Abstract: The presence of residues from frequent antibiotic use in animal feed can cause serious health risks by contaminating products for human consumption such as meat and milk. The present article gives an overview of the electrochemical methods developed for the detection of phenicol antibiotic residues (chloramphenicol, thiamphenicol, and florfenicol) in different kinds of foodstuffs. Electrochemical sensors based on different biomolecules and nanomaterials are described. The detection limit of various developed methods with their advantages and disadvantage will be highlighted.

Abstract: Phenicols are an effective and a broad spectrum class of antibiotics which has lost favour due to their side effects on human health. A rapid and sensitive electrochemical detection system is developed for the simultaneous detection of chloramphenicol (CAP), thiamphenicol (TAP) and florfenicol (FF). The electrochemical behaviour of CAP in the presence of its derivatives was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). At a gold electrode, CAP gives rise to a sensitive cathodic peak at −0.68V (versus SCE) in a tris buffer solution (pH 7.6). This behavior gives us the opportunity to introduce a method for sensing CAP electrochemically in the presence of its derivatives. Calibration graphs were linear in the 2.5-7.4 μmol L-1 concentration range. Deviations from linearity were observed for higher concentrations and this was interpreted to be due to kinetic limitation caused by the saturation of CAP and its reduction products onto the gold electrode surface. A limit of detection of 1 μmol L-1 was found.

Abstract: The potential-controlled electrochemical aldol condensation of acetone to diacetone alcohol in a standard batch electrolysis set-up was studied in this work. It is confirmed that the reaction proceeds at the cathode and that, contrary to what is mentioned in earlier literature, water in the electrolyte has a disadvantageous effect on the reaction. Similar to the chemical reaction, the electrochemical reaction reaches a maximum yield when the equilibrium is reached. Separating the anode and cathode prevents cross-over and degradation of products, leading to a higher yield. Starting with pure acetone and support electrolyte, it was possible to obtain a diacetone alcohol concentration of 15 m% after two hours electrolysis in a divided set-up with a platinum electrode at -2.5 V. The concentration gradient throughout the electrolysis follows an exponential curve up to its equilibrium concentration.

Abstract: The electrochemical activation of C-X bonds requires very negative electrode potentials. Lowering the overpotentials and increasing the catalytic activity requires intensive electrocatalytic research. A profound understanding of the reaction mechanism and the influence of the electrocatalyst allows optimal tuning of the electrocatalyst. This can be achieved by combining electrochemical techniques with electron paramagnetic resonance (EPR) spectroscopy. Although this was introduced in the mid-twentieth century, the application of this combined approach in electrocatalytic research is underexploited. Several reasons can be listed, such as the limited availability of EPR instrumentation and electrochemical devices for such in situ experiments. In this work, a simple and inexpensive construction adapted for in situ EPR electrocatalytic research is proposed. The proof of concept is provided by studying a model reaction, namely the reductive cyclisation of allyl 2-bromobenzyl ether which has interesting industrial applications.

Abstract: Wearable electrochemical sensors are driven by the user-friendly capability of on-site detection of key biomarkers for health management. Despite the advances in biomolecule monitoring such as glucose, still, several unmet clinical challenges need to be addressed. For example, patients suffering from phenylketonuria (PKU) should be able to monitor their phenylalanine (PHE) level in a rapid, decentralized, and affordable manner to avoid high levels of PHE in the body which can lead to a profound and irreversible mental disability. Herein, we report a wearable wristband electrochemical sensor for the monitoring of PHE tackling the necessity of controlling PHE levels in PHE hydroxylase deficiency patients. The proposed electrochemical sensor is based on a screen-printed electrode (SPE) modified with a membrane consisting of Nafion, to avoid interferences in biofluids. The membrane also consists of sodium 1,2-naphthoquinone-4-sulphonate for the in situ derivatization of PHE into an electroactive product, allowing its electrochemical oxidation at the surface of the SPE in alkaline conditions. Importantly, the electrochemical sensor is integrated into a wristband configuration to enhance user interaction and engage the patient with PHE self-monitoring. Besides, a paper-based sampling strategy is designed to alkalinize the real sample without the need for sample pretreatment, and thus simplify the analytical process. Finally, the wearable device is tested for the determination of PHE in saliva and blood serum. The proposed wristband-based sensor is expected to impact the PKU self-monitoring, facilitating the daily lives of PKU patients toward optimal therapy and disease management.

Abstract: The smuggling of illicit drugs urges the development of new tools for rapid on-site identification in cargos. Current methods rely on presumptive color tests and portable spectroscopic techniques. However, these methods sometimes exhibit inaccurate results due to commonly used cutting agents, the colorful nature of the sample or because the drugs are smuggled in common goods. Interestingly, electrochemical sensors can deal with these specific problems. Herein, an electrochemical device is presented that uses affordable screen-printed electrodes for the electrochemical profiling of several illicit drugs by square-wave voltammetry (SWV). The identification of the illicit compound is based on the oxidation potential of the analyte. Hence, a library of electrochemical profiles is built upon the analysis of illicit drugs and common cutting agents. This library allows the design of a tailor-made script that enables the identification of each drug through a user-friendly interface (laptop or mobile phone). Importantly, the electrochemical test is compared by analyzing 48 confiscated samples with other portable devices based on Raman and FTIR spectroscopy as well as a laboratory standard method (i.e., gas chromatography-mass spectrometry). Overall, the electrochemical results, obtained through the analysis of different samples from confiscated cargos at an end-user site, present a promising alternative to current methods, offering low-cost and rapid testing in the field.

Abstract: Amphetamine (AMP) is posing critical issues in our society being one of the most encountered drugs-of-abuse in the current illicit market. The continuous drug production in Europe urges the development of new tools for the rapid on-site determination of illicit drugs such as AMP. However, the direct electrochemical detection of AMP is a challenge because the molecule is non-electroactive at the potential window of conventional graphite SPEs. For this reason, a derivatization step is needed to convert the primary amine into an electroactive oxidizable group. Herein, the rapid electrochemical detection of AMP in seized samples based on the derivatization by 1,2-naphthoquinone-4-sulfonate (NQS) is presented by using square wave voltammetry (SWV) at graphite screen-printed electrodes (SPEs). First, a detailed optimization of the key parameters and the analytical performance is provided. The method showed a sensitivity of 7.9 µA mM-1 within a linear range from 50 to 500 µM, a limit of detection of 22.2 µM, and excellent reproducibility (RSD = 4.3%, n = 5 at 500 µM). Subsequently, the effect of NQS on common cutting agents for the selective detection of AMP is addressed. The comparison of the method with drugs-of-abuse containing secondary and tertiary amines confirms the selectivity of the method. Finally, the concept is applied to quantify AMP in 20 seized samples provided by forensic laboratories, exhibiting an accuracy of 97.3 ± 10.5%. Overall, the fast analysis of samples with the electrochemical profiling of derivatized AMP exhibits a straightforward on-site screening aiming to facilitate the tasks of law enforcement agents in the field.

Abstract: Wearable devices based on microneedle (MN) technology have recently emerged as tools for in situ transdermal sensing or delivery in interstitial fluid (ISF). Particularly, MN-based electrochemical sensors allow the continuous monitoring of analytes in a minimally invasive manner through ISF. Exogenous small molecules found in ISF such as therapeutic drugs are ideal candidates for MN sensors due to their correlation with blood levels and their relevance for the optimal management of personalized therapies. Herein, a hollow MN array patch is modified with conductive pastes and functionalized with cross-linked chitosan to develop an MN-based voltammetric sensor for continuous monitoring of methotrexate (MTX). Interestingly, the chitosan coating avoids biofouling while enabling the adsorption of MTX at the electrode’s surface for sensitive analysis. The MN sensor exhibits excellent analytical performance in vitro with protein-enriched artificial ISF and ex vivo under a Franz diffusion cell configuration. The MN sensor shows a linear range from 25 to 400 μM, which fits within the therapeutic range of high-dose MTX treatment for cancer patients and an excellent continuous operation for more than two days. Moreover, an iontophoretic hollow MN array patch is developed with the integration of both the anode and cathode in the single MN array patch. The ex vivo characterization demonstrates the transdermal on-demand drug delivery of MTX. Overall, the combination of both MN patches represents impactful progress in closed-loop systems for therapeutic drug management in disorders such as cancer, rheumatoid arthritis, or psoriasis.

Abstract: The wearable revolution is already present in society through numerous gadgets. However, the contest remains in fully deployable wearable (bio)chemical sensing. Its use is constrained by the energy consumption which is provided by miniaturized batteries, limiting the autonomy of the device. Hence, the combination of materials and engineering efforts to develop sustainable energy management is paramount in the next generation of wearable self-powered electrochemical devices (WeSPEDs). In this direction, this review highlights for the first time the incorporation of innovative energy harvesting technologies with top-notch wearable self-powered sensors and low-powered electrochemical sensors toward battery-free and self-sustainable devices for health and wellbeing management. First, current elements such as wearable designs, electrochemical sensors, energy harvesters and storage, and user interfaces that conform WeSPEDs are depicted. Importantly, the bottlenecks in the development of WeSPEDs from an analytical perspective, product side, and power needs are carefully addressed. Subsequently, energy harvesting opportunities to power wearable electrochemical sensors are discussed. Finally, key findings that will enable the next generation of wearable devices are proposed. Overall, this review aims to bring new strategies for an energy-balanced deployment of WeSPEDs for successful monitoring of (bio)chemical parameters of the body toward personalized, predictive, and importantly, preventive healthcare.

Abstract: This work reports the use of modified screen-printed carbon electrodes (SPCEs) for the identification of three drugs of abuse and two habitual cutting agents, caffeine and paracetamol, combining voltammetric sensing and chemometrics. In order to achieve this goal, codeine, heroin and morphine were subjected to Square Wave Voltammetry (SWV) at pH 7, in order to elucidate their electrochemical fingerprints. The optimized SPCEs electrode array, which have a differentiated response for the three oxidizable compounds, was derived from Carbon, Prussian blue, Cobalt (II) phthalocyanine, Copper (II) oxide, Polypyrrole and Palladium nanoparticles ink-modified carbon electrodes. Finally, Principal Component Analysis (PCA) coupled with Silhouette parameter assessment was used to select the most suitable combination of sensors for identification of drugs of abuse in presence of cutting agents.

Abstract: The World Health Organization (WHO) model “List of Essential Medicines” includes among indispensable medicines antibacterials and pain and migraine relievers. Monitoring their concentration in the environment, while challenging, is important in the context of antibiotic resistance as well as their production of highly toxic compounds via hydrolysis. Traditional detection methods such as high-performance liquid chromatography (HPLC) or LC combined with tandem mass spectrometry or UV-vis spectroscopy are time-consuming, have a high cost, require skilled operators and are difficult to adapt for field operations. In contrast, (electrochemical) sensors have elicited interest because of their rapid response, high selectivity, and sensitivity as well as potential for on-site detection. Previously, we reported a novel sensor system based on a type II photosensitizer, which combines the advantages of enzymatic sensors (high sensitivity) and photoelectrochemical sensors (easy baseline subtraction). Under red-light illumination, the photosensitizer produces singlet oxygen which oxidizes phenolic compounds present in the sample. The subsequent reduction of the oxidized phenolic compounds at the electrode surface gives rise to a quantifiable photocurrent and leads to the generation of a redox cycle. Herein we report the optimization in terms of pH and applied potential of the photoelectrochemical detection of the hydrolysis product of paracetamol, i.e., 4-aminophenol (4-AP), and two antibacterials, namely, cefadroxil (CFD, beta-lactam antibiotic) and doxycycline (DXC, tetracycline antibiotic). The optimized conditions resulted in a detection limit of 0.2 mu mol L-1 for DXC, but in a 10 times higher sensitivity, 20 nmol L-1, for CFD. An even higher sensitivity, 7 nmol L-1, was noted for 4-AP.

Abstract: Phenols are considered as toxic pollutants and their discharge into the environment by industries is regulated by a concentration limit. As these limits are in the low mg L−1 to µg L−1-range, sensitive methods are necessary to detect these phenols. Here, aqueous industrial phenolic samples throughout a cleaning process were analyzed by two novel electrochemical sensors. Both the photoelectrochemical (PEC) sensor and the square wave voltammetric (SWV) sensor could successfully follow the decrease of the concentration of phenols along the industrial cleaning process. The discharge sample (μg L−1) could only be analyzed by the PEC sensor and not by the SWV sensor, as the phenolic concentration was close to the LOD of the latter. With HPLC-diode array detector (DAD) measurements, classical phenols such as phenol (PHOH), hydroquinone, resorcinol and o-cresol could be identified in the industrial samples, and their presence could be linked to the electrochemical responses. At last, the performance of the PEC and SWV sensors were compared with commercial colorimetric and chemical oxygen demand (COD) test kits. This comparison demonstrated the high sensitivity of the PEC sensor in the μg L−1 concentrated phenolic samples. Together with the identification of the redox peaks through HPLC-DAD analysis, the SWV sensor can be a powerful tool in the qualitative analysis of mg L−1 concentrated phenolic samples due to its speed, simplicity and absence of laborious sample pre-treatment steps.

Abstract: Electron-withdrawing perfluoroalkyl peripheral groups grafted on phthalocyanine (Pc) macrocycles improve their single-site isolation, solubility, and resistance to self-oxidation, all beneficial features for catalytic applications. A high degree of fluorination also enhances the reducibility of Pcs and could alter their singlet oxygen (1O2) photoproduction. The ethanol/toluene 20:80 vol % solvent mixture was found to dissolve perfluorinated FnPcZn complexes, n = 16, 52, and 64, and minimize the aggregation of the sterically unencumbered F16PcZn. The 1O2 production ability of FnPcZn complexes was examined using 9,10-dimethylanthracene (DMA) and 2,2,6,6-tetramethylpiperidine (TEMP) in combination with UV–vis and electron paramagnetic resonance (EPR) spectroscopy, respectively. While the photoreduction of F52PcZn and F64PcZn in the presence of redox-active TEMP lowered 1O2 production, DMA was a suitable 1O2 trap for ranking the complexes. The solution reactivity was complemented by solid-state studies via the construction of photoelectrochemical sensors based on TiO2-supported FnPcZn, FnPcZn|TiO2. Phenol photo-oxidation by 1O2, followed by its electrochemical reduction, defines a redox cycle, the 1O2 production having been found to depend on the value of n and structural features of the supported complexes. Consistent with solution studies, F52PcZn was found to be the most efficient 1O2 generator. The insights on reactivity testing and structural–activity relationships obtained may be useful for designing efficient and robust sensors and for other 1O2-related applications of FnPcZn.

Abstract: Scanning electron microscopy (SEM) remains a popular approach to determine the shape, size, density and elemental composition of particles collected on leaf surfaces, but the effect of leaf micro-morphology on particle counts is not very well known. In this study, leaves of sixteen urban plant species were examined for particle density in June and September 2016 using SEM. The investigated plant species differed in leaf micro-morphology involving trichomes, raised stomata, epicuticular wax crystals and convex epidermal cells forming deep grooves between cells. The particle density on leaves of the investigated plant species was estimated by particle size fraction and leaf side. Particle density was significantly higher on the adaxial (AD) leaf side compared to the abaxial (AB) leaf side and higher for fine-particles than coarse-particles. The effect of trichome density on particle density of the AB and the AD leaf side was indicated to be significant and positive for both coarse and fine-particles in June but not in September. The successive repeated measurements elucidated that features constructing the topography of a leaf surface such as trichomes, stomata, and epidermal cells frequently contributed towards the edge enhancement effect, resulting in exaggerated particle counts. Besides, the mechanical drift contributed to the disparity in particle density measurements. Lastly, the reduction in particle density between successive measurements were imputed on the charging effect. These results enable us to suggest that in addition to characterization of micro-morphological features on a leaf surface, SEM will continue to be a useful approach for determining the particle: shape, size, elemental composition and density of the deposited particles. Nonetheless, the disparity in particle density measurements can occur due to abnormal particle recognition. Based on the results of September, we recommend that within-session successive repeated measurements (~ n ≥ 5) need to be performed to remove measurement uncertainties and obtain reliable quantitative data of particle counts using SEM.