Electrochemical screening of selected ß-blockers at a polarized liquid-liquid interface.

This paper describes the electrochemical behavior of five ß-blockers at the polarized liquid-liquid interface formed between aqueous solution (sodium chloride solution or Britton-Robinson buffers) and bis(triphenylphosphoranylidene)ammonium tetrakis(4-chlorophenyl)borate (BTPPATPBCl) dissolved in 1,2-dichloroethane (the organic phase). All measurements reported in this work were conducted using cyclic voltammetry (CV). The effects of the concentration of analytes, the pH of the aqueous phase, and applied electrochemical parameters on the analytical performance of the studied system are studied and discussed. The linear dynamic ranges (LDRs) of the studied ß-blockers were in the range of 5-200 µmol L-1 and the lowest limit of detection (LOD) value was determined for pindolol (LOD = 1.96 µM µmol L-1). The highest LOD value was 4.96 µmol L-1 found for nebivolol. In addition, physicochemical parameters such as the formal Galvani potential difference (Δaqorgϕ), formal Gibbs free energies of the ion transfer reaction (ΔaqorgG') and partition coefficients (log P'aq/org) for all studied molecules were determined. The latter were compared and correlated with the available literature values of log Poctanol. Finally, a standard addition method was used to determine the concentration of nebivolol in pharmaceutical preparations using a platform based on the electrified liquid-liquid interface.

Electroanalytical characterization of clozapine at the electrified liquid-liquid interface and its detection in soft and hard drinks.

Clozapine (CZ) is a prescribed benzodiazepine psychiatric drug that is often possessed as an illicit drug and is associated with drug-facilitated sexual assaults (DFSA) due to its strong sedative capabilities. Hence, we propose an electrified liquid-liquid interface (eLLI) based transducing element as an alternative electroanalytical platform for rapid screening of CZ in soft and hard drinks which is habitually associated with DFSA crimes. First, molecular partitioning and the effect of chemical composition, pH, and the presence of ethanol in the biphasic configuration of the aqueous phase on the interfacial behaviour and analytical performance of the CZ at the eLLI have been investigated with voltammetry. Next, the electrochemical profiles of various soft and hard drinks were studied at the eLLI. The eLLI-based CZ sensor has shown a broad dynamic range (15-150 µM), lower detection limits (1µM), and adequate reliability towards rapid CZ screening in spiked soft and hard drink samples with reference to the standard chromatographic analysis.

Phenylethylamine sensing at the electrified liquid-liquid interface. Can electrochemistry be used to follow the UHT milk spoilage process?

This study involved an investigation into the electrochemical characteristic of a few biogenic amines (BAs) occurring at the polarized interface between two immiscible electrolyte solutions (ITIES) with ion transfer voltammetry (ITV). The main focus of this research was the comprehensive electroanalytical and physicochemical analysis of phenylethylamine (PEA), allowing the determined of the formal Galvani potential of the ion transfer reaction (ΔorgaqΦ'), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (ΔG'aq→org) and water-1,2-dichloroethane partition coefficient (logPwater/DCEPEA). Furthermore, the collected data were employed to calculate analytical parameters, including voltametric detection sensitivity, limits of detection and the target analyte quantification. Moreover, the influence of the presence of 7 other BAs (histamine, spermine, spermidine, putrescine, cadaverine, tyramine and tryptamine) on the recorded signals originating from the PEA ion transfer was checked. The feasibility of the developed method was corroborated through experimentation with milk samples. Additionally, utilizing the devised methodology, an electrochemical assessment of the spoilage progression in milk samples was undertaken.

Solvent-activated 3D-printed electrodes and their electroanalytical potential.

This work is a comprehensive study describing the optimization of the solvent-activated carbon-based 3D printed electrodes. Three different conductive filaments were used for the preparation of 3D-printed electrodes. Electrodes treatment with organic solvents, electrochemical characterization, and finally electroanalytical application was performed in a dedicated polyamide-based cell also created using 3D printing. We have investigated the effect of the used solvent (acetone, dichloromethane, dichloroethane, acetonitrile, and tetrahydrofuran), time of activation (from immersion up to 3600 s), and the type of commercially available filament (three different options were studied, each being a formulation of a polylactic acid and conductive carbon material). We have obtained and analysed a significant amount of collected data which cover the solvent-activated carbon-based electrodes surface wettability, microscopic insights into the surface topography analysed with scanning electron microscopy and atomic force microscopy, and finally voltammetric evaluation of the obtained carbon electrodes electrochemical response. All data are tabulated, discussed, and compared to finally provide the superior activation procedure. The electroanalytical performance of the chosen electrode is discussed based on the voltammetric detection of ferrocenemethanol.

Lipid-based liquid crystalline materials in electrochemical sensing and nanocarrier technology.

Some biologically active substances are unstable and poorly soluble in aqueous media, at the same time exhibiting low bioavailability. The incorporation of these biologically active compounds into the structure of a lipid-based lyotropic liquid crystalline phase or nanoparticles can increase or improve their stability and transport properties, subsequent bioavailability, and applicability in general. The aim of this short overview is (1) to clarify the principle of self-assembly of lipidic amphiphilic molecules in an aqueous environment and (2) to present lipidic bicontinuous cubic and hexagonal phases and their current biosensing (with a focus on electrochemical protocols) and biomedical applications.

Nitrazepam and 7-aminonitrazepam studied at the macroscopic and microscopic electrified liquid-liquid interface.

Two benzodiazepine type drugs, that is, nitrazepam and 7-aminonitrazepam, were studied at the electrified liquid-liquid interface (eLLI). Both drugs are illicit and act sedative in the human body and moreover are used as date rape drugs. Existence of the diazepine ring in the concerned chemicals structure and one additional amine group (for 7-aminonitrazepam) allows for the molecular charging below their pKa values, and hence, both drugs can cross the eLLI interface upon application of the appropriate value of the Galvani potential difference. Chosen molecules were studied at the macroscopic eLLI formed in the four electrode cell and microscopic eLLI formed within a microtip defined as the single pore having 25 µm in diameter. Microscopic eLLI was formed using only a few µL of the organic and the aqueous phase with the help of a 3D printed cell. Parameters such as limit of detection and voltammetric detection sensitivity are derived from the experimental data. Developed methodology was used to detect nitrazepam in pharmaceutical formulation and both drugs (nitrazepam and 7-aminonitrazepam) in spiked biological fluids (urine and blood).

Heroin detection in a droplet hosted in a 3D printed support at the miniaturized electrified liquid-liquid interface.

Simple sensing protocols for the detection of illicit drugs are needed. Electrochemical sensing is especially attractive in this respect, as its cost together with the analytical accuracy aspires to replace still frequently used colorimetric tests. In this work, we have shown that the interfacial transfer of protonated heroin can be followed at the electrified water-1,2-dichloroethane interface. We have comprehensively studied the interfacial behavior of heroin alone and in the presence of its major and abundant cutting agents, caffeine and paracetamol. To maximally increase developed sensing protocol applicability we have designed and 3D printed a platform requiring only a few microliters of the aqueous and the organic phase. The proposed sensing platform was equipped with a cavity hosting a short section of Ag/AgCl electrode, up to 20 µL of the aqueous phase and the end of the micropipette tip being used as a casing of a fused silica capillary having 25 µm as the internal pore diameter. The volume of the organic phase was equal to around 5 µL and was present inside the micropipette tip. We have shown that under optimized conditions heroin can be detected in the presence of caffeine and paracetamol existing in a sample with 10,000 times excess over the analyte of interest. The calculated limit of detection equal to 1.3 µM, linear dynamic range spanning to at least 50 µM, good reproducibility, and very low volume of needed sample is fully in line with forensic demands.

3D Printed Platform for Impedimetric Sensing of Liquids and Microfluidic Channels.

Fused deposition modeling 3D printing (FDM-3DP) employing electrically conductive filaments has recently been recognized as an exceptionally attractive tool for the manufacture of sensing devices. However, capabilities of 3DP electrodes to measure electric properties of materials have not yet been explored. To bridge this gap, we employ bimaterial FDM-3DP combining electrically conductive and insulating filaments to build an integrated platform for sensing conductivity and permittivity of liquids by impedance measurements. The functionality of the device is demonstrated by measuring conductivity of aqueous potassium chloride solution and bottled water samples and permittivity of water, ethanol, and their mixtures. We further implement an original idea of applying impedance measurements to investigate dimensions of 3DP channels as base structures of microfluidic devices, complemented by their optical microscopic analysis. We demonstrate that FDM-3DP allows the manufacture of microchannels of width down to 80 µm.

Electrochemistry as a Powerful Tool for Investigations of Antineoplastic Agents: A Comprehensive Review.

Cancer is most frequently treated with antineoplastic agents (ANAs) that are hazardous to patients undergoing chemotherapy and the healthcare workers who handle ANAs in the course of their duties. All aspects related to hazardous oncological drugs illustrate that the monitoring of ANAs is essential to minimize the risks associated with these drugs. Among all analytical techniques used to test ANAs, electrochemistry holds an important position. This review, for the first time, comprehensively describes the progress done in electrochemistry of ANAs by means of a variety of bare or modified (bio)sensors over the last four decades (in the period of 1982-2021). Attention is paid not only to the development of electrochemical sensing protocols of ANAs in various biological, environmental, and pharmaceutical matrices but also to achievements of electrochemical techniques in the examination of the interactions of ANAs with deoxyribonucleic acid (DNA), carcinogenic cells, biomimetic membranes, peptides, and enzymes. Other aspects, including the enantiopurity studies, differentiation between single-stranded and double-stranded DNA without using any label or tag, studies on ANAs degradation, and their pharmacokinetics, by means of electrochemical techniques are also commented. Finally, concluding remarks that underline the existence of a significant niche for the basic electrochemical research that should be filled in the future are presented.

Interfacial Deposition of Titanium Dioxide at the Polarized Liquid-Liquid Interface.

The interfacial polycondensation of titanium dioxide was studied at the bare and fiberglass membrane supported polarized liquid-liquid interface (LLI). Titanium dioxide synthesis was derived from the titanium (IV) tetrabutoxide (initially dissolved in the 1,2-dichloroethane) interfacial hydrolysis followed by its condensation. Experimental parameters, such as the pH of the aqueous phase and the influence of titanium alkoxide concentration in the organic phase on the electrochemical signal and material morphology, were investigated. The latter was achieved with fiberglass membranes used as the LLI support during TiO2 interfacial deposition. Cyclic voltammetry was used for the in situ studies, whereas scanning electron microscopy, energy-dispersive X-ray spectroscopy, and infrared spectroscopy were used during ex situ examination. The interfacial polycondensation reaction could be studied using electrified LLI and resulted in the material being a TiO2 film alone or film decorated with particles.

Illicit drugs street samples and their cutting agents. The result of the GC-MS based profiling define the guidelines for sensors development.

In this work, we have focused on the profiling of 5647 street samples covering marijuana, common and new recreational illicit drugs. All samples were analyzed using gas chromatography-mass spectrometry (GC-MS) technique. In total we have identified 53 illicit drugs with Δ-9-tetrahydrocannabinol (THC), amphetamine, N-ethylhexedrone, 3,4-methylenedioxy methamphetamine (MDMA), 4-chloromethcathinone (4-CMC), α-pyrrolidinoisohexaphenone (α-PHiP), cocaine, and 4-chloroethcathinone (4-CEC) being most commonly found and making 38.5, 17.8, 15.5, 8.0, 3.5, 2.7, 2.1, and 2.0% of the total studied pool, respectively. Except for methadone, all analyzed street samples were spiked with at least one cutting agent. Caffeine was the most frequently found adulterating addition present in around 33% (excluding marijuana) of the analyzed samples. Other identified cutting agents make an impressive group of more than 160 compounds. Finally, we have tabulated, illustrated, and discussed presented data in a view of smart and portable sensors development.

Voltammetric study of cefotaxime at the macroscopic and miniaturized interface between two immiscible electrolyte solutions.

The electrochemical behavior of cefotaxime (CTX+) was investigated at the polarized macro- and micro-interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry and alternating current voltammetry. Miniaturization was achieved with fused silica microcapillary tubing entrapped in a polymeric casing. Scanning electron microscopy (SEM) was employed for the fabricated LLI support characterization. Voltammetric investigation of CTX+ at macro- and µ-ITIES allowed the determination of many physicochemical parameters, such as formal Galvani potential of the ion transfer reaction ([Formula: see text]), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G'aq → org), and water-1,2-dichloroethane partition coefficient ([Formula: see text]). Additionally, based on the results obtained the analytical parameters including voltammetric sensitivity, limits of detection and the limits of quantification (in micromolar range) were calculated. The applicability of the developed procedures was verified in spiked still mineral and tap water samples.

Determination of quinine in tonic water at the miniaturized and polarized liquid-liquid interface.

In this work we report an electrochemical approach to quantitative and qualitative analysis of quinine (QN) at the interface between two immiscible electrolyte solutions (ITIES). This was done at the macroscopic (macroITIES) and microscopic (µITIES) systems using ion transfer voltammetry (ITV). The linear response of the peak current vs. increasing concentrations of QN at the µITIES was from 2.50 µM to 29.13 µM and the corresponding calculated limit of detection (LOD) for the current signals originating from QN transfer from the aqueous to the organic phase was equal to 0.49 µM. Additionally, the influence of pH (2-12) of the aqueous phase on the recorded QN signals was investigated. We have found that our method is fully applicable for QN direct determination in non-treated tonic water, as confirmed on three different real samples from three different manufacturers. Finally, a number of validation parameters for the developed method are provided and discussed.

Electroanalytical study of five carbosilane dendrimers at the interface between two immiscible electrolyte solutions.

This work is focused on the electroanalytical study of a family of five imidazolium-terminated carbosilane dendrimers (from generation G1 to G3) at the polarized liquid-liquid interface formed between water and 1,2-dichloroethane solutions. All dendrimers with permanently and positively charged imidazolium groups located at the periphery within the branched carbosilane core were found to be electrochemically active. Based on the concentration and scan rate dependencies we have concluded that these molecules undergo interfacial ion transfer processes accompanied by interfacial adsorption/desorption rather than the electrochemically induced interfacial formation of the macromolecule-anion (tetrakis(4-chlorophenyl)borate) from the organic phase complex. Also, we report several physicochemical and electroanalytical parameters (e.g. diffusion coefficients, LODs, and detection sensitivities) for the studied family of dendrimers. Our work aims to contribute to the understating of the interaction between branched macromolecules and biomimetic interfaces.

Electrochemical study of ephedrine at the polarized liquid-liquid interface supported with a 3D printed cell.

In this work, we have examined an electrochemical behavior of the ephedrine at the polarized liquid-liquid interface (water/1,2-dichloroethane). In this respect, we first designed and then 3D printed polyamide-based electrochemical cell that was used as the liquid-liquid interface support during electroanalytical measurements. The protonated ephedrine undergoes a reversible ion transfer reaction with the standard Galvani potential difference equal to +0.269 V. This value was used to calculate the water - 1,2-dichloroethane logP equal to -4.6. Ion transfer voltammetry was used to build the calibration curve and allowed for the ephedrine detection from concentration equal to 20 µM. By varying the pH of the aqueous phase from 2 up to 12 we were able to plot the ion partition diagram that was further analyzed and provided several pharmacochemical information. To further push this work towards practical utility, we have formulated the artificial urine and studied the interfacial behavior of all its components at the polarized liquid-liquid interface. Ephedrine detection from real spiked urine samples was also performed.

Modified cation-exchange membrane for phosphate recovery in an electrochemically assisted adsorption-desorption process.

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.

Co-deposition of silica and proteins at the interface between two immiscible electrolyte solutions.

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.

Ion transfer voltammetry for analytical screening of fluoroquinolone antibiotics at the water - 1.2-dichloroethane interface.

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 (logPDCE). The latter were compared with the available literature values of logPoctanol. 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.

Locally pH controlled and directed growth of supramolecular gel microshapes using electrocatalytic nanoparticles.

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.

Lipid bilayers cushioned with polyelectrolyte-based films on doped silicon surfaces.

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.