Diffusion of DNA in nanoslits

We observed the free diffusion of individual 10 kbp, (1/2)λ (24.2 kbp), and A (48.5 kbp) double-stranded deoxyribonucleic acid (DNA) molecules in fused-silica nanoslits with depths from 541 to 24 nm using epifluorescence video microscopy. Diffusivity, D, scaled with nanoslit depth, h, according to D ∝ h^α, where a was 0.47 ± 0.05, 0.51 ± 0.06, and 0.47 ± 0.05 for 10 kbp, (1/2)λ, and λ DNA, respectively, in disagreement with the value of two-thirds predicted by blob theory. We observed no change in scaling behavior for h less than the persistence length of DNA, as predicted by reflecting rod theory. The scaling of D with DNA length, N, followed D ∝ N^-1, indicating hydrodynamic screening in accordance with Rouse dynamics. Our results establish these scaling exponents for smaller h and greater DNA confinement than previous studies.