Concentration of DNA in a flowing stream for high-sensitivity capillary electrophoresis

A novel sample pretreatment device is described, and its application to the concentration and purification of crude DNA samples in a flowing stream for subsequent capillary electrophoresis is demonstrated. The device consists of two gap junctions, each covered with a conductive membrane material and built upon a flow channel made of PEEK tubing. Upon the application of an electric field between the junctions, the negatively charged DNA fragments can resist the hydrodynamic flow stream and are trapped between the junctions. DNA fragments dissolved in microliter volumes are captured in a nanoliter-sized band by simply pushing the sample solution through the device. Depending on their electrophoretic mobility, other interfering materials in a crude sample can be removed from the trapped DNA fragments by washing. The selective permeability of the membrane to small ions allows efficient desalting. The concentrated and purified DNA fragments are released by simply turning off or reversing the electric field. Recovery is up to 95%. Performance of the device was evaluated using crude products of fluorescent dye-primer cycle-sequencing reactions. Compared to these crude reaction products, samples purified in the capture device and subsequently collected showed dramatically enhanced signal and resolution when run on a conventional capillary-electrophoresis instrument. Furthermore, the device could be connected in-line to a capillary system for direct injection. The device has great potential for enabling lab-on-a-chip systems to be used with real-world samples.