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黄曲霉毒素(aflatoxins, AFs)主要是由黄曲霉Aspergillus flavus和寄生曲霉Aspergillus parasiticus产生的有毒次级代谢物,可通过污染食品和饲料进入食物链,严重威胁动物和人类健康[1]。目前,国内外已发现超20种AFs,其中黄曲霉毒素B1(AFB1)毒性最强,危害最大,已被国际癌症研究机构(IARC)列为Ⅰ类致癌物[2-4]。AFB1具有强烈的“致突变、致癌和致畸作用”和免疫毒性,过量摄入可破坏人和动物的肝脏组织,引发急性中毒,长期摄入则会引发各组织器官癌变[5-6]。建立快速、高灵敏的AFB1检测方法对于保障食品安全具有重要意义。在AFB1检测手段中,仪器法如高效液相色谱法(HPLC)、气相色谱法(GC)和液相色谱-串联质谱法(LC-MS/MS)等虽灵敏度高,准确性和重现性较好,但设备耗材昂贵且操作繁琐,难以用于样本的初筛和在基层使用[7-10];相比仪器分析法,基于抗原抗体反应的免疫分析法因操作简单、灵敏度高且特异性好,在真菌毒素检测领域应用较广,特别是免疫层析法,省时高效且无需借助复杂仪器,尤其适合大量样本的现场筛查[11-16]。本研究基于免疫层析技术原理,采用金颗粒标记AFB1单克隆抗体,在竞争反应模式下,优化金颗粒尺寸、层析体系各组成材料及相关缓冲液配方,最终建立AFB1高灵敏定性定量免疫层析检测法,通过肉眼直接对检测结果定性判定,或借助便携式信号读取设备实现定量分析,以满足对AFB1污染情况快速筛查的检测需求。
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采用AFB1单克隆抗体对AFB1-BSA/OVA进行ELISA鉴定,结果如图3所示,完全抗原组D(450)与对照比值(BSA/OVA)远大于2.1,表明制备成功,可用于免疫学方法的建立。
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制备的金颗粒溶液颜色澄清鲜艳,40 nm金颗粒溶液颜色较20 nm深,无颗粒沉淀(图4A),透射电镜扫描结果显示颗粒粒径与预期相符,尺寸均匀(图4B),可用于后续抗体的标记。
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40和20 nm金颗粒标记物层析效果相当,但4 ℃储存时前者性质更稳定,可保存4周,因此综合考虑灵敏度和稳定性,后续试验将采用40 nm金颗粒进行单克隆抗体的标记。
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包被AFB1-BSA时,检测线显色清晰且灵敏度更好,后续试验将采用AFB1-BSA作为检测线包被抗原。
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层析组分材料会影响层析灵敏度、时间和稳定性。对各组分材料进行筛选,硝酸纤维素膜的比较结果显示:Sartorius CN 140相较于其他,流动性更佳且检测线不易弥散,层析15 min后即可判定结果,背景值低,为最优,封闭液为含质量分数为0.5%吐温20 (Tween-20)、1%聚乙二醇2000 (PEG 2000)、2%BSA和0.01%叠氮钠(NaN3)的10 mmol·L−1磷酸盐缓冲液(pH 7.4,PBS);金标抗体固定垫的比较结果显示:Ahlstrom 8964上固定的金标抗体可在15 min内释放完全且无聚沉,为最优,处理液为含质量分数为4%蔗糖、1%BSA和0.25%表面活性剂TritonX-100的50 mmol·L−1硼酸盐缓冲液(pH 7.4,BB);样品垫的比较结果显示:国产SB08对含甲醇、纤维素和蛋白质的样本承载能力和缓冲能力更强,为最优,前处理液种类与金标固定垫相同。
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对含不同质量浓度海藻糖、NaN3和OVA的10 mmol·L−1硼酸盐缓冲液(pH 7.4,BB)在4 ℃条件下对金标抗体的储存和稀释效果进行比较,结果显示:在质量分数为10%海藻糖、1% BSA的条件下,金标抗体复溶效果较好且可稳定保存30 d,最终确定金标抗体存储稀释液为含质量分数为10%海藻糖、1%BSA和0.05%NaN3的10 mmol·L−1的硼酸盐缓冲液(pH 7.4,BB)。抗原包被液优化结果显示:含体积分数为3%甲醇的10 mol·L−1硼酸盐缓冲液(pH 9.0,BB)可使检测线颜色更加均匀和清晰。
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为获得最佳的检测效果,对完全抗原包被质量浓度和金标抗体的使用质量浓度进行优化,最终确定AFB1-BSA的包被质量浓度为0.4 g·L−1,10倍稀释后的金标AFB1单克隆抗体喷涂量为20 μL·cm−2。
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如图5所示:与对照相比,随着AFB1质量浓度的升高,检测线逐渐变浅直至消失,肉眼条件下,使检测线质量浓度发生明显变化的最低标准品质量浓度即为检测限,因此,本免疫层析法的检测限为0.10 μg·L−1。配制系列梯度质量浓度的AFB1标准品溶液进行检测,层析结束后使用便携式信号读取仪分析检测线信号强度。以标准品质量浓度(x)为横坐标,检测线信号强度抑制率(y)为纵坐标,绘制标准抑制曲线,进行线性回归分析(图6),线性方程为y=0.631 9x+1.159 1,R2=0.984 3,定量区间为0.03~0.27 μg·L−1,检测下限为0.02 μg·L−1。
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以谷物类样本中其他常见真菌毒素如赭曲霉毒素A(OTA)、玉米赤霉烯酮(ZEN)、伏马毒素B1 (FB1)和呕吐毒素(DON)作为竞争抗原,进行特异性验证,结果如图7所示,建立的免疫层析检测法对上述毒素均不存在交叉反应,特异性较好,质量浓度均为5.00 μg·L−1。
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如图8所示:对玉米Zea mays样本进行加标试验,当AFB1加标质量分数为2.5 μg·kg−1可使检测线变化明显,说明该免疫层析检测法在实际样本中的定性检测限为2.5 μg·kg−1。
图 8 免疫层析法对黄曲霉毒素B1加标样本的定性检测
Figure 8. Qualitative detection of aflatoxin B1 spiked samples by immunochromatography
当AFB1加标质量分数依次为1.0、2.5、5.0和15.0 μg·kg−1时,如表1所示,该免疫层析法在玉米样本中的加标回收率为89.62%~110.43%,批内变异系数为4.51%~6.58%,批间变异系数为7.28%~9.72%,说明该方法准确率较高且稳定性较好。
表 1 免疫层析法对黄曲霉毒素B1加标样本的定量检测
Table 1. Quantitative detection of aflatoxin B1 spiked samples by immunochromatography assay
AFB1加标质量
分数/(μg·kg−1)批内 批间 回收
率/%变异系
数/%回收
率/%变异系
数/%1.0 89.62 ± 5.31 5.93 95.72 ± 8.03 8.39 2.5 96.47 ± 6.35 6.58 103.56 ± 7.54 7.28 5.0 95.16 ± 4.29 4.51 93.25 ± 9.06 9.72 10.0 110.43 ± 6.15 5.57 107.59 ± 8.56 7.96 说明:数据为平均值±标准差,n=3 -
37 ℃加速稳定性实验结果表明:建立的免疫层析试纸条放置30 d后仍能对AFB1进行定性检测与定量分析,灵敏度未受影响,表明稳定性良好,推测室温可稳定保存1 a。
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如表2和图9所示:免疫层析法检测结果与LC-MS/MS的相关性一致性较好(R2=0.863 1),与商品化试剂盒的检测结果经SPSS软件分析,同样显示显著相关(P<0.01)。综上表明:本研究建立的免疫层析检测法可适用于实际样本中AFB1的快速定量检测与分析。
表 2 免疫层析法、商品化试剂盒和LC/MS/MS对天然样本中黄曲霉毒素B1的定量检测结果
Table 2. Quantitative detection of AFB1 in natural samples by the developed immunochromatography assay, commercial ELISA kit and LC-MS/MS
样本编号 AFB1/(μg·kg−1) 样本编号 AFB1/(μg·kg−1) 免疫层析检测法 LC/MS/MS 商品化试剂 免疫层析检测法 LC/MS/MS 商品化试剂 1 5.11 ± 0.32 4.79 ± 0.29 5.65 ± 0.37 8 1.83 ± 0.14 2.15 ± 0.27 2.71 ± 0.19 2 3.17 ± 0.25 2.52 ± 0.16 2.08 ± 0.18 9 2.09 ± 0.17 2.86 ± 0.25 3.57 ± 0.26 3 1.06 ± 0.11 1.34 ± 0.14 2.33 ± 0.32 10 8.65 ± 0.35 7.21 ± 0.62 8.94 ± 0.19 4 6.63 ± 0.47 5.83 ± 0.43 5.36 ± 0.57 11 4.63 ± 0.29 5.93 ± 0.38 4.38 ± 0.23 5 2.69 ± 0.22 3.15 ± 0.29 2.25 ± 0.26 12 5.27 ± 0.41 6.07 ± 0.57 5.66 ± 0.35 6 1.82 ± 0.13 2.57 ± 0.15 3.35 ± 0.18 13 3.28 ± 0.37 2.19 ± 0.18 3.95 ± 0.31 7 7.16 ± 0.51 6.03 ± 0.31 7.82 ± 0.23 说明:数据为平均值±标准差
A highly sensitive qualitative and quantitative immunochromatographic method for the detection of aflatoxin B1
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摘要:
目的 真菌毒素可污染农产品和动物源性食品,其中黄曲霉毒素B1(AFB1)毒性强、危害大,建立AFB1快速、高灵敏和便捷的检测方法对于监测相关产品中AFB1污染水平,保障人和动物健康均具有重要意义。基于侧向层析技术原理,采用竞争模式,优化建立免疫层析检测方法,以实现AFB1的快速定性检测和定量分析。 方法 通过比较分析不同粒径金颗粒标记抗体效果,优化确定免疫层析各组分材料类型、相关缓冲液配方及最佳使用质量浓度,建立AFB1高灵敏定性定量免疫层析检测方法。 结果 优化建立的AFB1免疫层析检测法在实际样本中的定性和定量检测限分别为2.5和0.5 μg·kg−1,灵敏度高、特异性强,与其他常见真菌毒素无交叉反应,加标回收实验结果显示:该方法准确稳定,且对AFB1天然污染样本的定量检测结果与商品化试剂盒及LC-MS/MS一致性较好。 结论 本研究制备的免疫层析检测法可用于样本中AFB1污染的快速定性检测与定量分析,适合缺乏实验条件的基层检验检疫机构和农产品加工企业对大量样本进行快速筛查,样本检测结果疑似阳性再采用仪器法进行确认,可降低检测成本,提升检测效率,同时为建立其他病原微生物免疫层析检测方法提供参考。图9表2参26 Abstract:Objective Fungal metabolites, commonly known as mycotoxins, can pollute agricultural products and food of animal origin, among which aflatoxin B1 (AFB1) is the most common, toxic and detrimental. Establishing a rapid, highly sensitive and convenient detection method of AFB1 is of great significance for the protection of human and animal health. The objective of this study is to optimize the immunochromatographic detection method based on the principle of lateral-flow chromatography and competitive mode, so as to realize the rapid qualitative detection and quantitative analysis of AFB1. Method A highly sensitive qualitative and quantitative immunochromatographic detection method for AFB1 was established by comparing and analyzing the labeling effects of gold particles of varying sizes, optimizing the material types of each component of immunochromatography, as well as relevant buffer solution and the optimal mass concentration. Result The qualitative and quantitative detection limits of the optimized AFB1 immunochromatographic method in samples were 2.5 and 0.5 μg·kg−1, respectively, with high sensitivity and specificity and no cross reaction with other common mycotoxins. Standard addition recovery experiment showed that the method was accurate and stable, and the quantitative detection results of AFB1 natural contamination samples were in good agreement with commercial kit and LC-MS/MS. Conclusion The immunochromatographic detection method prepared in this study can be used for rapid qualitative detection and quantitative analysis of AFB1 contamination in samples. It is suitable for grass-roots inspection and quarantine institutions and agricultural product processing enterprises that lack experimental conditions to quickly screen a large number of samples. If the sample test result is suspected to be positive, the instrument method can be used for confirmation, which can reduce the test cost, improve the test efficiency and provide reference for the establishment of immunochromatographic detection methods for other pathogenic microorganisms. [Ch, 9 fig. 2 tab. 26 ref.] -
表 1 免疫层析法对黄曲霉毒素B1加标样本的定量检测
Table 1. Quantitative detection of aflatoxin B1 spiked samples by immunochromatography assay
AFB1加标质量
分数/(μg·kg−1)批内 批间 回收
率/%变异系
数/%回收
率/%变异系
数/%1.0 89.62 ± 5.31 5.93 95.72 ± 8.03 8.39 2.5 96.47 ± 6.35 6.58 103.56 ± 7.54 7.28 5.0 95.16 ± 4.29 4.51 93.25 ± 9.06 9.72 10.0 110.43 ± 6.15 5.57 107.59 ± 8.56 7.96 说明:数据为平均值±标准差,n=3 表 2 免疫层析法、商品化试剂盒和LC/MS/MS对天然样本中黄曲霉毒素B1的定量检测结果
Table 2. Quantitative detection of AFB1 in natural samples by the developed immunochromatography assay, commercial ELISA kit and LC-MS/MS
样本编号 AFB1/(μg·kg−1) 样本编号 AFB1/(μg·kg−1) 免疫层析检测法 LC/MS/MS 商品化试剂 免疫层析检测法 LC/MS/MS 商品化试剂 1 5.11 ± 0.32 4.79 ± 0.29 5.65 ± 0.37 8 1.83 ± 0.14 2.15 ± 0.27 2.71 ± 0.19 2 3.17 ± 0.25 2.52 ± 0.16 2.08 ± 0.18 9 2.09 ± 0.17 2.86 ± 0.25 3.57 ± 0.26 3 1.06 ± 0.11 1.34 ± 0.14 2.33 ± 0.32 10 8.65 ± 0.35 7.21 ± 0.62 8.94 ± 0.19 4 6.63 ± 0.47 5.83 ± 0.43 5.36 ± 0.57 11 4.63 ± 0.29 5.93 ± 0.38 4.38 ± 0.23 5 2.69 ± 0.22 3.15 ± 0.29 2.25 ± 0.26 12 5.27 ± 0.41 6.07 ± 0.57 5.66 ± 0.35 6 1.82 ± 0.13 2.57 ± 0.15 3.35 ± 0.18 13 3.28 ± 0.37 2.19 ± 0.18 3.95 ± 0.31 7 7.16 ± 0.51 6.03 ± 0.31 7.82 ± 0.23 说明:数据为平均值±标准差 -
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