Ultrasensitive electrochemical aptasensor based on palindromic sequence mediated bidirectional SDA and a DNAzyme walker for kanamycin detection

Abstract

Kanamycin residue has attracted much attention due to its potential risk to the environment and human health. Herein, an electrochemical platform with superior performance was proposed based on enzyme-assisted target recycling with a strand displacement amplification (SDA) reaction and a DNAzyme-derived DNA walker. Our sensing system consists of an SDA amplification system and a DNA walker system. In the DNA walker system, a DNAzyme walker (DW)–locking probe (LP) and signal hairpin (HP) were assembled on the surface of a gold electrode (AuE) through a gold sulfur bond (Au–S). The specific binding of kanamycin with its aptamer induced an enzyme-assisted SDA process, leading to the generation of output probes (OP) which can open the locked DW-LP. And then, in the presence of Mn²⁺, the unlocked DW walked along the HP on the electrode surface cutting the loop of HP, so that the HP was consumed to form a G-quadruplex (G4) in the presence of K⁺. G4/hemin has peroxidase-like activity and can catalyze the reduction of H₂O₂ to produce obvious electrical signals. Upon the optimization of the analytical conditions, the proposed biosensor showed a wide linear range from 100 fM–5 nM with a limit of detection (LOD) of 87.1 fM. In addition, the aptasensor also had good stability and specificity, showing good prospects in practical applications.