Electrochemical Detection of DNA Methylation and Application to Breast Cancer Screening

Epigenetic changes, specifically an increase of DNA methylation at site specific regions, have been shown to correlate with around 80% of all cancers (Stratton et al., 2009). Traditionally, DNA methylation changes are detected using bisulphate treatment and methylation specific PCR. However, this technique is labor intensive, non-portable and does not facilitate efficient disease detection. The creation of a point-of-care electrochemical test would be both cost effective and clinically applicable. Using the eMethylsorb technique (Koo et al., 2014), disrupted covalent methyl modification of DNA was measured at a promoter region of a known breast cancer gene. The eMethylsorb technique takes advantage of nucleotides’ differing affinities to gold. Post treatment unmethylated samples have a higher adenine composition compared to methylated samples. Adenine has the highest affinity to gold among nucleotides, and therefore, results in greater gold surface adsorption and a corresponding decrease in reactivity.  The latter can be analyzed by measuring electrochemical redox reactions at the gold surface. To improve upon the eMethylsorb method, electrical impedance spectroscopy (EIS) was used to analyze surface changes at a stationary disc electrode and a rotating disc electrode (RDE). It was believed EIS would be a better method than cyclic voltammetry (CV) and differential pulse voltammetry (DPV) because EIS directly measures the charge transfer resistance whereas CV and DPV do so via an indirect manner. Previous publications have demonstrated EIS as an invaluable tool in the analysis of electrode surfaces and diffusive properties. EIS measures the signal response of a cell when an alternating current is applied at a specific frequency. The output, Nyquist plot, is plotted in terms of imaginary impedance. Stationary disc electrodes were found to produce unreliable results due to diffusive inconsistencies. Using the RDE, more reliable differences were found among the methylated and unmethylated samples. With a focus on controlling diffusion and maintaining a consistent electrode surface, the EIS method combined with RDE was found to be more repeatable when compared to previously published methods.  

Koo, K.M., Ibn Sina, A.A., Carrascosa, L.G., Shiddiky, M.J. a., & Trau, M. (2014). eMethylsorb: rapid quantification of DNA methylation in cancer cells on screen-printed gold electrodes. Analyst 139, 6178–6184. 

Stratton, M.R., Campbell, P.J., & Futreal, P.A. (2009). The cancer genome. Nature 458, 719–724.

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