(618a) Label-Free Analysis of DNA Methylation Using an Optical Resonator

We report a highly specific and sensitive optical biosensor capable of detecting methylated DNA at picomolar levels.  5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) are epigenetic markers involved in gene regulation, cell differentiation, and development.  Several techniques have been used to identify and quantify epigenetic markers but many of these techniques are unable to clearly distinguish between 5-methylcytosine and 5-hydroxymethycytosine.  Therefore, we immobilized antibodies specific for methylated cytosine and hydroxymethylated cytosine to our resonator microtoroid devices by an epoxy silane which forms a covalent link between the epoxide ring and an amine group on the antibody. This allows for a coupling system that is stable in a buffered saline solution and does not compromise the ability of the resonator. Our functionalized devices are able to differentiate between cytosine, 5-mC, and 5-hmC, offering single nucleotide resolution. The data presented here show that microtoroid resonators can be used in biomedical research and are capable of providing quantitative analysis of DNA methylation in real time.