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Quantification of Low Concentrations of DNA Using Single Molecule Detection and Velocity Measurement in a Microchannel
Authors:Shu-Yi Chao  Yi-Ping Ho  Vasudev J Bailey  Tza-Huei Wang
Institution:(1) Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA;(2) Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA;(3) Whitaker Biomedical Engineering Institute, The Johns Hopkins University, Baltimore, MD 21218, USA;(4) The Johns Hopkins School of Medicine, The Johns Hopkins University, Baltimore, MD 21218, USA
Abstract:We present a novel method for quantifying low concentrations of DNA based on single molecule detection (SMD) for molecular counting and flow measurements inside a microchannel. A custom confocal fluorescence spectroscopic system is implemented to detect fluorescent bursts emitted from stained DNA molecules. Measurements are made one molecule at a time as they flow through a femtoliter-sized laser focal probe. Durations of single molecule fluorescent bursts, which are found to be strongly related to the molecular transit times through the detection region, are statistically analyzed to determine the in situ flow speed and subsequently the sample volume flowing through the focal probe. Therefore, the absolute concentration of a DNA sample can be quantified based on the single molecule fluorescent counts from the DNA molecules and the associated probe volume for a measured time course. To validate this method for quantifying low concentrations of biomolecules, we tested samples of pBR322 DNA ranging from 1 pM to 10 fM (∼3 ng/ml to 30 pg/ml). Besides molecular quantification, we also demonstrate this method to be a precise and non-invasive way for flow profiling within a microchannel.
Keywords:Single molecule detection  DNA quantification  Flow profiling  Microchannel
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