High-throughput flow cytometric DNA fragment sizing.

The rate of detection and sizing of individual fluorescently labeled DNA fragments in conventional single-molecule flow cytometry (SMFC) is limited by optical saturation, photon-counting statistics, and fragment overlap to approximately 100 fragments/s. We have increased the detection rate for DNA fragment sizing in SMFC to approximately 2000 fragments/s by parallel imaging of the fluorescence from individual DNA molecules, stained with a fluorescent intercalating dye, as they passed through a planar sheet of excitation laser light, resulting in order of magnitude improvements in the measurement speed and the sample throughput compared to conventional SMFC. Fluorescence bursts were measured from a fM solution of DNA fragments ranging in size from 7 to 154 kilobase pairs. A data acquisition time of only a few seconds was sufficient to determine the DNA fragment size distribution. A linear relationship between the number of detected photons per burst and the DNA fragment size was confirmed. Application of this parallel fluorescence imaging method will lead to improvements in the speed, throughput, and sensitivity of other types of flow-based analyses involving the study of single molecules, chromosomes, cells, etc.