An electrochemical biosensor based on AuNPs/Ti3C2 MXene three-dimensional nanocomposite for microRNA-155 detection by exonuclease III-aided cascade target recycling

A novel electrochemical biosensor based on AuNPs/Ti3C2 MXene three-dimensional nanocomposite for sensitive miRNA-155 detection by exonuclease III (Exo III)-aided cascade target recycling is reported. Ti3C2 MXene is synthesized and used as a support to immobilize Au nanoparticles (AuNPs) due to its special layered structure and metallic properties. The three-dimensional (3D) structure of the AuNPs/Ti3C2 MXene nanocomposite for the biosensor platform leverages the integrated advantages of a large specific surface area, excellent electrical conductivity and electrocatalytic properties. AuNPs are used to immobilize capture DNA (C-DNA) by AuS chemical bonds. The C-DNA was modified with methylene blue (MB) at the 3 ' end, resulting in an initial DPV electrochemical signal (Id). In the presence of target, miRNA-155 and C-DNA formed a double-stranded structure by complementary base pairing. Subsequently, Exo III digested the 3 ' end of the C-DNA in the double-stranded structure and caused the electrochemical signal to turn off (the final signal denoted as Ih). By Exo III-aided cascade cleavage of the target, one miRNA-155 chain causes the release of several C-DNAs under certain conditions, which significantly amplifies the peak current difference on the fabricated biosensor (Delta I = Id-Ih). The electrochemical sensor achieved a detection limit of 0.35 f. (S/N = 3) with a linear range from 1.0 f. to 10 nM. This sensor also shows desirable stability, reproducibility and specificity.