Transport of Charged Species across Solid-State Nanopores
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Transport of Charged Species across Solid-State Nanopores 1
Daisy Fung 1, E. Akdemir 1, M.J. Vitarelli 2, Eugene Sosnov 1, Shaurya Prakash 1,3 Department of Mechanical and Aerospace Engineering, 2Department of Chemistry, 3Institute of Advanced Materials, Devices, and Nanotechnology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 U.S.A.
ABSTRACT Nanofluidic devices are finding growing interest for a variety of applications. An initial report is presented here on a wide range of parameters influencing transport of ionic species as they translocate across solid-state nanopores. AC electrical bias at low ionic concentration with overlapping electric double layers provides an enhancement of ionic flux over pure DC bias. Furthermore, results also indicate that concentration and pH gradients can be maintained across solid-state nanopores for extended periods of time that can last for several hours in the absence of driving forces such as electric fields. INTRODUCTION Nanofluidic systems have generated tremendous interest in recent times due to the promise of revolutionary new fluidic technologies for separations, proteomics, genomics, next generation lab-on-chip devices, and water purification. Given this broad scientific and technological interest, many new nanofluidic devices are being developed for a myriad of applications [1, 2]. Therefore, there is a need to enhance fundamental understanding of ionic transport in confined nanoscale systems to better engineer devices to meet the diverse array of challenges presented by nanofluidic devices including interfacial properties that influence confined fluid transport [1, 3], and changes in transport regimes as function of electric double layer (EDL) thickness [4]. In this paper, we present an initial report on a wide range of parameters influencing transport of ionic species as they translocate across solid-state nanopores. The nanopores used in this work are monodisperse, nuclear track etched membranes that have been classified as nanocapillary array membranes (NCAMs). The transport measurements are characterized by UV/VIS spectroscopy, bulk electrical conductivity measurements, and electrochemical impedance spectroscopy (EIS). This multi-technique characterization provides information on the influence of EDLs and applied electrical bias across NCAMs. EXPERIMENT In this work, nanocapillary array membranes (NCAMs) were used [4]. The nominal pore sizes vary from 10 to 800 nm; however, only 10 nm diameter pores were used in this report. The NCAM thickness is approximately 6 µm. The NCAMs are commercially available from GE Osmonics (MN, USA). All chemicals used are purchased from Sigma-Aldrich (MO, USA) and used without further purification. The experimental set-up consists of a traditional permeation cell (Fig. 1) with the NCAM separating two reservoirs [2]. The volume in each reservoir is 200 ml. In a typical experiment the electrolyte concentration, pH, and electrical bias across the nanopores are varied in a systematic manner. The electroly
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