Electroanalytical Techniques Research Articles

Electroanalytical Study of Active Species to Deposit Ti Alloy from 1-Butyl-3-Methylimidazolium Chloride-Aluminum Chloride Ionic Liquid

Understanding the electrochemical deposition of titanium and its alloy from the ionic liquid electrolyte is technologically very essential and necessitates a wide range of attention to gain more insights into their electrochemistry. In this work, the electrochemical behavior of titanium-chloroaluminate anion species in the Lewis acidic alkyl imidazolium-chloroaluminate ionic liquid electrolyte is investigated by electroanalytical techniques such as cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP). The effect of scan rate on peak potential and peak current, constant current density, constant applied potential, and the electrolyte temperature are discussed. It is shown that the redox reaction of the Ti(II)/Ti(0) deposition from titanium hepta-chloroaluminate ([Ti(Al2Cl7)4]2−) anions is a quasi-reversible process with a 2-electron transfer reaction while that of Al(III)/Al(0) deposition from hepta-chloroaluminate ([Al2Cl7]−) anions proceeds through 3-electron transfer. The cyclic voltammograms indicated that the reduction of [Al2Cl7]− and [Ti(Al2Cl7)4]2− species to corresponding aluminum and titanium forms is a diffusion-controlled phenomenon. The diffusion coefficients of the titanium hepta-chloroaluminate anion are determined under the studied experimental conditions at different temperatures using CV and CP techniques.

Inexpensive, Three-Dimensional, Open-Cell, Fluid-Permeable, Noble-Metal Electrodes for Electroanalysis and Electrocatalysis.

This study describes the fabrication of three-dimensional, open-cell, noble-metal (Au, Ag, and Pt) electrodes that have a complex geometry, i.e., wire mesh, metallic foam, "origami" wire mesh, and helix wire mesh. The electrodes were fabricated using an ultrasonication-assisted electroplating method that deposits a thin, continuous, and defect-free layer of noble metal (i.e., Au, Ag, or Pt) on an inexpensive copper substrate that has the desired geometry. The method is inexpensive, easy to use, and capable of fabricating noble-metal electrodes of complex geometries that cannot be fabricated using established techniques like screen printing or physical vapor deposition. By minimizing the amount of the pure noble metal in the electrodes, their cost drops significantly and could become low enough even for single-use applications; for example, the cost of metal in a Au wire-mesh electrode is $0.007/cm2 of exposed area that is about 400 times lower than that of a wire-mesh electrode composed entirely of Au. The electrodes exhibit an almost identical electrochemical performance to noble-metal electrodes of similar shape composed of bulk noble metal; therefore, these electrodes could replace two-dimensional noble-metal electrodes (e.g., rods, disks, foils) in numerous electroanalytical and electrocatalytical systems or even allow the use of noble-metal electrodes in new applications such as flow-based electrochemical systems. In this study, wire-mesh and metallic foam noble-metal electrodes have been successfully used as working electrodes for the electrocatalytical oxidation of methanol and for the electrochemical detection of redox mediators, lead ions, and nitrobenzene using various electroanalytical techniques.

Utilizing a nanocomposite consisting of zinc ferrite, copper oxide, and gold nanoparticles in the fabrication of a metformin electrochemical sensor supported on a glassy carbon electrode.

The conception and development of a new electrochemical sensor is reported for the detection of metformin (MET). Zinc ferrite and copper oxide nanostructure (ZnFe2O4-CuO) and gold nanoparticles (AuNPs) have been used to prepare a nanocomposite in modifying a glassy carbon electrode (GCE). The unique ZnFe2O4-CuO/Au nanocomposite was applied as a sensor for the determination of traces of MET by some electroanalytical techniques. Experimental parameters affecting the results were investigated and optimized. Under the optimum conditions and at a working potential of 0.85V (vs. Ag/AgCl/3.0M KCl), the sensor response is linear in the MET range of1.0nmolL-1 to 1.0μmolL-1 MET. The limit of detection (LOD) is 0.3 nmolL-1 (at an S/N ratio of 3) and the sensitivity is 1.13μAμmolL-1cm-2. The sensor was applied to the determination of MET in real samples where it gave acceptable results. Graphical abstract.

Recent advances and challenges in electrochemical biosensors for emerging and re-emerging infectious diseases

The rise of emerging infectious diseases (EIDs) as well as the increase in spread of existing infections is threatening global economies and human lives, with several countries still fighting repeated onslaught of a few of these epidemics. The catastrophic impact a pandemic has on humans and economy should serve as a reminder to be better prepared to the advent of known and unknown pathogens in the future. The goal of having a set of initiatives and procedures to tackle them is the need of the hour.Rapid detection and point-of-care (POC) analysis of pathogens causing these diseases is not only a problem entailing the scientific community but also raises challenges in tailoring appropriate treatment strategies to the healthcare sector. Among the various methods used to detect pathogens, Electrochemical Biosensor Technology is at the forefront in the development of POC devices. Electrochemical Biosensors stand in good stead due to their rapid response, high sensitivity and selectivity and ease of miniaturization to name a few advantages.This review explores the innovations in electrochemical biosensing based on the various electroanalytical techniques including voltammetry, impedance, amperometry and potentiometry and discusses their potential in diagnosis of emerging and re-emerging infectious diseases (Re-EIDs), which are potential pandemic threats.

Electrochemical Sensors Coupled with Multivariate Statistical Analysis as Screening Tools for Wine Authentication Issues: A Review

Consumers are increasingly interested in the characteristics of the products they consume, including aroma, taste, and appearance, and hence, scientific research was conducted in order to develop electronic senses devices that mimic the human senses. Thanks to the utilization of electroanalytical techniques that used various sensors modified with different electroactive materials coupled with pattern recognition methods, artificial senses such as electronic tongues (ETs) are widely applied in food analysis for quality and authenticity approaches. This paper summarizes the applications of electrochemical sensors (voltammetric, amperometric, and potentiometric) coupled with unsupervised and supervised pattern recognition methods (principal components analysis (PCA), linear discriminant analysis (LDA), partial least square (PLS) regression, artificial neural network (ANN)) for wine authenticity assessments including the discrimination of varietal and geographical origins, monitoring the ageing processes, vintage year discrimination, and detection of frauds and adulterations. Different wine electrochemical authentication methodologies covering the electrochemical techniques, electrodes types, functionalization sensitive materials and multivariate statistical analysis are emphasized and the main advantages and disadvantages of using the proposed methodologies for real applications were concluded.

Photovoltaic performance of bipyridine and dipyridophenazine ligands anchored ruthenium complex sensitizers for efficient dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSCs) can be influenced by the sensitizer. Therefore, three heteroleptic ruthenium complexes, cis-[Ru(dcbpy)(bpy)(NCS)2] (Ru-bpy), cis-[Ru(dcbpy)(dppz)(NCS)2] (Ru-dppz) and cis-[Ru(dcbpy)(dppx)(NCS)2] (Ru-dppx) (dcbpy = 4,4′-dicarboxylic-2,2′-bipyridine, NCS = isothiocyanate) sensitizers, were synthesized using one pot synthesis. The structures and functionalization of the ligands in each complex sensitizer were confirmed using FT-IR and NMR analyses. They were then systematically studied to determine their light absorption spectrum, the metal-centered oxidation peak, and electron recombination properties using a UV–vis spectrophotometer and electroanalytical techniques (i.e., CV, EIS, and LSV). The criteria for an efficient DSSC ruthenium sensitizer were drawn based on the structure-property relationship. It was found that the power conversion efficiency (ɳ) of the sensitizers were in the sequence of Ru-dppz (ɳ = 0.40%) < Ru-bpy (ɳ = 0.58%) < Ru-dppx (ɳ = 0.61%) in comparison to a commercialized sensitizer N719 (ɳ = 0.93%), The introduction of the dimethyl group altered the LUMO to enhance the electron injection to the TiO2 conduction band and thus increased the power conversion efficiency of the DSSC.

Individual and Simultaneous Voltammetric Determination of Ultra-Trace Environmental Contaminant Dihydroxybenzene Isomers Based on a Composite Electrode Sandwich-like Structure.

An advanced electroanalytical technique for the simultaneous assessment of environmental contaminant dihydroxybenzene isomers, catechol (CC), hydroquinone (HQ), and resorcinol (RC), has been investigated using palladium nanoparticles (PdNPs) incorporated onto a poly(1,5-diaminonaphthalene) (DAN) matrix over a glassy carbon electrode (GCE). Concurrently, these types of phenols can be assessed by the PdDAN/GCE modified electrode employing square wave voltammetry and cyclic voltammetry (CV) techniques under optimal conditions. This modified electrode has demonstrated linear responses for CC, HQ, and RC from 50.0 to 1000.0 mM; concomitantly, low detection limits of 0.22, 0.22, and 0.47 nM and low quantification limits of 0.740, 0.758, and 1.590 nM, have been, respectively, shown. Successfully, the simultaneous assessment of the three isomers in river stream water, tap water, and underground water has been implemented via the modified electrode under investigation. In comparison to reported studies, the PdDAN catalytic electrode has shown an effective sensitivity, leverage reproducibility, long-term stability, and excellent anti-interference capability for the determination of dihydroxybenzene isomers.

Green preparation of reduced graphene oxide by Bougainvillea glabra flower extract and sensing application

In this paper, we report the application of Bougainvillea glabra flower extract as a green-reducing agent for the reduction of chemically prepared graphene oxide (GO). The removal of oxygen-containing functional groups after reduction of GO was due to the presence of phenolic compounds in the flower extract of Bougainvillea glabra. Towards the sensing of Pb2+, a simple drop-casting technique was adopted to fabricate the sensing element by modifying the surface of screen-printed carbon electrode (SPCE) with rGO-nafion nanocomposite. Differential pulse voltammetry was employed as an electroanalytical technique to study the sensing capability of the proposed electrode for different concentrations of Pb2+. The fabricated SPCE exhibited a low limit of detection of 0.05 nM toward Pb2+ with an improved sensitivity of 25.273 µA nM−1 over a linear range of 0.05–8.67 nM.

Bioelectrosynthesis technology for enhancing methane production using a thermophilic methanogenic consortium

This work investigated the electrocatalytic activity of a thermophilic methanogenic consortia (TMC) for developing a bioelectrosynthesis process to convert food and paper wastes to methane. Electroanalytical techniques were used to analyze the electrocatalytic activity of the TMC biofilm formed onto the electrodes. The developed electromethanogenesis process enhanced the yield of methane by 54.7% than control experiments. Scanning electron micrographs of the TMC bioelectrodes showed that the electrosynthesis process accelerates biofilm formation onto the electrodes leading to enhanced direct electron transfer reactions at electrode–electrolyte interface. This study will help in developing a novel approach for valorization of food and paper waste to biofuels.

Electrochemical Immunosensing Platform for the Determination of the 20S Proteasome Using an Aminophenylboronic/Poly-indole-6-carboxylic Acid-Modified Electrode.

The first electrochemical immunosensor for the determination of the 20S proteasome (P20S) was developed, entailing the immobilization of an antibody on an aminophenylboronic/poly-indole-6-carboxylic acid-modified electrode. The proposed electrochemical bioplatform is a simple and feasible analytical tool applicable for the determination of P20S in human plasma, considering its high clinical and biological relevance. Cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry (SWV) were used to determine the optimal step-by-step process to obtain the electrochemical immunosensor. The interaction of P20S with the recognition layer of the immobilized antibody on the nanostructured surface took place by incubating the electrode in a P20S solution at 20 °C for 2 h. Using SWV as an electro-analytical technique, this immunosensor can quantify P20S. The current was linear with the P20S concentration within two dynamic concentration ranges from 20.0 to 80.0 and 80.0 to 200.0 ng·mL-1 (r2 = 0.992 and 0.98, respectively) with a limit of detection and quantification of 6 and 18 ng·mL-1, respectively. Moreover, the immunosensor showed considerable repeatability and reproducibility, when the determination was done in human serum, which confirms that it is a promising alternative for direct detection of P20S in biological fluids with minimal interference.

The first attempt on fabrication of a nano-biosensing platform and exploiting first-order advantage from impedimetric data: Application to simultaneous biosensing of doxorubicin, daunorubicin and idarubicin

In this work, for the first time, we have developed a novel and very interesting electroanalytical methodology assisted by first-order multivariate calibration (MVC) for simultaneous determination of doxorubicin (DX), daunorubicin (DN) and idarubicin (ID) as three chemotherapeutic drugs at simulated physiological conditions. A sever overlapping was observed among signals of the three drugs which hindered us for simultaneous determination of them by conventional electroanalytical techniques. Therefore, we had to assist our method by chemometric approaches to develop a novel method for simultaneous determination of DX, DN and ID. Among the existing electroanalytical methods, electrochemical impedance spectroscopy (EIS) due to its high sensitivity was chosen. After individual calibration of the three drugs with the EIS data, a set of calibration samples was designed which was used to develop several first-order MVC models by partial least squares (PLS), continuum power regression (CPR), radial basis function-partial least squares (RBF-PLS), RBF-artificial neural network (RBF-ANN) and least squares-support vector machines (LS-SVM) as linear and non-linear chemometric algorithms. Then, performance of the developed MVC models in predicting concentrations of DX, DN and ID in synthetic samples was compared to choose the best model for the analysis of real samples. Our records confirmed more superiority of RBF-PLS algorithm than the other developed models which motivated us to choose it for the analysis of real samples. Fortunately, the results of the RBF-PLS in the analysis of real samples towards simultaneous determination DX, DN and ID was acceptable.

Optimization of oil palm-based cellulose and hydroxyapatite-carbon composite electrode for trace Pb(II) ions detection in aqueous system

An electroanalytical technique was devised using oil palm-based cellulose and hydroxyapatite as modifiers to carbon electrodes for Pb(II) ions detection in an aqueous system. The cyclic voltammetry scan suggested increased active binding sites and faster electron transfer with quasi-reversible redox peaks with a larger anodic current peak and smaller oxidation potential values. The optimal conditions were attained using 10% modifier at pH 2 in 0.1 M HCl, −1.2 V deposition potential, 270 s deposition time, 25 Hz frequency, 0.020 V amplitude, rotation speed of 700 rpm, and the step potential of 0.005 V. The square wave anodic stripping voltammetry established at optimum level exhibited excellent selectivity and stability from 10 ppb to 100 ppb for Pb(II) ions detection. Sharp anodic peaks were observed at -0.48 V for Pb(II) ions with the detection limit of 0.095 ± 0.32 ppb and limit of quantitation of 0.32 ± 0.32 ppb.

An Insight into Ionic Conductivity of Polyaniline Thin Films.

The work addresses an issue of the conductivity phenomenon in conductive polymer thin films. Polyaniline was chosen as a broadly used and thoroughly investigated conductive polymer in order to test and show capabilities of the developed original approach based on impedance spectra analysis. A number of films of different thickness were deposited onto a Pt electrode surface and consequently investigated in aqueous solution containing perchloric acid as an electrolyte. The processes that occur in polyaniline film were studied by cyclic voltammetry, electrochemical quartz crystal microgravimetry (EQCM) and electrochemical impedance spectroscopy (EIS). The role of incorporated ions as charge carriers was investigated with respect to the control of the conductivity properties of the film. Along with detailed polyaniline behavior study, the work makes up a fundamental scientific impact on theoretical electrochemistry and electroanalytical techniques.

Impedimetric immunosensor to determine patulin in apple juices using a glassy carbon electrode modified with graphene oxide

In this work, an electrochemical immunosensor to determine patulin mycotoxin in apple juice is developed. It consists of a glassy carbon electrode modified with a dispersion of graphene oxide and polyclonal anti-patulin antibodies bound to their oxygenated groups. Patulin determination was performed by electrochemical impedance spectroscopy. The calibration curve is linear for a concentration range from 1 × 10−2 to 10 ng mL−1. The limit of detection and the concentration of patulin to obtain 50% inhibition (IC50) were 9.8 pg mL−1 and 360 pg mL−1, respectively. In addition, an acceptable accuracy, with a percentage coefficient of variation (%CV) close to 20%, and recovery percentage (%R) of 86% were found. The electrochemical immunosensor has the advantage of allowing the determination of patulin without any pre-treatment of the samples. The results obtained from the electroanalytical technique were compared with those obtained by HPLC.

Hot-SWV: Square Wave Voltammetry with Hot Microelectrodes.

A promising strategy to lowering detection limits in electrochemical analysis is the active modulation of the electrode temperature. Specifically, by tuning the electrode's surface temperature one can enhance detection limits due to improved electrode process kinetics and increased mass transfer rates, all without affecting the bulk solution. Motivated by this argument, here we report the development of a new electroanalytical technique based on electrode-temperature modulation, which we call hot square wave voltammetry (Hot-SWV). The technique utilizes the superposition of conventional SWV, already considered as one of the most sensitive voltammetric techniques, and a high frequency alternating current (ac) waveform to electrically polarize microelectrodes. By applying about 100 MHz ac frequencies (with varying Vrms amplitudes), our method generates an electrothermal fluid flow (ETF) in the electrolyte surrounding the electrode, thereby increasing the sensitivity of the SWV-based detection. We demonstrate this by investigating the oxidation of ferrocyanide and iron(II) ions, as well as the reduction of the coordination compound ruthenium(III) hexamine under various experimental conditions. We validate our experimental results against a theoretical model built using finite element analysis and observe agreement within ≤15% error at temperatures ≤39 °C. Using Hot-SWV, we observe at least one-order-of-magnitude improvement in the limit of detection of ferrocyanide ions relative to conventional, mm-size electrodes at 25 °C. In addition, we anticipate that Hot-SWV will be particularly useful for electroanalytical measurements of ultralow (≤pM) concentrations of analytes in environmental and biomedical applications.

In Situ Real-Time Monitoring of ITO Film under a Chemical Etching Process Using Fourier Transform Electrochemical Impedance Spectroscopy.

As a novel approach to the in situ real-time investigation of an ITO electrode during the wet etching process, step-excitation Fourier-transform electrochemical impedance spectroscopy (FT-EIS) was implemented. The equivalent circuit parameters (e.g., Rct, Cdl) continuously obtained by the FT-EIS measurements during the entire etching process showed an electrode activation at the initial period as well as the completion of etching. The FT-EIS results were further validated by cyclic voltammograms and impedance measurements of partially etched ITO films using ferri- and ferrocyanide solution in combination with FESEM imaging, EDS, XRD analyses, and COMSOL simulation. We also demonstrated that this technique can be further utilized to obtain intact interdigitated array (IDA) electrodes in a reproducible manner, which is generally considered to be quite tricky due to delicacy of the pattern. Given that the FT-EIS allows for instantaneous snapshots of the electrode at every moment, this work may hold promise for in situ real-time examination of structural, electrokinetic, or mass transfer-related information on electrochemical systems undergoing constantly changing, transient processes including etching, which would be impossible with conventional electroanalytical techniques.

Hollow Reticular Shaped Highly Ordered Rice Husk Carbon for the Simultaneous Determination of Dopamine and Uric Acid

AbstractWe have prepared activated porous carbon material through simple pyrolysis method from rice husks (rhAC) for sensitive detection of dopamine (DA) and uric acid (UA). The prepared rhAC material was thoroughly characterized using various spectroscopic, microscopic, and electroanalytical techniques. Analysis of the voltammetric data showed that the analytes followed a first order reaction kinetics while following a 2e−/2H+ transfer process. We have discussed the possible oxidation mechanism for the analytes based on the results from our experimental analysis. The rhAC_GCE sensor was tested for interference, reproducibility, and stability. The sensor was also tested to evaluate its applicability in real life.

A novel binder-free electro-synthesis of hierarchical nickel sulfide nanostructures on nickel foam as a battery-type electrode for hybrid-capacitors

In this work, we have synthesized hierarchical nickel sulfide nanoparticles on nickel foam (NiS@Ni) via simple cathodic electrodeposition using aqueous nickel chloride (NiCl2) and thiourea mixtures as an electrolyte. The synthesized NiS@Ni are characterized using important surface analytical tools such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) with energy dispersive spectrum (EDS) and elemental mapping analysis. The positive electrode performance of NiS@Ni is tested in aqueous potassium hydroxide (KOH) by common electroanalytical techniques. The cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) curves of NiS@Ni exposed clear reversible redox peaks acknowledged the Faradaic battery-type performance in aqueous KOH. Moreover, the synthesized NiS@Ni delivers maximum specific capacities of 1109C/g (308.05 mAh/g) and 532C/g (147.8 mAh/g) at a scan rate of 5 mV/s and 2 A/g of current density, respectively. Therefore, the synthesized hierarchical NiS@Ni can be applied as a battery-type positive electrode in hybrid-capacitors.

Paper-Based Platform with an In Situ Molecularly Imprinted Polymer for β-Amyloid.

Alzheimer’s disease (AD) is one of the most common forms of dementia affecting millions of people worldwide. Currently, an easy and effective form of diagnosis is missing, which significantly hinders a possible improvement of the patient’s quality of life. In this context, biosensors emerge as a future solution, opening the doors for preventive medicine and allowing the premature diagnosis of numerous pathologies. This work presents a pioneering biosensor that combines a bottom-up design approach using paper as a platform for the electrochemical recognition of peptide amyloid β-42 (Aβ-42), a biomarker for AD present in blood, associated with visible differences in the brain tissue and responsible for the formation of senile plaques. The sensor layer relies on a molecularly imprinted polymer as a biorecognition element, created on the carbon ink electrode’s surface by electropolymerizing a mixture of the target analyte (Aβ-42) and a monomer (O-phenylenediamine) at neutral pH 7.2. Next, the template molecule was removed from the polymeric network by enzymatic and acidic treatments. The vacant sites so obtained preserved the shape of the imprinted protein and were able to rebind the target analyte. Morphological and chemical analyses were performed in order to control the surface modification of the materials. The analytical performance of the biosensor was evaluated by an electroanalytical technique, namely, square wave voltammetry. For this purpose, the analytical response of the biosensor was tested with standard solutions ranging from 0.1 ng/mL to 1 μg/mL of Aβ-42. The linear response of the biosensor went down to 0.1 ng/mL. Overall, the developed biosensor offered numerous benefits, such as simplicity, low cost, reproducibility, fast response, and repeatability less than 10%. All together, these features may have a strong impact in the early detection of AD.

Covalent attachment of laccase to carboxymethyl-botryosphaeran in aqueous solution for the construction of a voltammetric biosensor to quantify quercetin

Laccase from Botryosphaeria rhodina MAMB-05 was covalently immobilized on carboxymethyl-botryosphaeran by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) in aqueous solution. This approach was employed to fabricate a novel laccase-based biosensor to electrochemically quantify quercetin (QCT), using a simple carbon black paste electrode as a transducer. The proposed biosensor was characterized by electrochemical impedance spectroscopy and Nyquist plots were used to evaluate the immobilization of the enzyme. For determining QCT, variables were optimized, that included experimental conditions for laccase immobilization, pH of the supporting electrolyte, and instrumental parameters of the electroanalytical technique. From square-wave-voltammograms, a linear dependence between the cathodic current peak and QCT concentration was observed within the range 4.98–50.0 × 10−8 mol L−1, with a theoretical detection limit of 2.6 × 10−8 mol L−1. The proposed method was successfully applied to determine QCT in beverages, pharmaceuticals, and biological samples. The proposed biosensor device presented good selectivity in the presence of uric acid, various inorganic ions, as well as other phenolic compounds, demonstrating the potential application of this biosensing platform in chemically complex solutions. Operational and analytical stability of the laccase-biosensor were evaluated, and good intra-day (SD = 1.23%) and inter-day (SD = 2.32%) repeatability, and long storage stability (SD = 3.47%) are presented.