Target-Induced Payload Amplification for Spherical Nucleic Acid Enzyme (SNAzyme)-Catalyzed Electrochemiluminescence Detection of Circulating microRNAs.

A high level of circulating myocardial microRNAs (miRNAs) is commonly considered as one indicator of acute myocardial infarction (AMI) for early stage diagnosis, and hence, it is of particular significance to develop ultrasensitive methodologies for detecting these miRNAs in circulating blood. Here we build an electrochemiluminescence (ECL) sensing platform for circulating miRNAs utilizing AuNPs@G-quadruplex (G4) spherical nucleic acid enzyme (SNAzyme) as the nanocatalyst, which shows good stability, strong nuclease resistance, and improved catalytic performance toward a luminol-H2O2 ECL system than the commonly used G4 DNAzyme. Target miRNA is employed to open the probe hairpin DNA to trigger the cascade amplification and then produce a long dsDNA chain with many sticky linkers that capture the SNAzyme nanocatalyst onto the electrode. In this way, two AMI-related miRNAs are detected accurately. The detection limit is 0.4 fM (S/N = 3), and the platform shows high selectivity in circulating blood. Given the good controllability, our ECL biosensors are promising for developing clinical diagnostic platforms for multiple indicators.