Direct observation of single native DNA molecules in a microchannel by differential interference contrast microscopy

Direct observation of single native DNA molecules in a microchannel was monitored without fluorescence-dye labeling. At a PDMS/glass microchip, the image of individual lambda-DNA molecules appear sharp and distinct in Nomarski differential interference contrast microscopy. Intercalator dyes affected the physical properties and dynamic behavior of individual DNA molecules. From the migration velocities in the microchannel it is evident that native DNA molecules migrated faster than DNA molecules labeled with the intercalator YOYO-1. This is because YOYO-1 increases the molecular weight and size of lambda-DNA and decreases the charge. The electric field strength and pH also affected the dynamics of single DNA molecules. We also observed that YOYO-labeled DNA was more stretched out compared to native DNA.