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 ~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 (~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-µm 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.