Accurate Electrochemistry Analysis of Circulating Methylated DNA from Clinical Plasma Based on Paired-End Tagging and Amplifications.

Circulating methylated DNA has been a new kind of cancer biomarker, yet its small fraction of trace total DNA from clinical samples impairs the accurate analysis. Though fluorescence methods based on quantitative methylation specific PCR (qMSP) have been adopted routinely, yet alternative electrochemistry assay of such DNA from clinical samples remains a great challenge. Herein, we report accurate electrochemistry analysis of circulating methylated DNA from clinical plasma samples based on a paired-end tagging and amplifications strategy. Two DNA primers each labeled with digoxigenin (Dig) and biotin are designed for the recognition and amplification of methylated DNA. Paired-end tagging amplicons and avidin-HRP molecules are successively captured on the electrode modified with Anti-Dig. Then HRP executes catalytic reaction to generate amplified signal. The design of paired-end tagging can readily integrate downstream electrochemical amplified reaction, and two heterogeneous amplifications enable high assay sensitivity. As little as 40 pg of methylated genomic DNA (∼10 genomic equivalents) is well identified, and our strategy can even distinguish as low as 1% methylation level. Tumor-specific methylated DNA is clearly detected in the plasma of 10 of 11 NSCLC patients. The high clinical sensitivity of 91% (10/11) indicates the good consistency with clinical diagnosis. Excellent spatial control of electrochemistry allows simpler detection of more methylation patterns compared to fluorescence methods. The developed electrochemical assay is a promising liquid biopsy tool for the analysis of tumor-specific circulating DNA.