Rolling circle amplification assisted CRISPR/Cas12a dual-cleavage photoelectrochemical biosensor for highly sensitive detection of miRNA-21

Background: MicroRNA-21 has been determined to be the only microRNA overexpressed in 11 types of solid tumors, making it an excellent candidate as a biomarker for disease diagnosis and therapy. Photoelectrochemical (PEC) biosensors have been widely used for quantification of microRNA-21. However, most PEC biosensing processes still suffer from some problems, such as the difficulty of avoiding the influence of interferents in complex matrices and the false-positive signals. There is a pressing need for establishing a sensitive and stable PEC method to detect microRNA-21.Results: Herein, a nicking endonuclease-mediated rolling circle amplification (RCA)-assisted CRISPR/Cas12a PEC biosensor was fabricated for ultrasensitive detection of microRNA-21. The p-p type heterojunction PbS QDs/ Co3O4 polyhedra were prepared as the quencher, thus the initial PEC signal attained the "off" state. Furthermore, the target was specifically identified and amplified by the RCA process. Then, its product single-stranded DNA S1 activated the cis-and trans-cleavage abilities of CRISPR/Cas12a, leading to almost all of the PbS QDs/Co3O4 polyhedra to leave the electrode surface, the p-n semiconductor quenching effect to be disrupted, and the signal achieving the "super-on" state. This pattern of PEC signal changed from "off" to "on" eliminated the interference of false-positive signals. The proposed PEC biosensor presented a satisfactory linear relationship ranging from 1 fM to 10 nM with a detection limit of 0.76 fM (3 Sb/N).Significance and novelty: With innovatively synthesized PbS QDs/Co3O4 polyhedra as the effective quencher for PEC signal, the CRISPR/Cas12a dual-cleavage PEC biosensor possessed excellent selectivity, stability and repeatability. Furthermore, the detection of various miRNAs can be realized by changing the relevant base sequences in the constructed PEC biosensor. It also provides a powerful strategy for early clinical diagnosis and biomedical research.