Abstract: In the present study, a 3D porous graphene-carbon nanotube (G-CNT) network is successfully constructed on the surface of glassy carbon electrode (GCE) by electrochemical co-deposition from a concentrated graphene dispersion. The large accessible surface area provided by the interpenetrated graphene backbone in one hand and the enhanced electrical conductivity of the 3D network by incorporating CNTs on the other hand, dramatically improved the electrochemical performance of GCE in determination of Methotrexate (MTX) as an important electroactive drug compound. Under the optimum conditions, the electrode modification led to a significant increase in the anodic peak current (∼25 times) along with a considerable shift in the peak potential (∼111 mV). Voltammetric investigations revealed that the proposed method can determine MTX in a wide dynamic linear range with a low detection limit of 70 nM. Moreover, good sensitivity and high accuracy of the prepared modified electrode in voltammetric detections of MTX, which was further confirmed by UV–vis spectroccopy and HPLC methods, make it very suitable for accurate determinations of MTX in pharmaceutical formulations (commercial tablets) and clinical preparations (blood serum) with excellent recoveries.

Abstract: A novel and sensitive electrochemical method has been developed for the simultaneous determination of dopamine (DA) and 5-hydroxytryptamine (5-HT) using graphene (GR) and poly 4-amino-3-hydroxy-1-naphthalenesulfonic acid modified screen printed carbon sensor. The electrochemical measurements were studied using cyclic voltammetry, square wave voltammetry, whereas the surface morphology of the modified sensor was characterized by Electrochemical Impedance Spectroscopy and Field Emission scanning electron microscopy. The fabricated sensor facilitated the analysis of DA and 5-HT in the concentration range 0.05–100 μM and 0.05–150 μM with the detection limit of 2 nM and 3 nM respectively. The fabricated sensor has been explored for the determination of 5-HT in the plasma samples and the selectivity of the proposed work has been proved by the analysis of DA and 5-HT in the presence of common metabolites present in biological fluids. The analytical applicability of the fabricated sensor has also been successfully demonstrated for the simultaneous detection of DA and 5-HT in the pharmacological formulations, human urine and blood samples.

Abstract: Results of this paper related to fabrication of a simple, reproducible, stable and sensitive electrochemical sensing platform of progesterone (P4) based on graphene quantum dots (GQDs) nanocomposite. GQDs, Fe3O4 nanoparticles and functionalized multi–walled carbon nanotubes (f–MWCNTs) modified glassy carbon electrode (Fe3O4@GQD/f–MWCNTs/GCE) were constructed and the electrocatalytic properties of the modified electrode toward the oxidation of P4 were analyzed. GQDs with the size of about 15 nm were prepared by a facile and low expense bottom–up method by carbonization of citric acid and dispersing the carbonized products into alkaline solution. The characterization of the sensor was studied by transmission electron microscopy (TEM), X–ray diffraction (XRD), UV–vis spectroscopy, Fourier transform infrared spectroscopy (FT–IR) and voltammetry techniques. Electrochemical studies suggested that as–prepared sensor revealed some advantages in terms of high effective surface area, more reactive sites and excellent electrochemical catalytic activity toward the oxidation of P4. After optimization of analytical conditions, the peak currents for P4 were found to vary linearly with its concentrations in the wide range of 0.01–0.5 and 0.5–3.0 μM. The estimated detection limit and sensitivity of the electrode were 2.18 nM and 16.84 μA μM−1, respectively. This sensor exhibited excellent stability, selectivity, sensitivity and reproducibility and could be successfully applied for determination of P4 in human serum samples and pharmaceutical products with excellent recoveries and without the interferences of coexisting substances.

Abstract: The electrochemical reduction of CO2 into fuels has gained significant attention recently as source of renewable carbon-based fuels. The unique high selectivity of copper in the electrochemical reduction of CO2 to hydrocarbons has called much interest in discovering its mechanism. In order to provide significant information about the role of oxygen in the electrochemical reduction of CO2 on Cu electrodes, the conditions of the surface structure and the composition of the Cu single crystal electrodes were controlled over time. This was achieved using pulsed voltammetry, since the pulse sequence can be programmed to guarantee reproducible initial conditions for the reaction at every fraction of time and at a given frequency. In contrast to the selectivity of CO2 reduction using cyclic voltammetry and chronoamperometric methods, a large selection of oxygenated hydrocarbons was found under alternating voltage conditions. Product selectivity towards the formation of oxygenated hydrocarbon was associated to the coverage of oxygen species, which is surface-structure- and potential-dependent.

Abstract: Here, we introduce the preparation of the hybrid nanocomposite-modified electrode consisting of reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) using the one-step electrochemical method, allowing for the simultaneous and individual detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). RGO/AuNPs nanocomposite was formed on a glassy carbon electrode by the co-reduction of GO and Au3+ using the potentiodynamic method. The RGO/AuNPs nanocomposite-modified electrode was produced by subjecting a mixed solution of GO and Au3+ to cyclic sweeping from -1.5 V to 0.8 V (vs. Ag/AgCl) at a scan rate 10 mV/s for 3 cycles. The modified electrode was characterized by scanning electron microscopy, Raman spectroscopy, contact angle measurement, electrochemical impedance spectroscopy, and cyclic voltammetry. Voltammetry results confirm that the RGO/AuNPs nanocomposite-modified electrode has high catalytic activity and good resolution for the detection of DA, AA, and UA. The RGO/AuNPs nanocomposite-modified electrode exhibits stable amperometric responses for DA, AA, and UA, respectively, and its detection limits were estimated to be 0.14, 9.5, and 25 μM. The modified electrode shows high selectivity towards the determination of DA, AA, or UA in the presence of potentially active bioelements. In addition, the resulting sensor exhibits many advantages such as fast amperometric response, excellent operational stability, and appropriate practicality.

Abstract: A modified electrode using fullerene-functionalized carbon nanotubes and ionic liquid (IL, 1-butyl-3-methylimidazolium tetrafluoroborate) has been applied for the determination of diazepam in real samples including serum, urine, and tablets. The properties of fullerene-functionalized carbon nanotubes and ionic liquid were characterized by transmission electron microscopy, scanning electron microscope, electrochemical impedance spectroscopy, and voltammetry. The experimental results confirmed that modified electrode with fullerene-functionalized carbon nanotubes and ionic liquid has good electrocatalytic activity toward the reduction of diazepam. The electrocatalytic current increases linearly with the diazepam concentration in the ranges of 0.3–700.0 μM, and the detection limit is 87 ± 2 nM. The proposed electrode displayed excellent repeatability and long-term stability and it was satisfactorily used for determination of diazepam in real samples (commercially tablet, urine, and serum samples) with high recovery.

Abstract: The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of 'as is' graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, 'as is' GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications 'as is' rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family.

Abstract: In this paper, a new nanocomposite of polypyrrole (PPy) and carbon nanofibers (CNFs)-modified carbon paste electrode (CPE) has been reported for the determination of traces lead ions (Pb2+). The obtained nanocomposite was fabricated by combining the unique advantages of PPy and CNFs using a very simple approach, which consists on modifying the CPE by the functionalized CNFs and then by the PPy film using galvanostatic mode. Several techniques were used to investigate the functionalized CNFs and the PPy/CNFs nanocomposite including Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) for surface layers of CNFs, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) for the electrical proprieties of the PPy/CNFs nanocomposite. The surface morphologies were examined by field-emission gun scanning electron microscopy (FEG-SEM). The square wave anodic striping voltammetry (SWASV) was used to investigate the analytical performances of the designed electrode PPy/CNFs/CPE. Different parameters that affect the stripping analysis of Pb2+ including supporting electrolyte, deposition potential, and deposition time were investigated. Under the optimum experimental conditions, a good linearity between the stripping peak currents and the concentration of Pb2+ was obtained in the range of concentration from 0.2 to 130 μg L−1 Pb2+. The detection limit was estimated to be 0.05 μg L−1 Pb2+. Finally, the proposed method has been successfully applied for the determination of Pb2+ in real samples of tap water with satisfactory results.

Abstract: The monitoring of synthetic colorants in foods is very important due to their potential toxicity and pathogenicity. Therefore, we proposed a new and facile electrochemical method for the determination of sunset yellow (SY) in food samples. A highly sensitive and selective electrochemical sensor was fabricated by electropolymerization of molecularly imprinted polymer (MIP) in the presence of SY onto a functionalized multi-walled carbon nanotubes/glassy carbon electrode (f-MWCNTs/GCE) using cyclic voltammetry (CV). Scanning electron microscopy and CV were employed to characterize the fabricated sensor. The experimental parameters, such as supporting electrolyte and its pH, the monomer concentration, the number of cycles for the electropolymerization and the scan rate for the sensor preparation were optimized. The MIP sensor exhibited an excellent recognition capacity toward SY compared with other structurally similar molecules. Under the optimum operating conditions, the current response of the MIP sensor was linear to SY concentrations in the range from 0.05 to 100 μM, with the detection limit of 5.0 nM. Finally, the proposed electrode was successfully applied to determine SY in several food samples.

Abstract: At present, there is the whole area of research community occupied with developing of new materials and fabrication of new biosensors. With the intention to propose an effective, quick and inexpensive method for determination of biomolecules. Here in, we report the electrocatalytic oxidation of Estriol (ET) was analysed by poly (glycine) modified carbon paste electrode (PGMCPE) using cyclic voltammetry and differential voltammetry. Compared to bare carbon paste electrode (BCPE), the PGMCPE indicates good electrocatalytic activity towards the oxidation of ET in phosphate buffer solution (PBS) pH 6. PGMCPE shows a linear response between concentrations of ET. The prepared modified electrode showed high voltammetric responses with sensitivity for ET, results showed it very suitable for the detection of ET at trace levels. Under the optimized conditions, the peak current was linear to ET concentration over the concentration range of 2 × 10− 6 to 1 × 10− 4 M using cyclic voltammetry (CV). The detection limit and limit of quantification were 8.7 × 10− 7 M and 2.6 × 10− 6 M. The proposed method was successfully applied for the determination of ET in the real samples.

Abstract: A new sensor using a glassy carbon electrode modified with graphene and Au nanoparticles (Gr/Au/GCE) was designed to investigate the electrochemical behavior of furazolidone (FZD). The morphology and nature of the modified electrode were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). FZD was reduced on the Gr/Au/GCE at lower potentials with a higher peak current, compared to the bare GCE, through an irreversible process. These results arose from the synergistic effect of the deposited Gr/Au suspension on the GCE. For this article, several parameters, such as pH, scan rate, and the amount of modifier had been studied. Under optimal conditions, amperometry (AMP) and differential pulse stripping voltammetry (DPSV) were applied to the determination of FZD. Linear dynamic ranges of 1–674 μmol L−1, and 0.02–0.14 μmol L−1 and 0.14–400 μmol L−1 with detection limits of 0.64 μmol L−1 and 0.0126 μmol L−1 were obtained using AMP and DPSV, respectively. The sensor was also successfully applied to the determination of FZD in real samples, obtaining satisfactory recoveries.

Abstract: An electrochemical method for determination of Al(III) has been developed using Schiff base (JS-1) modified screen printed electrodes as a disposable chemosensor. The modified screen printed electrode was characterized with voltammetry and was further confirmed by SEM and EDX data. Differential pulse voltammogram of modified SPE in the presence of Al(III) showed a characteristic peak current at −0.054 V. A linear response of the sensor was observed in the concentration range of 0.67–4.59 μg L−1 of the analyte. The limit of detection (LOD) was found to be 2.26 ng L−1 for Al(III). The proposed chemosensor selectively detects Al(III) in the presence of some alkali, alkaline earth, transition metal ions like Zn(II), Cd(II), Hg(II) and Pb(II). Complexation behavior of the ionophore for the metal ion has also been supported by theoretical studies. The method has been used for the determination of Al(III) in the natural water samples. The proposed voltammetric sensor can be reused after washing with EDTA (0.1 M) as a cleaning agent.

Abstract: This review presents recent developments in electrochemical Hg2+ detection by voltammetry, summarizing and evaluating the use of different voltammetric techniques, working electrodes, and surface modifications. The remaining technical challenges are discussed and a future outlook offered.

Abstract: Objective: A new carbon nanotube (CNT)-graphite mixture paste electrode modified by Sodium dodecyl sulfate (SDS) surfactant (SDSMCNTGMPE) was prepared and applied for sensitive electrochemical determination of resorcinol (RS).Method: Cyclic voltammetry, variable pressure scanning electron microscopy, and differential voltammetry were employed for the surface analysis of the bare CNT-graphite mixture paste electrode and SDSMCNTGMPE. Comparison between the unmodified electrode and modified electrode, the modified electrode oxidation peak current significantly improved. The effects of the pH, scan rate, and concentration of RS on the peak current were investigated.Results: Results indicated that the peak current of RS is highest in 0.2 M pH 7.0 phosphate buffer solutions and that the electrode reaction corresponds to a rate controlled process. Under optimized experimental conditions, the oxidation peak current of RS was linear over a concentration range of 2A—10−6 to 1.0A—10−3 M with a detection limit of 5.8A—10−6 M and quantification limit of 19A—10−6 M.Conclusion: The prepared sensor also shows other features such as good stability, reproducibility and repeatability. The proposed sensor exhibits good application toward the detection of RS in commercial RS lotion samples.