Noncovalent Approach toward the Construction of Nanofluidic Diodes with pH-Reversible Rectifying Properties: Insights from Theory and Experiment

Gonzalo Pérez-Mitta,María Eugenia Toimil-Molares,Alberto Albesa,Facundo M Gilles,Omar Azzaroni,Christina Trautmann

doi:10.1021/acs.jpcc.7b01639

Abstract

In this paper, the fabrication of a biomimetic nanofluidic diode whose ionic transport characteristics can be completely modulated with the proton concentration in solution is demonstrated. The fabrication procedure involves the electrostatic assembly of poly(allylamine hydrochloride) (PAH) into a track-etched conical nanochannel. A fully reversible, zwitterionic-like behavior with important implications for the supramolecular interactions of the PAH within confined spaces was observed. The experimental design constitutes a facile venue for the fabrication of functional nanofluidic devices and paves the way for a number of applications in nanofluidics and biosensing. Furthermore, in order to explain the experimental results and to obtain physicochemical information about the system, theoretical modeling using a continuous model based on Poisson–Nernst–Planck equations and a stochastic model using Monte Carlo simulations were performed. Good agreement between experiments and theory was found.

Highlights

Nanofluidics is an important emerging field within nanosciences that promises interesting applications in materials science, engineering, and biomedical research among other disciplines.[1−4,4] The unique transport properties of solid-state nanocannels, which resemble several functional features of biological channels, such as ion selectivity and ionic-gating, has sparked the interest of “nanoscientists” worldwide and has increased their willingness to use these nanoarchitectures as nanofluidic elements.[5−7]Several approaches to the construction of artificial nanometric fluidic devices have been developed, from biological to fully abiotic designs,[8] each of them with particular advantages and disadvantages
We observed a monotonic increase in the rectification factor upon increasing the surface charge (Figure 1b), which confirms that a functional molecule that can finely modify its state of charge can transduce these changes into the direction and magnitude of the ionic transport
Poisson−Nernst−Planck equations were used to calculate the surface charge densities under different pH conditions, and Monte Carlo simulations were performed to study the relationship between the protonation degrees of the poly(allylamine hydrochloride) (PAH) layer and the ionizable surface groups on the nanochannel wall, and the solution pH

Summary

Introduction

Nanofluidics is an important emerging field within nanosciences that promises interesting applications in materials science, engineering, and biomedical research among other disciplines.[1−4,4] The unique transport properties of solid-state nanocannels, which resemble several functional features of biological channels, such as ion selectivity and ionic-gating, has sparked the interest of “nanoscientists” worldwide and has increased their willingness to use these nanoarchitectures as nanofluidic elements.[5−7]Several approaches to the construction of artificial nanometric fluidic devices have been developed, from biological to fully abiotic designs,[8] each of them with particular advantages and disadvantages. The focused ion beam technique demands that the thickness of the substrate that would contain the nanopore does not exceed few hundreds of nanometers.[9] In this regard, the track-etching method emerges as one of the most interesting procedures for obtaining abiotic nanochannels. For example, for typical condensation polymers such as polycarbonate or polyethylene terephthalate, the etching procedure consists of an alkaline hydrolysis using highly concentrated alkali solutions. This procedure allows the reproducible fabrication of nanoscale channels,[10] with tailored geometry (e.g., conical, cylindrical, biconical) and controlled diameter (>10 nm)

Methods

Results

Conclusion