Robust noncovalent spherical nucleic acid enzymes (SNAzymes) for ultrasensitive unamplified electrochemiluminescence detection of endogenous myocardial MicroRNAs.

Here we develop robust noncovalent spherical nucleic acid enzymes (SNAzymes) for direct electrochemiluminescence (ECL) detection of acute myocardial infarction (AMI) related endogenous microRNAs in both circulating blood and cardiomyocytes, which circumvents the need for time-consuming signal amplification widely used in previous counterparts. It mainly relies on the super peroxidase-like activity of the designed noncovalent SNAzymes, promoted by a few nucleotides flanking on the 3'-terminals of common parallel G-quadruplexes (G4). For this reason, an unmodified G4 with an A5T30 head is well chosen and then attached robustly onto bare AuNPs via microwave-assisted heating-drying. A probe strand is meanwhile attached onto SNAzymes, enabling the target microRNA-triggered formation of a Y-shaped junction together with a capture strand tethered to a DNA tetrahedron on the electrode surface. The utilization of this tetrahedral nanoscaffold favors the ECL readout and thereby contributes to high sensitivity of the sensing platform. In this way, an AMI-related microRNA, miR-499, can be probed in a wide linear range, with a detection limit of 33 aM and high selectivity over other analogues. Furthermore, our developed sensing platform is employed to analyze endogenous miR-499 in AMI patients' blood, revealing an apparently higher level than the mean value of the healthy. What it means to patients, heart injury, is elucidated by comparing the miR-499 levels of cardiomyocytes and other tissue cells, with endogenous miR-16 as an intrinsic reference.