A Target-Feedback Rolling-Cleavage signal amplifier for ultrasensitive electrochemical detection of miRNA with Self-Assembled CeO₂@Ag hybrid nanoflowers

Currently, developing an effective and easy-to-operate signal amplification assay to detect the trace-amount miRNAs in serum remains a significant challenge. Herein, an ultrasensitive CeO2@Ag hybrid nanoflower (CeO2@Ag HNF)-labeled electrochemical biosensor was developed for sensing miRNA, based on a target -feedback rolling-cleavage (TFRC) signal amplifier. CeO2@Ag HNFs possessing a unique three-dimensional layered structure were synthesized without any complex reaction conditions, such as heating and vacuum. The bimetallic nanoflowers provided a large surface area and excellent CAT-like activity, thereby enhancing electrochemical performance. Based on the principle of branched catalytic hairpin assembly, target miRNA could continuously trigger the assembly of branched junctions with ends composed of DNAzyme. The activated DNAzyme was able to cleave the hairpin substrate efficiently and release to capture more CeO2@Ag HNFs label. The process combining target-driven branched catalytic hairpin assembly and DNAzyme-assisted rolling cleavage were defined as TFRC signal amplification. This sensitive electrochemical biosensor exhibited good linear relationship of 1 fM -1 nM with a detection limit down to 0.89 fM. The proposed method is expected to have a promising application in the miRNA-associated fundamental research and clinical diagnosis.