K-junction structure mediated exponential signal amplification strategy for microRNA detection in electrochemiluminescence biosensor.

Based on the novel designed K-junction structure, an economic and efficient exponential signal amplification strategy with simple protocol combining hemin/G-quadruplex, a mimetic peroxidase, as a catalyzer was proposed and utilized in an electrochemiluminescence biosensor for sensitive microRNA detection. It was noteworthy that the K-junction structure was formed with guanine-rich reporter DNA and substrate DNA modified by phosphate at the 5'-terminus. Thus, the activity of the reporter DNA could be inhibited and the recognition domain for the target microRNA constructed through the K-junction structure formed. When the target microRNA was sensed, the paired domains of the substrate DNA was completely digested from the 5'-terminus, accompanied by the release of the target microRNA and unpaired DNA fragment of the substrate DNA called the trigger DNA. Afterwards, the released microRNA and trigger DNA were recycled over and over causing the linear and exponential digestion of the K-junction structure, respectively. As a result, numerous uninhibited reporter DNAs were left on the electrode to capture hemin with the yielded hemin/G-quadruplex, which could enhance the ECL emission significantly due to its catalysis for the luminol-H2 O2 . As expected, this method exhibited excellent specificity and high sensitivity for microRNA detection from 0.033 fM. What's more, the application in human lung cancer cell lines achieved good sensitivity for 10 tumor cells.