Entropic trapping constitutes a novel scheme for separating various length strands of DNA using microfluidic chips etched to periodically varying depths. Deep portions of the chip, acting as entropic traps in a chain-length dependent manner, hinder DNA solute transport occurring under the influence of an externally-applied electric field. Together with knowledge of the average solute holdup time and device connectivity, as well as a lumped-parameter trap-scale (local) DNA transport model, generalized Taylor-Aris dispersion (macrotransport) theory for spatially periodic networks is employed to derive analytical expressions for a trio of chip-scale (global) transport process parameters, namely the solute dispersivity, number of theoretical plates, and separatin resolution. These expresions are shown to furnish results that accord, at least qualitatively, with both experimental trends and data reported in the literature. In conjunction with simple macroscale experiments suggested by the theory, this coarse-grained model furnishes a paradigm for exploring the microscale phenomenon of entropic trapping in the context of the rational design of such devices.
Bibliographical noteFunding Information:
This work was partially supported by a Graduate Research Fellow ship from the National Science Foundation to KDD and an unrestricted grant from Eli Lilly and Company to HB to encourage microfluidic research. We are grateful to Sangtae Kim of the latter organization for his interest in our microfluidic analyzes, and to Prof. Martin Z. Bazant of MIT for calling our attention to the existence of anomalous diffusion results.
- Taylor dispersion