MicroRNAs (miRNAs), a class of endogenous noncodesmall molecules (18-22nt), play important roles as significant regulators to regulate fundamental cellular procedures via the modulation toward the expression of target genes that associated with a wide range of biological processes, such as cell proliferation, apoptosis and death. Research evidence has shown that miRNA is a potential class of biomarker candidate for cancer classification, early disease diagnosis, especially human cancers, neurological diseases, viral infections and diabetes. So far, there are many kinds of biosensors for microRNA detection that have been reported.
For example, as illustrated in Fig. 19, Zhang and co-worker constructed an off?on switching of a dual amplified electrochemiluminescence (ECL) biosensor based on Pb2+-induced DNAzyme-assisted target recycling and rolling circle amplification (RCA) for microRNA (miRNA) detection. In this study, a dual amplified ECL biosensor by coupling Pb2+-requiring DNAzyme-assisted target recycling amplification with Y junction has been developed for highly sensitive miRNA detection in an off?on manner for the first time.
Herein, the “switch-off” sensing platform was obtained by the quenching effect of dopamine towards a luminol/H2O2 system owing to the DNA hybridization reaction of the dopamine modified DNA sequence (S1) with HP hairpin probe. At first, the primer probe was incubated with the assistant probe and the target RNA to form the Y junction structure which was cleaved with the addition of Pb2+ to release miRNA. The released miRNA could initiate the next recycling process, leading to the generation of abundant intermediate DNA sequences (S2). Afterward, the treated glassy carbon electrode (GCE) was electrodeposited with HAuCl4, which presented an outstanding Au nanoparticles platform to modify numerous hairpin probe (HP) through Au?S bonding.
Then, dopamine (DA) – modified DNA sequence (S1) was applied to unfold the hairpin loop of HP DNA and hybridize with HP hairpin probe, which switching off the sensing system. Due to the quenching effect of DA toward luminol, the ECL signal was reduced which indicated that the system presented the OFF state.
Then, S2 produced by the target recycling process was loaded onto the prepared electrode to displace S1 and served as an initiator for RCA, where numerous repeated DNA sequences coupling with hemin to form a hemin/G-quadruplex exhibited strongly catalytic effect toward H2O2, which could amplified the ECL signal to obtain the second “switch-on” state of the sensing system.
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