
%0 Journal Article
%A Zheng, Jinjian 
%A Yeung, Edward S. 
%T Counting Single DNA Molecules in a Capillary with Radial Focusing
%J Australian Journal of Chemistry
%D 2003/03/20
%V 56
%N 3
%P 149-153
%K 
%R https://doi.org/10.1071/CH02192
%U https://www.publish.csiro.au/paper/CH02192 
%X For single-molecule detection, usually a small detection volume of 10 pL or less is used to improve the signal-to-noise ratio. Detection of every molecule in a sample requires that the sample be driven through a well-defined volume to facilitate laser excitation. We report a novel approach to count single DNA molecules with nearly 100&#37; efficiency. By applying an electric field across a 40 cm long, 75 &#215; 75 &#181;m2 square capillary together with hydrodynamic flow from cathode to anode, we were able to concentrate more than 95&#37; of DNA molecules into a 10 &#181;m region at the centre of the capillary. The YOYO-1 labelled &#955;-DNA molecules were imaged with an intensified CCD camera. We found that the single DNA molecule detection efficiency in a 10&#8211;17 M solution was 114 &#177; 21&#37;. The mobility of the DNA molecules after radial focusing was relatively constant, with relative standard deviations ranging from 0.8&#37; to 1.4&#37;. This allowed us to match the sampling rate to the length of the detection window to maximize counting efficiency. Analysis of a 40.2 nL injected plug of 2 &#215; 10&#8211;14 M &#955;-DNA gave a result of 492 &#177; 73 molecules, which agreed well with the estimated value of 484. This method should be generally useful for counting deformable molecules or non-spherical particles at extremely low concentrations. 
