A paper-based visual fluorescence immunoassay is presented for the detection of matrix metalloproteinase-7 (MMP7) that is related to renal cancer. The method is based on the distance-dependent fluorescence quenching of CdTe quantum dots (QDs) on a nitrocellulose membrane by Ag+ following a sandwich-type immunoreaction on microtiter wells using silver nanoparticle (AgNP)–labeled secondary antibody– and primary antibody–coated microtiter wells. The silver nanoparticles captured in the well are dissolved with HNO3, while the quenching effect of QDs is based on silver ion-exchange reaction under 365-nm excitation light irradiation. Increasing concentration of released Ag+, thus higher concentration of the protein, leads to an increased distance of quenching on the nitrocellulose membrane. The paper-based immunoassay by combination of AgNP-assisted ion-exchange reaction with QD gives good distance-dependent responses and allows the detection of MMP7 at a concentration as low as 7.3 pg mL−1. The coefficients of variation are less than 6.9% and 12.4% for intra-assay and inter-assay, respectively. High specificity and long-term stability are achieved during the assay. Importantly, the testing of human serum samples using our strategy shows well-matched results with commercial human MMP7 ELISA kits. Graphical abstract A distance-dependent visual immunoassay is developed for the determination of serum matrix metalloproteinase-7 on CdTe quantum dot–impregnated paper with silver ion-exchange reaction. A distance-dependent visual immunoassay is developed for the determination of serum matrix metalloproteinase-7 on CdTe quantum dot–impregnated paper with silver ion-exchange reaction.

中文翻译：

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通过银离子交换反应对 CdTe 量子点浸渍纸进行距离相关视觉荧光免疫分析

提出了一种基于纸张的视觉荧光免疫测定法，用于检测与肾癌相关的基质金属蛋白酶 7 (MMP7)。该方法基于使用银纳米颗粒 (AgNP) 标记的二抗和一抗包被的微量滴定器在微量滴定孔上进行夹心型免疫反应后，Ag+ 对硝化纤维素膜上的 CdTe 量子点 (QD) 进行距离依赖性荧光猝灭井。孔中捕获的银纳米粒子被 HNO3 溶解，而 QD 的猝灭效应是基于 365 nm 激发光照射下的银离子交换反应。增加释放的 Ag+ 的浓度，因此更高的蛋白质浓度，导致硝酸纤维素膜上淬灭距离的增加。AgNP 辅助离子交换反应与 QD 相结合的纸基免疫测定提供了良好的距离依赖性响应，并允许检测浓度低至 7.3 pg mL-1 的 MMP7。测定内和测定间的变异系数分别小于 6.9% 和 12.4%。在测定过程中实现了高特异性和长期稳定性。重要的是，使用我们的策略测试人血清样品显示出与商业人 MMP7 ELISA 试剂盒匹配良好的结果。图形摘要 开发了一种距离依赖性视觉免疫分析，用于在 CdTe 量子点浸渍纸上通过银离子交换反应测定血清基质金属蛋白酶 7。