The authors describe an aptamer-based colorimetric assay for the specific detection of the toxic microcystin leucine-arginine (MC-LR). The method is based on the use of graphene oxide (GO) in a hydrogel matrix, Methylene Blue (MB) acting as an optical probe, streptavidin-modified magnetic particles, and an aptamer (Apt) as a the recognition probe. A complementary strand of the aptamer and adenosine act as promoters in the formation of the GO hydrogel, and the hairpin structure of the aptamer warrants selectivity. In the absence of MC-LR, the gelation of GO sheets is promoted by complementary strand and adenosine, and MB is trapped between GO sheets. Hence, no blue color can be observed in the sample solution. In the presence of MC-LR, GO does not cause the formation of a strong hydrogel structure and a distinct blue color can be observed and measured (at 660 nm) because MB is present in solution. The assay has high selectivity for MC-LR, with a limit of detection (LOD) as low as 219 pM. It was successfully applied to the determination of MC-LR in spiked tap water and serum samples where it gave LODs of 221 and 412 pM, respectively.

中文翻译：

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基于使用发夹适体、氧化石墨烯和亚甲蓝作为光学探针的微囊藻毒素亮氨酸-精氨酸的比色测定

作者描述了一种用于特异性检测有毒微囊藻毒素亮氨酸-精氨酸 (MC-LR) 的基于适配体的比色法。该方法基于在水凝胶基质中使用氧化石墨烯 (GO)、亚甲蓝 (MB) 作为光学探针、链霉抗生物素蛋白修饰的磁性颗粒和适体 (Apt) 作为识别探针。适配体和腺苷的互补链在 GO 水凝胶的形成中充当启动子，适配体的发夹结构保证了选择性。在没有 MC-LR 的情况下，互补链和腺苷促进了 GO 片的凝胶化，并且 MB 被困在 GO 片之间。因此，在样品溶液中不能观察到蓝色。在 MC-LR 存在的情况下，GO 不会形成强水凝胶结构，并且可以观察和测量（在 660 nm 处）明显的蓝色，因为 MB 存在于溶液中。该测定对 MC-LR 具有高选择性，检测限 (LOD) 低至 219 pM。它成功应用于测定加标自来水和血清样品中的 MC-LR，其 LOD 分别为 221 和 412 pM。