▎ 摘　　要

The detection of microRNA is widely used in the early diagnosis of diseases such as cancer and acute kidney injury. In this work, we successfully constructed a label-free ultrasensitive biosensor for the instant detection of miRNA-21. The MXene-reduced graphene oxide (rGO)-Au was synthesized as electrode materials to immobilize DNA probes and MXene-AuPd was used as signal amplification materials. The highly sensitive biosensor had a wide range of linearity from 1 fM to 1 nM, and the limit of detection of as-fabricated biosensor was lower as 0.42 fM under optimized conditions. The biosensor also showed high specificity, outstanding stability and desirable reproducibility, which could also realize the accurate detection of miRNA-21 in real urine samples of both mouse and human with high sensitivity. The label-free electrochemical biosensor based on MXene nanocomposites is a promising candidate for potential applications on the early diagnosis of cancers and acute kidney injury.