Rapid bacteria electrochemical sensor based on cascade amplification of 3D DNA walking machine and toehold-mediated strand displacement

The foodborne pathogens have caused many life-threatening diseases. Herein, a new electrochemical platform was developed for detection, using 3D walking machine and enzyme-free toehold-mediated strand displacement. High-variable region of 16S rDNA fragment of Escherichia coli (E. coli) was used as the target to verify the approach. In presence of target, Exonuclease III (Exo III)-powered hairpin-loaded Au nanoparticles (hpDNA@AuNPs) was aroused, which emerged large amounts of 3D toehold-loaded AuNPs (toehold@AuNPs) walking machine. The "legs " of the walking machine hybridized with hairpin2 (HP2) tracks probe modified on surface of electrode and exposed toehold region of HP2 probe. The toehold-mediated strand displacement triggered rolling of AuNPs along the electrode, through the interaction of hairpin3-F-c (HP3-F-c ) probe with toehold region of HP2 probe. Thus large amounts of F(c )were closed to the electrode and led to significant current responses for E. coli detection. The method could continuously recycle low-concentration targets. Furthermore, due to the increase of "legs " and decrease of the derailment of leg DNA, which was beneficial to shorten detection time and amplify response. The detection limits (LOD) was 20 CFU/mL, the detection time was less than 1.5 h. This method was promising to be applied in early diagnosis of foodborne pathogen.