Edge Plane Pyrolytic Graphite Electrode Research Articles

Label-free voltammetric screening of human blood serum

The current study presents a comprehensive voltammetric investigation into the direct analysis of untreated human blood serum in a phosphate buffer at an unmodified, graphite electrode by means of voltammetry. By employing advanced square-wave voltammetry at an edge plane pyrolytic graphite electrode (EPPGE), the basic principles were established for developing a sensitive, fast, simple, and label-free method for the simultaneous screening of uric acid, bilirubin, and albumin analytes that are present in human blood serum and are quite essential for rapid medical diagnostics. The electrochemical protocol utilizes the specific structural patterns of the EPPGE, the inherent redox and adsorption properties of the analysed analytes, and the sensitivity and rapidity of the employed advanced voltammetric technique. The methodology has been successfully applied for quantification of the considered analytes in a series of samples of human blood serum and was compared with the standard methods used in a clinical biochemical laboratory. This novel method represents a significant advancement towards the development of point-of-care devices aimed at swiftly and simultaneously quantifying uric acid, bilirubin, and albumin levels in human serum.

A novel and intelligent chemometric-electrochemical-enzymatic biosensing procedure and mimicking a clinical condition environment to trick the red blood cells for counting them under physiological conditions: A new connection among chemometry, electrochemistry and hematology

Here, a novel electrochemical biosensing procedure has been developed for determination of the number of red blood cells (RBCs) under physiochemical conditions based on chemometric modeling of hydrodynamic differential pulse voltammetric (HDPV), and amperometric data as responses of a modified edge plane pyrolytic graphite electrode (EPPGE). In order to obtain a good sensitivity from the EPPGE, its surface was modified with a thin layer of multiwalled carbon nanotubes-ionic liquid (MWCNTs-IL). Catalase (CAT) was immobilized onto the surface of MWCNTs-IL/EPPGE with help of nafion. The response of the biosensor was based on electrochemical reduction of oxygen of the blood samples which was enhanced by a trick based on addition of hydrogen peroxide (H2O2) to blood samples which can be reduced by the CAT to produce extra oxygen. Prior to experiments, the solution in electrochemical cell was bubbled with pure N2 to purge the oxygen in the solution, but in order to increase the selectivity of the biosensor towards detection of the oxygen obtained from the red blood cells, voltammetric responses of the biosensor were modeled by multivariate chemometric calibration methods with the help of radial basis function-partial least squares (RBF-PLS), least squares-support vector machines (LS-SVM), recursive weighted partial least squares (rPLS), ant colony optimization-mathematical pre-processing selection by genetic algorithm-sample selection through a distance-based procedure-partial least squares-1 (ACO-GA-SS-PLS1), and radial basis function-artificial neural networks (RBF-ANN) to select the best method for determination of the number of the RBCs. The results confirmed the amperometric methods modeled by RBF-ANN showed the best performance for supporting the biosensor in determination of the number of the RBCs with a performance which had an excellent compatibility with the results of a hemocytometer. The results of this study as the newest application of chemometric-electrochemical methods can make a strong connection among electrochemists, chemometricians and hematologists to expand their collaborations on determination of blood factors.

A Theoretical and Experimental Square-Wave Voltammetric Study of Ascorbic Acid in Light of Multi-Step Electron Transfer Mechanism

A detailed theoretical and experimental study of the complex redox mechanism of ascorbic acid in aqueous phosphate buffer solution (pH = 7.3) by square-wave voltammetry is presented. Experimental square-wave voltammograms at edge plane pyrolytic graphite electrode consist of a typical irreversible peak for a direct two-step electrode oxidation of the ascorbic acid. The complex mechanism of oxidation of the ascorbic acid was represented by a theoretical model for E1C’E2C mechanism. Morphology of theoretical square-wave voltammograms greatly depended on different specific parameters of the model. This feature was used to make the best fit between experimental and theoretical voltammograms for 2 different step potentials, which resulted in revelation of all specific parameters (standard electrochemical rate constant, diffusion coefficient, electron transfer coefficient and rate constants for both chemical reactions) of the model. Therefore, we showed that using only square-wave voltammetry, both experimentally and theoretically, it is possible to make a detailed study of the complex oxidation of ascorbic acid and further enlighten its redox mechanism.

Square-wave voltammetry of human blood serum

A study on voltammetric analysis of blood serum diluted in a phosphate buffer is presented using advanced square-wave voltammetry at an edge plane pyrolytic graphite electrode. The results demonstrate that even in a complex medium like human blood serum, electrochemical characterization can be achieved through the use of advanced voltammetric techniques in conjunction with an appropriate commercially available electrode, such as the edge plane pyrolytic graphite electrode, which boosts superior electrocatalytic properties. Without undergoing any chemical treatment of the serum sample, the square-wave voltammetry technique reveals, for the first time, the electrode reactions of uric acid, bilirubin, and albumin in a single experiment, as represented by well-defined, separated, and intense voltammetric signals. All electrode processes are surface-confined, indicating that the edge plane sites of the electrode serve as an ideal platform for the competitive adsorption of electroactive species, despite the extensive chemical complexity of the serum samples. The speed and differential nature of square-wave voltammetry are crucial for obtaining an outstanding resolution of the voltammetric peaks, maintaining the quasi-reversible nature of the underlying electrode processes, while reducing the impact of follow-up chemical reactions that are coupled to the initial electron transfer for all three detected species, and minimizing fouling of the electrode surface.

Poly(Alizarin Red S) on pyrolytic graphite electrodes as a new multi-electronic system for sensing oxandrolone in urine

This study presents a new polymeric and multielectronic system, the poly-Alizarin Red S (PARS), obtained from the electropolymerization of Alizarin Red S (ARS) dye on an edge-plane pyrolytic graphite electrode (EPPGE) surface. During EPPGE/PARS electrochemical characterization, we identified seven stable and reversible redox peaks in acidic medium (0.10 mol L−1, pH 1.62 KH2PO4), which indicated its mechanisms underlying electropolymerization and electrochemical behavior. To the best of our knowledge, this is the first study to use an EPPGE/PARS electrode to detect oxandrolone (OXA) in artificial urine, where PARS acts as a synthetic receptor for OXA. The interactions of OXA with EPPGE/PARS as well as the properties of PARS were investigated using density functional theory (DFT). Atomic force microscopy (AFM) was used to characterize EPPGE/PARS, and it was found that the PARS polymer formed a semi-globular phase on the EPPGE surface. The limit of detection for OXA found by the sensor was close to 0.50 nmol L−1, with a recovery rate of approximately 100% in artificial urine. In addition to the application proposed in this study, EPPGE/PARS is a low-cost product that could be applied in several devices and processes, such as supercapacitors and electrocatalysis.

A Comparison of Edge‐plane and Basal‐plane Pyrolytic Graphite Electrodes towards Sensitive Determination of the Fungicide Mandipropamid

AbstractA sensitive square‐wave voltammetry (SWV) method based on basal‐plane pyrolytic graphite electrode (BPPGE) and edge‐plane pyrolytic graphite electrode (EPPGE) was developed to determine the concentration of the pesticide mandipropamid (MAN) in spiked river water and grape juice samples. Under optimal experimental conditions, the SWV response of EPPGE and BPPGE was linear over the concentration ranges of 0.7 to 9.0 μmol L−1 and 0.5 to 10.0 μmol L−1, respectively. The method was successfully used to determine MAN in spiked samples with good recovery. Cyclic voltammetry (CV) was conducted to understand the mechanism underlying the electrode process of MAN.

Edge plane pyrolytic graphite as a sensing surface for the determination of fluvoxamine in urine samples of obsessive-compulsive disorder patients

There is an increasing demand for fast and sensitive determination of antidepressants in human body fluids because of the present scenario of rising depression cases at the global level. A simple and sensitive voltammetric method using edge plane pyrolytic graphite electrode (EPPGE) as a novel sensor is presented for the determination of antidepressant fluvoxamine in urine and blood plasma samples of obsessive-compulsive disorder (OCD) patients. EPPGE is delineated the first time for this determination. EPPGE exhibited strong electrocatalytic activity and enhanced reduction signal towards the sensing of fluvoxamine. Fluvoxamine gave a well-defined reduction peak at ~ – 670 mV using EPPGE. The fluvoxamine reduction peak current was linear to its concentration in the range 5.00 × 10−9 – 0.1 × 10−6 mol L−1 and the limit of detection was found to be 3.5 × 10−9 mol L−1. The pre-eminence of EPPGE over mercury electrodes has been proved in terms of sensitivity and imperative analytical parameters. The pH study reveals the involvement of an equal number of electrons and protons in the reduction reaction mechanism. The frequency study indicated the adsorption controlled irreversible reaction mechanism. The stability and reproducibility of the offered sensor were also found most favorable. The interference study confirmed the optimum selectivity of the proposed sensor. The edge plane pyrolytic graphite sensing platform is recommended as a potential contender for the accurate and fast determination of fluvoxamine in depression medications as well as biological specimens of OCD patients.

Cobalt ferrite nanoparticles as a source of intrinsic metals for simultaneous electrosynthesis of Prussian blue and cobalt hexacyanoferrate

A novel method is proposed for the simultaneous electrochemical formation of Prussian blue (PB) and cobalt hexacyanoferrate (CoHCF) on the surface of edge-plane pyrolytic graphite electrodes (EPPGE) modified by CoFe2O4/Chit/PTCA nanoparticle (NP) (where CoFe2O4 = cobalt ferrite, Chit = chitosan, and PTCA = Perylene-3,4,9,10-tetracarboxylic acid). The PB and CoHCF films are formed from the NP intrinsic metals (Fe3+ and Co2+) in the presence of ferrocyanide ([FeII(CN)6]4−) dissolved in a Britton-Robinson (BR) buffer at pH 1.60. The extent of the film formation is determined by the amount of the PTCA immobilised on the CoFe2O4/Chit NP surface and is influenced by the components of the BR buffer medium. Larger amounts of immobilised PTCA enhance electrosynthesis and generate modified electrodes in situ with excellent electrochemical properties. Optimized electrodes increased electroactive area approximately 420% compared to bare EPPGE. We believe that the combination of NP intrinsic metals, PTCA immobilisation, use of [FeII(CN)6]4− and BR buffer components provides a new electrochemical structure for simultaneous production of PB and CoHCF films. The quality of the electrodes generated in situ by the present method is evidenced by their increased sensitivity and enhanced active surface area relative to bare EPPGE, which indicates its potential for future application in electrochemical sensors.

Electrochemical Properties of pH-Dependent Flavocytochrome C 3 from Shewanella Putrefaciens Adsorbed Onto Catechol-Modified Carbon Electrode

A century after the demonstration that electrons from microbial metabolism can be harvested with electrodes, electron transfer processes in biofilms of microorganisms performing respiration on extracellular solids are now being studied in order to increase the performance of microbial electrochemical technologies such as microbial fuel cells. Extracellular electron transfer occurring at the microorganism/electrode interface stimulated a wide range of fundamental and applied studies because of important implications in biotechnology, bioenergetics and bioremediation. Most studies focus on two Gram-negative mesophilic bacteria able to transfer electrons from their respiratory metabolism to extracellular solids, namely Shewanella oneidensis MR-1 and Geobacter sulfurreducens. In these model electroactive microorganisms, multiheme c-type cytochromes transfer electrons from cytoplasmic and inner-membrane oxidizing enzymes towards cell surface redox proteins that are responsible for the reduction of solid phase electron acceptors. It is also known that electron transfer is usually coupled to proton transfer which causes acidification in the anodic biofilms and in the anolyte with deleterious consequences for the biofilm metabolism and stability. The fundamental understanding of these processes that involve large proteins (>70 kDa) often with complex redox properties (with ≥10 heme centers in some multihemes cytochromes) is still in its infancy and precludes the optimization of microbial electrochemical technologies. In Gram-negative electroactive bacteria such as Shewanella, several redox proteins have pH-dependent potentials, such as flavocytochrome c 3 (M r = 63.8 kDa) which is one of the most abundant proteins in the periplasm and the only functional fumarate reductase in this microorganism.This work focuses on the design and the development of an efficient and versatile electrochemical platform able to probe charge (electron/proton) transfer properties of proteins from Gram-negative electroactive bacteria on modified carbon electrodes.[1] The electrodes are first modified with pH-responsive electrophores such as quinone units and then proteins are immobilized for electrochemical studies. If relevant, the protein electroactivity can be probed directly at the modified electrode while proton transport, if any, performed by the protein can be detected thanks to the grafted pH sensor.The electrochemical detection of a pH-dependent redox protein from electroactive bacteria at an electrode modified to act additionally as an efficient pH sensor based on a redox readout is demonstrated. The pH sensing electrode was previously designed and showed to allow the immobilization and study of pH-independent and redox active cytochrome c.[1] Here we extend this work to flavocytochrome c 3, a tetraheme FAD-containing periplasmic flavoenzyme isolated from the bacterium Shewanella putrefaciens, taken as a model pH-dependent redox protein from electroactive bacteria [2]. The modification of the electrode surface with the pH sensing modifier (catechol) stems from our previous experience in the tailoring of bio-interfaces of carbon electrodes with covalent electrografting. Flavocytochrome c 3 adsorption onto the modified electrode surface is successfully achieved by cyclic voltammetry in a flavocytochrome c 3 solution containing polymyxin as co-adsorbate. The electrochemical activity of the immobilized flavocytochrome c 3 is detected without alteration of its native structure and by keeping intact its electrochemical properties and its catalytic fumarate reductase activity.[2] The redox activity of the protein arises from its FAD and four hemes cofactors. The experiments evidence that the hemes’ redox potentials of flavocytochrome c 3 from Shewanella putrefaciens, for which no crystal structure is yet available, depend on pH which is at variance with data from the other strains Shewanella frigidimarina or Shewanella oneidensis.[1] Lebègue, E.; Louro, R. O.; Barrière, F. Electrochemical Detection of pH-Responsive Grafted Catechol and Immobilized Cytochrome c onto Lipid Deposit-Modified Glassy Carbon Surface. ACS Omega 2018, 3 (8), 9035–9042. https://doi.org/10.1021/acsomega.8b01425.[2] Lebègue, E.; Costa, N. L.; Fonseca, B. M.; Louro, R. O.; Barrière, F. Electrochemical Properties of pH-Dependent Flavocytochrome C3 from Shewanella Putrefaciens Adsorbed onto Unmodified and Catechol-Modified Edge Plane Pyrolytic Graphite Electrode. Journal of Electroanalytical Chemistry 2019, 847, 113232. https://doi.org/10.1016/j.jelechem.2019.113232. Figure 1

Direct electrochemistry of bacterial surface displayed cytokinin oxidase and its application in the sensitive electrochemical detection of cytokinins

Cytokinin oxidase from Nipponbare (OsCKX4) was successfully displayed on the surface of E. coli cells by an ice nucleation protein from Pseudomonas borealis DL7 as an anchoring motif and a maltodextrin-binding protein(MBP) from E. coli as a solubility enhancer. The OsCKX4-displayed bacteria can be directly immobilized onto an electrode to selectively detect cytokinins, thus eliminating the need for enzyme extraction and purification. Direct electrochemistry of the cofactor FADH2 in OsCKX4 has been achieved on an edge-plane pyrolytic graphite electrode (PGE) with a formal potential (E0’) of −0.45 V at pH 7.0 in phosphate buffer. With the addition of isopentenyladenine, the reduction peak current for FADH2 decreased, and the oxidative peak current increased gradually. Therefore, a bacteria-OsCKX4-modified PGE has been developed for the detection of isopentenyladenine with a linear range of 1.0–11.0 μM and a lower limit of detection of 0.7 μM (S/N = 3). Slight interference was observed in the presence of other phytohormones, including brassinosteroid, abscisic acid, methylene jasminate and gibberellin. The proposed bacterial biosensor is stable, specific and simple and has great potential for applications that require the detection of cytokinins.

Electroanalysis of the Anthelmintic Drug Bithionol at Edge Plane Pyrolytic Graphite Electrode

AbstractAn electrochemical study of the anthelmintic drug bithionol using edge plane pyrolytic graphite electrode (EPPGE) is presented for the first time by applying different electrochemical techniques, such as cyclic voltammetry (CV), square‐wave voltammetry (SWV), square‐wave adsorptive stripping voltammetry (SWAdSV), and alternating current (AC) impedance spectroscopy. Mechanistic aspects of the electrode reaction were studied implying a quasireversible electrode reaction from an adsorbed state of the reactant, coupled with a follow‐up chemical reaction to a final electroinactive product. The overall mechanism appears totally irreversible under conditions of CV at moderate scan rate, while being quasireversible under conditions of the fast SWV. Furthermore, an optimisation of the analytical procedure for quantitative determination of bithionol was conducted by applying SWV in an adsorptive stripping mode. The calibration curve was constructed in the concentration range of 0.1–1.0 μmol L−1 (R2=0.9984) with a sensitivity of 3.6 μA L μmol−1 and LOD of 26.7 nmol L−1. The simple and sensitive SWAdSV procedure was proved to be suitable for the analysis of spiked urine samples.

Electrochemical properties of pH-dependent flavocytochrome c3 from Shewanella putrefaciens adsorbed onto unmodified and catechol-modified edge plane pyrolytic graphite electrode

The electroactivity of adsorbed flavocytochrome c3, a tetraheme FAD-containing flavoenzyme isolated from the bacterium Shewanella putrefaciens, is investigated by cyclic voltammetry at an edge plane pyrolytic graphite electrode before and after modification with grafted catechol serving as an efficient pH sensor based on a redox readout. Flavocytochrome c3 adsorption onto the unmodified or modified electrode surface is successfully achieved by cyclic voltammetry (100 consecutive cycles) in a flavocytochrome c3 solution containing polymyxin as co-adsorbate. The immobilized flavocytochrome c3 retains its electrochemical activity and its catalytic fumarate reductase activity. The redox activity of the protein arises from its FAD and four hemes cofactors. The experiments evidence that the hemes' redox potential of flavocytochrome c3 from Shewanella putrefaciens, for which no crystal structure is yet available, depend on pH which is at variance with data from the other strains Shewanella frigidimarina or Shewanella oneidensis.

Oxidation potentials of guanine, guanosine and guanosine-5′-monophosphate: Theory and experiment

Guanine, having lower one-electron oxidation potential than other nucleobases, is of relevance to oxidative degradation of nucleic acids in mutagenesis, carcinogenesis, and aging. Here we compare oxidation potentials of guanine (G), guanosine (Guo), deoxyguanosine (dGuo), guanosine -5′- monophosphate (GMP) and 2′- deoxyguanosine -5′- monophosphate (dGMP) obtained by theoretical and experimental methods. Structures of G species were optimized and the identities of minima were verified by vibration frequency calculations. Redox equilibria were modelled in terms of corresponding thermochemical cycles. The changes in free energy were calculated at DFT level using the two different functionals: (i) general purpose B3LYP functional, and (ii) more specific ωB97X-D functional (both with 6-31 + G(d) basis set). Experimental oxidation potentials of all G analogues were measured voltammetrically on a polymer pencil graphite electrode (pPeGE) providing the best results from all carbon electrodes used (glassy carbon electrode, basal and edge plane pyrolytic graphite electrodes). The oxidation process is strongly dependent on the pH value and with increasing pH a linear shift of G oxidation peaks (Epa) towards negative potentials is observed. The theoretically and experimentally obtained oxidation potentials were compared for the pH 5. Anodic peak potentials increase in the order G « dGMP ≤ GMP < dGuo ≤ Guo and correlate with the calculated thermodynamic redox potentials as well as with NBO charges in purine moiety. The oxidation of deoxy analogues was predicted theoretically to occur at lower potentials than that of corresponding parent compounds and this fact was experimentally verified. The assumption that due to negatively charged phosphate group of GMP or dGMP their oxidation potentials could be observed at lower positive potential has not been confirmed and the significant difference (more than 200 mV) between the oxidation potentials of G nucleobase and its nucleosides and nucleotides is discussed. Moreover, conformity of theoretical and experimental data for radicals (cation, neutral) indicates that while the deprotonation process of G differs from its analogues, the oxidation process of all species takes place on imidazole ring.

Electrochemical behaviors of alizarin and Cr(VI)–Alizarin complex adsorbed on edge-plane pyrolytic graphite electrode

Metal complexes have been subject of study worldwide. These compounds are useful for a multitude of applications in industry and medicine, or in chemical and electrochemical analysis. For the first time, the electrochemical behaviors of alizarin (Alz) and a Cr(VI)–Alz complex adsorbed on an edge-plane pyrolytic graphite electrode (EPPGE) surface were studied. The complex was investigated at pH 5.10–6.52; the best voltammetric response was obtained at pH 6.52. Alz and the metallic complex both exhibited adsorptive behavior and high electrochemical stability and were strongly influenced by the electrolyte pH. EPPGE modification with Alz, together with square-wave-adsorptive stripping voltammetry, enabled quantification of Cr(VI) ions in an aqueous medium (Britton–Robinson buffer); the detection limit was 0.107 nmol L−1. A linear response was achieved in the concentration range between 0.10 and 2.30 nmol L−1. Therefore, this system is expected to be a useful electrochemical sensor for Cr(VI) at ultra-trace levels.

Development and first application of the edge plane pyrolytic graphite electrode modified with graphene nanoplatelets for highly sensitive voltammetric determination of oxolinic acid

In this paper, a graphene nanoplatelets (GNPs) were used as a modifier of an edge plane pyrolytic graphite electrode (EPPGE) surface, and the graphene nanoplatelets modified edge plane pyrolytic graphite electrode (GNPs–EPPGE) was prepared by simple drop casting procedure. The as-prepared GNPs–EPPGE was characterized by a cyclic voltammetry (CV), a scanning electron microscopy (SEM), and an atomic force microscopy (AFM). The electrochemical behavior of OxA on the EPPGE and the GNPs–EPPGE was performed using the cyclic voltammetry and an electrochemical impedance spectroscopy (EIS). Further, a sensitive and selective square–wave voltammetric (SWV) procedure using the GNPs–EPPGE was developed for the determination of a quinolone antibiotic oxolinic acid (OxA). An oxidation peak of OxA was observed in Britton–Robinson buffer solution with the highest response at pH 5.0 at potential c.a. +1.4 V vs. Ag/AgCl reference electrode. Compared to the unmodified EPPGE, the EPPGE modified GNPs exhibited a marked enhancement in the current response of OxA. Calibration curve on the GNPs–EPPGE was constructed in the concentration range of 3.0 × 10−7–9.1 × 10−6 mol L−1 with a correlation coefficient of 0.9997, a sensitivity of 1.39 μA L μmol−1, a limit of detection (LOD) of 5.2 × 10−8 mol L−1, and a limit of quantification (LOQ) of 1.7 × 10−7 mol L−1. The determination of OxA in the spiked human urine samples was carried out using the GNPs–EPPGE with the satisfactory recovery of 99.6%. The selectivity of the developed method for the determination of OxA using the GNPs–EPPGE was tested.

Improved electrocatalytic metabolite production and drug biosensing by human liver microsomes immobilized on amine-functionalized magnetic nanoparticles

A biocatalytic system constructed by electrostatically immobilizing drug metabolizing human liver microsomes (HLM, negatively charged due to phospholipids) onto positively charged amine-functionalized magnetic nanoparticles (MNPamine, 100 nm hydrodynamic diameter) for biosensing of cytochrome P450 (CYP)-specific drug candidates and electrocatalyzing drug conversion into metabolites is reported. The MNP-adsorbed HLM biomaterial (denoted as MNPamine/HLM) was magnetically separated from the bulk suspension of HLM, washed twice in phosphate buffer (pH 7.0), and adsorbed onto polished edge-plane pyrolytic graphite (EPG) electrodes. Direct electrochemical properties and oxygen reduction currents were obtained by cyclic voltammetry (CV). Direct electron transfer kinetics from the microsomal redox proteins present in the adsorbed film of MNPamine/HLM on EPG surface was accomplished using square wave voltammetry due to its smaller background charging currents and improved faradaic peak intensity than CV. The MNPamine/HLM bioelectrodes exhibited a formal potential of −0.46 V vs Ag/AgCl reference (1 M KCl), which was in agreement with the FAD/FMN cofactor containing CYP-reductase (CPR) as the electron receiver from the electrode. This conclusion was drawn based on the formal potentials of only CPR (∼-0.47 V vs Ag/AgCl) containing bactosomal films adsorbed on EPG electrodes (bactosomes are bacterial membrane expressed enzymes). Whereas, bactosomal CYP 2C9 film showed a much more positive formal potential (−0.34 V vs Ag/AgCl). A heterogeneous electron transfer rate constant of 19 ± 5 s−1 was exhibited by the MNPamine/HLM film. Oxygen reduction currents and electrocatalytic diclofenac hydroxylation characteristics of the CYP enzymes present in the HLM film indicated the electron mediation by the CYP-reductase from the electrode to CYP-heme centers to initiate the catalytic cycle. Amperometric i-t curves with diclofenac drug concentration yielded the apparent Michaelis-Menten affinity constants (KMapp) of MNPamine/HLM and only HLM films as 302 ± 33 and 365 ± 36 μM, respectively. This is the first electrocatalysis report of bioelectrodes featuring HLM-bound MNPamine for applications in drug activity assays, enhanced metabolite production, and sensitive biosensing of CYP-specific drugs and environmental pollutants. Eliminations of tedious isolation and purification of membrane-containing CYPs, and the need for expensive NADPH cofactor (as electrode donates the reducing equivalents in an inexpensive and sustainable manner) are added advantages. Our future work aims to gain quantitative metabolite estimations upon scalability of such bioelectrode designs useful for pharmacological and toxicological evaluations of new drugs in development.

Influence of Carbon Material Properties on Activity and Stability of the Negative Electrode in Vanadium Redox Flow Batteries: A Model Electrode Study

The V2+/V3+ reaction occurring at the negative electrode in the all-vanadium redox flow battery has been identified as performance limiting in the system. Given the complexity of the commercial carbon electrodes typically used for this application, a model electrode approach is adopted in this work to study electrode activity and stability. This was done using edge and basal plane pyrolytic graphite electrodes modified by electrochemical oxidation. Differential electrochemical mass spectrometry was used for the first time in this work to investigate the parasitic hydrogen evolution reaction on the oxidized carbon surfaces. The basal plane surface showed a higher faradaic efficiency for V3+ reduction compared to that for the edge plane surface. The oxidized surfaces were subject to extended cycling, after which the basal electrode showed a dramatic loss in activity compared to the edge surface which was relatively stable. This activity loss was related to the poor mechanical stability of the basal plane su...

Development of an electroanalytical method to control quality in fish samples based on an edge plane pyrolytic graphite electrode. Simultaneous determination of hypoxanthine, xanthine and uric acid

A simple, rapid and non-expensive method is proposed to determine hypoxanthine (Hx), xanthine (Xa) and uric acid (UA) in untreated fish samples based on an edge plane pyrolytic graphite electrode (EPPGE). The square wave voltammetry was the electrochemical technique used. In addition, the experimental design and multi-response assays were used to optimize the pretreatment of the working electrode. Therefore, the EPPGE is used in the simultaneous determination of these analytes for the first time. The optimal accumulation conditions of the analytes on the surface of the working electrode were obtained through a composite central design. The linear range was from 0.1 to 50μM for Hx and Xa, and from 0.1 to 25.0μM for UA. The limits of detection (LOD) were 0.08, 0.06 and 0.03μM for Hx, Xa and UA, respectively. Recovery assays were made in order to validate the proposed method. Recovery percentages were between 90 and 110%. Therefore, the method is a good, simple and fast option for the simultaneous determination of Hx, Xa and UA in fish samples, allowing to perform a control quality of samples.

Determination of Curcumin in Turmeric Sample Using Edge Plane Pyrolytic Graphite Electrode

Phenolic compounds are an important class of the antioxidants and found in several natural products. Research on the phenolic compounds having antioxidant properties present in natural pruducts like fruits, spices and herbs are increased in recent years. Electroanalytical methods have low detection limits very short analysis time and require less budge as well. These advantages make the electroanalytical methods favorable and voltammetric analysis methods are one of the preferred methods in determination of the compounds having antioxidant properties present in different matrices. In this study, curcumin in turmeric samples were quantitatively determined by using edge plane pyrolytic graphite electrode (EPPG) and differential pulse voltammetry. Electrooxidation behaviour of curcumin was also examined by using cyclic voltammetry method. A three electrode electrochemical cell was used for voltammetric analysis. Edge plane pyrolitic graphite (EPPG), was used as working electrode, saturated calomel electrode (SCE) was used as reference electrode and Pt wire electrode was used as counter electrode in the cyclic voltamety and differential pulse voltametry studies. A linear relationship between anodic peak current and curcumin concentration was observed between 0.325 μM to 1.95μM at EPPG electrode with differential pulse voltammetry. Detection limit was calculated as 0,296 μM and the method successfully applied for detection of curcumin amount in a turmeric sample.

Spectroscopic and electrochemical behavior of the novel tetra-2-methyl-pyrazinoporphyrazines

This study presents the synthesis and characterization of novel metal-free (H2Pc) and metallo porphyrazines (magnesium(II) (MgPz), copper(II) (CuPz), iron(II) (FePz), manganese(II) (MnPz) and nickel(II) (NiPz)) substituted with four 2-methylpyrazine groups on the peripheral positions. The spectroscopic properties of newly synthesized porphyrazines were investigated. The electrochemical behaviors of these porphyrazines were also determined in DMSO solution by cyclic voltammetry (CV) and square wave voltammetry (SWV) methods on edge plane pyrolytic graphite electrode (EPPG) electrode.