High-resolution electrophoretic separation and integrated-waveguide excitation of fluorescent DNA molecules in a lab on a chip.

By applying integrated-waveguide laser excitation to an optofluidic chip, fluorescently labeled DNA molecules of 12 or 17 different sizes are separated by CE with high operating speed and low sample consumption of approximately 600 pL. When detecting the fluorescence signals of migrating DNA molecules with a PMT, the LOD is as low as 2.1 pM. In the diagnostically relevant size range (approximately 150-1000 base-pairs) the molecules are separated with reproducibly high sizing accuracy (> 99%) and the plug broadening follows Poissonian statistics. Variation of the power dependence of migration time on base-pair size--probably with temperature and condition of the sieving gel matrix--indicates that the capillary migration cannot be described by a simple physical law. Integrated-waveguide excitation of a 12-microm narrow microfluidic segment provides a spatio-temporal resolution that would, in principle, allow for a 20-fold better accuracy than the currently supported by state-of-the-art electrophoretic separation in microchips, thereby demonstrating the potential of this integrated optical approach to fulfill the resolution demands of future electrophoretic microchips.