(6a) Stochastic Resonance Enhances DNA Transport In the Entropic Trapping Regime

Recent interest in entropic trapping (ET) phenomena in nanoporous hydrogels has been excited by their potential to enable enhanced electrophoretic separations of charged biomolecules (e.g., DNA, proteins). For example, an unexpected trend of increasing separation resolution with DNA size has been observed in microchip-based electrophoresis experiments under ET-dominated conditions. But despite this great promise, it has proven challenging to apply these novel effects in practical settings due to lingering problems associated with inherently high diffusion relative to conventional reptation-based transport. Here we show how both the source and solution to this problem are intimately linked to the activated nature of the entropic trapping process. Under a continuous electric field, DNA transport between neighboring pores becomes increasingly uncorrelated over time, leading to undesirable diffusion enhancement. We have found that this condition can be overcome by applying a pulsed electric field at a frequency chosen to match the system's activation events, creating a stochastic resonance effect that can be exploited to significantly improve separation resolution in the entropic trapping regime. The underlying transport principle and effect of decreasing diffusion are demonstrated by our physical model.