| The mobility and partition coefficient are two important properties of DNA molecules that have been the subject of many theoretical and experimental investigations. They attract special interest because both of them are length dependent in confined environments, which indicates a useful method for size-based DNA separations. We studied the mobility and partition coefficient of DNA molecules in fused silica nano-fluidic devices experimentally. To study the mobility, DNA molecules were driven through a nano-fluidic device containing a periodic array of deep and shallow regions (entropic traps) by an electric field. Consistent with previous experimental results, a nonlinear relationship between the mobility and electric field strength was observed, and that longer DNA molecules have higher mobility. Fluctuations in the mobility significantly larger than those expected from statistical variation in repeated measurements under seemingly identical conditions were also observed. The variation was more pronounced at lower electric field strengths where the trapping time is considerable relative to the drift time. We investigated the dependence of the mobility on several variables to determine the origin of these fluctuations. DNA Partitioning happens when there is chemical potential difference between molecules in different regions of different size, because the entropy is different in each region. The chemical potential in each region is equal at equilibrium leads to a concentration difference. The partition coefficient K is equal to the ratio of equilibrium concentration of two different regions. We use fused silica nano-slits with regions of different depths to study the partitioning of -DNA molecules. Images of -DNA molecules throughout the nano-slits were taken with a CCD camera at varying time intervals. We count the total number of DNA molecules in each region with custom software. The partitioning appears to follow a different trend from a previous experimental study. |
