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 siliconnitride nanopore array membranes. Nanopores in the range from 75 nm radius down to 17 nm radiuswere used to form the nano-interfaces. It was found that the liquid organic phase electrolyte solutionfilled the pores so that inlaid nano-interfaces were formed with the aqueous phase. Cyclic voltammetryat these nano-interface arrays demonstrated steady-state behaviour at the larger interfaces but thevoltammetric wave-shape became progressively worse as the interface size decreased. It was found thatthe ion transfer currents were ca. 50% of those expected based on theoretical calculations, which isattributed to overlap of diffusion zones at adjacent nano-interfaces. Here, the separation betweenadjacent nano-interfaces was 20-times the interface radius. The analytical sensitivity for ion transferfrom the aqueous to the 1,6-dichlorohexane organic phase was estimated from calibration plots ofcurrent density versus concentration of aqueous tetraethylammonium cation. The sensitivity was in therange of 65 mA cm2 mM1 (at 75 nm radius interfaces) to 265 mA cm2 mM1 (at 17 nm radiusinterfaces). The sensitivity depended directly on the inverse of the nano-interface radius, implying thatsmaller interfaces will provide better sensitivity, due to the enhanced flux of analyte arising fromconvergent diffusion to smaller electrochemical interfaces.