An enzyme-free electrochemical biosensor combining target recycling with FeO/CeO@Au nanocatalysts for microRNA-21 detection.

In this study, an electrochemical biosensor was proposed for microRNA-21 detection based on FeO/CeO @Au magnetite nanoparticles (FeO/CeO @Au MNPs) as nanocatalyst and catalytic hairpin assembly (CHA) for signal application. Firstly, target microRNA-21 hybridized with hairpin H to form H-T duplex stranded DNA (dsDNA), which could further open the hairpin H for the formation of H-H dsDNA. Simultaneously, the FeO/CeO @Au-S not only hybridized with single stranded fragment of H-H dsDNA with producing long dsDNA to absorb a large amount of electroactive substances of methylene blue (MB), but also acted as nanocatalyst to directly catalyze the reduction of MB for amplifying the electrochemical signal. Herein, compared with pure FeO nanoparticles, FeO/CeO @Au MNPs exhibited excellent catalytic performance since the cerium oxide (CeO) nanoparticles and Au nanoparticles can greatly improve the catalytic activity of FeO nanoparticles and effectively prevent the agglomeration of FeO nanoparticles. Owing to the signal amplification strategy, the proposed biosensor provided a wide linear range of 1 fM to 1 nM with a low detection limit of 0.33 fM (defined as S/N = 3) for microRNA-21 detection, and exhibited excellent specificity and sensitivity. This strategy provided a novel avenue for the detection of other biomarkers in electrochemical biosensors.