In Situ Electrochemical Generation of Electrochemiluminescent Silver Naonoclusters on Target-Cycling Synchronized Rolling Circle Amplification Platform for MicroRNA Detection.

On the basis of a novel target-cycling synchronized rolling circle amplification (RCA) as a signal amplification strategy and in situ electrochemical generation of silver nanoclusters (Ag NCs) as signal probes, an ultrasensitive and simple electrochemiluminescence (ECL) biosensor was proposed for microRNA (miRNA) detection. It was worth mentioning that the circular template was subtly designed to consist of a guanine-rich (G-rich) region and a binding region for realizing target-cycling synchronized RCA. In the presence of target miR-21, the binding region hybridized with the primer and the target miR-21 to form a ternary "P" junction structure, and then the RCA was triggered from the 3'-end of the primer. Along with the proceeding of RCA, the target miR-21 was released and participated into another trigger of the RCA. On account of the G-rich region in the circular template, the product DNA of the target-cycling synchronized RCA possessed tandem periodic cytosine-rich (C-rich) sequences, which acted as ligands to further in situ electrochemically generate silver nanoclusters (Ag NCs) as ECL signal probes. As expected, the obtained ECL intensity dependent on the amount of the Ag NCs, which was positively related to the concentration of the target miR-21. The ECL assay for miR-21 detection demonstrated excellent linear response to a concentration variation from 100 aM to 100 pM and limit of detection down to 22 aM.