Planar intercalated copper (II) complex molecule as small molecule enzyme mimic combined with Fe3O4 nanozyme for bienzyme synergistic catalysis applied to the microRNA biosensor

Enzyme mimics have been developed for bioassay of nucleic acids, with some of them involving complicated labeling. Herein, we report a label-free bioassay for ultrasensitive electronic determination of microRNA at an ultralow concentration based on target-triggered long-range self-assembly DNA-based hybridization chain reaction (HCR) protocol coupled with bienzyme mimics synergistic catalysis strategy. In this work, a planar intercalation molecule, copper (II) complex, is applied for the first time as a small molecule enzyme mimic as well as intercalation molecule in microRNA biosensor for signal amplification. Fe3O4 nanozyme were used as a separate and enriched target under magnetic field, and also in combination with HCR protocol detected in 3,3',5,5'-tetramethylbenzidine + hydrogen peroxide (TMB + H2O2) system to improve the sensitivity of the biosensor. Under optimal conditions, these strategies present good electrochemical behaviors for the detection of microRNA with a wide range from 100 aM to 100 nM and at relatively low detection limit of 33 aM This remarkable sensitivity can make this proposed approach a promising scheme for development of next-generation microRNA sensors without the need of enzyme labeling or fluorophore labeling.