Electroanalytical Performance Research Articles

Reduced graphene oxide supported 2D-NiO nanosheets modified electrode for urea detection

Nickel oxide (NiO) nanosheets (NSs) deposited on different amounts (0.025, 0.05, 0.1, and 0.2 wt%) of reduced graphene oxide (rGO) are synthesized through hydrothermal method. The NiO NSs on rGO (rGO-NiO) are characterized by using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) analyses, and electrochemical analysis. Electrocatalytic activity of rGO-NiO nanocomposite modified glassy carbon (GC/rGO-NiO) electrode is examined towards electrocatalytic oxidation of urea in 0.1 M NaOH using cyclic voltammetry and amperometry techniques. The GC/rGO0.1-NiO nanocomposite modified electrode shows enhanced electrocatalytic oxidation of urea than that of other modified electrodes due to the incorporation of NiO NSs on an optimum amount of rGO. The GC/rGO0.1-NiO modified electrode is used for designing electrochemical sensor for urea, and the detection limit is estimated as 0.47 μM using the amperometry technique. The sensitivity of GC/rGO0.1-NiO modified electrode is found to be 2450 μA mM−1 cm−2. In addition to good electroanalytical performance, the present urea sensor displayed good stability and acceptable anti-interference ability in the presence of 20-fold excess concentration of relevant interferents. The GC/rGO0.1-NiO nanocomposite modified electrode is successfully used for the determination of urea in water sample.

Sodium-Polyacrylate-Based Electrochemical Sensors for Highly Sensitive Detection of Gaseous Phenol at Room Temperature.

The detection of volatile organic compounds with electrochemical gas sensors is still very challenging regarding their sensitivity, selectivity, and operation at room temperature. There is a need for robust, sensitive, inexpensive, and yet easy-to-operate sensors for phenol and other phenolic compounds that function reliably under ambient conditions. Herein, we present a phenol gas sensor based on a combination of a semisolid, alkaline sodium polyacrylate, and commercial screen-printed electrodes. Sodium polyacrylate was employed as a multifunctional sensing material serving as a (i) gel-like electrolyte, (ii) accumulation milieu, and (iii) derivatization medium. Under ambient conditions, the sensor showed excellent sensitivity in the low ppbv (μg m–3) range, a good linear operation in the examined concentration range of 0.1–1.0 ppmv for up to 105 min accumulation, and low sensitivity toward examined interferences. The sensor also indicated a possibility to differentiate between several phenolic compounds based on their oxidation potential. Given its favorable electroanalytical performance, a strong application potential is envisioned in topical fields such as environmental monitoring, cultural heritage preservation, and occupational health and safety.

Inspection of electrochemical behavior of tolnaftate a topical antifungal agent and its active hydrolysis products by disposable screen-printed carbon electrode

Inspection of the electrochemical behavior tolnaftate (TNF), of a topical antifungal agent and its active hydrolysis products, was carried out by utilizing a disposable screen-printed carbon electrode (SPCE) for the first time. The voltammetric behavior of TNF was studied in various pH values using cyclic voltammetry and differential pulse voltammetry. A well-defined irreversible oxidation wave of TNF was observed at 1.20 V (vs. pseudo Ag/AgCl) and did not shift with different pH of solutions. The electro-analytical performance of the disposable SPCE was investigated in wide concentration ranges with limits of detection (LOD) of 0.24 μM and 3.76 μM in 0.1 M H2SO4 and B.R. buffer pH 7, respectively. Thus, the disposable SPCEs offer a sensitive and reproducible electrochemical platform for TNF in dosage forms. Further, the TNF was hydrolyzed in an alkaline medium to release its possible lethal products i.e. 2- Naphthol which can be analyzed voltammetrically without any interference so it is considered as a first selective stability-indicating assay for TNF.

Comparative Electroanalytical Studies of Graphite Flake and Multilayer Graphene Paste Electrodes.

In this paper, the fabrication, surface characterisation and electrochemical properties of graphite flake (GFPE) and multilayer graphene (MLGPE) paste electrodes are described. The Raman investigations and scanning electron microscopy were used to analyze and compare structure of both carbon materials. The electroanalytical performance of both electrodes was examined and compared on the basis of the square-wave and cyclic voltammetric behavior of acetaminophen and model redox systems. Results of those studies revealed that GFPE has a larger electroactive surface area and better conductive properties, whilst MLGPE demonstrate better analytical characteristic in case of acetaminophen (AC) determination. AC determination was developed using square wave voltammetry (SWV) and square wave stripping voltammetry (SWSV). For both working electrodes, the process of accumulation enabled us to obtain an extended linear range and to lower the detection limit. In pharmaceutical formulations, AC was determined with good recovery.

Graphene Supported Boron Nitride Nanosheets as Advanced Electroanalytical Performance for Rechargeable Magnesium Storage System

Graphene Supported Boron Nitride Nanosheets as Advanced Electroanalytical Performance for Rechargeable Magnesium Storage System

Modified Screen Printed Electrode Suitable for Electrochemical Measurements in Gas Phase.

We describe a convenient assembly for screen printed carbon electrodes (SPCE) suitable for analyses in gaseous samples which are of course lacking in supporting electrolytes. It consists of a circular crown of filter paper, soaked in a RTIL or a DES, placed upon a disposable screen printed carbon cell, so as to contact the outer edge of the carbon disk working electrode, as well as peripheral counter and reference electrodes. The electrical contact between the paper crown soaked in RTIL or DES and SPCE electrodes is assured by a gasket, and all components are installed in a polylactic acid holder. As a result of this configuration, a sensitive, fast-responding, membrane-free gas sensor is achieved where the real working electrode surface is the boundary zone of the carbon working disk contacted by the paper crown soaked in the polyelectrolyte. This assembly provides a portable and disposable electrochemical platform, assembled by the easy immobilization onto a porous and inexpensive supporting material such as paper of RTILs or DESs which are characterized by profitable electrical conductivity and negligible vapor pressure. The electroanalytical performance of this device was evaluated by voltammetric and flow injection analyses of oxygen which was chosen as prototype of electroactive gaseous analytes. The results obtained pointed out that this assembly is very profitable for the analysis of gaseous atmospheres, especially when used as detector for FIA in gaseous streams.

Synthesis of a Conductive Glassy System Based on Inorganic Oxides and Carbon Materials and Their Possible Electroanalytical Application

New materials based on V2O5, TeO2 and a combination of graphite, graphene oxide and multiwalled carbon nanotubes were developed and tested as potential electrochemical sensors. A mixture design with three components in combination with multi-response assays based on the desirability function was used as multivariate optimization for the system composition. The optimal sensor contains graphene oxide and multiwalled carbon in approximately equal amounts. The new sensors characterizations were performed with X-ray diffraction, differential scanning calorimetry, impedance spectroscopy and cyclic voltammetry. The main advantage of this electrodes are does not requires surface activation and exhibited a potential electroanalytical performance with different targeted analytes such as ascorbic acid, aspartame and lead.

Highly sensitive detection of rutin in pharmaceuticals and human serum using ITO electrodes modified with vertically-ordered mesoporous silica-graphene nanocomposite films.

Herein we report a simple and rapid approach to fabricate a vertically-ordered mesoporous silica-electrochemically reduced graphene oxide nanocomposite film (VMSF/ErGO) on an indium tin oxide (ITO) electrode surface by the electrochemically-assisted self-assembly (EASA) method, which is capable of greatly promoting the electroanalytical performance of rutin compared to the previously reported VMSF modified ITO electrode and, meanwhile, displaying excellent anti-fouling and anti-interference ability in pharmaceutical formulations and human serum. Due to the excellent electrocatalytic activity of ErGO and the synergistic enrichment effects from the π-π interaction of ErGO and the hydrogen bond effect from the VMSF, the present VMSF/ErGO/ITO sensor is able to detect rutin with a wide linear range, a high sensitivity and a low limit of detection. Moreover, the VMSF/ErGO/ITO electrode could retain the high sensing performance with high transmittance upon tailoring the concentration of the modified graphene oxide (GO), which provides a simple approach for modifying transparent ITO electrodes and could be potentially used for optoelectronic devices.

Evaluation of the electroanalytical performance of carbon-on-gold films prepared by electron-beam evaporation.

Carbon film electrodes can often be used without pretreatment, and their fabrication allows for flexibility in size and shape and for mass production. In this work, we are exploring layered structures comprised of thin films of carbon on gold (eC/Au) prepared by electron-beam evaporation. These extremely flat films are not pyrolyzed and are comprised of mainly amorphous carbon but still exhibit reasonable conductivity due to the underlying gold layer. eC/Au electrodes, without any pretreatment, yield similar heterogeneous electron-transfer rates for benchmark redox systems and significantly lower background current in comparison with polished glassy carbon. Interestingly, they show insignificant adsorption of quinones, which is uncommon for most carbon electrode materials. However, eC/Au is still prone to adsorption of airborne hydrocarbons when exposed to ambient air like most graphitic materials. With reproducibly fast electron transfer kinetics, low background current, negligible adsorption, and ultraflat surface, eC/Au films are a promising candidate for electrochemical and sensor applications.

In-situ prepared copper film electrode for adsorptive stripping voltammetric detection of trace Ni(II)

In this work, we present a copper film electrode (CuFE) as a simple and environmentally-friendly sensor for adsorptive stripping voltammetric detection of trace Ni(II). The CuFE was prepared directly in-situ on a supporting glassy carbon electrode, and revealed excellent electroanalytical performance in a 0.01 M ammonia buffer solution (pH 9.2), without using any stabilizing agent for copper ions. The sensor was used in combination with nioxime as a ligand for Ni(II). After the optimization of several key operational parameters, such as concentration of copper ions, accumulation potential, and accumulation time, the CuFE exhibited good linear response in the examined low concentration range of 1–10 μg L−1 Ni(II) (r2 of 0.995), and low limit of detection (3σ criterion) of 0.2 μg L−1. Finally, its applicability was successfully demonstrated by measuring Ni(II) in a real sample of seawater.

A comparative study of carbon nanotube dispersions assisted by cationic reagents as electrode modifiers: Preparation, characterization and electrochemical performance for gallic acid detection

In this work, we report on the preparation of electrodes modified with carbon nanotubes (CNT) films, which provide improved electroanalytical performance towards the polyphenol gallic acid. These films were obtained from aqueous dispersions of the unmodified nanomaterial by the drop-casting method. Cationic reagents such as polyethylenimine (PEI), poly(diallyldimethylammonium chloride) (PDDA) or cetyltrimethylammonium chloride (CTAC) were employed to assist in the dispersion process of carbon nanotubes by ultrasonic treatment. A critical analysis of the influence of the experimental conditions set for the preparation of such dispersions on the electrochemical performance of the modified electrodes has been carried out. The voltammetric experiments have demonstrated that films produced from PEI/CNT and CTAC/CTN dispersions prepared under optimized conditions showed excellent electrochemical performance for gallic acid detection. Raman and Electrochemical Impedance (EIS) Spectroscopies, Field Emission Scanning Electron Microscopy (FESEM) and electrochemical techniques were used to characterize and compare the CNT-modified electrodes. The results obtained revealed that the dispersion and subsequent film formation processes allow the effective non-covalent functionalization of CNT while maintaining their structural integrity and the CNT ability to facilitate the electrochemical transfer processes. Glassy carbon electrodes modified with CNT showed excellent electrochemical performance for the detection of gallic acid by Differential Pulse Voltammetry (DPV), with good sensitivity and stability. The approach was used to evaluate gallic acid content of wines (red and white) and clove (Syzygium aromaticum) without complex sample preparation.

Determination of Heavy Metals in Herbal Food Supplements using Bismuth/Multi-walled Carbon Nanotubes/Nafion modified Graphite Electrodes sourced from Waste Batteries

An electrochemical sensor based on graphite electrode extracted from waste zinc-carbon battery is developed. The graphite electrode was modified with bismuth nanoparticles (BiNP), multi-walled carbon nanotubes (MWCNT) and Nafion via the drop coating method. The bare and modified graphite electrodes were used as the working electrode in anodic stripping voltammetry for the determination of trace amounts of cadmium (Cd2+) and lead (Pb2+). The modified electrode exhibited excellent electroanalytical performance for heavy metal detection in comparison with the bare graphite electrode. The linear concentration range from 5 parts per billion (ppb) to 1000 ppb (R2 = 0.996), as well as detection limits of 1.06 ppb for Cd2+ and 0.72 ppb for Pb2+ were obtained at optimized experimental conditions and parameters. The sensor was successfully utilized for the quantification of Cd2+ and Pb2+ in herbal food supplement samples with good agreement to the results obtained by atomic absorption spectroscopy. Thus, the BiNP/MWCNT/Nafion modified graphite electrode is a cost-effective and environment-friendly sensor for monitoring heavy metal contamination.

Au nanoparticle-poly(ionic liquid) nanocomposite electrode for the voltammetric detection of triclosan in lake water and toothpaste samples

Triclosan (TCS), a powerful bactericide agent found in personal care products, has been recently recognized as a contaminant of emerging concern, with endocrine disrupting chemical activity, and whose detection in environmental, biological and/or PCP samples is of great concern nowadays. Therefore, this contribution describes indium-doped tin oxide (ITO) substrates modified with Au nanoparticle-poly(ionic liquid) (Au-PIL) nanocomposite films for the voltammetric detection of TCS in lake water and toothpaste samples. The electroanalytical performance evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV), shows the modified electrode oxidizes TCS at much higher oxidation currents than bare ITO. At optimized conditions, the analytical method is linear (R2 > 0.99) in the selected working range (10–60 µmol L−1), presents a sensitivity of 57.1 µA cm−2/mol L−1•and a limit of detection of 0.098 µmol L−1 (28.3 µg L−1). TCS determinations are successfully carried out in spiked lake water samples showing that the electrode response is not affected by such a complex matrix. The concentration of TCS found in a commercial brand toothpaste, simultaneously determined by voltammetry and HPLC, is similar (95% confidence level, t-test) between both techniques and comparable to that described in the product package.

Metallic Film Modified Screen-Printed Carbon Electrode for Determination of 17α-Methyltestosterone

17α-methyltestosterone (MT) is a synthetic androgen. It is used widely for inducing an all-male population of Nile tilapia (Oreochromis niloticus). In this work, the detection of MT was conducted using screen-printed carbon electrodes (SPCE). These were a bare electrode, a bismuth modified electrode (Bi-SPCE) and an antimony modified electrode (Sb-SPCE). The successful electrode modification was confirmed by scanning electron microscopy. The electroanalytical performance of the SPCE modified electrodes for MT detection was examined by cyclic voltammetry. The highest active surface area of 1.073x10-4 cm2 was obtained on Sb-SPCE. This indicates that Sb-SPCE can enhance the sensitivity of MT detection better than the bare-SPCE and the Bi-SPCE. The Sb-SPCE showed a linear response for MT concentrations ranging from 2 to 8 mg.L-1. The sensitivity obtained from the slope of a calibration curve was -0.452 mA.mol-1.L-1 in a Britton-Robinson buffer pH 4.0 containing Sb 16 mg.L-1 with deposition potential and deposition time of 1 V and 90 seconds, respectively. A linear relationship between the square root of the scan rate and the peak current revealed that mass transfer of MT to the electrode was driven by a diffusion mechanism. The limit of detection was found to be 1 mg.L-1.

Selective sensor for simultaneous determination of mesalazine and folic acid using chitosan coated carbon nanotubes functionalized with amino groups

First analytical method was developed for simultaneous determination of aminosalycilate drug mesalazine (5-ASA) and folic acid (FA) used as a supplement in treatment of inflammatory bowel diseases. Various types of functionalized multi-walled carbon nanotubes embedded in different kinds of polymer matrix were evaluated to design selective and sensitive electrochemical sensor for this purpose. Carbon nanotubes functionalized with amino groups and chitosan as biopolymer modifier exhibited an excellent electroanalytical performance due to strong adsorptive ability of ionized analytes and subtle electronic properties followed by well-separated oxidation peaks towards 5-ASA and FA at potential of 0.33 and 0.81 V, respectively. After 60 s preconcentration at deposited nanocomposite layer, the voltammetric response had linear relationship with 5-ASA concentration in the range of 1.25 × 10−7–8.0 × 10−6 M, while FA gave a good linear correlation in a broad range from 1.25 × 10−8 to 1.25 × 10−6 M. Applicability of proposed nanosensor for rapid and precise measurements of 5-ASA and FA in human serum samples and pharmaceutical products was demonstrated.

AuPt/MOF-Graphene: A Synergistic Catalyst with Surprisingly High Peroxidase-Like Activity and Its Application for H2O2 Detection.

Here, we report ZIF-8-reduced graphene oxide (ZIF-8-rGO)-supported bimetallic AuPt nanoparticles (AuPtNPs) as a novel peroxidase mimic for high-sensitivity detection of H2O2 in neutral solution. ZIF-8-graphene oxide (ZIF-8-GO) is first synthesized via a simple wet-chemistry process and subsequently immobilized with AuPtNPs via a reduction method. The resultant AuPt/ZIF-8-rGO shows enhanced peroxidase-like catalytic activity and it is applied for the electrochemical detection of H2O2 in a wide concentration range, from 100 nM to 18 mM, with a very low detection limit of 19 nM (S/N = 3). This good electroanalytical performance of AuPt/ZIF-8-rGO is owing to the ultrasmall size and high dispersion of the AuPtNPs, the strong metal-support interaction between the AuPtNPs and ZIF-8-rGO bisupport, and the sandwich-like structure comprising porous ZIF-8 and loosely packed rGO nanosheets. The AuPt/ZIF-8-rGO is employed for the practical detection of H2O2 in human serum samples with desirable properties. Therefore, the novel AuPt/ZIF-8-rGO is a promising nanozyme for various biotechnological and environmental applications.

Synthesis of 3D hierarchically porous carbon@Bi-BiOCl nanocomposites via in situ generated NaCl crystals as templates for highly sensitive detection of Pb2+ and Cd2+

A facile, environmentally friendly and scalable method was reported to synthesize highly dispersed Bi-BiOCl nanoparticles dispersed on three dimensional porous networks of carbon nanosheet using NaCl as template and citric acid as carbon source. The novel 3D architecture demonstrated easily accessible porous structure, large surface area, superior electrical conductivity and good mechanical flexibility, which was capable of accelerating three dimensional diffusion of ions and transport of electrons in the whole electrode. In addition, the highly dispersed Bi-BiOCl nanoparticles on the carbon backbone could facilitate the utilization of these active materials in electrochemical sensing. Under optimized conditions, Bi-BiOCl@C-3 modified glassy carbon electrode exhibited preeminent electroanalytical performance for the simultaneous sensing of Pb2+ and Cd2+ in the linear range of 1–60 μg L−1, with sensitivities of 0.38 and 0.49 μA L μg−1, respectively. The developed protocol has shown limits of detection (S/N = 3) of 0.2 and 0.4 μg L−1 for Pb2+ and Cd2+, respectively, which complies with the limits set by the World Health Organization (WHO). Moreover, high resistance to interference, long-term stability, good reproducibility and satisfactory testing recoveries were realized for real water sample, suggesting that the proposed 3D Bi-BiOCl@C-3 nanocomposite could be utilized as a promising candidate for the fabrication of high-performance electrochemical sensor.

Effect of thickness and additional elements on the filtering properties of a thin Nafion layer

Nafion is widely used as a filtering membrane in electroanalytical applications to improve selectivity towards cations. However, the role of the thickness of Nafion on its electroanalytical performance is poorly understood. Furthermore, Nafion is often modified with additional elements without characterizing their influence on Nafion's filtering properties. To understand in-depth these uncharacterized effects on Nafion, we approach these issues systematically by studying first (i) the role of Nafion film thickness on top of a well characterized tetrahedral amorphous carbon electrode and second (ii) introducing nanodiamonds into the same Nafion films with different thicknesses. With careful electrochemical and structural analyses, we show that already ultrathin Nafion film significantly reduces limiting currents of anionic species IrCl63−/4− and uric acid. With a thicker film (~3.6μm) the selective nature of Nafion is demonstrated as anionic species are completely filtered and enrichment of cationic species Ru(NH3)62+/3+ is achieved. However, diffusion within the film controls the overall kinetics of the cation reactions and the electrochemical performance of Nafion is heavily dependent on the width of the potential window used. In addition, we show that modifying Nafion with nanodiamonds increases permeability of both cationic and anionic species. Hence, Nafion's ability for selective detection of cations is greatly reduced. Interestingly, chemical effects were also observed between nanodiamonds and an inner sphere redox probe uric acid. Thus, additional elements in Nafion do not only affect the physical structure of the film, but may produce chemical changes as well. Based on the results presented here, we emphasize the importance of an in-depth investigation to understand the case specific effects of modified Nafion films to guarantee the reliability of the sensor devices in the final application.

A novel non-enzymatic electrochemical biosensor based on the nanohybrid of bimetallic PdCu nanoparticles/carbon black for highly sensitive detection of H2O2 released from living cells

Hydrogen peroxide (H2O2) is a major metabolite of oxygen known as reactive oxygen species (ROS) in living organisms. Monitoring H2O2 released from living cells is of great significance as its concentration level is related to several diseases, which imposes stricter requirements on the sensitivity of detection technology. In this work, we have found that carbon black (CB) could preserve bimetallic PdCu alloy’s nanostructure, meanwhile improve the dispersion of nanoparticles, provided high conductivity and large specific surface area, thus the PdCu/CB nanohybrid exhibited enhanced electroanalytical performance of H2O2. Under the optimal conditions, the PdCu/CB nanohybrid modified electrode showed a low detection limit of 54 nM with a wide detection range from 0.4 μM to 5.0 mM. Finally, the application of PdCu/CB/GCE in real-time monitoring H2O2 released from Raw 264.7 cells was achieved, suggesting the PdCu/CB nanohybrid was the promising nanomaterial in monitoring physiological processes.

Electroanalytical Performance of Nitrogen-Doped Graphene Films Processed in One Step by Pulsed Laser Deposition Directly Coupled with Thermal Annealing.

Graphene-based materials are widely studied to enable significant improvements in electroanalytical devices requiring new generations of robust, sensitive and low-cost electrodes. In this paper, we present a direct one-step route to synthetize a functional nitrogen-doped graphene film onto a Ni-covered silicon electrode substrate heated at high temperature, by pulsed laser deposition of carbon in the presence of a surrounding nitrogen atmosphere, with no post-deposition transfer of the film. With the ferrocene methanol system, the functionalized electrode exhibits excellent reversibility, close to the theoretical value of 59 mV, and very high sensitivity to hydrogen peroxide oxidation. Our electroanalytical results were correlated with the composition and nanoarchitecture of the N-doped graphene film containing 1.75 at % of nitrogen and identified as a few-layer defected and textured graphene film containing a balanced mixture of graphitic-N and pyrrolic-N chemical functions. The absence of nitrogen dopant in the graphene film considerably degraded some electroanalytical performances. Heat treatment extended beyond the high temperature graphene synthesis did not significantly improve any of the performances. This work contributes to a better understanding of the electrochemical mechanisms of doped graphene-based electrodes obtained by a direct and controlled synthesis process.