Graphite-epoxy Composite Electrode Research Articles

Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite–epoxy composite electrode: Hydrogen adsorption capacity of graphite–epoxy composite is one–third of that of platinum

A new possibility of indirect determination of free chlorine using a graphite–epoxy composite(GEC) electrode instead of Pt disk electrode was suggested by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of the free chlorine. The linear response range of concentration was 0.06–0.2 mg∙L−1 with correlation coefficient of 0.9951 (n = 5) and the sensitivity of 1225 μA cm−2 mg−1 L. The limit of detection (LOD) calculated from the 3σ IUPAC criteria was 1.2 × 10−2 mg L−1. The relative standard deviation (RSD) to 0.06 mg L−1 was 4.65%(n = 10). The results show that the amount of free chlorine in the disinfected seawater can be indirectly determined by using a GEC electrode without influence of interferences unlike a Pt disk electrode. On the other hand, in this paper, a new method is proposed to evaluate the relative hydrogen adsorption capacity by the sensitivity of GEC electrode compared with that of Pt disk electrode. During the investigation of the hydrogen adsorption on the surface of the working electrode, we obtained the result that the hydrogen adsorption capacity of GEC is one-third of that of platinum.

Dual-template imprinted polymer electrochemical sensor for simultaneous determination of malathion and carbendazim using graphene quantum dots.

Malathion (MAL) and carbendazim (CBZ) are organophosphate pesticides and fungicides, respectively. They are often used simultaneously in agriculture, and both have been shown to have harmful effects on humans and animals. Therefore, it is important to be able to measure both of these toxins simultaneously in order to assess their potential risks. This study aims to design a dual template electrochemical sensor using a cost-effective graphite-epoxy composite electrode (GECE) modified with molecularly imprinted polymers (MIPs) coated on graphene quantum dots (GQDs) for simultaneous detection of MAL and CBZ in real samples. GQDs were synthesized initially, and their surface was coated with MIPs that were formed using MAL and CBZ as the template molecules, ethylene glycol dimethyl acrylate as the cross-linker, and methacrylic acid as the functional monomer. The GQDs@MIP were characterized using Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and X-ray scattering spectroscopy. Parameters affecting the sensor response, such as the percentage of GQDs@MIP in the fabricated electrode, the pH of the rebinding solution and analysis solution, and the incubation time, were optimized. The optimum pH values of the rebinding solution were verified using density functional theory (DFT) calculations. Under the optimized conditions, differential pulse voltammetry (DPV) response calibration curves of MAL and CBZ were generated, and the results showed that the sensor had a linear response to MAL in the range of 0.02-55.00 μM with a limit of detection (LOD) of 2 nM (S/N = 3) and to CBZ in the range of 0.02-45.00 μM with a low LOD of 1 nM (S/N = 3). The results also demonstrated the proposed sensor's long-term stability and anti-interference capability. The practical applicability of the fabricated electrode was evaluated for real sample analysis, and good recovery values were obtained.

Characterization of graphite-epoxy composite electrodes for free electrochemical detection of adenine and guanine in DNA

Graphite-epoxy composites (GECs) are alternative construction materials for electro­chemical sensors. For these materials, the electron transfer rate constant of some redox reaction depends additionally on the stoichiometric relationship between the insulating and conducting phases of the composite. In this work, the influence of dif­fe­rent ratios of araldite/hardener/graphite on the electrochemical properties of GEC electrodes is evaluated for the simultaneous determination of adenine and guanine in the single chain DNA, using the square wave voltammetry technique. Six GEC electro­des were prepared with different ratios of components, and electrochemically charac­terized by cyclic voltammetry in the presence of ferri/ferrocyanide redox couple as a redox probe. GEC electrodes that showed the best electrochemical responses of redox probe were characterized by thermogravimetric analysis (TGA) and used for the simul­taneous determination of free adenine and guanine in a solution, and DNA oligonu­cle­otides. The best results were obtained for GEC electrodes containing twice higher volu­me of araldite resin with respect to the hardener. TGA analysis revealed presence of 15-26 % of resin for these GEC electrodes. The obtained results revealed potential appl­ication of these GEC electrodes as DNA sensors based on the oxidation signal of guanine.

Development of magnetic nanoparticles modified with new molecularly imprinted polymer (MIPs) for selective analysis of glutathione

The present work aims to develop electroanalytical strategies for separating and quantifying one of the most important biothiols, the reduced glutathione (GSH), based on developing and applying a new and selective magnetic molecular imprinted polymer (mag-MIP). This magnetic-supported polymer was synthesized by precipitation, using GSH as a template, having acrylamide as the functional monomer and trimethylolpropane trimethacrylate as a cross-linking agent. These materials' morphological and physical characteristics were investigated by scanning electron microscope, Fourier transform infrared, and vibrating sample magnetometry. Physicochemical parameters, such as adsorption capacity, were obtained and compared with the respective mag-NIP, which are control polymers without the selective cavity. After all characterizations, mag-MIP and mag-NIP were evaluated on magnetic graphite-epoxy composite (m-GEC) electrodes. The characteristics of the obtained sensors were investigated by cyclic voltammetry and differential pulse voltammetry. After optimizing experimental and operational conditions, a linear response for the concentration of GSH, in the range of 1–1400 μmol/L, with low detection and quantification limits of 7 and 20 nmol/L, respectively, were obtained. The GSH levels in mice liver samples were measured by electrochemical and spectrophotometric techniques to compare the method's effectiveness. A high correlation between them and a low relative error of 1.06 % were obtained, indicating the good functionality of the proposed sensor.

Determination of temporary dye Basic Red 51 in commercial hair dye, river water and wastewater from hairdressing salon using graphite-epoxy composite electrode modified with magnetic nanoparticles

The present work reports the development of a simple, fast and inexpensive method for the determination of Basic Red 51 (BR 51) dye, known to be widely employed in comercial formulations of temporary dyes. The method involved the use of graphite-epoxy magnetic composite electrode (GEMCE) modified by carboxyl-functionalyzed magnetic nanoparticles (CFMNs) for the pre-concentration of the dye aiming at increasing the electrode sensitivity through the application of square wave voltammetry. The pre-concentration of BR 51 occurs via strong interaction between charged imidazole group present in the dye and the carboxyl group in the magnetic nanoparticles. This reaction is the basis for BR 51 determination through a well-defined peak at +0.89 V vs. Ag/AgCl, which is attributed to the oxidation of tertiary amine after the transfer of one electron and one proton. Under optimized conditions, which consisted of 30 sec. exposure of the GEMCE/CFMNs to BR 51 dye immersed in phosphate buffer (pH 7.0), an analytical curve was constructed in the concentration range of 1.50 × 10−6 mol L−1 to 5.50 × 10−5 mol L−1 using square wave voltammetry (SWV). The limits of detection and quantification obtained were 1.19 × 10−7 and 3.97 × 10−7 mol L−1, respectively. The proposed method was successfully applied for the determination of BR 51 dye in samples of commercial hair dye, wastewater from hairdressing salon, and river water, and was validated using high performance chromatography coupled to diode array detector (HPLC-DAD).

Voltammetric Electronic Tongue for the Simultaneous Determination of Three Benzodiazepines.

The presented manuscript reports the simultaneous detection of a ternary mixture of the benzodiazepines diazepam, lorazepam, and flunitrazepam using an array of voltammetric sensors and the electronic tongue principle. The electrodes used in the array were selected from a set of differently modified graphite epoxy composite electrodes; specifically, six electrodes were used incorporating metallic nanoparticles of Cu and Pt, oxide nanoparticles of CuO and WO3, plus pristine electrodes of epoxy-graphite and metallic Pt disk. Cyclic voltammetry was the technique used to obtain the voltammetric responses. Multivariate examination using Principal Component Analysis (PCA) justified the choice of sensors in order to get the proper discrimination of the benzodiazepines. Next, a quantitative model to predict the concentrations of mixtures of the three benzodiazepines was built employing the set of voltammograms, and was first processed with the Discrete Wavelet Transform, which fed an artificial neural network response model. The developed model successfully predicted the concentration of the three compounds with a normalized root mean square error (NRMSE) of 0.034 and 0.106 for the training and test subsets, respectively, and coefficient of correlation R ≥ 0.938 in the predicted vs. expected concentrations comparison graph.

Electrodeposition of 4-Benzenesulfonic Acid onto a Graphite-Epoxy Composite Electrode for the Enhanced Voltammetric Determination of Caffeine in Beverages.

Caffeine is widely present in food and drinks, such as teas and coffees, being also part of some currently commercialized medicines, but despite its enhancement on several functions of human body, its exceeding use can promote many health problems. In order to develop new fast approaches for the caffeine sensing, graphite-epoxy composite electrodes (GECE) were used as substrate, being modified by different diazonium salts, synthetized as their tetraflouroborate salts. An analytical method for caffeine quantification was developed, using sware wave voltammetry (SWV) in Britton–Robinson buffer pH 2.0. Detection limits for bare electrode and 4-benzenesulfonic modified electrode were observed circa 145 µmol·L−1 and 1.3 µmol·L−1, respectively. The results have shown that the modification shifts the oxidation peaks to lower potential. Kinetics of the reaction limited by diffusion was more expressive when caffeine was added to the solution, resulting in decreases of impedance, characterized by lower Rct. All results for caffeine determination were compared to a reference chromatographic procedure (HPLC), showing no statistical difference. Analytical parameters for validation were suitably determined according to local legislation, leading to a linear behaviour from 5 to 150 µmol·L−1; precision of 4.09% was evaluated based on the RDC 166/17, and accuracy was evaluated in comparison with the reference method, with recovery of 98.37 ± 2.58%.

Label-Free Aptasensor for Lysozyme Detection Using Electrochemical Impedance Spectroscopy.

This research develops a label-free aptamer biosensor (aptasensor) based on graphite-epoxy composite electrodes (GECs) for the detection of lysozyme protein using Electrochemical Impedance Spectroscopy (EIS) technique. The chosen immobilization technique was based on covalent bonding using carbodiimide chemistry; for this purpose, carboxylic moieties were first generated on the graphite by electrochemical grafting. The detection was performed using [Fe(CN)6]3−/[Fe(CN)6]4− as redox probe. After recording the frequency response, values were fitted to its electric model using the principle of equivalent circuits. The aptasensor showed a linear response up to 5 µM for lysozyme and a limit of detection of 1.67 µM. The sensitivity of the established method was 0.090 µM−1 in relative charge transfer resistance values. The interference response by main proteins, such as bovine serum albumin and cytochrome c, has been also characterized. To finally verify the performance of the developed aptasensor, it was applied to wine analysis.

A Voltammetric Electronic Tongue for the Resolution of Ternary Nitrophenol Mixtures.

This work reports the applicability of a voltammetric sensor array able to quantify the content of 2,4-dinitrophenol, 4-nitrophenol, and picric acid in artificial samples using the electronic tongue (ET) principles. The ET is based on cyclic voltammetry signals, obtained from an array of metal disk electrodes and a graphite epoxy composite electrode, compressed using discrete wavelet transform with chemometric tools such as artificial neural networks (ANNs). ANNs were employed to build the quantitative prediction model. In this manner, a set of standards based on a full factorial design, ranging from 0 to 300 mg·L−1, was prepared to build the model; afterward, the model was validated with a completely independent set of standards. The model successfully predicted the concentration of the three considered phenols with a normalized root mean square error of 0.030 and 0.076 for the training and test subsets, respectively, and r ≥ 0.948.

CELLOBIOSE DEHYDROGENASE/ EPOXY- GRAPHITE COMPOSITE WITH ARYL DIAZONIUM REDUCTION FOR LACTOSE DETECTION

Milk is an important ingredient in our day to day diet bacause of the high quality nutrients in it. In the dairy industry including cheese fermentation processes, there is a need to control the release of lactose into wastewater streams. There are methods adopted to recover the lactose and to transform the lactose into energy through renewable energy (RE) pathways. These methods however are expensive and require certain skill to operate them. In this study, in-house electrode, which is simple and can be applied after one day of fabrication were investigated. The method was by using graphite-epoxy composite electrode, surface modified with cellobiose dehydrogenase (CDH) enzyme using aryl diazonium. These designed composite electrodes were tested on its capability as biosensor for sensitivity on detecting the lactose as well as its capability as an anode in enzymatic fuel cell (EFC) on long term electrochemical stability in generating electricity from lactose oxidation. The results showed that the CDH-Aryl diazonium modified on surface of fabricated graphite-epoxy electrodes had Michaelis Menten constant Km for CDH (0.65 – 0.75 mM) comparable to available commercial electrodes reported in the literature (0.7 mM). They are also conductively sensitive with the current intensity 86% more with the above mentioned electrodes when modified with embedded multi-walled carbon nanotube (MWCNT) and gave a high reproducibility signal (63% more than fabricated electrodes without MWCNT). In addition to the above, its performance stability in continuous mode operation for 25 days, recorded almost consistent in current detection (19.2 ± 3.8 µA/ cm2). Hence, these fabricated electrodes give alternative for a sensitive lactose detector which is cheap and simple to fabricate.

Characterization and Evaluation of Silver-Nanoparticle-Incorporated in Composite Graphite Aiming at their Application in Biosensors

Abstract Biosensors based on nanomaterial composites have been investigated for their potential to function as high sensitivity signal response devices. In the present study, we report the fabrication of silver nanoparticles (AgNPs) on a graphite epoxy composite electrode (GEC) and mixed with the polyaniline (a conductive emeraldine salt form polymer) composite electrode (AgNPs/PANI/GEC), in order to compare the performance of the generated electrochemical response signals. Cyclic voltammetry tests were conducted to compare the quality and intensity of signals from the different prepared electrodes. Tests for the AgNPs/PANI/GEC electrodes were made with and without the enzymes alcohol oxidase and horseradish peroxidase immobilized on the composite surface. The prepared AgNPs/PANI/GEC nanocomposite was evaluated by thermal analysis. Scanning electron microscopy images and EDX were obtained for characterization of the electrode surface morphology. Square wave voltammetry techniques were then employed for ethanol analysis with the AOX/HRP/AgNPs/PANI/GEC biosensor achieving good results in a range of 0.37M to 0.65 M.

Determination of pesticides using a low-temperature co-fired ceramic microfluidic platform

ABSTRACTThe aim of this work is the integration of an improved graphite–epoxy composite electrode modified with the acetylcholinesterase enzyme as a detector into a green tape ceramic microfluidic device for the online amperometric determination of pesticides. First, the operational conditions of the microfluidic system were optimized for the enzymatic substrate determination of acetylthiocholine. Good results were achieved for acetylthiocholine determination, obtaining a low detection limit and optimal sensitivity. The analytical performance of the microanalyzer was evaluated with organophosphorus and carbamate pesticides across a wide concentration range. Pesticides were determined indirectly measuring the enzymatic inhibition effect that they caused. The analysis was based on stopped-flow methodology with a three-step strategy: enzymatic substrate measurement, enzymatic inhibition by pesticide contact with the biosensor, and enzymatic substrate measurement after the inhibition process. The pesticide concentrations were determined by the percentage of inhibition produced. The microanalyzer was used for the analysis of spiked irrigation water samples using this indirect method. The low-temperature co-fired ceramic/epoxy–graphite–acetylcholinesterase microfluidic system showed low limits of detection and adequate sensitivity. The recoveries of the spiked water samples were approximately 100% with relative standard deviation values lower than 5% for three replicate measurements. All results obtained are indicative of a convenient, rapid, sensitive, and economic method for the determination of pesticides in environmental samples.

Graphene electrode platform for impedimetric aptasensing

In this study, we synthesized graphene oxide (GO) at different oxidation times (30, 60 and 120min) using a modified Hummer’s method and investigated their carbon-to-oxygen (C/O) ratios, the % C–C double bond, the diffraction pattern, their topography and their electrochemical behaviour both by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). All GOs synthesized were compared with a GO from commercial source. Graphite-epoxy composite (GEC) electrodes fabricated in our laboratory were modified with GO and electrochemically reduced graphene oxide (ERGO) in preliminary assays to elucidate its applicability for enhanced DNA aptamer biosensing applications.

Use of a composite electrode modified with magnetic particles for electroanalysis of azo dye removed from dyed hair strands

The analysis of dyes in hair samples can provide useful information for forensic purposes. The present work describes a novel method for the extraction of dye from a hair sample and its determination using a composite electrode to pre-concentrate carboxyl-functionalyzed magnetic nanoparticles (CFMP) employed to collect the dye in solution, hence increasing the sensitivity of the analysis. The Basic Brown 16 dye, which is widely used in temporary hair dying, was chosen as a model compound. After 15s of reaction between 1.5×10−5molL−1 of dye and 0.1mgmL−1 of carboxyl-functionalyzed magnetic nanoparticles in phosphate buffer electrolyte at pH7.0, the derivative dye was collected during 40s at the graphite-epoxy composite electrode and then transferred to a new solution of phosphate buffer at pH7.0. The dye presented a peak current at a potential of 0.42V that was almost 400 times higher than without the preconcentration step, suggesting that the dye was pre-accumulated due to strong magnetic interaction with the composite electrode. Under optimized conditions, the analytical curve constructed using square wave voltammetry was linear for BB16 dye concentrations between 1.00×10−7 and 1.00×10−6molL−1. The limits of detection and quantification were 1.01×10−8 and 2.37×10−8molL−1, respectively. The proposed method was successfully applied in the determination of BB16 dye extracted from a dyed hair strand sample by alkaline digestion.

Voltammetric sensor based on magnetic particles modified composite electrode for determination of triamterene in biological sample

Some diuretic substances are controlled and monitored by the World Anti-Doping Agency as prohibited substances for use by athletes, such as triamterene (TRT). Thus, this work describes a voltammetric method based on graphite-epoxy composite electrode modified by tosyl-functionalized magnetic particles (GECE/MPs-To) for determination of TRT diuretic in urine sample. The TRT presented an oxidation peak at +1.24 V at GECE/MPs-To with irreversible behavior. Controlled potential electrolysis of the TRT at +1.26 V indicated the two electrons are transferred during amine group oxidation and the main product was identified by LC-MS/MS. The anodic peak current is 25 % higher at the modified electrode, suggesting that TRT is adsorbed on the magnetic particles. Using optimized conditions by using multivariate optimization of the parameters inherent of the square wave voltammetry, a calibration curve was constructed with a linear relationship for TRT from 0.500 to 99.8 μmol L−1. The limits of detection and quantification were 1.47 and 4.91 × 10−7 mol L−1, respectively. The proposed method was applied to urine sample and validated by LC-MS/MS technique where the values found and compared between the two techniques showed no significant difference at 95 % confidence.

Simultaneous Voltammetric Determination of Heavy Metals by Use of Crown Ether‐modified Electrodes and Chemometrics

AbstractA three‐sensor array consisting of a graphite‐epoxy composite electrode (GEC), 4‐carboxybenzo‐18‐crown‐6‐GEC and 4‐carboxybenzo‐15‐crown‐5‐GEC was employed for the simultaneous determination of Cd(II), Pb(II) and Hg(II) by differential pulse anodic stripping voltammetry (DPASV). Sensors were firstly studied for the determination of Hg(II); secondly, peak current responses confirmed that all sensors showed differentiated response for the three considered metals. A response model was developed to resolve mixtures of Cd(II), Pb(II) and Hg(II) at the µg L−1 level; Discrete Wavelet Transform was selected as preprocessing tool and artificial neural network used for the modelling of the obtained responses.

Crown ether-modified electrodes for the simultaneous stripping voltammetric determination of Cd(II), Pb(II) and Cu(II)

This work describes the immobilization of 4-carboxybenzo-18-crown-6 (CB-18-crown-6) and 4-carboxybenzo-15-crown-5 (CB-15-crown-5) assisted by lysine on aryl diazonium salt monolayers anchored to the surface of graphite–epoxy composite electrodes (GEC), and their use for the simultaneous determination of Cd(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetry (DPASV). These modified electrodes display a good repeatability and reproducibility with detection and quantification limits at levels of µgL−1 (ppb), confirming their suitability for the determination of Cd(II), Pb(II) and Cu(II) ions in environmental samples. The overlapped nature of the multimetal stripping measurements was resolved by employing the two-sensor array CB-15-crown-5-GEC and CB-18-crown-6-GEC, since the metal complex selectivity exhibited by the considered ligands could add some discrimination power. For the processing of the voltammograms, Discrete Wavelet Transform and Causal Index were selected as preprocessing tools for data compression coupled with an artificial neural network for the modeling of the obtained responses, allowing the resolution of mixtures of these metals with good prediction of their concentrations (correlation with expected values for an external test subset better than 0.942).

Array of peptide-modified electrodes for the simultaneous determination of Pb(II), Cd(II) and Zn(II)

This paper reports the development of three peptide modified sensors in which glutathione (GSH) and its fragments Cys–Gly and γ-Glu–Cys were immobilized respectively through aryl diazonium electrochemical grafting onto the surface of graphite–epoxy composite electrodes (GEC), and used for the simultaneous determination of Cd(II), Pb(II) and Zn(II). The concentration interval ranged from 0.1 to 1.5μmolL−1 for each metal, and the technique used was differential pulse adsorptive stripping voltammetry. This study aimed to the comparison of the information provided by one single modified electrode at both fixed and multiple pH values (pH 6.8, 7.5 and 8.2) for the simultaneous determination of the three metals, with those supplied by the three-sensor array at multiple pH values. For the processing of the voltammograms, the fast Fourier transform was selected as the preprocessing tool for data compression coupled with an artificial neural network for the modeling of the obtained responses.

A comparison of four protocols for the immobilization of an aptamer on graphite composite electrodes

We have performed a comparative study on four protocols for the immobilization of the thrombin aptamer on a graphite-epoxy composite electrode with the aim to identify the most practical method for designing the corresponding impedimetric aptasensor. The protocols included (a) physical adsorption, (b) avidin-biotin affinity interaction, (c) electrochemical activation and covalent bonding via amide groups, and (d) electrochemical grafting using 4-carboxybenzenediazonium coupling. The properties of the sensing surface were probed by electrochemical impedance measurements in the presence of the (ferri/ferro)hexacyanide redox couple. An increase in the interfacial charge transfer resistance (Rct) was noted in all cases after the aptamer-thrombin interaction had occurred. The selectivity of the aptasensor over common serum proteins was also systematically investigated. Physical adsorption resulted in the lowest detection limit of the probe (4.5 pM), while avidin-biotin interaction resulted in highest selectivity and reproducibility exhibiting a 4.9 % relative standard deviation at pM thrombin concentration levels.

An electrochemical magneto immunosensor (EMIS) for the determination of paraquat residues in potato samples

An electrochemical magneto immunosensor for the detection of low concentrations of paraquat (PQ) in food samples has been developed and its performance evaluated in a complex sample such as potato extracts. The immunosensor presented uses immunoreagents specifically developed for the recognition of paraquat, a magnetic graphite-epoxy composite (m-GEC) electrode and biofunctionalized magnetic micro-particles (PQ1-BSAMP) that allow reduction of the potential interferences caused by the matrix components. The amperometric signal is provided by an enzymatic probe prepared by covalently linking an enzyme to the specific antibodies (Ab198-cc-HRP). The use of hydroquinone, as mediator, allows recording of the signal at a low potential, which also contributes to reducing the background noise potentially caused by the sample matrix. The immunocomplexes formed on top of the modified MP are easily captured by the m-GEC, which acts simultaneously as transducer. PQ can be detected at concentrations as low as 0.18 ± 0.09 μg L(-1). Combined with an efficient extraction procedure, PQ residues can be directly detected and accurately quantified in potato extracts without additional clean-up or purification steps, with a limit of detection (90% of the maximum signal) of 2.18 ± 2.08 μg kg(-1), far below the maximum residue level (20 μg kg(-1)) established by the EC. The immunosensor presented here is suitable for on-site analysis. Combined with the use of magnetic racks, multiple samples can be run simultaneously in a reasonable time.