Electrokinetically-driven transport of DNA through focused ion beam milled nanofluidic channels

The electrophoretically driven transport of double-stranded λ-phage DNA through focused ion beam (FIB) milled nanochannels is described. Nanochannels were fabricated having critical dimensions (width and depth) corresponding to 0.5×, 1×, and 2× the DNA persistence length, or 25 nm, 50 nm, and 100 nm, respectively. The threshold field strength required to drive transport, the threading mobility, and the transport mobility were measured as a function of nanochannel size. As the nanochannel dimensions decreased, the entropic barrier to translocation increased and transport became more constrained. Equilibrium models of confinement provide a framework in which to understand the observed trends, although the dynamic nature of the experiments resulted in significant deviations from theory. It was also demonstrated that the use of dynamic wall coatings for the purpose of electroosmotic flow suppression can have a significant impact on transport dynamics that may obfuscate entropic contributions. The nonintermittent DNA transport through the FIB milled nanochannels demonstrates that they are well suited for use in nanofluidic devices. We expect that an understanding of the dynamic transport properties reported here will facilitate the incorporation of FIB-milled nanochannels in devices for single molecule and ensemble analyses.