A FEN 1-assisted swing arm DNA walker for electrochemical detection of ctDNA by target recycling cascade...

A flap endonuclease 1 (FEN 1)-assisted swing arm DNA walker was constructed to achieve the signal amplification detection of ctDNA. The MB-labeled hairpin DNA was designed as the track and a long swing-arm DNA strand as the capture probe. The introduction of ctDNA unlocked a helper hairpin DNA, which could be captured to form the DNA duplex walker with the capture probe, and also activated the catalyst hairpin assembly. The DNA duplex walker opened the hairpin track and formed a three-base overlapping DNA structure, which was recognized and cleaved by FEN 1. Driven by the FEN 1 and the high reaction temperature, the DNA walker was initiated to hybridize with the track DNA and release multiple MB-labeled flaps for signal amplification. Owing to the excellent amplification capacity of the target recycling-induced DNA walker and programmed catalysis hairpin assembly, the one-step biosensor showed a linear detection range from 1 fM to 100 pM with a detection limit of 0.33 fM. Moreover, the sensitive detection of ctDNA in serum samples was verified, suggesting its potential application in liquid biopsy for clinical diagnosis.