Ion-Transfer Voltammetric Behavior of Propranolol at Nanoscale Liquid–Liquid Interface Arrays

Abstract

In this work, the ion-transfer voltammetric detection of the protonated β-blocker propranolol was explored at arrays of nanoscale interfaces between two immiscible electrolyte solutions (ITIES). Silicon nitride nanoporous membranes with 400 pores in a hexagonal arrangement, with either 50 or 17 nm radius pores, were used to form regular arrays of nanoITIES. It was found that the aqueous-to-organic ion-transfer current continuously increased steadily rather than reaching a limiting current plateau after the ion-transfer wave; the slope of this limiting current region was concentration dependent and associated with the high ion flux at the nanointerfaces. Electrochemical data were examined in terms of an independent nanointerface approach and an equivalent microdisc approach, supported by finite element simulation. In comparison to the larger interface configuration (50 nm radius), the array of 17 nm radius nanoITIES exhibited a 6.5-times higher current density for propranolol detection due to the enhanced ion flux arising from the convergent diffusion to smaller electrochemical interfaces. Both nanoITIES arrays achieved the equivalent limits of detection, 0.8 μM, using cyclic voltammetry. Additionally, the effect of scan rate on the charging and faradaic currents at these nanoITIES arrays, as well as their stability over time, was investigated. The results demonstrate that arrays of nanoscale liquid-liquid interfaces can be applied to study electrochemical drug transfer, and provide the basis for the development of miniaturized and integrated detection platforms for drug analysis.

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

“…The ion-transfer voltammetric detection of propranolol was also explored at arrays of nano-ITIES formed at silicon nitride nanoporous membranes with 400 pores in a hexagonal arrangement, with either 50 or 17 nm radius pores. [42] Both arrays achieved the equivalent detection limit of 0.8 µM using CV, and the smaller nano-ITIES exhibited higher sensitivity toward propranolol transfer than the larger one, which can be attributed to the enhanced ion flux resulting from the convergent diffusion at smaller electrochemical interfaces (Figure 7). However, diffusion zone overlap occurred at the nanoITIES in this array, leading to depletion zones between neighbouring nanointerfaces, and which was illustrated by finite element simulation of an interface in the midst of the array.…”

“…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. Since the silicon nitride is naturally hydrophobic, the organic electrolyte fills the pores, enabling the formation of nanoITIES at the mouths of the pores.…”

Applications of Electrochemistry at Liquid/Liquid Interfaces for Ionizable Drug Molecule Sensing

“…For example, Arrigan et al demonstrated that nanoscale-ITIES array based ion sensors could be 50 times more sensitive than those using microscale-ITIES arrays and 1000 times more sensitive than a single macro-ITIES. 18) A single (or dual) nanopipette prepared by pulling a quartz capillary or placing nanoporous materials containing geometrically irregular or regular arrays of pores can be utilized for creating nanoscale-ITIES (see the scheme in Figure 3a). A regular array of nano-ITIES featuring silicon nitride nanoporous membranes with 400 pores in a hexagonal arrangement, with either 50 or 17 nm radius was successfully used to monitor different concentrations of propranolol.…”

“…A regular array of nano-ITIES featuring silicon nitride nanoporous membranes with 400 pores in a hexagonal arrangement, with either 50 or 17 nm radius was successfully used to monitor different concentrations of propranolol. 18) Similar to the microhole supported ITIES, the hemispherical diffusion flux governs when the ion transfer occurs across the nanoscale interface resulting in steady-state voltammograms.…”

“…Voltammetric sensing of protonated propranolol using arrays of nanoscale ITIES were further investigated. 18) Nanoporous silicon nitride membranes having 400 pores (r = 17 or 50 nm) in a hexagonal configuration were used to create nano arrays supported ITIES. It was shown that the current density measured for propranolol sensing was at least 6 times higher for the nanoITIES with 17 nm radius pores than that of using 50 nm radius pore array, which can be explained by the increased ion flux due to the convergent diffusion to the smaller interfacial area.…”