DNA configurations and concentration in shearing flow near a glass surface in a microchannel

We characterize the configurations and concentration of X-phage deoxyribose nucleic acid (DNA) molecules in shear flow near a glass surface in a microchannel through epifluorescence microscopy. We observe that in Poiseuille flow, over a region extending from a glass surface up to about one third of the contour length of the DNA molecule, the average stretch of a X-phage DNA molecule is significantly lower than in the bulk, in agreement with results obtained in a steady torsional shear flow by Li et al. (2004). We also find that the concentration of DNA molecules in this same region is notably lower than in the bulk, to a degree that increases with increasing Weissenberg number. A simplified explanation is proposed for the behavior of DNA molecules near the glass surface based on wall influences on hydrodynamic interaction within the chain, motivated by the recent theoretical work of Jendrejack et al. (2003, 2004). (C) 2005 The Society of Rheology.