Electrochemical behaviour and voltammetric sensitivity at arrays of nanoscale interfaces between immiscible liquids

Abstract

Arrays of nanoscale interfaces between immiscible electrolyte solutions were formed using silicon nitride nanopore array membranes. Nanopores in the range from 75 nm radius down to 17 nm radius were used to form the nano-interfaces. It was found that the liquid organic phase electrolyte solution filled the pores so that inlaid nano-interfaces were formed with the aqueous phase. Cyclic voltammetry at these nano-interface arrays demonstrated steady-state behaviour at the larger interfaces but the voltammetric wave-shape became progressively worse as the interface size decreased. It was found that the ion transfer currents were ca. 50% of those expected based on theoretical calculations, which is attributed to overlap of diffusion zones at adjacent nano-interfaces. Here, the separation between adjacent nano-interfaces was 20-times the interface radius. The analytical sensitivity for ion transfer from the aqueous to the 1,6-dichlorohexane organic phase was estimated from calibration plots of current density versus concentration of aqueous tetraethylammonium cation. The sensitivity was in the range of 65 μA cm(-2) μM(-1) (at 75 nm radius interfaces) to 265 μA cm(-2) μM(-1) (at 17 nm radius interfaces). The sensitivity depended directly on the inverse of the nano-interface radius, implying that smaller interfaces will provide better sensitivity, due to the enhanced flux of analyte arising from convergent diffusion to smaller electrochemical interfaces.

Chronoamperometric response at nanoscale liquid–liquid interface arrays

“…Each membrane contained 400 pores in a hexagonal close-packed arrangement with pore centre-to-centre separations, , of 20-times the pore radius, ( ). Scanning electron microscopy (SEM) micrographs of these nanopore arrays have been reported previously [11,15,38].…”

“…NanoITIES can offer benefits comparable to those experienced at nanoelectrode arrays, such as enhanced mass transport (due to radial diffusion), decreased charging current and decreased impact of solution resistance [11,16]. NanoITIES studies reported by Rimboud et al [15], Liu et al [4] and Shao and Mirkin [7] focussed on ion sensing using cyclic voltammetry as a technique. However, there is little information published on the chronoamperometric response at nano-interface arrays [13] despite numerous studies reporting the chronoamperometric response at microelectrochemical devices, e.g.…”

“…Track-etched polyester [12,13] and -alumina ultrafiltration membranes [14] with high pore densities have been used to form irregular nanoITIES arrays, while silicon nitride membranes prepared by electron-beam lithography and chemical etching methods [11,15] were used to form regular nanoITIES arrays. NanoITIES can offer benefits comparable to those experienced at nanoelectrode arrays, such as enhanced mass transport (due to radial diffusion), decreased charging current and decreased impact of solution resistance [11,16].…”

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

“…A B [43] copyright 2011 Royal Society of Chemistry, from Analyst, 2011, 136, 4674, [40] copyright 2011 Royal Society of Chemistry, respectively).…”

“…This approach allowed the determination of structural properties of the nanopores, including their density, shape and size, and provided a basis for understanding the permeability of nanoporous membranes. In addition, arrays of nano-ITIES were developed for the investigation of electrochemical behaviour and detection of ions such as TEA + , [36,40] tetrapropylammonium (TPrA + ) [37a, 41] and protonated propranolol. [42] These nanoITIES arrays were formed by placing nanoporous membranes, such as silicon nitride perforated with EBL-patterned nanopores, at the interface.…”