Electrochemical detection of methylated DNA on a microfluidic chip with nanoelectrokinetic pre-concentration.

DNA methylation is considered to be a promising marker for the early diagnosis and prognosis of cancer. However, direct detection of the methylated DNAs in clinically relevant samples is still challenging because of its extremely low concentration (~fM). Here, an integrated microfluidic chip is reported, which is capable of pre-concentrating the methylated DNAs using ion concentration polarization (ICP) and electrochemically detecting the pre-concentrated DNAs on a single chip. The proposed chip is the first demonstration of an electrochemical detection of both level and concentration of the methylated DNAs by integrating a DNA pre-concentration unit without gene amplification. Using the proposed chip, 500 fM to 500 nM of methylated DNAs is pre-concentrated by almost 100-fold in 10 min, resulting in a drastic improvement of the electrochemical detection threshold down to the fM level. The proposed chip is able to measure not only the DNA concentration, but also the level of methylation using human urine sample by performing a consecutive electrochemical sensing on a chip. For clinical application, the level as well as the concentration of methylation of glutathione-S transferase-P1 (GSTP1) and EGF-containing fibulin-like extracellular matrix protein 1 (EFEMP1), which are known to be closely associated with prostate cancer diagnosis, are electrochemically detected in human urine spiked with these genes. The developed chip shows a limit of detection (LoD) of 7.9 pM for GSTP1 and 11.8 pM for EFEMP1 and is able to detect the level of methylation in a wide range from 10% to 100% with the concentration variation from 50 pM to 500 nM.