲酸(ABA)和1,4-丁二醇缩水甘油醚(BDE)将莱克多巴胺分别和cBSA、cOVA偶联,合成了莱克多巴胺的免疫原和包被抗原,并对其进行了紫外分析。用免疫原免疫新西兰大白兔,获得了高灵敏度和特异性的莱克多巴胺多克隆抗体,采用间接ELISA法检测抗体的IC50值为4.34ng/ml,所得多克隆抗体效价达到102400。     

抗莱克多巴胺单克隆抗体杂交瘤细胞株的建立及其免疫学特性鉴定

莱克多巴胺(RAC)经化学修饰引入功能基团羧基,合成半抗原RAC- 戊二酸酐半醛化合物(RAC-SA),用混合酸酐法(MA)将RAC-SA 偶联于牛血清白蛋白(BSA),合成人工抗原BSA-RAC,用红外(IR)、紫外(UV)和凝胶电泳(SDS-PAGE)对其进行鉴定;用BSA-RAC免疫Balb/C 小鼠,细胞融合技术建立抗RAC的单克隆抗体(RAC mAb)杂交瘤细胞株,体内诱生腹水法制备RAC mAb,并鉴定其免疫学特性。结果表明,BSA-RAC 偶联成功,偶联率为24.5:1;筛选出3F10、3H12、4D8 共3 株杂交瘤细胞,其中最好的4D8 株间接ELISA 效价细胞培养上清为1:1.28 × 103,腹水为1:6.4 × 105,同种型为IgG1/κ,亲和常数(Ka)为1.65 × 1010L/mol,对RAC 的半数抑制浓度(IC50)为5.7ng/ml,与多巴酚丁胺的交叉反应率(CR)为22.3%,与其他化合物无CR。     

对硫磷酶联免疫吸附分析方法的建立和评价

通过制备对硫磷的多克隆抗体,建立了对硫磷的间接竞争酶联免疫吸附分析方法(icELISA)。通过活泼酯法将半抗原分别与牛血清蛋白(BSA)和卵清蛋白(OVA)偶联,获得免疫抗原和包被抗原。使用对硫磷抗血清,经优化条件参数建立了对硫磷的icELISA分析方法。该方法检测线性范围为3.39～533.05ng/mL,最低检测限为0.90ng/mL,对蔬菜样品和水样品的平均添加回收率为75.6%～127.4%,能用于实际样品中对硫磷的检测。     

An ultra-sensitive monoclonal antibody-based competitive enzyme immunoassay for aflatoxin M1 in milk and infant milk products

A sensitive and specific monoclonal antibody (Mab) against aflatoxin M₁ (AFM₁), named as 2C9, was selected by semi-solid HAT medium. It exhibited high affinity for AFM₁ of 1.74 × 10⁹ L/mol and no cross-reactivity to aflatoxin B₁, B₂, G₁ and G₂. Based on the antibody, an ultra-sensitive competitive enzyme-linked immunosorbent assay (ELISA) was developed for AFM₁ in milk and infant milk products. Assays were performed in the AFM₁-BSA coated (0.0625 μg/mL) ELISA format in which the antibody was diluted 1:10,000. Several physicochemical factors (pH, ionic strength and blocking solution) that influence assay performance were optimised. Finally, the limits of detection were 3 ng/L for milk and 6 ng/L for milk-based cereal weaning food, inter-assay and intra-assay variations were less than 10%, and the recovery ranged from 91% to 110%. Thirty samples were analysed, and concordant results were obtained when the data were compared with a reference high-performance liquid chromatography method.     

双酚A单克隆抗体的制备及酶联免疫分析方法的建立

采用活泼酯法将双酚A的结构类似物双酚酸与载体蛋白偶联制备人工抗原,用制备的人工抗原免疫BALB/c小鼠,采用聚乙二醇法进行细胞融合制备双酚A单克隆抗体,成功获得一株分泌抗双酚A单克隆抗体的细胞株3H1,经鉴定抗体属于IgG1亚型,轻链为κ,并建立了间接竞争酶联免疫分析法。线性范围为1～50 ng/mL,最低检测限为0.43 ng/mL,半数抑制浓度为6.56 ng/mL。回收率为82.83%～101.94%,变异系数为2.94%～12.95%。该方法具有较高的灵敏度和特异性,具有良好的应用前景。     

氧氟沙星完全抗原的合成鉴定及其单克隆抗体的制备纯化

本试验通过碳二亚胺(EDC)法把氧氟沙星(OFLX)与载体蛋白BSA和OVA分别进行偶联制备免疫抗原和包被抗原,并采用紫外扫描法和SDS-聚丙烯酰胺凝胶电泳方法对合成抗原进行了鉴定。通过杂交瘤常规技术获得了抗OFLX的单克隆抗体杂交瘤细胞株7株,用辛酸-硫酸铵法对腹水进行了纯化。纯化腹水均属IgG1型。经过ELISA方法鉴定,纯化后的抗体效价>1:128000;交叉实验证明所得抗体与达氟沙星、洛美沙星、环丙沙星、诺氟沙星、卡那霉素、庆大霉素、泰乐菌素均没有交叉反应,表现了良好的敏感性和特异性。