Construction of a sensitive ratiometric electrochemical sensing platform for DNA methylation detection based on the design of multistep DNA amplification circuits

Methylated DNA is a promising epigenetic biomarker for diseases diagnosis, therapy monitoring, and prognosis. Here, we developed a sensitive ratiometric electrochemical biosensor for the detection of methylated DNA based on the design of multistep DNA amplification circuits. The methylated target DNA firstly initiates the DNAzyme-assisted amplification circuit and produces a number of single-stranded triggers that catalyze the subsequent double-step catalytic hairpin assembly circuits to release numerous four-way DNA junctions. The four-way DNA junctions displace the methylene blue (MB)-modified signal probes for intercalating doxorubicin (DOX) molecules on the sensing interface, resulting in a significantly increased value of iDOX/iMB to achieve sensitive monitoring of methylated DNA. Taking advantage of the significant signal amplification of multistep DNA amplification circuits, the proposed method exhibited high sensitivity for target analysis with a detection limit of 4 aM and a dynamic linear range of 10 aM to 20 pM. Moreover, the proof-of-concept application of the sensing platform was investigated, suggesting that the system is promising for potential applications in early cancer diagnosis and the fundamental research of epigenetics.