Two-Dimensional Graphene-Based Potassium Channels Built at an Oil/Water Interface

Graphene-based laminar membranes exhibit remarkable ion sieving properties, but their monovalent ion selectivity is still low and much less than the natural ion channels. Inspired by the elementary structure/function relationships of biological ion channels embedded in biomembranes, a new strategy is proposed herein to mimic biological K+ channels by using the graphene laminar membrane (GLM) composed of two-dimensional (2D) angstrom(Å)-scale channels to support a simple model of semi-biomembrane, namely oil/water (O/W) interface. It is found that K+ is strongly preferred over Na+ and Li+ for transferring across the GLM-supported water/1,2-dichloroethane (W/DCE) interface within the same potential window (-0.1-0.6 V), although the monovalent ion selectivity of GLM under the aqueous solution is still low (K+/Na+~1.11 and K+/Li+~1.35). Moreover, the voltammetric responses corresponding to the ion transfer of NH4+ observed at the GLM-supported W/DCE interface also show that NH4+ can often pass through the biological K+ channels due to their comparable hydration-free energies and cation-π interactions. The underlying mechanism of as-observed K+ selective voltammetric responses is discussed and found to be consistent with the energy balance of cationic partial-dehydration (energetic costs) and cation-π interaction (energetic gains) as involved in biological K+ channels.

Electrochemical investigation of adsorption of graphene oxide at an interface between two immiscible electrolyte solutions

Graphene oxide (GO) has been recognized as an amphiphilic molecule or a soft colloidal particle with the ability to adsorb and assemble at the liquid/liquid (L/L) interface. However, most extant works concerning the adsorption behaviors of GO at the L/L interface have been limited to the non-polarized L/L interface. Here, we studied what would happen if GO nanosheets met with a polarizable L/L interface, namely an interface between two immiscible electrolyte solutions (ITIES). On one hand, the adsorption behavior of GO nanosheets at the L/L interface was electrochemically investigated firstly by using cyclic voltammetry (CV) and alternating current voltammetry (ACV). On the other hand, the influence of the adsorbed GO layers at the L/L interface on the ion transfer reactions was studied by employing ion-transfer voltammetry of TEA⁺ and ClO₄⁻ selected as probe ions. Capacitance measurements show that the interfacial capacitance increases greatly in the presence of GO nanosheets inside the aqueous phase, which can be attributed to the increases of interfacial corrugation and charge density induced by the parallel adsorption and assembly of GO at the L/L interface. In addition, it is found that the application of an interfacial potential difference by external polarization can promote the adsorption of GO at the L/L interface. Moreover, the ion-transfer voltammetric results further demonstrate that the GO layers formed at the interface can suppress the ion transfer reactions due to interfacial blocking and charge screening, as well as the hindrance effect induced by the GO layers. All the results with insights into the interfacial behavior of GO under polarization with an external electric field enable understanding the adsorption behavior of GO at the L/L interface more comprehensively.

The adsorption behavior of graphene oxide (GO) nanosheets at an interface between two immiscible electrolyte solutions (ITIES) was electrochemically investigated firstly by using cyclic voltammetry (CV) and alternating current voltammetry (ACV).

Anion sensing properties of electrospun nanofibers incorporating a thiourea-based chromoionophore in methanol

To sense hydrophilic anions in protic solvents, we fabricated polymethylmethacrylate (PMMA) nanofibers incorporating 4-nitrophenyl azo thiourea polymer as a chromoionophore. When methanol solutions containing anions contacted the PMMA nanofiber, a bathochromic shift from 386 nm was observed in the absorption maximum of the chromoionophore. This spectral change is due to hydrogen bond formation between the urea moiety of the thiourea-based polymer and anions penetrating the nanofiber. This spectral change was not observed in PMMA film incorporating the same anion sensor, and the difference is attributed to the much larger specific surface area of the nanofiber compared to the film. As a result, many anions could react with the anion-sensing polymers in the nanofiber and induce a large spectral response.

Electrified Soft Interface as a Selective Sensor for Cocaine Detection in Street Samples

A straightforward, direct, and selective method is presented for electrochemical cocaine identification in street samples. The sensing mechanism is based on a simple ion transfer reaction across the polarized liquid–liquid interface. The interfacial behavior of a number of cutting agents is also reported. Interfacial miniaturization has led to improved electroanalytical properties of the liquid–liquid interface based sensor as compared with the macroscopic analogue. The reported method holds great potential to replace colorimetric tests with poor selectivity for on-site street sample analysis.

Electroanalytical Ventures at Nanoscale Interfaces Between Immiscible Liquids

Ion transfer at the interface between immiscible electrolyte solutions offers many benefits to analytical chemistry, including the ability to detect nonredox active ionized analytes, to detect ions whose redox electrochemistry is accompanied by complications, and to separate ions based on electrocontrolled partition. Nanoscale miniaturization of such interfaces brings the benefits of enhanced mass transport, which in turn leads to improved analytical performance in areas such as sensitivity and limits of detection. This review discusses the development of such nanoscale interfaces between immiscible liquids and examines the analytical advances that have been made to date, including prospects for trace detection of ion concentrations.

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

This review presents an introduction to electrochemistry at interfaces between immiscible electrolyte solutions and surveys recent studies of this form of electrochemistry in electroanalytical strategies. Simple ion and facilitated ion transfers across interfaces varying from millimetre scale to nanometre scales are considered. Target detection strategies for a range of ions, inorganic, organic, and biological, including macromolecules, are discussed.

Nickel ion coupled counter complexation and decomplexation through a modified supported liquid membrane system

Complexation and decomplexation stoichiometry between nickel and D2EHPA in an SLM system are determined, confirmed by Job’s method and loading test.

Ion-transfer voltammetric determination of folic acid at meso-liquid–liquid interface arrays

Voltammetric studies on the simple ion transfer (IT) behaviors of an important water-soluble B-vitamin, folic acid (FA), at the liquid–liquid (L–L) interface were firstly performed and applied as a novel detection method for FA under physiological conditions. This work provides a new and attractive strategy for the detection of FA⁻ and other biological anions.