In Situ Reduction of Gold Nanoparticle-Decorated Ti3C2 MXene for Ultrasensitive Electrochemical Detection of MicroRNA-21 with a Cascaded Signal Amplification Strategy

Sensitive detection of miRNA-21 provides remarkable results for the diagnosis of early breast cancer. Here, we fabricated a novel electrochemical biosensor for the ultrasensitive detection of miRNA-21 via in situ reduction of gold nanoparticles (AuNPs)-decorated Ti3C2 MXene, combined with a cascaded signal amplification strategy, that is, strand displacement of DNA walker-induced multi-DNA (product DNA) release and cyclic enzymatic signal amplification. First, in situ reduction of AuNPs on a Ti3C2 MXene layer was not only used as a carrier of capture DNA (C-DNA) and a way to make DNA hybridization accessible but also to provide a predominant (111) facet with high electrocatalytic activity of AuNPs that significantly ameliorated the electrochemical signal, in which MXene acted as both reductant and stabilizer. In addition, in the presence of miRNA-21, multi-DNA fragments (p-DNA) that were produced by strand displacement of the DNA walker could be captured by C-DNA on the fabricated biosensor and trigger Exo III cyclic digestion for further amplification of electrochemical signals. By cascaded signal amplification, the changes in peak signal currents (Delta I) using differential pulse voltammetry were amplified. Under optimal conditions, the electrochemical biosensor achieved a detection limit of 50 aM (S/N = 3) with a linear range from 100 aM to 1.0 nM. With its excellent analytical performance, this biosensor may have the potential to be used in early diagnosis and biomedical applications.