Photocurrent response after enzymatic treatment of DNA duplexes immobilized on gold electrodes: electrochemical discrimination of 5-methylcytosine modification in DNA.

We demonstrate a photoelectrochemical approach to the detection of the methylation status of cytosine bases in DNA. We prepared anthraquinone (AQ) photosensitizer-tethered oligodeoxynucleotide (ODN) duplexes bearing 5-methylcytosine (mC) or the corresponding cytosine (C) at a restriction site of the ODN strand immobilized on gold electrodes, and measured their photocurrent responses arising from hole transport after enzymatic digestion. Treatment with HapII or HhaI of the duplexes bearing normal C led to strand cleavage, and the photosensitizer unit was eliminated from the ODN strand immobilized on the gold electrode, exclusively reducing the photocurrent density. With a similar treatment, the duplexes bearing mC showed higher photocurrent responses arising from hole transport through the duplex. This significant difference in the photocurrent response between mC and normal C residues in DNA on the gold electrodes is potentially applicable to the detection of mC modification in DNA.