(398af) Diffusiophoresis of a Charged Sphere in a Necked Nanopore

In an attempt to improve the performance of single-molecule nanopore based biosensors, we study theoretically the diffusiophoresis of a particle along the axis of a charged, necked nanopore, and the mechanisms involved. Numerical simulation is conducted by varying the geometry of the nanopore and its charged status, the particle position, and the background salt concentration to examine the particle behavior under various conditions, and to gather necessary information for future device design. We show that the strength of the local concentration gradient, the charge density of the nanopore, and the presence of the nanopore wall yield complicated and interesting diffusiophoretic behaviors. For instance, if both the particle and the nanopore are negatively charged, the particle mobility decreases monotonically as it approaches the throat region, shows a local minimum in its throat region, and a local maximum in the outlet region. In the inlet and outlet regions of the nanopore, if the nanopore is negatively (positively) charged, the mobility is larger (smaller) than that if it is uncharged. These arise from the effect of ion concentration polarization. In nanopore based DNA sequencing, raising the DNA capture rate by the nanpore and reducing its translocation velocity inside the nanopore are crucial challenging problems. These problems can at least be partially solved by adopting our design.