Voltammetric Studies of Topotecan Transfer Across Liquid/Liquid Interfaces and Sensing Applications

Self-assembled ordered AuNRs-modified electrodes for simultaneous determination of dopamine and topotecan with improved data reproducibility

Gold nanomaterials have been widely explored in electrochemical sensors due to their high catalytic property and good stability in multi-medium. In this paper, the reproducibility of the signal among batches of gold nanorods (AuNRs)-modified electrodes was investigated to improve the data stabilization and repeatability. Ordered and random self-assembled AuNRs-modified electrodes were used as electrochemical sensors for the simultaneous determination of dopamine (DA) and topotecan (TPC), with the aim of obtaining an improved signal stability in batches of electrodes and realizing the simultaneous determination of both substances. The morphology and structure of the assemblies were analyzed and characterized by UV-Vis spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Electrochemical studies showed that the ordered AuNRs/ITO electrodes have excellent signal reproducibility among several individuals due to the homogeneous mass transfer in the ordered arrangement of the AuNRs. Under the optimized conditions, the simultaneous detection results of DA and TPC showed good linearity in the ranges 1.75-45 μM and 1.5-40 μM, and the detection limits of DA and TPC were 0.06 μM and 0.17 μM, respectively. The results showed that the prepared ordered AuNR/ITO electrode had high sensitivity, long-term stability, and reproducibility for the simultaneous determination of DA and TPC, and it was expected to be applicable for real sample testing.

Dual modulation of blue-fluorescent carbon dots for simultaneous detection of topotecan and pantoprazole

This study introduces a novel approach for the simultaneous determination of topotecan (TOP) and pantoprazole (PNT), two drugs whose interaction is critical in clinical applications. The significance of this study originates from the need to understand the pharmacokinetic changes of TOP after PNT administration, which can inform necessary dose adjustments of TOP. To achieve this, nitrogen blue emissive carbon dots (B@NCDs) were produced and employed due to their unique fluorescent properties. When TOP is added to B@NCDs, it exhibits strong native fluorescence at 545 nm without influencing the B@NCDs' fluorescence at 447 nm. Conversely, PNT causes quenching of B@NCDs fluorescence, a property that enables the distinct detection of both drugs. The B@NCDs were fully characterized using different techniques, including ultraviolet-visible spectrophotometry, fluorescence analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), and FTIR spectroscopy. The proposed method demonstrated excellent linearity, selectivity, and sensitivity, with low detection limits (LOD, S/N = 3); 0.0016 μg mL-1 for TOP and 0.36 μg mL-1 for PNT. Applied to spiked rabbit plasma samples, this method offers a new approach for evaluating the pharmacokinetic interaction between TOP and PNT. It enables the determination of all pharmacokinetic parameters of TOP before and after coadministration with PNT, providing essential insights into whether dose adjustments are necessary. This research not only contributes to the field of drug monitoring and interaction studies but also exemplifies the potential of B@NCDs in complex biological matrices, paving the way for further pharmacological and therapeutic applications.

Microliquid/Liquid Interfacial Sensors: Biomimetic Investigation of Transmembrane Mechanisms and Real-Time Determinations of Clemastine, Cyproheptadine, Epinastine, Cetirizine, and Desloratadine

Antihistamines relieve allergic symptoms by inhibiting the action of histamine. Further understanding of antihistamine transmembrane mechanisms and optimizing the selectivity and real-time monitoring capabilities of drug sensors is necessary. In this study, a micrometer liquid/liquid (L/L) interfacial sensor has served as a biomimetic membrane to investigate the mechanism of interfacial transfer of five antihistamines, i.e., clemastine (CLE), cyproheptadine (CYP), epinastine (EPI), desloratadine (DSL), and cetirizine (CET), and realize the real-time determinations. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques have been used to uncover the electrochemical transfer behavior of the five antihistamines at the L/L interface. Additionally, finite element simulations (FEMs) have been employed to reveal the thermodynamics and kinetics of the process. Visualization of antihistamine partitioning in two phases at different pH values can be realized by ion partition diagrams (IPDs). The IPDs also reveal the transfer mechanism at the L/L interface and provide effective lipophilicity at different pH values. Real-time determinations of these antihistamines have been achieved through potentiostatic chronoamperometry (I-t), exhibiting good selectivity with the addition of nine common organic or inorganic compounds in living organisms and revealing the potential for in vivo pharmacokinetics. Besides providing a satisfactory surrogate for studying the transmembrane mechanism of antihistamines, this work also sheds light on micro- and nano L/L interfacial sensors for in vivo analysis of pharmacokinetics at a single-cell or single-organelle level.

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.

Nanoelectrochemistry at liquid/liquid interfaces for analytical, biological, and material applications

Herein, we feature our recent efforts toward the development and application of nanoelectrochemistry at liquid/liquid interfaces, which are also known as interfaces between two immiscible electrolyte solutions (ITIES). Nanopipets, nanopores, and nanoemulsions are developed to create the nanoscale ITIES for the quantitative electrochemical measurement of ion transfer, electron transfer, and molecular transport across the interface. The nanoscale ITIES serves as an electrochemical nanosensor to enable the selective detection of various ions and molecules as well as high-resolution chemical imaging based on scanning electrochemical microscopy. The powerful nanoelectroanalytical methods will be useful for biological and material applications as illustrated by in situ studies of solid-state nanopores, nuclear pore complexes, living bacteria, and advanced nanoemulsions. These studies provide unprecedented insights into the chemical reactivity of important biological and material systems even at the single nanostructure level.

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).

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.

Investigation of Dendrimer Transfer Behaviors at the Micro-Water/1,2-Dichloroethane Interface Facilitated by Dibenzo-18-Crown-6

Trans-interfacial behaviors of multiple ionic species at the interface between two immiscible electrolyte solutions (ITIES) are of importance to biomembrane mimicking, chemical and biosensing, and interfacial molecular catalysis. Utilizing host-guest interaction to facilitate ion transfer is an effective and commonly used method to decrease the Gibbs energy of transfer of a target molecule. Herein, we investigated a facilitated ion transfer (FIT) process of poly(amidoamine)dendrimer (PAMAM, G0-G2) by dibenzo-18-crown-6 (DB18C6) at the microinterfaces between water and 1,2-dichloroethane (μ-W/DCE). Because of the host-guest interaction between a dendrimer and a ligand, negative shifts of the transfer potentials were observed using cyclic voltammetry or Osteryoung square wave voltammetry. From the FIT behavior of the dendrimer, we revealed that each DB18C6 could selectively coordinate with one amino group. We first evaluated the protonated status of the intermediate state (1:2) exactly under the conditions the dendrimer (G1) transfers across the interface using the electrochemical mass spectrometry (EC-MS)-hyphenated technique, which is much smaller than the protonated status in the water phase (1:8 to 14). Using the same methodology, we also studied the facilitated transfer behaviors of G0 and G2. Based on these results, we put forward the mechanism of the FIT process, which might involve a deprotonating process at the interface for higher-generation dendrimers.

Quantitative Analysis of Redox-Inactive Ions by AC Voltammetry at a Polarized Interface between Two Immiscible Electrolyte Solutions

The interface between two immiscible electrolyte solutions (ITIES) is ideally suited to detect redox-inactive ions by their ion transfer. Such electroanalysis, based on the Nernst-Donnan equation, has been predominantly performed using amperometry, cyclic voltammetry, or differential pulse voltammetry. Here, we introduce a new electroanalytical method based on alternating-current (AC) voltammetry with inherent advantages over traditional approaches such as avoidance of positive feedback iR compensation, a major issue for liquid|liquid electrochemical cells containing resistive organic media and interfacial areas in the cm² and mm² range. A theoretical background outlining the generation of the analytical signal is provided and based on extracting the component that depends on the Warburg impedance from the total impedance. The quantitative detection of a series of model redox-inactive tetraalkylammonium cations is demonstrated, with evidence provided of the transient adsorption of these cations at the interface during the course of ion transfer. Since ion transfer is diffusion-limited, by changing the voltage excitation frequency during AC voltammetry, the intensity of the Faradaic response can be enhanced at low frequencies (1 Hz) or made to disappear completely at higher frequencies (99 Hz). The latter produces an AC voltammogram equivalent to a "blank" measurement in the absence of analyte and is ideal for background subtraction. Therefore, major opportunities exist for the sensitive detection of ionic analyte when a "blank" measurement in the absence of analyte is impossible. This approach is particularly useful to deconvolute signals related to reversible electrochemical reactions from those due to irreversible processes, which do not give AC signals.

Electrochemical Behavior and Detection of Diclofenac at a Microporous Si3N4 Membrane Modified Water–1,6-dichlorohexane Interface System

The electrochemical behavior when the liquid–liquid interface was modified by commercially available, microporous silicon nitride membrane, was achieved using cyclic voltammetry with tetramethyl ammonium. The transfer characteristics of the ionizable drug diclofenac ( DCF − ), as an anti-inflammatory, anti-rheumatic, antipyretic, and analgesic treatment in common use in biomedical applications, were also investigated across microporous silicon nitride-modified liquid interface. Thus, some thermodynamic variables for DCF − , such as the standard Gibbs energy of transfer, the standard transfer potential and lipophilicity were estimated. Furthermore, the influence of possible interfering substances (ascorbic acid, sugar, amino acid, urea, and metal ions) on the detection of DCF − was investigated. An electrochemical DCF sensor is investigated using differential pulse voltammetry (DPV) as the quantification technique, a linear range of 8–56 µM and a limit of detection of 1.5 µM was possible due to the miniaturized interfaces formed within silicon nitride.

Portable Sensor for the Detection of Choline and Its Derivatives Based on Silica Isoporous Membrane and Gellified Nanointerfaces

A portable amperometric ion sensor was fabricated by integrating silica isoporous membrane (SIM) and organogel composed of polyvinyl chloride and 1,2-dichloroethane (PVC-DCE) on a 3D-printed polymer chip. The detection of ionic species in aqueous samples could be accomplished by adding a microliter of sample droplet to the sensor and by identifying the ion-transfer potential and current magnitude at the water/organogel interface array templated by SIM. Thanks to the ultrasmall channel size (2-3 nm in diameter), high channel density (4 × 10⁸ μm^-2), and ultrathin thickness (80 nm) of SIM, the ensemble of nanoscopic water/organogel (nano-W/Gel) interface array behaved like a microinterface with two back-to-back hemispherical mass diffusion zones. So, the heterogeneous ion-transfer across the nano-W/Gel interface array generated a steady-state sigmoidal current wave. The detection of choline (Ch) and its derivatives, including acetylcholine (ACh), benzoylcholine (BCh), and atropine (AP), in aqueous samples was examined with this portable sensor. Using differential pulse stripping voltammetry (DPSV), the quantification of these analytes was achieved with a limit of detection (LOD) down to 1 μM. Moreover, the portable ion sensor was insensitive to various potential interferents that might coexist in vivo, owing to size-/charge-based selectivity and antifouling capacity of SIM. With this priority, the portable ion sensor was able to quantitatively determine Ch and its derivatives in diluted urine and blood samples. The LODs for Ch, ACh, AP, and BCh in urine were 1.12, 1.30, 1.08, and 0.99 μM, and those for blood samples were 3.61, 3.38, 2.32, and 1.81 μM, respectively.

Detection of Metoprolol in Human Biofluids and Pharmaceuticals via Ion-Transfer Voltammetry at the Nanoscopic Liquid/Liquid Interface Array

Metoprolol (MTP) is one of the most widely used antihypertensive drugs yet banned to use in sport competition. Therefore, there has been an increasing demand for developing simple, rapid, and sensitive methods suited to the identification and quantification of MTP in human biofluids. In this work, ultrathin silica nanochannel membrane (SNM) with perforated channels was employed to support nanoscale liquid/liquid interface (nano-ITIES) array for investigation of the ion-transfer voltammetric behavior of MTP and for its detection in multiple human biofluids and pharmaceutical formulation. Several potential interfering substances, including small molecules, d-glucose, urea, ascorbic acid, glycine, magnesium chloride, sodium sulfate and large molecules, bovine serum albumin (BSA), were chosen as models of biological interferences to examine their influence on the ion-transfer current signal of MTP. The results confirmed that the steady-state current wave barely changed in the presence of small molecules. Although BSA displayed an apparent blockade on the transfer of MTP, the accurate determination of MTP in multiple human biofluids (i.e., urine, serum and whole blood) and pharmaceutical formulation were still feasible, thanks to the molecular sieving and antifouling abilities of SNM. A limit of detection (LOD) within the physiological level of MTP during therapy could be achieved for all cases, i.e., 0.5 and 1.1 μM for 100 times diluted urine and serum, respectively, and 2.2 μM for 1000 times diluted blood samples. These results demonstrated that the nano-ITIES array behaved as a simplified and integrated detection platform for ionizable drug analysis in complex media.

Trends in Hydrophilicity/Lipophilicity of Phosphonium Ionic Liquids As Determined by Ion-Transfer Electrochemistry

Ionic liquids (ILs) have become valuable new materials for a broad spectrum of applications including additives or components for new hydrophobic/hydrophilic polymer coatings. However, fundamental information surrounding IL molecular properties is still lacking. With this in mind, the microinterface between two immiscible electrolytic solutions (micro-ITIES), for example, water|1,2-dichloroethane, has been used to evaluate the hydrophobicity/lipophilicity of 10 alkylphosphonium ILs. By varying the architecture around the phosphonium core, chemical differences were induced, changing the lipophilicity/hydrophilicity of the cations. Ion transfer (IT) within the polarizable potential window (PPW) was measured to establish a structure-property relationship. The Gibbs free energy of IT and the solubility of their ILs were also calculated. For phosphonium cations bearing either three butyl or three hydroxypropyl groups with a tunable fourth arm, the latter displayed a wide variety of easily characterizable IT potentials. The tributylphosphonium ILs, however, were too hydrophobic to undergo IT within the PPW. Utilizing a micro-ITIES (25 μm diameter) housed at the tip of a capillary in a uniquely designed pipet holder, we were able to probe beyond the traditional potential window and observe ion transfer of these hydrophobic phosphonium ILs for the first time. A similar trend in lipophilicity was determined between the two subsets of ILs by means of derived solubility product constants. The above results serve as evidence of the validation of this technique for the evaluation of hydrophobic cations that appear beyond the conventional PPW and of the lipophilicity of their ILs.

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.

Recent developments in electrochemistry at the interface between two immiscible electrolyte solutions for ion sensing

The most recent developments on electrochemical sensing of ions at the liquid–liquid interface are reviewed here.