From Ion Current to Electroosmotic Flow Rectification in Asymmetric Nanopore Membranes.

Juliette Experton,Xiaojian Wu,Charles Martin

doi:10.3390/nano7120445

Abstract

Asymmetrically shaped nanopores have been shown to rectify the ionic current flowing through pores in a fashion similar to a p-n junction in a solid-state diode. Such asymmetric nanopores include conical pores in polymeric membranes and pyramidal pores in mica membranes. We review here both theoretical and experimental aspects of this ion current rectification phenomenon. A simple intuitive model for rectification, stemming from previously published more quantitative models, is discussed. We also review experimental results on controlling the extent and sign of rectification. It was shown that ion current rectification produces a related rectification of electroosmotic flow (EOF) through asymmetric pore membranes. We review results that show how to measure and modulate this EOF rectification phenomenon. Finally, EOF rectification led to the development of an electroosmotic pump that works under alternating current (AC), as opposed to the currently available direct current EOF pumps. Experimental results on AC EOF rectification are reviewed, and advantages of using AC to drive EOF are discussed.

Highlights

Nanofluidics involves the study and control of the transport of fluids through spatially confined nanostructures, such as nanopores [1,2,3]
The frequency range used for the electroosmotic flow (EOF) rate experiments (Figure 13a) was different than for the rac case (Figure 13b)
As discussed in the original paper [33], gas evolution at the electrodes was observed at frequencies below about 20 Hz, and in the EOF studies, the gas bubbles generated interfered with the measurement of the flow rate

Summary

Introduction

Nanofluidics involves the study and control of the transport of fluids through spatially confined nanostructures, such as nanopores [1,2,3] Inside these nanostructures, the physical constraints due to charge, chemistry, or roughness of the surface can affect the behavior of the fluid [4]. We will focus on two nanofluidic rectification effects: ion current rectification (ICR) [13] and electroosmotic flow rectification (EFR) [14] Both phenomena are observed when an electrolyte solution is confined in asymmetrically shaped nanopores within a film or membrane.

Electroosmotic Flow Rectification in Asymmetric Pores

Alternating Current Electroosmotic Flow Pump

Conclusions