Carbon dots (CDs)-based biosensors have attracted considerable interest in reliable and sensitive detection of microRNA (miRNA) because of their merits of ultra-small size, excellent biosafety and tunable emission, whereas complicated labeling procedure and expensive bioenzyme associated with current strategies significantly limit their practical application. Herein, we developed a label-free and enzyme-free fluorescence strategy based on strand displaced amplification (SDA) for highly sensitive detection of miRNA using sulfydryl-functionalized CDs (CDs-SH) as probe. CDs-SH displayed excellent response to G-quadruplex DNA against other DNAs based on based on the catalytic oxidation of –SH into –S–S– by hemin/G-quadruplex. Further, CDs-SH were employed to detect miRNA, using miRNA-21 as target model, which triggered the SDA reaction of P1 and P2 to generate hemin/G-quadruplex, subsequently making CDs-SH transform from dot to aggresome along with the quenched fluorescence. Therefore, label-free, enzyme-free, and highly sensitive analysis of miRNA-21 was readily acquired with a limit of detection at 0.03 pM. This proposed biosensor couples the advantages of CDs and label-free/enzyme-free strategy, and thus has a significant potential to be used in early and accurate diagnosis of cancer.

由于基于碳点（CD）的生物传感器具有超小尺寸，出色的生物安全性和可调发射性的优点，因此对微小RNA（miRNA）的可靠和灵敏检测引起了极大的关注，而复杂的标记程序和昂贵的生物酶与当前的策略相关联限制了它们的实际应用。在本文中，我们开发了基于链置换扩增（SDA）的无标记和无酶的荧光策略，用于使用巯基功能化CD（CDs-SH）作为探针进行miRNA的高灵敏度检测。CDs-SH在血红素/ G-四链体将–SH催化氧化为–S–S–的基础上，显示出对G-四链体DNA相对于其他DNA的出色响应。此外，以miRNA-21为目标模型，使用CDs-SH检测miRNA，它触发了P1和P2的SDA反应，生成了血红素/ G-四链体，随后使CDs-SH伴随着猝灭的荧光从点变为聚集体。因此，可以轻松获得miRNA-21的无标记，无酶和高灵敏度的分析，检测限为0.03 pM。提出的生物传感器结合了CD和无标记/无酶策略的优点，因此具有用于癌症的早期和准确诊断的巨大潜力。