A novel ion separation methodology using a cation-exchange membrane modified with iron oxide nanoparticles (Fe3O4 NPs) coated with polyhexamethylene guanidine (PHMG) is proposed. The separation is performed in an electrodialysis cell, where firstly phosphate is electro-adsorbed to the PHMG@Fe3O4 NP coating, followed by a desorption step by applying an electric current.

In this work, the electrified liquid–liquid interface (LLI) was supported with the bare and polyelectrolyte modified fiberglass membranes. The permeability of these supports was then investigated with ion transfer voltammetry (ITV). This work descends from three mutually interconnected experimental tasks. (i) The study of an interfacial behavior of three polyelectrolytes, poly(ethyleneimine) (PEI), polystyrene sulfonate (PSS), and polyhexamethylene guanidine (PHMG) at the polarized LLI. (ii) Electrochemical characterization of the LLI supported by the unmodified fiberglass membrane. (iii) Polyelectrolyte multilayer placement, using layer-by-layer processing, at the surface of the fiberglass membrane and its further utilization as the support for the electrified LLI. Bare and modified membranes were characterized using ITV in the presence of a family of quaternary ammonium cations: tetramethylammonium (TMA⁺), tetraethylammonium (TEA⁺), tetrapropylammonium (TPrA⁺) and tetrabutylammonium (TBA⁺) initially dissolved in the aqueous phase as the chloride salts. The ionic currents related to their transmembrane transfer were affected already after the first polyelectrolyte layer placement. In addition to electrochemistry, the modification process was followed using several complementary techniques, including optical microscopy (OM), atomic force microscopy (AFM), infra-red (IR) spectroscopy, and scanning electron microscopy (SEM). The proposed methodology offers very simple, fast, and versatile (having in mind the available selection of functional polyelectrolytes) protocol for a membrane preparation having size sieving properties. In turn, the electrochemistry at the LLI can be used as an insightful tool to study the ionic transmembrane currents.

In this work, we have simultaneously examined, electrochemically driven deposition of three proteins (haemoglobin, acid phosphatase, and α-amylase) and silica films at a polarized liquid–liquid interface. The interfacial adsorption of the proteins occurs efficiently within the acidic pH range (pH = 2–4). The interfacial charge transfer reactions recorded in the presence of fully positivity charged macromolecules were followed with cyclic voltammetry on the positive side of the potential window. Faradaic currents attributed to the presence of proteins in the aqueous phase appeared for concentrations equal to ca. 0.1 µM for haemoglobin and acid phosphatase and ca. 1 µM for the α-amylase. Concomitant deposition of silica films was achieved via the addition of tetraethoxysilane molecules to the organic phase (1,2-dichloroethane). The hydrolysis and condensation reactions of tetraethoxysilane were controlled via the interfacial transfer of H⁺ coinciding with the potential for protein adsorption. The effect of tetraethoxysilane concentration – up to 50% by volume – revealed significant shrinkage of the potential window (the region where capacitive currents are recorded). The optimized platform was then used to prepare silica-proteins co-deposits. These could be easily collected from the interface and further analyzed with infrared spectroscopy and transmission electron microscopy.

This work describes a facile approach allowing Dibenzoyl-L-Cystine (DBC) based hydrogel controlled deposition and controlled detachments over a conducting support. The method itself is an electrochemically assisted approach, where the water oxidation at the electrode surface results in a local pH drop inducing DBC gelation and hydrogel formation. We have comprehensively described the possibility of the hydrogel shaping by alternating the anodic deposition potential, DBC concentration and finally the working electrode geometry. The latter includes macro-electrodes in a form of platinum discs having diameter equal to 200 and 500 μm; hexagonal arrays of circular platinum microelectrodes with a diameter of a single electrode equal to 5 or 10 μm and custom made platinum microelectrodes, having the shape of circles, triangles and squares, that are used to shape the microgels. Over the course of our work we were able to define the conditions to form a number of different hydrogel shapes such as: (i) flat and planar deposits; (ii) hemispherical deposits with an oxygen bubble pocket; (iii) spongy hydrogel structures or (iv) hemispherical micro-cups build from radially oriented DBC fibres directionally growing from the support. Furthermore, we were also able to remotely form and then detach the hydrogel deposit in the initial formulation solution using only an electrochemical trigger. Our work represents a solid proof of concept and opens a number of new avenues for the electrochemically assisted soft matter fabrication down to micrometre scale.

In this review, we describe the importance and possible electrochemical screening methods for the illicit drug – cocaine. It covers the detection at bare and modified solid electrodes, soft electrified junctions and nanopore sensing. Emphasis is given on interfacial modification techniques and electroanalytical parameters for cocaine detection in different environments, covering the detection from both, model and real samples.

The ability to study the adsorption behavior of surfactant species is of interest in the field of enhanced oil recovery (EOR), especially pertaining to alkaline surfactant flooding. In this work, a calcite model mineral surface was obtained by electrochemically assisted deposition. This was achieved via the nitrate and/or oxygen electroreduction reactions in the presence of bicarbonate and calcium ions, by which controlled deposition of calcium carbonate was effected on a quartz crystal microbalance sensor covered with an electroactive gold layer. In addition, the effect of pH and Ca ²⁺ concentration on the effective surface charge of the deposited calcite particles was mapped. Calcite-modified sensors were used in conjunction with a quartz crystal microbalance with dissipation monitoring to study the effect of Na ⁺ and Ca ²⁺ concentration on the adsorption behavior of an anionic alcohol alkoxy sulfate (AAS) surfactant. Adsorption of the surfactant remained indifferent to ionic concentrations around the isoelectric point of calcite. Still, electrostatics play an important role in this regard, and it is essential to decrease the Ca ²⁺ concentration sufficiently to minimize AAS adsorption. The results from this study show that a relatively simple method allows for the controlled deposition of a model rock surface, and there is ample opportunity to extend the work to other metal oxide surface types, including complex mixtures as can be obtained by co-deposition. Furthermore, the findings from these adsorption studies aid in the determination of optimal flooding parameters, with the aim to increase the efficiency and efficacy of EOR.

Controlled localization of platinum nanoparticles (Pt NPs) at a solid support assisted by a polarized liquid-liquid interface is reported. Electrocatalytic water oxidation resulted in local pH modulation followed by the directed self-assembly of a dibenzoyl-l-cystine hydrogelator forming a structured hydrogel retaining the shape of the Pt NP deposit.

In this paper, the electrochemical behavior of four fluoroquinolone antibiotics (FAs) [Ciprofloxacin (Cip), Enrofloxacin (Enr), Marbofloxacin (Mar) and Ofloxacin (Ofl)] at a polarized interface between two immiscible electrolyte solutions (ITIES) has been studied using ion–transfer voltammetry (ITV). The measurements were conducted in the traditional macroscopic (macro-ITIES) and a recently developed miniaturized (micro-ITIES) platform. The latter was obtained from fused silica micro-capillaries having an internal diameter of 25 μm. We used macroITIES to obtain a number of analytical parameters such as: standard Galvani potential of ion transfer (ΔΦ⁰), diffusion coefficients (D), free Gibbs energy of ion transfer (ΔG⁰) and partition coefficients (logP_DCE). The latter were compared with the available literature values of logP_octanol. The effect of concentration of the studied antibiotics on the electrochemical response was investigated with the microITIES platform, setting statistical parameters such as: linear dynamic ranges (LDRs – studied from 1 μM up to 50 μM), lower limit of detections (LODs – around 1 μM) and sensitivity (found in the range from 2.6·10⁻² to 6.8·10⁻² nA·μM⁻). MicroITIES were further used to study the effect of pH on the analytical signal and the results are plotted in a form of ion partition diagrams. Working with microITIES supported with the fused silica capillaries significantly reduced the volumes of consumed chemicals and expedite all analytical experiments. The provided results can be successfully applied in pharmacology and electroanalysis for testing and determination of the chosen fluoroquinolone antibiotics.

The behaviour of acid phosphatase at an electrified liquid–liquid interface was studied in this work. It was found that only the protonated form of the protein can undergo interfacial adsorption which is affected by the pH of the aqueous phase. With ion transfer voltammetry we could detect acid phosphatase in concentrations as low as 0.1 μM. We were able to co-deposit the protein and silica at the electrified liquid–liquid interface via controlled proton transfer to the organic phase where it catalyzed tetraethoxysilane hydrolysis, followed by polycondensation to silica.

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.

Short pieces of fused silica capillary tubing were used to support an electrified liquid-liquid interface. A methyl deactivated silica capillary having a diameter of 25 μm was filled with 1,2-dichloroethane solution and served as the organic part of the liquid-liquid interface. A nondeactivated fused silica capillary having a diameter of 5, 10, or 25 μm was filled with an aqueous HCl solution and served as the aqueous part of the electrochemical cell. For the latter, silanization of the capillary interior with chlorotrimethylsilane allowed for a successful phase reversal. All capillaries were characterized by ion transfer voltammetry using tetramethylammonium cation as a model ion. This simple, fast, and low-cost miniaturization technique was successfully applied for detection of the antibiotic ofloxacin.

Recently various porous organic frameworks (POFs, crystalline or amorphous materials) have been discovered, and used for a wide range of applications, including molecular separations and catalysis. Silicon nanowires (SiNWs) have been extensively studied for diverse applications, including as transistors, solar cells, lithium ion batteries and sensors. Here we demonstrate the functionalization of SiNW surfaces with POFs and explore its effect on the electrical sensing properties of SiNW-based devices. The surface modification by POFs was easily achieved by polycondensation on amine-modified SiNWs. Platinum nanoparticles were formed in these POFs by impregnation with chloroplatinic acid followed by chemical reduction. The final hybrid system showed highly enhanced sensitivity for methanol vapour detection. We envisage that the integration of SiNWs with POF selector layers, loaded with different metal nanoparticles will open up new avenues, not only in chemical and biosensing, but also in separations and catalysis.

Silicon semiconductors with a thin surface layer of silica were first modified with polyelectrolytes (polyethyleneimine, polystyrene sulfonate and poly(allylamine)) via a facile layer-by-layer deposition approach. Subsequently, lipid vesicles were added to the preformed polymeric cushion, resulting in the adsorption of intact vesicles or fusion and lipid bilayer formation. To study involved interactions we employed optical reflectometry, electrochemical impedance spectroscopy and fluorescent recovery after photobleaching. Three phospholipids with different charge of polar head groups, i.e. 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) were used to prepare vesicles with varying surface charge. We observed that only lipid vesicles composed from 1:1 (mole:mole) mixture of DOPC/DOPS have the ability to fuse onto an oppositely charged terminal layer of polyelectrolyte giving a lipid bilayer with a resistance of >100 kΩ. With optical reflectometry we found that the vesicle surface charge is directly related to the amount of mass adsorbed onto the surface. An interesting observation was that zwitterionic polar head groups of DOPC allow the adsorption on both positively and negatively charged surfaces. As found with fluorescent recovery after photobleaching, positively charged surface governed by the presence of poly(allylamine) as the terminal layer resulted in intact DOPC lipid vesicles adsorption whereas in the case of a negatively charged silica surface formation of lipid bilayers was observed, as expected from literature.

We have investigated in detail properties of hybrid polyelectrolyte-anion exchange membranes (AEMs) having different amounts of a guanidinium-modified poly(allylamine hydrochloride) (PAH-Gu) derivative (2, 5, and 8 wt%). The presence of guanidinium groups at the membrane surface was confirmed by XPS. For 2 and 5 wt% the blended membranes are homogeneous, while at 8 wt% segregation is observed by AFM. The membrane permselectivity and ionic electrical resistance for phosphate reduce upon incorporation of the PAH-Gu in the membrane, reflecting an increased co-ion (H⁺ and Na⁺) permeation. We conclude that PAH-Gu loaded in the AEM favors an interaction with phosphate. In electrodialysis, using sodium sulfate and sodium dihydrogen phosphate at equal concentrations in the source phase a slight preference for phosphate was observed. Our work shows that this facile membrane fabrication procedure shows great potential in terms of tuning the membrane properties. One way to boost selective ion transport could be by increasing the number of functional groups in the membrane.

The electrochemical behavior of three differently charged drug molecules (zwitter-ionic acetylcarnitine, bi-cationic succinylcholine and tri-cationic gallamine) was studied at the interface between two immiscible electrolyte solutions. Tetramethylammonium was used as a model mono cationic molecule and internal reference. The charge and molecular structure were found to play an important role in the drug lipophilicity. The studied drugs gave a linear correlation between the water – octanol (logP_octanol) partition coefficients and the electrochemically measured water – 1,2-dichloroethane (logP_DCE) partition coefficients. Comparison with tetraalkylammonium cations indicating that the correlation between logP_octanol and logP_DCE is molecular structure dependent. The highest measured sensitivity and lowest limit of detection were found to be 0.543 mA·dm³·mol^{− 1} and 6.25 μM, respectively, for the tri-cationic gallamine. The sensitivity for all studied ions was found to be a linear function of molecular charge. The dissociation constant of the carboxylic group of zwiter-ionic acetylcarnitine was calculated based on voltammetric parameters and was found to be 4.3. This study demonstrates that electrochemistry at the liquid – liquid interface is powerful technique when it comes to electroanalytical or pharmacokinetic drug assessment.

The interface formed between two immiscible electrolyte solutions (ITIES) constitutes a fantastic playground for the investigation of charge (under the form of either ion or electron) transfer processes. We have reviewed here the routes for the modification of such soft interfaces by an accurate electrochemical control. The three main strategies developed in the past four decades include (i) the electrochemically controlled assembly of molecules and nano-objects; (ii) the in situ electrogeneration of nanomaterials and (iii) the use of ex situ synthesized membranes. Applications of functionalized ITIES in the fields of redox catalysis and electroanalysis of modified soft interfaces are also discussed.