Ionic and Biomolecular Transport in Nanochannels

Abstract

In this work, both steady and transient ionic and biomolecular transport in nanochannels is considered. Electroosmotic flow (EOF) has been analyzed for both steady and transient two and three ionic components in a nanochannel. The sudden introduction of a species at the inlet of a channel generates a short transient regime followed by fully developed and steady-state EOF in which the concentrations, potential, and velocity are independent of the streamwise coordinate. The flux of any species is composed of Fickian diffusion, electrophoresis, and bulk convection and the mutual balance between these driving forces determines the direction of the movement of the species as well as its transit time. In a channel with negatively charged walls and the cathode on the upstream side, a negatively charged species may move in a direction opposite to the direction of bulk fluid flow. A positively charged species is transported in the direction of fluid flow and there is a significant decrease in transit time as compared to an uncharged or negatively charged species. Results for concentration and species flux are presented for both charged and uncharged species. The steady-state model is compared with a number of experimental results and the comparisons are extremely good.

KEY WORDS:

• fluid mechanics
• electroosmosis
• mass transfer
• electrical double layer

The work described herein was partially funded by DARPA under agreement number F30602‐00‐2‐0613. The authors are grateful to the contract monitors Dr. Anantha Krishnan (DARPA), Clare Thiem, and Duane Gilmour of Air Force Research Lab (IFTC) for their support. Partial support of this work from the National Science Foundation Nanoscale Science and Engineering Center, Center for the Affordable Nanoengineering of Polymeric Biomedical Devices, program monitor Bruce Kramer is gratefully acknowledged. The authors are also grateful to NSF Chemical and Thermal Systems Division and Dr. Mike Plesniak for their support of portions of this work. ATC is grateful for the help from his other graduate students who are doing work related to what is presented here: Lei Chen, Prashanth Ramesh, and Pradeep Gnanaprakasam. In particular, Lei Chen read the manuscript and suggested many changes that have improved the paper.

Notes

13. J.M. Ramsey, Private communication, Oak Ridge National Laboratory, May 15, 2002.