Elegant biosensor based on magnetic beads and target-directed enzyme-free dual-amplification for the detection of miRNA-let-7a

Research on the use of microRNAs (miRNAs) for cancer diagnosis is a hot topic because miRNAs are a key indicator of gene expression and hopeful biomarkers. The high-performance detection of miRNAs in early disease diagnosis has attracted attention from the research community. Herein, we construct a robust fluorescence biosensor for miRNA-let-7a detection that uses an enzyme-free dual-signal amplification strategy that combines magnetic bead-combined entropy-driven catalysis (MB-EDC) and catalytic hairpin assembly (CHA). MB-EDC uses a multifunctional DNA probes of M1-MB that contain a three-stranded substrate M1 and magnetic beads. By using the EDC reaction and magnet recovery technology, the reversibility of target recirculation process is effectively reduced. When miRNA-let-7a is introduced, MB-EDC occurs, recirculating the target and eliminating the interference of other strands by using a magnet. The trigger released in the MB-EDC then activates the CHA reaction, giving rise to an amplified fluorescence signal. This isothermal enzyme-free MB-EDC and CHA scheme can provide double signal amplification for precise analysis of miRNA-let-7a. The biosensor system for miRNA-let-7a detection has a low detection limit of 8.3 pM. Moreover, it has high specificity and relatively good detection capabilities under challenging conditions. Therefore, this sensor can promote the exploration of miRNAs in cancer diagnostics.