Electroanalytical Techniques Research Articles

Time-Frequency Design of a Multi-Sine Excitation With Random Phase and Controllable Amplitude for (Bio) Impedance Measurements

Impedance spectroscopy has become a standard electroanalytical technique to study (bio)electrochemical and physiological systems. From an instrumentation point of view, the measurement of impedance can be carried out either in the frequency domain using the classical frequency sweep method or in the time domain using a variety of broadband signals. While time-domain techniques can be implemented with relatively simple hardware and can achieve faster acquisition time, they are still not that popular because of their lower accuracy and modularity. In this work we present a method and an algorithm for computing the impedance spectrum of samples using an arbitrary time-domain signal excitation initially engineered from a multi-sine summation. The signal is designed in such a way that its spectral phase is derived from a discrete uniform distribution (obtained from a physically-true random number generator), but its time-domain maximum amplitude remains controllable. As such, samples can be excited with adjustable amplitude signals (as low as 50mV to 2V in the current setup) in order to avoid exciting the nonlinearities in the samples under test, which is critical for the very definition of the impedance. Furthermore, the method is proved to combine both speed of measurement, given that it permits to excite at once a large number of frequency components of the sample, as well as accuracy given that the signal’s power spectrum is relatively flat. We verified our method and algorithm for monitoring yogurt quality using (bio)impedance measurements over a period of 48 hours.

Classification of As, Pb and Cd Heavy Metal Ions Using Square Wave Voltammetry, Dimensionality Reduction and Machine Learning

The detection and classification of heavy metals is a growing need to guarantee the quality of process water in different industries. However, the official methodologies to evaluate the presence of these contaminants require samples pre-processing, making them time-consuming and expensive; these elements do not allow online monitoring. For this reason, new technologies are required for online monitoring and evaluation. In this work, a new methodology is presented for the detection and classification of different heavy metal ions such as: As, Pb and Cd. Commercial graphite sensors modified with 2D molybdenite were used applying an electroanalytical technique of square wave voltammetry. Subsequently, signal processing based on pattern recognition and machine learning methods was carried out. This classification methodology includes the following steps: data display and arrangement, dimensionality reduction through the t-distributed stochastic neighbor embedding (t-SNE) method, which serves as feature extraction, and the support vector machines (SVM) method as a classifier. The validation is carried out with a data set of 118 aqueous samples. Leave one out cross-validation (LOOCV) was used to obtain classification accuracy. The results showed a classification accuracy of 98.31% with only two errors of the experimental validation with this data set. It is concluded that this methodology is a useful tool for detecting the presence of these ions in aqueous samples with MoS2-2D.

Nitric acid concentration strongly influences low level uranium determination on PEDOT-PSS coated glassy carbon electrodes.

Understanding the parametric optimization and addition of modifications in existing techniques are the keys to successful research in the analytical sciences. The present study reports an electroanalytical technique by modifying an electrode with PEDOT-PSS and adjusting the analyte solution to lower acidity (0.05 M) levels. The proposed methodology achieved a detection limit of 1.24 ppb of uranium, which is far below the available concentrations of uranium in seawater; the WHO permissible limit for uranium in drinking water; and the allowed disposal limit for uranium in radioactive waste solutions. Redox characteristics and speciation analysis supported by theoretical prediction helped to understand the basic mechanism which lay behind the achievement of such low detection limits. The technique was successfully employed for uranium determination in real water samples and the results were validated by another independent technique (ICP-MS).

Microelectrode-Based Sensor for Measuring Operando Active Species Concentrations in Redox Flow Cells

The assessment of candidate materials for redox flow batteries requires effective diagnostic techniques for monitoring the evolution of electrolyte state of charge and state of health to interrogate time-dependent changes in system behavior. Further, such tools can be applied in practical embodiments to inform maintenance schedules and optimize energy utilization. In this work, we develop and test a flow-through, microelectrode-based electrochemical sensor to continuously measure active species concentrations in redox flow cells. A gold microelectrode (working electrode) and platinum wire (pseudoreference electrode) are sealed into a stainless steel fitting (counter electrode), and three-electrode electroanalytical techniques (i.e., voltammetry, chronoamperometry) are performed to correlate steady-state current to concentration. To validate transport and thermodynamics that govern the sensing mechanism, we combine multiphysics simulation with ex situ experimental testing, confirming that the device is capable of accurately determining individual species concentrations. We then evaluate the microelectrode sensor in a symmetric redox flow cell, demonstrating the utility of this approach for measuring operando concentrations, and discuss additional considerations for successful implementation (e.g., measurement protocol, material selection, flow cell design). Assembled from commercially available, off-the-shelf components, the sensor can be readily adopted by research laboratories and integrated into existing experimental workflows, making it a promising tool for studying flow battery materials.

Growth mechanism of pulse electrodeposited cadmium sulfide and zinc sulfide thin films with tartaric acid and glycerol as additives

Room temperature electrodeposition of thin films is beneficial, especially for cadmium sulfide (CdS) and zinc sulfide (ZnS), which are utilized in optoelectronic applications. The present study is unique, owing to its utilization of tartaric acid in the electrochemical deposition of these binary sulfides. This organic acid has been shown to play a vital role in mitigating the precipitation of sulfides and facilitating deposition. Also, the impact of this organic acid on the growth mechanism is evaluated by electroanalytical techniques including cyclic voltammetry and chronoamperometry. From the Randles-Sevcik plot, it is verified that the deposition is governed by a diffusion-controlled process. The elemental analyses unveil that the composition at deposition potentials of -1.1 V for cadmium sulfide and -1.4 V for zinc sulfide are near stoichiometric. The electrocrystallization of the films is interpreted employing Scharifker-Hills nucleation model and is observed to follow progressive nucleation for cadmium sulfide and instantaneous nucleation for zinc sulfide. The deposition process is characterized using impedance measurements that have affirmed the formation of cadmium sulfide and zinc sulfide via intermediate metal tartrate complex. The X-ray diffraction and Raman spectroscopy of as-deposited cadmium sulfide and zinc sulfide thin films confirm the hexagonal and cubic phases, respectively. The results show the adequacy of the method for the deposition of crystalline quality thin films at room temperature in the presence of tartaric acid.

Optimizing an Electrochemical Protocol for Quantitative Analysis of Ascorbic Acid in Dietary Supplements

AbstractElectroanalytical techniques are versatile and dynamic tools used extensively in research and industrial applications; however, they are not adequately covered in the undergraduate chemistry curriculum. Herein, a fast‐scan cyclic voltammetry (FSCV) protocol is presented as a simple but efficient method of analysis that can be incorporated into analytical chemistry labs to demonstrate the utility and versatility of electrochemical techniques. The simplicity of ascorbic acid's electrochemistry makes it an excellent candidate for evaluating an electroanalytical method. In this work, flow cell‐based FSCV was used to measure the ascorbic acid content in a dietary supplement. The protocol involved optimization of the excitation waveform and scan rate, and external standard calibration analysis. The method was evaluated using spike recovery and a standard addition analysis as a secondary method of validation. The external calibration method exhibited excellent accuracy (relative error=−0.6 %, Recovery=100.5 %), suggesting no significant matrix effect, high precision (RSD=±0.4 %) and sensitivity (m=2224.4 nA mm−1). These observations were comparable to results from the standard addition method as revealed by the statistical analysis. Overall, this work demonstrates the use of a cutting‐edge electroanalytical technique in quality control.

A comprehensive overview of common conducting polymer-based nanocomposites; Recent advances in design and applications

• In the present review article, we focus on the synthetic routs and important applications of conducting polymers. • Their recently advanced conducting materials and their important developments. • Outline the important properties of some selected conducting monomers. • Highlights the new research directions on the bases of current trends. Currently, conducting polymers have attracted tremendous attention due to their unique characteristics and significant applications, such as ionic conductivity, electroanalytical technique, optical transparency, metal-like conductivity, environmental pollutant-sensitive materials, and mechanical flexibility. There is an urgent need to develop momentum in the utilization of conducting polymers for the preparation of special types of conducting nanocomposites from both commercial and other essential perspectives. Traditional material preparation procedures suffer from various shortcomings such as blank determination, sample preparation, calibration, need for skilled operators, time-consuming techniques, non-universal approaches, and high cost. The objective of this review article is to provide details regarding the fabrication of conducting polymer-based nanocomposites for continuous and different advanced materials monitoring and other important applications. Particularly, attention has been paid towards the design, classification, and the development of nanocomposites of conducting polymers (CP) and their applications for the elimination of environmental pollutants present in the ecosystem. We primarily emphasize the significant applications and synthesis routes of conducting polymers and the nanocomposites from the perspectives of biomedical, energy, photocatalysis, environmental, and sensor applications, because they all are closely related areas and have been widely explored. Moreover, we discuss some important fundamental research trends in fabrication, raw material sources, and newly developed approaches and highlight new research directions.

Design, synthesis, bioanalytical, photophysical and chemo-phototherapeutic studies of heteroleptic Cu(II) complexes

BackgroundA broad investigation has been paid to design an alternative metal-based anticancer drug, bearing metal ions other than platinum, with more target specificity. In this regard, Cu(II) complexes showed a remarkable intercalation binding property with DNA which have received much attention in the development of efficient anticancer drugs. MethodsA series of mononuclear ternary Cu(II) complexes A, B and C were prepared with H2L and auxiliary ligand. The synthesized H2L and corresponding complexes were characterized using various electroanalytical and physicochemical techniques. The thermodynamic parameters were calculated using Gibb's-Helmholtz, Arrhenius and Eyring equations. Morphology, binding energies of core electrons and crystallographic nature of the metal complexes were evaluated by SEM, XPS and PXRD techniques. Binding studies of the metal complexes with CT-DNA were conducted by absorption, fluorescence and viscometric methods. Significant FindingsThe pBR322 cleavage, antioxidant and molecular docking studies revealed the potent biological activity of title complexes. In-vitro cytotoxicity of these biologically active biomaterials tested against HeLa and MCF-7 by MTT assay and DAPI staining revealed their anticancer activity. Such results are supportive for advanced studies which would come through insight for their possible applications.

Wastewater Nitrate Reduction to Ammonia By a Co-Centered Molecular Catalyst

The U.S. spends $2.2 billion annually on remediation of harmful algal blooms (eutrophication), primarily caused by anthropogenic nitrogen pollution in wastewater discharge.1 Eutrophication perturbs coastal ecosystems by disrupting food chains, decreasing biodiversity, and causing nutrient deficiencies.2 Selective nitrate reduction (NO3RR) of wastewater is an attractive remediation strategy that prevents eutrophication and recovers a value-added commodity chemical in the form of ammonia. Recovering ammonia from nitrate in fertilizer runoff and municipal wastewater could offset up to 13% of ammonia produced worldwide through the Haber-Bosch process.3–6 With renewable-sourced energy, this strategy would also offset 320,000 metric tons of CO2-eq in greenhouse gas emissions.7 In this study, we present a Co-centered macrocycle, called Co-DIM, as a homogeneous molecular catalyst for the selective reduction of nitrate to ammonia. The advantages of Co-DIM include high water solubility, tunable product selectivity by ligand modification, and a wide range of pH operability.8 Despite comprehensive studies of promising molecular catalysts performed in the CO2 reduction (CO2RR) literature,9 NO3RR has not received a similar level of attention, and comparative frameworks do not yet exist to critically evaluate catalyst activity, selectivity, and stability. In this study we combine electroanalytical techniques in model systems to bench-scale, membrane-separated electrolysis in real wastewater. By doing so, we quantify the performance of a model NO3RR electrocatalyst, and demonstrate a generalizable approach for comparative benchmarking against heterogeneous and homogeneous reduction catalysts for other reactions (e.g., CO2RR).Determining the reaction mechanism of homogeneous molecular electrocatalysis requires careful understanding of the reaction environment. Using electroanalysis techniques, such as cyclic voltammetry (CV), and electrode surface identity modification (through atomic layer deposition and self-assembled monolayers), we were able to probe the electron transfer kinetics of Co-DIM activation and NO3RR catalysis. We found that Co-DIM is activated by an outer-sphere electron transfer mechanism, thereby deemphasizing electrode material identity for catalysis. We also leveraged key features of the obtained sigmoidal CVs to build the first ever TOF-eta relationship for a NO3RR molecular catalyst. Finally, we demonstrated greater than 50% removal of nitrate using Co-DIM in electrolysis of municipal wastewater. With this experiment, we present the novelty of using rational cell architecture and observable electrocatalysis in real wastewater for substantial nitrate removal and ammonia recovery. This work aims to encourage a framework for NO3RR evaluation to foster next-generation catalyst design and device implementation for large-scale nitrate removal from wastewater.(1) Dodds, W. K.; Bouska, W. W.; Eitzmann, J. L.; Pilger, T. J.; Pitts, K. L.; Riley, A. J.; Schloesser, J. T.; Thornbrugh, D. J. Eutrophication of U.S. Freshwaters: Analysis of Potential Economic Damages. Environ. Sci. Technol. 2009, 43 (1), 12–19. https://doi.org/10.1021/es801217q.(2) Kemp, W. M.; Boynton, W. R.; Adolf, J. E.; Boesch, D. F.; Boicourt, W. C.; Brush, G.; Cornwell, J. C.; Fisher, T. R.; Glibert, P. M.; Hagy, J. D.; Harding, L. W.; Houde, E. D.; Kimmel, D. G.; Miller, W. D.; Newell, R. I. E.; Roman, M. R.; Smith, E. M.; Stevenson, J. C. Eutrophication of Chesapeake Bay: Historical Trends and Ecological Interactions. Mar. Ecol. Prog. Ser. 2005, 303, 1–29. https://doi.org/10.3354/meps303001.(3) Wastewater: The Untapped Resource; Unesco, Ed.; The United Nations world water development report; UNESCO: Paris, 2017.(4) Food and Agriculture Organization of the United Nations. World Fertilizer Trends and Outlook to 2020. 2020, 38.(5) Kato, T.; Kuroda, H.; Nakasone, H. Runoff Characteristics of Nutrients from an Agricultural Watershed with Intensive Livestock Production. J. Hydrol. 2009, 368 (1), 79–87. https://doi.org/10.1016/j.jhydrol.2009.01.028.(6) Lang, M.; Li, P.; Yan, X. Runoff Concentration and Load of Nitrogen and Phosphorus from a Residential Area in an Intensive Agricultural Watershed. Sci. Total Environ. 2013, 458–460, 238–245. https://doi.org/10.1016/j.scitotenv.2013.04.044.(7) Smith, C.; Hill, A. K.; Torrente-Murciano, L. Current and Future Role of Haber–Bosch Ammonia in a Carbon-Free Energy Landscape. Energy Environ. Sci. 2020, 13 (2), 331–344. https://doi.org/10.1039/C9EE02873K.(8) Xiang, Y.; Zhou, D.-L.; Rusling, J. F. Electrochemical Conversion of Nitrate to Ammonia in Water Using Cobalt-DIM as Catalyst. J. Electroanal. Chem. 1997, 424, 1–3.(9) Costentin, C.; Robert, M.; Savéant, J.-M. Catalysis of the Electrochemical Reduction of Carbon Dioxide. Chem Soc Rev 2013, 42 (6), 2423–2436. https://doi.org/10.1039/C2CS35360A.

Robust fabrication of silver pyro-vanadates via sonochemical approach for advanced energy storage application

One of the major challenges in the twenty-first century is the development of ultrahigh performance electrical energy storage (ES) devices with faster, safer, and more efficient ES materials. Herein, we report newly designed silver vanadates (Ag4V2O7), which serve as significant electrode material for upcoming ES devices due to its greater electrical conductivity as well as electrochemical activity. Ag4V2O7 were synthesized by the ultrasonication method. The as-synthesized material was characterized with various spectral as well as analytical methods. Furthermore, the supercapacitive property of Ag4V2O7 was evaluated using different electroanalytical techniques. The Ag4V2O7 electrode exhibited well electrochemical performance with a specific capacity (Csp) of 548 C g−1 at the current density of 1 Ag−1 and significant capacity retention of 88.7% even after 5000 GCD cycles at 6 Ag−1. The lowest value of charge transfer resistance (Rct = 4.12 Ω), and equivalent series resistance (ESR =6.33 Ω) exposed the faster reaction kinetics. The superior electrochemical performance was ascribed to its unique structure, which contributes to high conductivity, easy electron transfer, short ion diffusion distances, fast kinetics as well as a huge number of active sites in the electrode material. The electrochemical results demonstrated that Ag4V2O7 could be utilized as electro-active material for advanced energy storage systems.

Alternating Current Techniques for a Better Understanding of Photoelectrocatalysts

Several spectroscopic and electroanalytical techniques are in use when it comes to the investigation of interfaces in photoelectrocatalysis (PEC). Among them, AC techniques are the least used ones except for electrochemical impedance analysis despite having several advantages over DC electroanalytical techniques. Though AC electrolysis of water was known in the early years of the 20th century, it was not given significant attention either. In this Perspective, we discuss how these barely used yet powerful AC techniques, namely, (1) Mott–Schottky in impedance and photoelectrochemical impedance analyses (equivalent circuit analysis, capacitance spectroscopy), (2) intensity-modulated photocurrent spectroscopy (IMPS), (3) FS-HA-FT-AC voltammetry, and (4) paired electrolysis, can lead us ahead in the way of further fathoming interfaces in PEC with highlights on prospects of these AC techniques for energy conversion reactions.

Developed electrochemical sensors for the determination of beta-blockers: A comprehensive review

Beta-blockers (β-blockers) are a special type of medicine that are prescribed for a wide range of health problems including cardiovascular diseases. There is a narrow border between the therapeutic and toxic levels of β-blockers and at high dosages. β-blockers can cause serious side effects. Besides, β-blockers are used as a doping agent at some sports and their usages is banned by world anti-doping agency (WADA). Therefore, developing a simple, precise and sensitive methodology to determine β-blockers is greatly important. Among the different reported analytical approaches for β-blockers quantification, electroanalytical techniques offer high sensitivity, wide dynamic range, straightforward instrumentation, low price and short analysis time. The applicability in opaque and colored samples, high selectivity and the capability at determining several components simultaneously are other upsides of electrochemical sensors. In this regard, this review copes with critically comparing electrochemical sensors as well as measurement protocols for electroanalytical measurement of β-blockers. It is also highly concentrated on the employed working electrodes and their modification that are vital for effective determination. Moreover, important conclusions are made from the surveyed studies and some propositions are presented for future works.

W76. DECIPHERING THE DYNAMIC ROLE OF MIR-137 TARGETOME IN SCHIZOPHRENIA: TEMPORAL PROFILING AND COMORBIDITY WITH PSYCHIATRIC DISORDERS

This chapter introduces the main bibliographic resources in electroanalysis. Then, books and monographs as well as relevant journals dealing with electrochemical techniques are considered. It also contains some web pages with general information or links to materials and supporting resources related to electroanalytical techniques.

Determination of Diphenyl Amine (DPA) Stabilizer in Propellants – A Minireview

AbstractThere is concern about the aged propellants as the proportion of stabilizer, diphenyl amine (DPA), keeps on reducing while maintaining the propellant formulation safe. This is a very important issue as it keeps the propellant as well as the surrounding safe from any possible mishap. Therefore, the determination of residual DPA/DPA derivatives in the propellant is of utmost importance. Various attempts have been made to determine residual DPA/derivatives content in the propellant. In this review the detection methods have been compiled and analysed for their implications, detection limit and standard deviation. The methods attempted for detection comprise volumetric, chromatographic, electroanalytical, spectroscopic and thermoanalytical techniques. The volumetric method was tried in the initial attempts by adopting chemical reactions. Chromatographic methods were reported by adopting different procedures and variations. These have been discussed in details. Electroanalytical methods have become one of the important techniques to determine the residual DPA that has been discussed in detail with incorporation of various modifications. Spectroscopic methods were also deployed to determine the DPA content in the propellant. The methods, being very straight forward and clean, have been considered effective in determination. Differential scanning calorimetry has also been tried for finding the DPA content in the propellant sample by adopting different combinations, which is also incorporated for discussion in this paper.

Post‐Transition Metal Electrodes for Sensing Heavy Metal Ions by Stripping Voltammetry

AbstractHeavy metal ions contamination is an ever‐growing threat to human health and ecosystems. Analytic sensing of heavy metal ions is a prerequisite step toward addressing this challenge. Electroanalytical technique is an effective and convenient way to detect heavy metal ions. Especially, stripping voltammetry techniques have been utilized for sensing metal ions at trace levels in different sample matrices. The choice of the working electrode materials plays a decisive role in the precision and sensitivity of stripping voltammetry. Post‐transition metals (including elements in group 12) are elements with low melting points, demonstrating unique properties including amalgamation with heavy metal ions that enhance the performance of stripping voltammetry during the pre‐concentration step, which make them particularly suitable for heavy metal ion sensing. Here, for better understanding the features and advantages of post‐transition metals in stripping voltammetry, eight classes of working electrodes based on zinc (Zn), mercury (Hg), gallium (Ga), indium (In), tin (Sn), lead (Pb), antimony (Sb), and bismuth (Bi), are reviewed, with their efficiency and effectiveness compared and recent progresses discussed. Additionally, liquid metal electrodes based on post‐transition metals and alloys are also presented. This review provides viable directions for future development of heavy metal ion sensors based on post‐transition metals.

Electroanalytical Measurements of Oxide Ions in Molten CaCl2 on W electrode

The electrochemical interaction of oxide ions with tungsten electrodes in molten calcium chloride (CaCl2) was analyzed by combining electroanalytical techniques with X-ray photoelectron spectroscopy. During a cyclic voltammetry (CV) scan, the oxide ions appear to interact with the tungsten working electrode via a multi-step oxidation and reduction process. The overall redox peaks behave reversibly up to 750 mV s−1. This electrochemical process enables the oxide ion concentration to be correlated to CV oxidation peaks. The resulting correlation agrees well (8.8% difference) with back titration measurements and can be used to monitor oxide content in the salt in real-time during CaCl2 based pryoprocesses.

Efficiency of Nanomaterials for Electrochemical Diagnostics based Point-of-Care Detection of Non-Invasive Oral Cancer Biomarkers

Oral tumours are the sixth most incessant infection with high mortality and morbidity rates in human beings and they pose a serious threat worldwide owing to their soaring case-fatality rate and metastatic characteristics of spreading to other parts of the body. Nanomaterials as of late have become indispensable components for biosensor platforms due to their fantastic mechanical, electronic, and optical properties. Specific emphasis is laid in this review on electrochemical biosensors working at the molecular levels, which can be classified into mainly three groups i.e., DNA biosensors, RNA biosensors, and protein biosensors as indicated by the type of the analytes. The carbon-based and non-carbon-based nanomaterials utilizing electrochemical procedures for recognizing oral cancer biomarkers are also reviewed. An extensive review has been made to cover ongoing advancements in the field of nanomaterials based as electrochemical biosensors. This study mostly sums up the significant electrochemical methods, the ongoing advancements of electrochemical technique-based biosensor frameworks for the discovery of oral cancer biomarkers. This effort aims to provide the reader with a concise view of new advances in areas on oral cancer biomarkers for electrochemical signal amplification and the innovative electroanalytical techniques which have been utilized in the miniaturization and integration of the sensors.

Electrochemical immunosensor for detection of CA 15-3 biomarker in point-of-care

This work reports the development of a simple and rapid electrochemical immunosensor for the determination of breast cancer biomarker Cancer Antigen 15–3 (CA 15–3). Disposable and cost-effective chips, consisting of gold screen-printed electrodes (AuSPEs), were used to develop the portable electrochemical devices for monitoring the biomarker in point-of-care (PoC), under clinical context.The biosensor preparation consisted of two simple steps. First, a self-assembled monolayer (SAM) of mercaptosuccinic acid (MSA) was formed at the AuSPE surface. Then, the CA 15–3 antibody was covalently bound to the carboxylic groups standing at the electrode surface using EDC/NHS chemistry.The performance of the developed immunosensor was evaluated by assessing the sensor sensitivity, linear response interval, selectivity and detection limit (LOD). The developed immunosensor provided a wide linear concentration range (from 1.0 to 1000 U mL−1) and low detection levels were achieved (LOD of 0.95 U mL−1), enabling the sensitive detection of the cancer biomarker at clinically relevant levels, using square wave voltammetry (SWV) as electroanalytical technique. Moreover, selectivity studies performed against other cancer biomarkers (CA 125 and CA 19–9) revealed that the antibody has high selectivity for CA 15–3 antigen. The immunosensor was applied to the quantification of CA 15–3 in artificial serum samples with satisfactory results.

A Disposable Saliva Electrochemical MIP-Based Biosensor for Detection of the Stress Biomarker α-Amylase in Point-of-Care Applications

The design and synthesis of artificial receptors based on molecular imprinting (MI) technology for the development of a new MIP-based biosensor for detection of the stress biomarker α-amylase in human saliva in point-of-care (PoC) applications is described in this work. The portable electrochemical devices for monitoring α-amylase consists of cost-effective and disposable gold screen-printed electrodes (AuSPEs). To build the electrochemical device, the template biomolecule was firstly immobilized directly over the working area of the gold chip previously activated with a self-assembled monolayer (SAM) of cysteamine (CA). Then, pyrrole (Py) monomer was selected as building block of a polymeric network prepared by CV electropolymerization. After the electropolymerization process, the enzyme was removed from the polymer film in order to build the specific recognition sites for the target enzyme. The MIP biosensor showed a very wide linear concentration range (between 3.0 × 10−4 to 0.60 mg mL−1 in buffer solution and between 3.0 × 10−4 to 3.0 × 10−2 mg mL−1 in human saliva) and low detection levels were achieved (LOD < 3.0 × 10−4 mg mL−1) using square wave voltammetry (SWV) as the electroanalytical technique.

A review on recent electroanalytical methods for the analysis of antiviral COVID-19 drugs

Currently, there are no specific drugs for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, designated as coronavirus disease 2019 (COVID-19). Several therapeutic options including antiviral, antithrombotic, immunosuppressive, and anti-rheumatic drugs are researched all over the world. Analytical methods are needed in every step of innovation, research, development, and manufacturing process of pharmaceuticals, therefore new analytical methods for pharmaceuticals are developed and validated increasingly over time. In this review, recent reports on electroanalytical techniques for the determination of selected COVID-19 drugs, favipiravir (FAV), remdesivir (REM), lopinavir (LOP) / ritonavir (RIT), and hydroxychloroquine (HCQ) were emphasized. Electroanalysis of antiviral active pharmaceutical ingredients carried out at various modified or non-modified electrodes by cyclic voltammetry (CV), linear sweep voltammetry (LSV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) were compiled from the literature. The effects of supporting electrolyte and pH on the current and potential of the analytical signal were evaluated. Scan rate results obtained by the CV method showed whether the redox process of the drug active ingredient diffusion or adsorption controlled at the electrode used in the selected solvent-supporting electrolyte and pH systems. Linearity range and the limit of detection (LOD) of applied electroanalytical methods were compared by combining the results obtained from drug active ingredients given in references.