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We observed reptation of single DNA molecules in fused silica nanoslits of sub-30 nm height. The reptation behavior and the effect of confinement are quantitatively characterized using orientation correlation and transverse fluctuation analysis. We show tube-like polymer motion arises for a tense polymer under strong quasi-2D confinement and interaction with surface- passivating polyvinylpyrrolidone (PVP) molecules in nanoslits, while etching- induced device surface roughness, chip bonding materials and DNA-intercalated dye-surface interaction, play minor roles. These findings have strong implications for the effect of surface modification in nanofluidic systems with potential applications for single molecule DNA analysis., Comment: 22 pages. 4 figures

The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles sub jected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in the experiments of Duhr, et al[1]. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimental value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal fluctuations-fluid momentum flux coupling induces a gradient in the stress which leads to thermal migration in both systems., Comment: 6 pages, 5 figues