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Dynamics of DNA molecules in a cross-slot microchannel

The conformation and dynamics of double-stranded DNA molecules in cross-slots with equal arm length are examined with the use of fluorescent labeled λ-DNA at 1.2 ⩽ De ⩽ 4.1. The stretching and diffusing of individual DNA molecules in the flow was visualized/recorded with confocal laser scanning microscopy (CLSM). The onset of coil–stretch transition of DNA molecules in the elongational flow was determined at the microscale. Time-dependent velocity distribution with a mean velocity of 50 µm s−1 for DNA molecules was observed by using FluoSpheres, carboylate-modified microspheres over a time period of 1.12 s. The effect of channel geometry (corner and outlet regions) and the solution viscosity (1.9 cP and 9.5 cP) on the conformation and diffusion are also studied and discussed. We report the maximum and the distribution of the fractional extension of DNA molecules, and show that the maximum fractional extension may be up to 0.64 at De = 4.1, and at a strain of 1.8 there is a corresponding stretching force of about 200 pN.