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In a new approach, we considered the special affinity between Ni and poly-histidine tags of recombinant urate oxidase to utilize Ni-MOF for immobilizing the enzyme. In this study, a carbon paste electrode (CPE) was modified by histidine-tailed urate oxidase (H-UOX) and nickel-metal–organic framework (Ni-MOF) to construct H-UOX/Ni-MOF/CPE, which is a rapid, sensitive, and simple electrochemical biosensor for UA detection. The use of carboxy-terminal histidine-tailed urate oxidase in the construction of the electrode allows the urate oxidase enzyme to be positioned correctly in the electrode. This, in turn, enhances the efficiency of the biosensor. Characterization was carried out by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), and field emission scanning electron microscopy (FE-SEM). At optimum conditions, the biosensor provided a short response time, linear response within 0.3–10 µM and 10–140 µM for UA with a detection limit of 0.084 µM, repeatability of 3.06%, and reproducibility of 4.9%. Furthermore, the biosensor revealed acceptable stability and selectivity of UA detection in the presence of the commonly coexisted ascorbic acid, dopamine, L-cysteine, urea, and glucose. The detection potential was at 0.4 V vs. Ag/AgCl. [ABSTRACT FROM AUTHOR]

In the present study, we utilized a novel electrochemical sensor for the determination of colchicine in 0.1 M phosphate buffer solution (pH 4.0) using differential pulse voltammetry. 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim]FeCl4) was synthesized, investigated by FT-IR, Raman and UV–Vis spectrometer and applied as magnetic ionic liquid in electrode modification. The other modifier was copper oxide nanoparticles/carbon nanofiber composite (CuO/CNF) provided by electrospinning and evaluated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Several electro-analytical parameters such as the electrochemical behavior of the modified electrode, scan rate, type and supporting electrolyte pH were studied for the determination of colchicine. Under the optimized experimental conditions, oxidative peak current increased linearly by increasing colchicine concentration in the range of 1.0 to 100.0 nM and detection limit was obtained 0.25 nM. The relative standard deviation for six replicate analyses of 20.0 nM and 58.0 nM colchicine solution was obtained to be ± 3.17% and ± 2.08%, respectively. The proposed electrochemical sensor was successfully applied for colchicine quantification in colchicine tablet and health human plasma with satisfying results. [ABSTRACT FROM AUTHOR]

• The preparation of Au/reduced graphene oxide nanocomposite through a one-pot method. • The fabrication of an Au/RGO modified carbon paste elecrode. • Electrochemical determination of agnuside by differential pulse voltammetry technique. • A novel and sensitive technique with good merit figures for agnuside determination in real samples. Agnuside despite its good properties for the body, can be harmful to the kidneys in extra concentrations. So, its measurement is important. For the first time, we developed a simple, rapid and inexpensive method for the investigation of agnuside electrochemical behavior by designing a gold/reduced graphene oxide/carbon paste electrode (Au/RGO/CPE). The Au/RGO nanocomposite was synthesized through a one-pot in situ reduction of graphene oxide (GO) and HAuCl 4 in the presence of sodium citrate and the obtained product was studied by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The anodic oxidation of agnuside has been carried out at a modified carbon paste electrode in 0.1 M phosphate buffer solution (pH 6.0) using sensitive differential pulse voltammetry (DPV). Several parameters such as the type and pH of supporting electrolyte and scan rates were optimized. This study reported a good linearity in the range of 0.050–250.0 nM and a low detection limit of 0.016 nM. The relative standard deviations (RSDs) for 10.0 nM and 100.0 nM of agnuside were obtained 3.3% and 1.2%, respectively. The sensor was successfully applied to determine agnuside in Vitex agnus castus fruit and urine sample. [ABSTRACT FROM AUTHOR]

Abstract In the present study, for the first time, we develop a sensitive voltammetric technique for the determination of pemetrexed using Pd/carbon nanofibers/methyl (trioctyl)ammonium bis(trifluoromethylsulfonyl)imide ([M3OA]+[NTF2]−) ionic liquid modified carbon paste electrode in which Nafion was utilized as binder (CPE/Pd/CNF/[M3OA]+[NTF2]−/Nafion). Composite nanofibers were synthesized by electrospinning method and characterized by SEM, TEM, XRD and FT-IR and the synthesized ionic liquid was also investigated by FT-IR and UV–Vis. Square wave voltammetry (SWV) measurements were performed to investigate the electrochemical oxidation of pemetrexed using the proposed electrode in 0.1 M phosphate buffer solution at pH 6.0. Several parameters such as pH amount, scan rate and the type of supporting electrolyte were studied for pemetrexed oxidation. In addition, selectivity, repeatability, reproducibility and stability were also evaluated. Under optimized conditions, a linear concentration was detected in the range of 1.00–35.0 nM with a detection limit of 0.33 nM by SWV. The proposed sensor was successfully applied for the quantification of pemetrexed in cancerous human plasma, pharmaceutical and health urine samples. Graphical abstract Unlabelled Image Highlights • Fabrication of Pd/carbon nanofibers by electrospinning method • Modification of carbon paste electrode by Pd/CNF/[M3OA]+[NTF2]−. • Electrochemical pemetrexed determination using SWV technique • The developed sensor being successfully applied for the determination of pemetrexed in real samples [ABSTRACT FROM AUTHOR]

A simple and novel ferrocene-nanofiber carbon paste electrode was developed to determine curcumin in a phosphate buffer solution at pH = 8. ZnO nanoparticles were produced via a sonochemical process and composite nanofibers of PVP/ZnO were prepared by electrospinning. The characterization was performed by SEM, XRD and IR. The results suggest that the electrospun composite nanofibers having a large surface area promote electron transfer for the oxidation of curcumin and hence the FCNFCPE exhibits high electrocatalytic activity and performs well in regard to the oxidation of curcumin. The proposed method was successfully applied for measurement of curcumin in urine and turmeric as real samples. [ABSTRACT FROM AUTHOR]

A novel carbon paste electrode modified with ZnO nanorods and 3-(4′-amino-3′-hydroxy-biphenyl-4-yl)-acrylic acid (3,4′AAZCPE) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of dopamine, is described. It has been found that the oxidation of dopamine at the surface of modified electrode occurs at a potential of about 180 mV less positive than that of an unmodified carbon paste electrode. The detection limit of 5.6 × 10 −8 M for dopamine was obtained using square wave voltammetry (SWV). In addition, this modified electrode was used for simultaneous determination of dopamine, melatonin, methionine and caffeine. Finally, the modified electrode was used for determination of dopamine, melatonin, methionine and caffeine in human blood serum and urine samples. [ABSTRACT FROM AUTHOR]

A carbon paste electrode was modified with ZnO nanorods and 3-(4′-amino-3′-hydroxy-biphenyl-4-yl)-acrylic acid (3,4′AAZCPE) to cause electrocatalysis of norepinephrine oxidation. It has been found that the oxidation of norepinephrine at the surface of modified electrode occurs at a potential of about 180 mV less positive than that of an unmodified carbon paste electrode. Square wave voltammetry (SWV) exhibits linear dynamic range from 1.0×10−7 to 8.0×10−5 M and a detection limit of 3.9×10−8 M for norepinephrine. In addition, this modified electrode was used for simultaneous determination of norepinephrine, tyrosine and nicotine. [ABSTRACT FROM AUTHOR]

A simple and sensitive label-free electrochemical DNA biosensor was proposed for the rapid determination of uric acid (UA) using a carbon nano tube paste electrode (CNTPE) modified with salmon sperm dsDNA. At first, the interaction between UA and the DNA was studied using differential pulse voltammetry (DPV). The addition of the DNA to UA solution resulted in a decrease in the peak current of UA and at the same time, a positive shift in the peak potential indicating an intercalative interaction. Then, the voltammetric response of a DNA-immobilized CNTPE was investigated for the determination of UA. The immobilization of the DNA was carried out using acid-functionalized carbon nanotubes and studied using Fe(CN)6 3−/Fe(CN)6 4− redox indicator. Compared with unmodified CNTPE, the oxidation signal of UA showed a significant increase at the DNA-coated electrode, and shifted to more positive potentials attributed to the pre-concentration of UA at the electrode surface due to interaction with the surface-confined DNA layer. This interaction was used for the fabrication of a simple and sensitive biosensor for determining UA. After the optimization of operational parameters, a linear dependence of the peak current on the UA concentration was observed in the range of 7.0×10−7 to 1.1×10−4 molL−1, with the detection and quantification limits of 1.8×10−7 and 5.8×10−7 molL−1, respectively. The proposed biosensor was successfully applied to validate its capability for the analysis of UA in human serum and urine samples. [ABSTRACT FROM AUTHOR]

In this study, a carbon paste electrode modified with TiO2 nanoparticles and ferrocene monocarboxylic acid (FM) was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for the detection of methyldopa in the presence of folic acid and glycine. The peak potentials recorded in a phosphate buffer solution (PBS) of pH7.0 were 325, 750 and 880mV vs. Ag/AgCl/KCl (3.0M) for methyldopa, folic acid and glycine, respectively. Under the optimum pH of 7.0, the oxidation of methyldopa occurred at a potential about 160mV less positive than that of the unmodified carbon paste electrode (CPE). The response of catalytic current with methyldopa concentration showed a linear relation in the range from 2.0×10−7 to 1.0×10−4 M with a detection limit of 8.0 (±0.2)×10−8 M. [ABSTRACT FROM AUTHOR]

Abstract: A new modified carbon paste electrode (CPE) and a coated wire PVC membrane electrode (CWE) based on a recently synthesized Schiff base of [bis 5-(4-nitrophenyl azo)salisylaldimine] 1,8-diamino, 3,6-dioxo octan (BNSAO) as a suitable carrier for Ag+ ion are described. The electrodes exhibit a Nernstian slope of 56.2±0.7 (CWE) and 58.4±0.3 (CPE)mV per decade for Ag+ ion over a wide concentration range from 3.1×10−2 to 9.0×10−7 M for CPE and 2.7×10−2 to 1.9×10−6 M Ag+ for CWE. The lower detection limits are 4.2×10−7 M Ag+ for CPE and 7.8×10−7 M Ag+ for CWE electrode. Their electrodes have a fast response time (∼5s), a satisfactory reproducibility and relatively long life time. The proposed sensors show a fairly good selectivity toward Ag+ ion in comparison to other common cations. The potentiometric responses are independent of the pH of the test solution in the pH range 3.5–7.0 for CPE and 2.5–7.0 for CWE. The proposed electrodes were used as indicator electrodes in potentiometric titration of silver ion with standard solution of potassium iodide. The direct determination of silver in spiked wastewater and radiology film gave results that compare favorably with those obtained by the atomic absorption spectrometric method. [Copyright &y& Elsevier]

• The MIP/Fe 3 O 4 /MoS 2 /GCE was fabricated for determination of pomalidomide. • The Fe 3 O 4 MNPs-decorated MoS 2 was prepared through hydrothermal method. • MIP/Fe 3 O 4 /MoS 2 was obtained by electro-polymerization in the presence of pomalidomide. • The novel sensitive and selective sensor was applied for pomalidomide determination in real samples. Despite the importance and necessity of pomalidomide determination due to the dual activity of it in vitro and in vivo , electrochemical methods have not been applied for this purpose, so far. We have developed a sensor based on molecular imprinted polymer/iron oxide nanoparticles/molybdenum disulfide nanosheets/glassy carbon electrode (MIP/Fe 3 O 4 /MoS 2 /GCE) to electrochemical determine pomalidomide. Fe 3 O 4 /MoS 2 nanocomposite was obtained through hydrothermal method and characterized by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Afterwards, the nanocomposite was casted on the GCE to improve the response signal. Then, MIP was fixed on the Fe 3 O 4 /MoS 2 /GCE surface using electrochemical polymerization process to selectively recognize pomalidomide. The electrochemical measurements was studied by square wave voltammetry (SWV) as a rapid and sensitive technique for determination of pomalidomide. Under the optimum conditions, the calibration curve linear range was found to be 1.0 nM-200.0 nM. The limit of quantification and detection were calculated 1.0 nM and 0.33 nM, respectively. Furthermore, the prepared sensor was successfully employed to quantify pomalidomide in health volunteer plasma and pharmaceutical samples with satisfy results. [ABSTRACT FROM AUTHOR]

Despite its useful properties, imiquimod (IMQ), known as an anti-cancer drug, can be harmful to the skin at high concentrations. Therefore, we have developed a novel electrochemical sensor to determine IMQ, for the first time. A glassy carbon electrode (GCE) was modified by a new composite comprising of ionic liquid-based molecularly imprinted polymer (MIP) and gold nanoparticles/graphene oxide (Au/GO). The MIP/Au/GO nanocomposite was synthesized through non-covalent imprinting process in the presence of IMQ, as template molecule and characterized by SEM and FT-IR. The square wave voltammetry technique (SWV) was applied for IMQ determination in 0.1 M phosphate buffer solution (PBS) at pH 7.0. Several parameters affecting the IMQ quantification were evaluated and optimized. Under the optimized conditions, the sensor presented a linear range of 0.02–20.0 μM, a limit of quantification and detection of 0.02 μM and 0.006 μM, respectively. Low RSD values indicate the good repeatability and reproducibility of the modified electrodes in preparation and determination procedures. The satisfactory results indicated that the proposed sensor could be successfully applied for IMQ determination in real samples. • The MIP was prepared using [VAIM]+Brˉ ionic liquid as monomer, imiquimod as template and EGDMA as a cross-linker. • The MIP/Au/GO nanocomposite was prepared through non-covalent imprinting process on the surface of Au/GO. • The MIP/Au/GO modified glassy carbon electrode was fabricated for selective determination of imiquimod. • Electrochemical determination of imiquimod was performed by square wave voltammetry and cyclic voltammetry techniques. • The novel sensitive and selective sensor was successfully applied for imiquimod determination in real samples with good merit figures. [ABSTRACT FROM AUTHOR]

Triclosan is broadly utilized as preservative or antiseptic in various cosmetic and personal care products. It becomes hazardous for environmental safety and human health more than a certain concentration. In this research, graphene oxide (GO) nanosheets were prepared by composing Fe3O4@Au nanostructure decorated GO together with polypyrrole (PPy) (Fe3O4@Au‐PPy/GO nanocomposite) in a facile way. The composite excellent increased the electrochemical response, presenting a high sensitive electrochemical method for triclosan detection. The synthesized Fe3O4@Au‐PPy/GO nanocomposite was characterized for its morphological, magnetically and structural properties by FESEM‐mapping, TEM, and XRD. The Fe3O4@Au‐PPy/GO nanocomposites modified glassy carbon electrodes (GCE), Fe3O4@Au‐PPy/GO GCE, showed a higher sensitivity good stability, reproducibility, lower LOD (2.5×10−9 M) and potential practical application in electrochemical detection of triclosan under optimized experimental conditions. [ABSTRACT FROM AUTHOR]

A new electrochemical sensor based on Fe3O4@SiO2‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe3O4@SiO2‐PANI‐Au GCE). The Fe3O4@SiO2‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe3O4@SiO2‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10−8 to 1.5×10−5 mol L−1, and the limit of detection was 3.8×10−9 mol L−1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids. [ABSTRACT FROM AUTHOR]

Abstract: A highly selective and sensitive carbon paste electrode modified with multi-walled carbon nanotubes and 4-[1-(4-methoxyphenyl) methylidene]-3-methyl-5-isoxazolone was used for accumulation and determination of trace amounts of bismuth using the differential pulse anodic stripping voltammetric method. The analytical procedure consisted of a closed-circuit accumulation step onto the modified carbon paste electrode. An anodic peak related to the oxidation of accumulated Bi(0) on the electrode surface was observed at about −0.05V. The calibration curve was linear in the range of 1–400μgL−1. The limit of detection was 0.2μgL−1 and the relative standard deviations for seven replicated determinations at 30, 100 and 300μgL−1 of bismuth were 3.6, 2.4 and 1.6%, respectively. The modified electrode was applied for the determination of bismuth in pharmaceutical, biological and several water samples. The accuracy and precision of results were comparable to those obtained by the graphite furnace atomic absorption spectroscopy method. [Copyright &y& Elsevier]

[Display omitted] • Synthesize and characterize of nanocomposite of polyaniline and Au (PANI/Au). • Use of the DNA probe to detect the complementary sequence associated with the hepatitis B virus. • Employ esculetin as a novel electroactive indicator to produce an electrochemical DNA hybridization biosensor for the first time. • In-silico study to elucidate and validate the results obtained from experimental measurements of the esculetin and the target DNAs. In the present study, esculetin, as a novel electroactive indicator, was used to produce an electrochemical DNA hybridization biosensor for Hepatitis B Virus (HBV) detection. At first, alkanothiol-modified DNA probe (from Hepatitis B) was self-assembled on the surface of a glassy carbon electrode modified by the nanocomposite of polyaniline and Au nanoparticles (PANI-Au). Hybridization conditions were enhanced, including the immobilization of the probe strands, the hybridization process and the indicator accumulation. For evaluating the DNA hybridization, the differential pulse voltammetric response of the accumulated esculetin was used as an electroactive indicator on different electrode surfaces. According to the obtained results, the voltammetric responses of esculetin accumulated on the probes interacted with non-complementary, mismatch and complementary targets were significantly different. Therefore, in optimum conditions, electrochemical signals of esculetin were linear in the concentration range of 0.01–3.00 × 10−6 M of the complementary strands, and a detection limit of 3.80 × 10−9 M was obtained for the target. Subsequently, the modified electrode was utilized for the detection of the HBV in spiked serum and plasma samples. The results obtained from electrochemical technique were confirmed by computational molecular simulation using MOE software. Moreover, the simulation outcomes provided valuable information about quantum chemical properties including the HOMO–LUMO maps and chemical reactivity for esculetin-the DNA target components. [ABSTRACT FROM AUTHOR]

In the present study, a carbon paste electrode chemically modified with gold nanoparticles was used as a sensitive electrochemical sensor for determination of eugenol. The differential pulse voltammetric method was employed to study the behavior of eugenol on this modified electrode. The effect of variables such as percent of gold nanoparticles, pH of solution, accumulation potential and time on voltammogram peak current were optimized. The proposed electrode showed good oxidation response for eugenol in 0.1 mol L − 1 phosphate buffer solution (pH 8) and the peak potential was about + 285 mV (vs. Ag/AgCl). The peak current increased linearly with the eugenol concentration in the range of 5–250 μmol L − 1 . The detection limit was found to be 2.0 μmol L − 1 and the relative standard deviation was 1.2% (n = 7). The effect of interferences on the eugenol peak current was studied. The method has been applied to the determination of eugenol in different real samples, spiked recoveries were in the range of 96%–99%. [ABSTRACT FROM AUTHOR]