Modular Engineering of the DNAzyme-Based Electrochemiluminescence Biosensor with the Nitrogen and Sulfur Codoped Carbon Dots as Near-Infrared Emitters for MicroRNA detection

-specific 8-17 DNAzyme. We engineered the DNAzyme strand with incorporation of a blocker strand to inhibit the DNAzyme activity. The blocker strand formed a duplex structure that prohibited the hybridization of the DNAzyme strand with the one arm of the substrate strand, leading to the formation of an inactive DNAzyme structure. In the presence of target miRNA, the hybridization between the target miRNA and the blocker strand would induce the breakage of the duplex, followed by the formation of the active DNAzyme. Thus, the activity of the DNAzyme biosensors could be switched from the OFF state into the ON state. Moreover, the nitrogen and sulfur codoped near-infrared emission carbon dots (NIR NS-CDs) were used as neoteric ECL emitters, which not only possessed an NIR ECL emission to reduce the photochemical damage but also had a low excitation potential range to avoid the side reaction. Therefore, by combining the DNAzyme modular engineering strategy and NIR NS-CDs as neoteric ECL emitters, the constructed ECL biosensor could realize the ultrasensitive analysis of miRNA-155 with an identification limit of 58.5 aM. This DNAzyme-guided NIR ECL emission of the neoteric CD strategy provides a sensitive and reliable method for miRNA detection, and it has great potential in clinical diagnosis.