DNA molecular configurations in an evaporating droplet near a glass surface

We report an experimental and computational investigation of lambda-phage DNA molecules that stretch and orient in an evaporating droplet resting on an adsorbing 3-aminopropyltriethoxysilane (APTES)-coated surface, which has potential applications for high-throughput gene analysis [J. Jing et al., Proc. Nat. Acad. Sci. USA 95, 8046-8051 (1999)]. Using Brownian dynamics simulations and the microscopic flow field from a lubrication analysis, we predict that the degree of stretch obtainable by this method is substantially less than can be obtained by deposition from a simple uniform shear flow. This prediction is confirmed by detailed comparisons of the degree of stretch, orientation, and molecular configurations measured directly on DNA molecules deposited onto an APTES-coated surface. Statistical analysis reveals that the inefficiency of stretching in the drying droplet results from the presence of a velocity component normal to the surface, which reduces the time available for the chain to unravel sequentially as it adsorbs to the surface. (C) 2003 The Society of Rheology.