Herein, DNA nanostructures were prepared via a palindromic padlock probe-based rolling circle amplification (called P-RCA) and then employed to implement the sensitive and specific detection of let-7a miRNA extracted from cancer cells without chemical modification. The presence of target let-7a miRNA as a polymerization primer can trigger the P-RCA process, generating a long tandemly repetitive DNA strand. The resulting products can fold into nanostructures via self-hybridization of palindromic regions and possess numerous double-stranded fragments. In this case, the strong fluorescent signal is detected upon exposure to SYBR Green I. As a result, in homogeneous solution, target miRNA can be detected down to 6.4 pM with a wide dynamic range. A high specificity was demonstrated by the excellent discrimination between let-7 miRNA family members, while the applicability of this sensing system in complex biological environments was confirmed by the analysis of target miRNAs extracted from HeLa cells. It should be noted that increasing numbers of palindromic fragments in padlock probe further increases signal amplification efficiency. The experimental results indicate that the newly proposed P-RCA DNA nanostructures have potential to become a promising analytical platform in biomedical research and clinical diagnosis for the miRNA detection with high sensitivity and good specificity.

本文中，DNA纳米结构是通过基于回文挂锁探针的滚环扩增（称为P-RCA）制备的，然后用于对从癌细胞中提取的let-7a miRNA进行灵敏而特异的检测，而无需进行化学修饰。作为聚合引物的目标let-7a miRNA的存在可以触发P-RCA过程，生成长的串联重复DNA链。所得产物可通过回文区的自杂交折叠成纳米结构，并具有许多双链片段。在这种情况下，当暴露于SYBR Green I时会检测到强荧光信号。结果，在均相溶液中，可以检测到低至6.4 pM的靶miRNA，并具有宽广的动态范围。let-7 miRNA家族成员之间的出色区分证明了其高度的特异性，同时通过分析从HeLa细胞提取的靶miRNA证实了该传感系统在复杂生物环境中的适用性。应当指出，挂锁探针中回文片段数量的增加进一步提高了信号放大效率。实验结果表明，新提出的P-RCA DNA纳米结构具有潜力，有望成为具有高灵敏度和高特异性的miRNA检测的生物医学研究和临床诊断中有希望的分析平台。