Label-free DNA methylation analysis using opto-fluidic ring resonators.

The opto-fluidic ring resonator (OFRR) is a sensitive label-free optical biosensor that is uniquely well suited for photonic and fluidic integration. For the first time we have explored the utility of this novel instrument for the analysis of methylation in oligonucleotides using the MBD-2 (methyl binding) protein as the capture molecule. This application has strong relevance to cancer research and future clinical tools through the study of methylation patterns in important gene promoters. In this work we quantitatively characterized the OFRR's response to artificially methylated ssDNA and dsDNA as a function of the number of methylated cytosines and DNA concentration. The effect of hemi- versus fully methylated oligonucleotides was also investigated. Additionally, anti 5-methylcytidine antibody was also used as the capture molecule and compared with MBD-2. It is found that the antibody has stronger affinity for ssDNA, whereas MBD-2 is much better at binding dsDNA.