Chemically Modified Electrode Research Articles

Advancements in electrochemical sensor technology for warfarin detection: a comprehensive review.

Warfarin (WA), the most prescribed oral anticoagulant in patients with atrial fibrillation, is widely utilized for the treatment of various diseases, such as vascular disorders, venous thrombosis, and atrial fibrillation. However, its abnormal concentration is linked to a variety of disorders and diseases, namely bleeding while brushing teeth, skin tissue issues, hair loss, and chest pain. Therefore, WA monitoring in blood serum is vital due to its narrow therapeutic window. Accordingly, WA determination has been conducted using various methods, such as high-performance liquid chromatography, fluorescent, surface-enhanced Raman scattering, and electrochemical methods. Electrochemical methods have received considerable attention due to their outstanding selectivity, remarkable sensitivity, great time efficiency, and cost-effectiveness. Herein, a comprehensive literature survey on electrochemical methods for determining WA is presented. This review discusses the development of various chemically modified electrodes (CMEs). These CMEs, such as multi-wall carbon nanotubes, molecularly imprinted polymers, metal oxide nanoparticles, and polymer nanocomposites, owing to their morphology and structure, high selectivity, high conductivity, and high volume/area ratio, are designed to overcome the limitations of bare electrodes, which include reduced electrocatalytic activity, slower electron transfer rates, and poor sensitivity. Also, this review presents the advantages and disadvantages of various modified electrodes applied in WA detection.

Immobilization of cobalt phthalocyanine-imbedded electrospun nanofibers on a gold electrode for the electrocatalytic detection of mercury(II)

This research study describes the nanofabrication of electrospun nanofibers (ENFs) containing a coumarin tetra-substituted cobalt phthalocyanine (CoPc-cou), polyaniline (PANI) and polyvinyl alcohol (PVA). This nanocomposite was used to modify a gold substrate which was followed by the immobilisation of a 5 % Nafion (Nf) solution affording the CoPc-cou-ENFs-Nf|Au modified electrode. Comparison of the chemically modified electrode (CME) with the bare and other modified electrodes shows that the CME under optimised conditions displayed superior detection of Hg(II) attaining a linear range of 10 – 3000 µM. Furthermore, the CME exhibits selectivity and sensitivity in an interference sample containing multiple heavy metals. A good percentage recovery of 96 % was attained when the CoPc-cou-ENFs-Nf|Au electrode was applied to a real water sample which was comparable to a percentage recovery of 98 % which was attained using the ICP-OES to analyse the same water samples.

Synergism in the electrocatalytic properties of cobalt phthalocyanine-carbon nanotube-polymeric electrospun nanofibers immobilized on a gold electrode for the detection of lead(II) ions

Core-shelled electrospun nanofibers (ENFs) comprising of a polyvinyl acetate (PVA) shell encapsulating a composite of polyaniline (PANI), tetra-4-(3-oxyflavonephthalocyaninato)cobalt(II) (CoPc-flav), carboxylic acid functionalized multiwalled carbon nanotubes (f-MWCNTs) and an annealed conductive top layer of Nafion (Nf) were used to fabricated a chemically modified gold electrode (Au|ENFs-1-Nf) via the adsorption method. The electrocatalytic sensing capabilities of the Au|ENFs-1-Nf electrode towards Pb(II) ions were evaluated. In comparison to the bare gold electrode and other chemically modified electrodes (CMEs), the Au|ENFs-1-Nf electrode was less prone to fouling showing more stable analyte signal and less compromised background electrolyte currents. The Au|ENFs-1-Nf electrode could detect the Pb(II) cations in a reproducible manner ranging from 8 to 125 μM where limits of detection and quantification of 0.51 and 1.55 μM were obtained, respectively. The analytical performance of the aforementioned CME rendered a comparable percentage recovery (103 %) with that of Inductively coupled plasma-optical emission spectroscopy (ICP-OES) (115 %).

Electrocatalytic detection of Hg(II) using a platinum electrode modified with composite film of cobalt(II) phthalocyanine tetra-substituted with 1-(methoxymethyl)-benzotriazole groups and co-electropolymerized polypyrrole

The presence of mercury adversely affects the daily lives of humankind due to its acute toxicity and environmental persistence. Therefore, the development of cost-effective smart materials which can allow the real time, ultrasensitive and discriminatory monitoring of mercury concentrations in industrial and municipal water treatment plants is an imperative. It is foreseen that this proposed water quality assurance measure will be of utmost importance to identify the culprits for the wide prevalence of this heavy metal ion in the environment. Herein, a platinum electrode (Pt) was modified via the simultaneous electropolymerization of polypyrrole (PPy) and the co-electrodeposition of tetra-[4-((1H-benzotriazole)methoxy)phthalocyaninato]cobalt(II) (CoPc-Bzt, 2, (Btz = benzotriazole)). The complementary electrode modification processes were performed in a 1:1 (v: v) DMF: acetonitrile containing 1 M tetrabutylammonium hexafluorophosphate electrolyte solution over 20 cycles using cyclic voltammetry to afford the chemically modified electrode (CME), Pt|PPy/2. Differential pulse anodic stripping voltammetry (DPASV) was used to detect Hg(II) ions using the CME within a 10 µM to 100 µM linear range while calculated limits of detection and quantification (LOD and LOQ) were determined as 3.11 and 10.00 µM, respectively. The analytical performance of the CME rendered a statistically accepted percentage recovery (97.4%) whereas that of Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) is 112.3%.

Chemically Modified Electrodes Based on 4-((5-Isopropyl-3,8-dimethylazulen-1-yl)methylene)-2-phenyloxazol-5(4H)-one

Novel chemically modified electrodes (CMEs) based on azulene were prepared by electrooxidation of guaiazulene derivative 4-((5-isopropyl-3,8-dimethylazulen-1-yl)methylene)-2-phenyloxazol-5(4H)-one (G). G is based on guaiazulene non-alternating aromatic hydrocarbon exhibiting a less symmetrical structure compared to naphthalene skeletal derivative. Therefore, it can be used as a building block for the preparation of novel materials. To evaluate the chemical structure and surface images, the CMEs based on G (G-CMEs) were characterized by ferrocene redox probe, X-ray photon spectroscopy (XPS), and scanning electron microscopy (SEM). They were also tested for the analysis of synthetic samples of heavy metal (HM) ions. The influence of preparation conditions (electric charge and potential) on the properties of these CMEs was examined. This paper highlights the importance of electropolymerization conditions on electrodeposited film surfaces, especially on their analytical properties vs. Cd(II), Pb(II), Cu(II), and Hg(II) investigated ions. This study is relevant for further design and development of advanced materials based on azulenyl-phenyloxazolone for the HM analysis in water. A linear dependence of the peak currents for Pb(II) ion on the concentration in test aqueous solutions was obtained between 10−7 M and 5·10−5 M. The detection limits of 5·10−6 M; 10−7 M; 5·10−6 M; and 10−5 M were estimated for Cd(II), Pb(II), Cu(II), and Hg(II), respectively, for G-CMEs.

Voltammetric MDMA Analysis of Seized Ecstasy Samples

(1) Background: 3,4-Methylenedioxymethamphetamine (MDMA) is an illicit drug that is sold as ecstasy. We aimed to develop a voltammetric method based on a chemically modified electrode (CME) to analyze MDMA. (2) Methods: The CME was evaluated with respect to the percentage of modifier, pre-concentration time, electroanalytical parameters, and selectivity. Then, the performance of the new voltammetric method was compared to the performance of color tests and chromatographic analyses (GC-MS and UPLC-MS) during the analysis of 11 seized ecstasy batches. (3) Results: The modifier percentage (v/v) of 1.5% provided the best CME. The electroanalytical parameters were in a linear range from 4.06 to 25.42 µmol L−1, SD = 0.018 µA, m = 84.0 × 103 µA L mol−1, r = 0.999, LD = 0.64 µmol L−1, and LQ = 2.17 µmol L−1. The CME was selective for MDMA. The MDMA concentration in the analyzed ecstasy lots ranged from 0 (without MDMA) to 63% (w/w). The voltammetric method developed for quantifying MDMA in ecstasy lots proved feasible and accurate (with a relative percentage error of ≤ ±13.2%). (4) Conclusions: The CME developed herein showed greater sensitivity (m) and lower LD and LQ for quantifying MDMA traces, paving the way for the use of voltammetric methods during forensic investigations.

Construction of a Functional and Robust Cobalt(II) Phthalocyanine‐Modified Electrode for the Electrocatalytic Detection of Paraquat

AbstractThis study explores the optimization and application of a gold‐modified electrode, CoPc‐cou‐f‐MWCNTs/3‐HT|Au, for the electrocatalytic detection of a water pollutant, paraquat (PQ). It was fabricated via a sequential modification procedure entailing the formation of self‐assembled monolayers (SAMs) of a nanocomposite comprising of a coumarin tetra‐substituted cobalt phthalocyanine (CoPc‐cou) and carboxylic acid functionalized multiwalled carbon nanotubes (f‐MWCNTs). This was followed by the in‐situ immobilization of poly(3‐hexylthiophene) ([3‐HT]n) through electropolymerisation to render the chemically modified electrode (CME). Subsequently, the CME illustrated enhanced sensitivity towards PQ compared to the bare or CoPc‐cou‐f‐MWCNTs modified electrodes. The CoPc‐cou‐f‐MWCNTs/3‐HT|Au electrode displayed a linear PQ detection range of 0.584–1000 μM with a limit of detection (LOD) and limit of quantification (LOQ) of 0.193 μM and 0.584 μM, respectively. Comparison between calibration curves for the modified electrode and HPLC‐MS illustrates that the former method has a lower but comparable calibration sensitivity for PQ. In addition, this CME could electrocatalytically distinguish PQ within a real water sample collected from the Durban lagoon. Furthermore, the direct recovery of PQ in the lagoon water by the modified Au electrode was found to be 86 %, which is lower than the calculated value of 97 % obtained by HPLC‐MS after rigorous solid‐phase microextraction of the analyte. However, the lower percentage recovery could be rationalized by the interference studies.

A Novel Electrochemical Sensing Platform Based on Bimetallic Ru-Cu-MOF for the Voltammetric Detection of Ciprofloxacin Antibiotic

Metal-organic frameworks (MOFs) are an attractive class of highly ordered, crystalline, porous materials that exhibit large specific surface area, porosity, tunable structure and ease of functionalization. The presence of a number of uniformly dispersed metal components i.e. catalytic molecular units throughout the framework make MOF based materials a potential candidate for electrochemical sensing studies. However, pristine MOFs have the inherent drawbacks such as the inferior electrical conductivity that need to be addressed for its direct application in sensing platforms. In this context, the design of redox-active and highly conducting MOF is a research hotspot in the material science since it can overcome the inferior electrocatalytic activity of chemically modified electrodes (CME) based on pristine MOF. The integration of highly conducting metals into the framework is an efficient method to enhance the electric conductivity and thereby the electrochemical activity of synthesized material. The synergistic effect arising from the combination of different metal ions changes the surface electronic structure of MOF and thereby improve the mobility of charge carriers.Herein, an electrochemical sensing platform based on ruthenium doped Cu-MOF was developed for the sensitive detection of ciprofloxacin antibiotic. This work focuses on the synthetic strategy of Ru-Cu-TMA where the parent MOF, Cu-TMA, was synthesised by a facile room temperature mixing at ambient pressure. The present synthetic method is found to be a simple and efficient method compared to the conventional solvothermal method reported commonly for MOF synthesis. The successful integration of ruthenium into Cu-MOF created a number of electrocatalytic active sites which can favour the interaction with analyte species in sensing studies. The structural features and morphology of the synthesized MOF materials were studied using different characterization techniques like XRD, IR, SEM, XPS etc. The porous structure of MOF combined with higher reaction kinetics due to the incorporation of ruthenium cause a synergistic effect which makes the mixed-valent MOF a promising candidate for sensing studies. The composite, Ru-Cu-TMA, prepared was used as an electrode modifier for the sensitive detection of ciprofloxacin by electrochemical technique. Initially, the electrochemical activity of the chemically modified electrodes were examined and Ru-Cu-TMA modified electrode shows the higher current and fast electron transfer which paves the way for its application as sensing material. In addition, more number of active sites formed in MOF by ruthenium doping considerably increases the sensing performance of Ru-Cu-TMA. The electrochemical oxidation of ciprofloxacin on electrode surface is confirmed as an irreversible, diffusion-controlled process. The sensor exhibited a wide linear dynamic range (2.5 – 100 µM) with a lower limit of detection (3.29 nM) and sensitivity 0.0524 µA/µM. Moreover, the sensor demonstrates excellent selectivity, adequate stability, repeatability and can be used for real sample analysis.The porous structure of MOF combined with the enhanced reaction kinetics due to ruthenium doping together increased the electrochemical activity of the developed sensor. The enhanced electrochemical surface area and the increased number of active sites generated with the doping of ruthenium facilitates electron transfer with the electrode surface. Further, the aromatic ring system of CIP can interact with the conjugated ᴨ-electrons in MOF through stacking which further makes the Ru-Cu-TMA modified electrode a promising sensing platform. Figure 1

Comments from the Editor‐in‐Chief

I also want to recognize Professor Yoon-Bo Shim for his many years of dedicated service as an Editor. He ended his tenure on December 31, 2022. His efforts have been instrumental in growing the journal's presence in South Korea and Asia proper during the past decade. He has done a wonderful job promoting the journal and handling submissions from the region. We will miss his creative ideas, leadership, and editorial expertise. Electroanalysis is a peer-reviewed international journal that disseminates impactful and scientifically important research pertaining to the field of electroanalytical chemistry. Articles may address conceptual advances in sensing or detection that are applicable to many types of analytes or more applied papers that report on the use of existing concepts in a new way or for new types of analytes. Articles on advances in analytical voltammetry and potentiometry, novel electrochemical sensors and detection schemes coupled with separation science, the preparation of metal and carbon electrode materials and their characterization, chemically-modified electrodes for molecular recognition and electrocatalysis, electrochemical sensors and biosensors, nanoscale electrochemistry, nano bioelectronics, neuroelectrochemistry, point-of-care diagnostics and wearable sensors, hyphenated electrochemical techniques and advanced electrochemical instrumentation are sought. Basic science and application papers in the biomedical, environmental, industrial, pharmaceutical, and food fields are welcome. A goal of the journal is to guide the electroanalytical chemistry community on the latest in measurement advances and on where measurement opportunities and challenges exist. Wishing all the best in 2023!! Greg M. Swain Editor-in-Chief

Advanced Materials Based on Azulenyl-Phenyloxazolone

Chemically modified electrodes (CMEs) based on 2-phenyl-4-((4,6,8-trimethylazulen-1-yl)methylene)oxazol-5(4H)-one (M) were obtained by irreversible electrooxidation of M in millimolar solutions in 0.1 M tetrabutylammonium perchlorate (TBAP) in acetonitrile. These CMEs were characterized by a ferrocene redox probe, electrochemical impedance spectroscopy (EIS), X-ray photon spectroscopy (XPS), and scanning electron microscopy (SEM). The influence of the preparation conditions (charge and potential) was examined. The CMEs were finally used for the analysis of synthetic samples of heavy metal (HM) ions. The paper highlights the importance of potential and electropolymerization charge on the film properties, with accent on recognition of HMs, in order to identify the best conditions for their detection in water. The observed findings are relevant for further design and development of advanced materials based on azulenyl-phenyloxazolone for the analysis of HMs in water.

Electrochemical and spectral studies of rhodanine in view of heavy metals determination

AbstractThe electrochemical study of 2‐Sulfanylidene‐1,3‐thiazolidin‐4‐one (rhodanine, R) was performed on a glassy carbon working electrode by using three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) at rotating disk electrode voltammetry (RDE). The CV, DPV, and LSV at RDE curves for R were recorded at different concentrations in 0.1 M TBAP/CH3CN. Polymeric films were formed by successive cycling at different potentials and by controlled potential electrolysis. The film formation was proved by recording the CV curves of the chemically modified electrodes (CMEs) in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. The obtained CMEs were used for the detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd (II), Pb (II), Cu (II), Hg (II)) of concentrations between 10−7 and 10−5 M were analyzed using CMEs prepared in different conditions. The most intense signal was obtained for Pb(II) ion (estimated detection limit = 10−7 M), which shows that these CMEs can be used for Pb(II) ion detection. The ability of R to form complexes with Pb(II) ion was also tested by UV‐Vis spectrometry. The obtained results showed the formation of Pb(II)R2 as the most stable complex.

Nanocrystalline SnO₂-Modified Electrode for Ultra-Sensitive Mercury Ion Detection

Chemically modified electrode (CME) has shown significant potential for achieving on-site and real-time detection of heavy metal ions. In this paper, a nanocrystalline SnO₂-modified Au electrode as an electrochemical sensor for ultrasensitive mercury ion (Hg^2+) detection was proposed and demonstrated. The modification method is simply employing the spin-coating process of colloidal SnO₂ quantum wires at room temperature in ambient air without further heat treatment. Nanocrystalline SnO₂ possesses a large surface area with abundant dangling bonds, through which the enrichment and dissolution of ions were enhanced and converted to significant current signal under anodic stripping voltammetry (ASV) scanning mode. According to the results of DFT analysis, SnO₂ has a greater adsorption energy for Hg^2+ than that of Au, which further improves its sensitivity. The nanocrystalline SnO₂-modified electrode exhibits sensitive response to Hg^2+ in the range of 10^−9 M~10^−4 M, with the limit-of-detection (LOD) of 0.036 nM. The selectivity was ascribed to the higher adsorption energy of Hg on SnO₂ surface compared with other metals in this study. The electrode modification strategy based on colloidal semiconductor nanocrystals may promote the design of sensitive sensors for rapid and reliable ion detection.

Electrochemical and Spectral Studies on Benzylidenerhodanine for Sensor Development for Heavy Metals in Waters

Electrochemical and spectral studies of benzylidenerhodanine (BR) were performed in order to develop new sensors for heavy metals (HMs) based on chemically modified electrodes (CMEs). CMEs were obtained by cycling and by controlled potential electrolysis at different potentials and charges. Film formation was demonstrated by recording the CV curves of CMEs in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. BR-CMEs were used for the analysis of HMs. Samples of Cd(II), Pb(II), Cu(II), and Hg(II), each possessing concentrations between 10−7 and 10−5 M, were analyzed by using CMEs prepared in different conditions. The most intense signal was obtained for the Pb(II) ion. These BR-CMEs can be used for the analysis of Pb(II) in monitored waters. An electrochemical study was performed at different concentrations of BR in 0.1 M TBAP/CH3CN on a glassy carbon electrode by differential pulse voltammetry, cyclic voltammetry, and rotating disk electrode voltammetry. The complexation ratio in the homogeneous solution has been established by the Mollard method in acetonitrile solutions.

Electrochemical Biosensor Employing Bi2S3 Nanocrystals-Modified Electrode for Bladder Cancer Biomarker Detection

Bladder cancer is a kind of malignant tumor with high incidence in the urinary system, complex pathogenic causes, and the high recurrence rate. Biosensors capable of rapid, on site, and accurate bladder cancer diagnosis method continue to be lacking. Here, the electrochemical biosensor for detecting cytokeratin 18 (CK18, bladder cancer biomarker) was constructed based on the chemically modified electrode (CME). The work electrode (WE) was modified by bismuth sulfide semiconductor nanocrystals (Bi2S3 NCs), and then immobilized with CK18 antibodies and blocking agents to complete the electrode preparation. The results indicated that the interface of a flexible carbon electrode with Bi2S3 NCs film was steady with reliable charge transfer capability. With the large specific area and quantum size effect, the proposed sensor could detect CK18 antigen protein with an ultralow detection limit of 1.87 fM (fmol L−1) and wide linear dynamic range of 1–1000 pg mL−1, respectively. Detecting results could be read in less than 30 s with the portable, planar flexible CME. The sensitive and specific electrochemical biosensor possessed the characteristics of rapidity, ease-of-use, and non-invasive detection, indicating the application prospect in the early screening of bladder cancer and other diseases.

Recent Advantages of Mediator Based Chemically Modified Electrodes; Powerful Approach in Electroanalytical Chemistry

Background:Modified electrodes have advanced from the initial studies aimed at understanding electron transfer in films to applications in areas such as energy production and analytical chemistry. This review emphasizes the major classes of modified electrodes with mediators that are being explored for improving analytical methodology. Chemically modified electrodes (CMEs) have been widely used to counter the problems of poor sensitivity and selectivity faced in bare electrodes. We have briefly reviewed the organometallic and organic mediators that have been extensively employed to engineer adapted electrode surfaces for the detection of different compounds. Also, the characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed.Objective:Improvement and promotion of pragmatic CMEs have generated a diversity of novel and probable strong detection prospects for electroanalysis. While the capability of handling the chemical nature of the electrode/solution interface accurately and creatively increases , it is predictable that different mediators-based CMEs could be developed with electrocatalytic activity and completely new applications be advanced.

Surface Characterization of New Azulene-Based CMEs for Sensing

Films of 2-(azulen-1-yldiazenyl)-5-phenyl-1,3,4-thiadiazole (T) were successfully deposited on glassy carbon surfaces to prepare chemically modified electrodes (CMEs). Their surface characterization was analyzed by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). This complexing monomer has been deposited through direct electropolymerization in conditions established during the electrochemical characterization of T performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and rotating disk electrode voltammetry (RDE). These methods put in evidence the high degree of asymmetry of oxidation and reduction curves, which is due to the irreversible processes occurring at opposite potentials. The film formation was confirmed by ferrocene redox assay probe. The properties of the electrodes modified with T (T-CMEs) were investigated for sensing heavy metal (HM) ions in water solutions, with promising results for Pb(II) among Cd(II), Cu(II), and Hg(II) ions.

Polyazulene-Based Materials for Heavy Metal Ion Detection. 3. (E)-5-((6-t-Butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole-Based Modified Electrodes

A recently synthesized azulene-tetrazole molecular receptor is proposed in this paper to continue the series of azulene substituted compounds that have been developed to build polyazulene-based materials for heavy metal (HM) ion detection. This study focuses on characterization of (E)-5-((6-t-butyl-4,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) by electrochemical techniques in view of its use for designing electrochemical sensors for HM ion complexation. The character of redox processes was proved by cyclic, differential pulse, and rotating disk electrode voltammetry. An in-depth thermodynamic study of the complexation properties of the free ligand with Pb(II) and Cd(II) from aqueous solutions was performed, and the stoichiometry and stability constant values were determined. Chemically modified electrodes (CMEs) based on L (L-CMEs) prepared by controlled potential electrolysis (CPE) at different applied potentials and charges were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Their surface morphology was examined by scanning electron microscopy (SEM). The complexing properties of L-CMEs were investigated towards the detection of HM ions by anodic stripping and compared to the stability constants of the complexes in solution. Voltametric curves showed well-defined peaks for Pb (II), Cd (II), Cu (II) and Hg (II), but the responses differ from each other and vary depending on the ion concentrations in the accumulation solutions. The best results were obtained for Pb(II) and Cd(II) ions. The results obtained for Pb(II) are promising and can be used for its analysis in water solutions (detection limit of about 10−9 M).

Molecular orientation and dynamics of ferricyanide ion-bearing copoly(ionic liquid) modified glassy carbon electrode towards selective mediated oxidation reaction of cysteine versus ascorbic acid: A biomimicking enzyme functionality

Understanding the electron-transfer (ET) functionality of enzymes in relation to their molecular orientation and dynamics is a cutting-edge research interest in the interdisciplinary areas of chemistry and biology. In this work, we demonstrate how the molecular structure and orientation of a redox polymer influence the ET behavior and specific catalytic functionality to target substance, ascorbic acid (AA) or cysteine (CySH) in a physiological condition. In the literature, Fe(CN)63−, a well-known benchmarking redox system, based chemically modified electrodes (CME) prepared by the ion-exchange method, has been widely used as an electrocatalyst for ascorbic acid oxidation reaction without the interference of CySH. In this work, a Fe(CN)63− bearing copoly(ionic liquid)-ethanol solution modified glassy carbon electrode, designated as GCE@{Fe(CN)63−}-coPIL, prepared as a homogenous solution followed by CME formation, has shown a unique and selective CySH oxidation reaction, rather than expected AA mediation, similar to the Thiol Oxidase enzyme-based biomimetic functionality. Andrieux and Saveant and Michaelis-Menten kinetic models were adopted to explain the reaction mechanism. The polymer network orientation and dynamics are found to influence strongly on the electrocatalytic functionality of the new CME. It has been revealed that underlying surface, functional groups, and solvent nature impact the molecular architectures of the {Fe(CN)63−}-caped polymer back-bone (insulating) network as a fully (H2O and CHCl3) or partially (C2H5-OH and CH3CN) shielded structures and decide its electron-transfer and selective mediated oxidation reaction functionalities. This observation is similar to the protein folding of enzymes at various external stimuli conditions and its unfolded structures for direct electron transfer and selective mediated oxidation/reduction reaction. As a proof of concept, electroanalytical application of thiol functional group (CySH) oxidation to disulfide bond (CyS-SyC) catalyzed by the GCE@{Fe(CN)63−}-coPIL in neutral pH solution has been demonstrated.

Electrocatalytic determination of mercury cations at the interfaces of gold electrodes modified with self-assembled monolayers of cobalt phthalocyanines and electropolymerized 3-hexylthiophene films

In-situ fabrication of gold electrodes was performed by self-assembled monolayer (SAM) formations of peripherally furan (3) or benzothiazole (4) substituted cobalt phthalocyanines followed by electropolymerization of 3-hexylthiophene (3-HT) molecules. The resultant chemically modified electrodes (CMEs) portrayed optimal electrocatalytic activities during the voltammetric detection of Hg(I) and Hg(II) cations. Operational parameters including the accumulation potential, accumulation time and pH studies were fine-tuned. Under optimized conditions, the SAMs-3|Poly(3-HT) and SAMs-4|Poly(3-HT) Au electrodes displayed linear ranges in specific examined concentration regions with detection limits of 1.48 × 10−5 and 4.06 × 10−5 M, respectively. The CMEs illustrated good selectivity when tested in the presence of other divalent cations, viz. Zn(II), Pb(II) and Cu(II). Real sample studies were carried out using a river water sample where an acceptable recovery of 104% was attained for the SAMs-3|Poly(3-HT) Au electrode.

Recognition of Heavy Metal Ions by Using E-5-((5-Isopropyl-3,8-Dimethylazulen-1-yl) Dyazenyl)-1H-Tetrazole Modified Electrodes

Chemically modified electrodes (CMEs) based on polymeric films of E-5-((5-isopropyl-3,8-dimethylazulen-1-yl) diazenyl)-1H-tetrazole (L) deposited on the surface of the glassy carbon electrode have been used for the recognition of heavy metal (Me) ions. The electrochemical study of L was done by three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE). The CV, DPV, and RDE studies for L were performed at different concentrations in 0.1 M tetrabutylammonium perchlorate solutions in acetonitrile. The polymeric films were formed by successive cycling or by controlled potential electrolysis (CPE). The film formation was proven by recording the CV curves of the CMEs in ferrocene solution. The CMEs prepared at different charges or potentials were used for detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd(II), Pb(II), Cu(II), Hg(II)) of concentrations between 10−8 and 10−4 M were analyzed. The most intense signal was obtained for Pb(II) ion (detection limit of about 10−8 M). Pb(II) ion can be detected by these CMEs in waters at such concentrations. The ability of the ligand L to form complexes with Pb(II) and Hg(II) ions was also tested by UV-Vis spectrometry. The obtained results showed the formation of Me(II)L2 complexes.