High-efficient Pt@COF nanospheres-based electrochemical-chemical-chemical redox cycling for ultrasensitive microRNAs biosensing

MicroRNAs (miRNAs) have been perceived as important regulators in multifarious biological processes as well as potential biomarkers in clinical diagnosis. Exploring high-efficient sensing platforms for tracing miRNAs in complex biological samples is of great vital. Herein, an ultrasensitive and enzyme-free electrochemical biosensor was constructed based on integration of efficiently catalytic electrochemical−chemical−chemical (ECC) redox cycling with target-induced magnetic DNAzyme walker. Employing porous and easily functionalized covalent organic framework (COF) as carriers, Pt@COF nanospheres (Pt@COF NSs) were facilely prepared by in-situ reduction of platinum precursors in the nanopores-structure of COF. This not only addressed the inevitable migration of pure Pt nanoparticles, but endowed Pt@COF NSs with desirable stability and excellent catalytic activity to boost ECC redox cycling for effective signal enhancement. On this basis, a target-induced magnetic DNAzyme walker was obediently induced to recognize, separate and convert low-abundant miRNA-21 targets into plentiful output DNA chains for accumulated signal amplification. Finally, the as-prepared robust biosensor manifested highly sensitive and selective determination of miRNA-21 with a wide detection range from 100 aM to 10 pM and a low detection limit of 47.5 aM. Meanwhile, the credible detectability and anti-interference were also demonstrated in serum and cell samples, indicating its promising application toward diseases warning.