Molecularly Imprinted Electrochemical Sensor Based on Modified Reduced Graphene Oxide‐gold Nanoparticles‐polyaniline Nanocomposites Matrix for Dapsone Determination

This work was designed to develop an electrochemical sensor based on molecular imprinted polyaniline membranes onto reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode for dapsone (DDS) determination. The prepared RGO/AuNPs/PANI‐MIPs nanocomposite was characterized by Ultra‐Violet‐Visible (UV‐Vis), Fourier transform infrared spectroscopy (FT‐IR) and scanning electronic microscopy (SEM) images. The feature of the imprinted electrode was evaluated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and impedance spectroscopy (IS). Throughout this study several analytical parameters, such as incubation time, pH value, concentration of monomer/template molecules and electro‐polymerization cycles were investigated. Under the optimized conditions, the experimental results showed best analytical performances for DDS detection with a sensitivity of 0.188 Ω/mol L^?1, a linear range from 1.0×10^?7 M to 1.0×10^?3 M and a detection limit of 6.8×10^?7 M. The bioanalytical sensor was applied to the determination of dapsone in real samples with high selectivity and recovery.     

Electrochemical Synthesis of β‐Cyclodextrin Functionalized Silver Nanoparticles and Reduced Graphene Oxide Composite for the Determination of Hydrazine

β‐cyclodextrin (β‐CD) functionalized silver nanoparticles (AgNPs) and reduced graphene oxide (RGO) via one step electrochemical potentiodyanamic method has been prepared. Scanning electron microscopy, Energy‐Dispersive X‐ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the role of β‐CD on preparation of AgNPs and RGO. RGO/β‐CD/AgNPs modified GCE showed good electrochemical activity towards electro‐oxidation of hydrazine in terms of decreasing the over potential and increasing the peak current. The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) of the modified electrode towards hydrazine were determined to be 0.66 and 0.97×10^?6 cm² s^?1, respectively. The LOD of our sensor was many folds lower than that of recommended concentration of hydrazine in drinking water by United States Environmental Protection Agency and World Health Organization. The sensor exhibited a wide linear range from 0.08 to 1110 µM and a very low detection limit (LOD) of 1.4 nM. In addition, the sensor selectively determined hydrazine even in the presence of common interferents.     

A novel palladium nanoparticles-polyproline-modified graphite electrode and its application for determination of curcumin

A novel-modified electrode has been developed, by electrodeposition of palladium nanoparticles (PdNps) on polypyroline film-coated (Poly(Pr)) graphite electrode. The modified electrode (PdNps/Poly(Pr)/GE) was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques. SEM proved that the palladium nanoparticles were uniform distributed with an average particle diameter of 20–45 nm. A higher catalytic activity was obtained for curcumin oxidation using this new modified electrode (PdNps/Poly(Pr)/GE). The square wave voltammogram of curcumin in pH 2 phosphate buffer exhibited an anodic peak at 0.504 V. This oxidation peak current was found to be linearly related to curcumin concentrations in the ranges of 5.0?×?10^?9 to 1.0?×?10^?7 M with a detection limit of 1.2?×?10^?9 M. This novel-modified electrode showed excellent sensitivity, compared with the existing reports about determination of curcumin.     

β‐Cyclodextrin Incorporated Carbon Nanotube Paste Electrode as Electrochemical Sensor for Nifedipine

In this work a carbon paste electrode modified with multiwalled carbon nanotubes/β‐cyclodextrin (MWCNTs/β‐CD) was constructed and applied to the determination of nifedipine. The electrochemical behavior of nifedipine at this electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Characterization of the modified electrode was conducted with electrochemical impedance spectroscopy and scanning electron microscopy. After adsorption of nifedipine on the MWCNTs/β‐CD paste electrode at 0.0 V for 6 min, a well defined reduction peak was produced in sodium hydroxide of 0.05 M. The calibration curve was linear from 7.0×10^?8 to 1.5×10^?5 M. The detection limit was obtained as 2.5×10^?8 M. The results demonstrated that this electrochemical sensor has excellent sensitivity and selectivity. This sensor was applied for determination of nifedipine in drug dosage and blood serum with excellent recoveries.     

Electropolymerization of Acid Chrome Blue K on Glassy Carbon Electrode for the Determination of Curcumin

Acid chrome blue K (ACBK) was electropolymerized on the surface of a glassy carbon electrode (GCE) by cyclic voltammetric sweep in the potential range from –0.2 to 0.9 V. The characteristic of poly‐ACBK film was studied by different methods such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. This modified electrode showed excellent electrocatalytic response to curcumin with the increase of the electrochemical responses. Under the optimal conditions a good linear voltammetric response could be obtained over the range of 1.0 × 10^?7‐7.0 × 10^?5 M and the detection limit was got as 4.1 × 10^?8 M (S/N = 3). The method was successfully applied for the determination of curcumin in human urinev samples.     

Gold nanoparticles-carbon nanotubes modified sensor for electrochemical determination of organophosphate pesticides

An electrochemical sensor was developed for the detection of organophosphate pesticides based on electrodeposition of gold nanoparticles on a multi-walled carbon nanotubes modified glassy carbon electrode. Cyclic voltammetry was employed in the process of electrodeposition. Field emission scanning electron microscope and X-ray diffraction techniques were used for characterization of the composite. Organophosphate pesticides (e.g. parathion) were determined using linear scan voltammetry. A highly linear response to parathion in the concentration range from 6.0?×?10^?5 to 5.0?×?10^?7 M was observed, with a detection limit of 1.0?×?10^?7 M estimated at a signal-to-noise ratio of 3. The method has been applied to the analysis of parathion in real samples.     

Amperometric Determination of Maltol using a Cobalt Oxide-Assembled MCM-41 Composite-Modified Glassy Carbon Electrode

A sensitive and selective amperometric method for maltol is reported based on a nanostructural Co₃O₄-assembled Mobil composite material (MCM-41). The amperometric sensor was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, cyclic voltammetry, electrochemical impedance spectroscopy, and ultraviolet–visible absorption spectroscopy. The obtained calibration curve showed that the oxidative peaks increased linearly with the maltol concentration from 1.66?×?10^?6?M to 1.15?×?10^?4?M with a detection limit of 0.42?µM. Furthermore, the mechanism of oxidation of the analyte on the modified electrode surface was investigated using electrochemical techniques. The modified electrode was used for the determination of maltol using the method of standard addition with satisfactory results.     

Electrocatalytical Oxidation of Nitrite and Its Determination Based on Au@Fe3O4 Nanoparticles

A promising electrochemical nitrite sensor was fabricated by immobilizing Au@Fe₃O₄ nanoparticles on the surface of L ‐cysteine modified glassy carbon electrode, which was characterized by scanning electron microscopy, X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The proposed sensor exhibited excellent electrocatalytic activity toward nitrite oxidation. The kinetic parameters of the electrode reaction process were calculated, (1–α)n_α was 0.38 and the heterogeneous electron transfer coefficient (k) was 0.13 cm s^?1. The detection conditions such as supporting electrolyte and pH value were optimized. Under the optimized conditions, the linear range for the determination of nitrite was 3.6×10^?6 to 1.0×10^?2 M with a detection limit of 8.2×10^?7 M (S/N=3). Moreover, the as‐prepared electrode displayed good stability, repeatability and selectivity for promising practical applications.     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid at Pt Nanoparticles Decorated Multiwall Carbon Nanotubes Modified GCE

A modified electrode was fabricated by electrochemically deposition of Pt nanoparticles on the multiwall carbon nanotube covered glassy carbon electrode (Pt nanoparticles decorated MWCNT/GCE). A higher catalytic activity was obtained to electrocatalytic oxidation of ascorbic acid, dopamine, and uric acid due to the enhanced peak current and well‐defined peak separations compared with both, bare and MWCNT/GCE. The electrode surfaces were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). Individual and simultaneous determination of AA, DA, and UA were studied by differential pulse voltammetry. The detection limits were individually calculated for ascorbic acid, dopamine, and uric acid as being 1.9×10^?5 M, 2.78×10^?8 M, and 3.2×10^?8 M, respectively. In simultaneous determination, LODs were calculated for AA, DA, and UA, as of 2×10^?5 M, 4.83×10^?8 M, and 3.5×10^?7 M, respectively.     

Electrochemical Detection of Epinephrine Using an L-Glutamic Acid Functionalized Graphene Modified Electrode

The development and application of an L-glutamic acid functionalized graphene nanocomposite, modified glassy carbon electrode are reported for the determination of epinephrine. The properties of the nanocomposite were characterized by scanning electron microscopy, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The modified electrode had high sensitivity and strongly catalytic activity for the detection of epinephrine. A linear relationship between the epinephrine concentration and the current response was obtained in the range of 1 × 10^?7 M to 1 × 10^?3 M by differential pulse voltammetry with a limit of detection of 3 × 10^?8 M. The modified electrode was employed to determine epinephrine in urine with satisfactory results.     

Simultaneous determination of dopamine, uric acid and ascorbic acid with LaFeO3 nanoparticles modified electrode

LaFeO₃ nanoparticles of approximately 22 nm in size were synthesized and characterized by XRD and TEM. A novel glassy carbon electrode modified with LaFeO₃ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.145 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The anodic peak current (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range from 1.5?×?10^?7 to 8.0?×?10^?4 M. The detection limit was 3.0?×?10^?8 M. The relative standard deviation of eight successive scans was 3.47% for 1.0?×?10^?6 M DA. The interference by ascorbic acid was eliminated efficiently. The method was used to determine DA in dopamine hydrochloride injections and showed excellent sensitivity and recovery.     

Electrochemical Characterization of Gold 6‐Amino‐2‐mercaptobenzothiazole Self‐Assembled Monolayer for Dopamine Detection in Pharmaceutical Samples

A new sensor, gold‐6‐amino‐2‐mercaptobenzothiazole (6A2MBT), was fabricated via a self‐assembly procedure. Electrochemical properties of the monolayer were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent antifouling property against the oxidation products of DA, allowed us to construct a dynamic calibration curve with two linear parts, 1.00×10^?6 to 3.72×10^?4 and 3.72×10^?4 to 6.42×10^?4 M DA, with correlation coefficients of 0.997 and 0.992 and a detection limit of 1.57×10^?7 M DA by using differential pulse voltammetry (DPV), respectively. Finally, the performance of the Au‐6A2MBT modified electrode was successfully tested for electrochemical detection of DA in a pharmaceutical sample.     

Electrochemical sensor for ultrasensitive determination of ceftazidime using hollow platinum nanoparticles/reduced graphene oxide/pencil graphite electrode

In this paper, an electrochemical sensor was prepared based on the modification of pencil graphite electrode (PGE) by hollow platinum nanoparticles/reduced graphene oxide (HPtNPs/rGO/PGE) for determination of ceftazidime (CFZ). Initially, rGO was electrodeposited on the electrode surface, and then, hollow platinum nanoparticles were placed on the electrode surface via galvanic displacement reaction of Pt(IV) ions with cobalt nanoparticles (CoNPs) that had electrodeposited on the electrode surface. Several significant parameters controlling the performance of the HPtNPs/rGO/PGE were examined and optimized using central composite design as one optimization methodology. The surface morphology and elemental characterization of the bare PGE, rGO/PGE, CoNPs/rGO/PGE, and HPtNPs/rGO/PGE-modified electrodes was analyzed by field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electrochemical impedance spectroscopy. The electrochemical activity of CFZ on resulting modified electrode was investigated by cyclic voltammetry (CV) and adsorptive differential pulse voltammetry (AdDPV). Adsorptive differential pulse voltammetry indicates that peak current increases linearly with respect to increment in CFZ concentration. CFZ was determined in the linear dynamic range of 5.0 × 10^?13 to 1.0 × 10^?9 M, and the detection limit was determined as 2.2 × 10^?13 M using AdDPV under optimized conditions. The results showed that modified electrode has high selectivity and very high sensitivity. The method was used to determine of CFZ in drug injection and plasma samples.     

Electrochemical Behavior of a Gold Electrode Modified with SWNTs/DDAB Films and Its Electrocatalytic Activity Towards Ascorbic Acid

A film of single-wall carbon nanotubes (SWNTs) and didodecyldimethylammonium bromide (DDAB) is prepared by casting a solution of SWNTs and DDAB onto the surface of a gold electrode. The electrochemical behavior of the film is investigated by electrochemical impedance spectroscopy and cyclic voltammetry. In a 0.10 M phosphate buffer solution of pH 7.0, the film-modified electrode gives a pair of redox peaks in cyclic voltamograms, with the anodic and cathodic peak potentials of 0.095 and 0.042 V. The peak currents change linearly with the scan rate at 30–500 mV/s. The modified electrode has an excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA). The catalysis currents are proportional to the AA concentration in the range of 5.0 × 10⁻⁴ to 3.2 × 10⁻² M. The linear-regression equation is i (μA) = 1.2079 + 1.3987 × 10³ c _AA (M), with a correlation coefficient of 0.9995. The detection limit is 2.2 × 10⁻⁴ M (signal-to-noise ratio of 3). The Michaelis-Menten constant (K _m) is 1.0 × 10⁻⁴ M by the Lineweaver-Burk equation. __________ From Elektrokhimiya, Vol. 41, No. 10, 2005, pp. 1193–1199. Original English Text Copyright ? 2005 by Cheng, Jin, Zhang. The text was submitted by the authors in English.     

Selective Detection of Dopamine in Presence of Ascorbic Acid by Use of Glassy‐Carbon Electrode Modified with Amino‐β‐Cyclodextrin and Carbon Nanotubes

A glassy carbon electrode modified with per‐6‐amino‐β‐cyclodextrin (β‐CDNH₂) and functionalized single‐walled carbon nanotubes (SWCNT‐COOH) was elaborated. This structure was investigated for the detection of dopamine acid (DA) in presence of ascorbic acid (AA). The sensor behavior was studied by cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The analysis results show that the electrode modification with CD derivative improves the sensitivity and selectivity of the DA recognition; the electrochemical response was further improved by introduction of SWCNT‐COOH. The sensor shows good and reversible linear response toward DA within the concentration range of 7×10^?7–10^?4 M with a detection limit of 5×10^?7 M.     

Selective Electroanalysis of Ascorbic Acid Using a Nickel Hexacyanoferrate and Poly(3,4‐ethylenedioxythiophene) Hybrid Film Modified Electrode

The mixed‐valent nickel hexacyanoferrate (NiHCF) and poly(3,4‐ethylenedioxythiophene) (PEDOT) hybrid film (NiHCF‐PEDOT) was prepared on a glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. The films were characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and electrochemical impedance spectroscopy (AC impedance). The advantages of these films were demonstrated for the detection of ascorbic acid (AA) using cyclic voltammetry and amperometric techniques. The electrocatalytic oxidation of AA at different electrode surfaces, such as the bare GCE, the NiHCF/GCE, and the NiHCF‐PEDOT/GCE modified electrodes, was determined in phosphate buffer solution (pH 7). The AA electrochemical sensor exhibited a linear response from 5×10⁻⁶ to 1.5×10⁻⁴ M (R²=0.9973) and from 1.55×10⁻⁴ to 3×10⁻⁴ M (R²=0.9983), detection limit=1×10⁻⁶ M, with a fast response time (3 s) for AA determination. In addition, the NiHCF‐PEDOT/GCE was advantageous in terms of its simple preparation, specificity, stability and reproducibility.     

Application of graphene oxide nanosheets as probe oligonucleotide immobilization platform for DNA sensing

In this work, a simple and novel electrochemical biosensor based on a glassy carbon electrode (GCE) modified with graphene oxide nanosheets (GO) was developed for detection of DNA sequences. The morphology of prepared nanoplatform was investigated by scanning electron microscopy, infrared (FTIR) and UV/Vis absorption spectra. The fabrication processes of electrochemical biosensor were characterized with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in an aqueous solution. The optimization of experimental conditions such as immobilization of the probe BRCA1 and its hybridization with the complementary DNA was performed. Due to unique properties of graphene oxide nanosheets such as large surface area and high conductivity, a wide liner range of 1.0 × 10^?17–1.0 × 10^?9 M and detection limit of 3.3 × 10^?18 M were obtained for detection of BRCA1 5382 mutation by EIS technique. Under the optimum conditions, the proposed biosensor (ssDNA/GO/GCE) revealed suitable selectivity for discriminating the complementary sequences from non-complementary sequences, so it can be applicable for detection of breast cancer.     

Electrocatalytic determination of propranolol hydrochloride at carbon paste electrode based on multiwalled carbon-nanotubes and γ-cyclodextrin

A carbon paste electrode based on γ-cyclodextrin–carbon nanotube composite (γ-CD–CNT–CME) was developed for the determination of propranolol hydrochloride (PRO). The electrochemical behaviour of PRO was investigated employing cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse adsorptive stripping voltammetry (DPAdSV). Surface morphology of the electrode has been studied by means of scanning electron microscopy. The results revealed that the oxidation of PRO is facilitated at γ-CD–CNT–CME. Under the optimized conditions in Britton–Robinson buffer pH 1.5, the peak currents were found to vary linearly with their concentrations in the range of 1.42 × 10^?7 to 4.76 × 10^?5 M. A detection limit (S/N = 3) of 4.01 × 10^?8 M was obtained for PRO by means of DPAdSV. The proposed method was employed for the determination of PRO in pharmaceutical formulations, urine and blood serum samples.     

Construction of a modified carbon paste electrode based on TiO2 nanoparticles for the determination of gallic acid

A modified carbon paste electrode was prepared by incorporating the TiO₂ nanoparticles in the carbon paste matrix. The electrochemical behavior of gallic acid (GA) is investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry. The surface morphology of the prepared electrode was characterized using the scanning electron microscopy. The results indicate that the electrochemical response of GA is improved significantly at the modified electrode compared with the unmodified electrode. Furthermore, the capabilities of electron transfer on these two electrodes were also investigated by electrochemical impedance spectroscopy. Under the optimized condition, a linear dynamic range of 2.5?×?10^?6 to 1.5?×?10^?4?mol?L^?1 with detection limit of 9.4?×?10^?7?mol?L^?1 for GA is obtained in buffered solutions with pH 1.7. Finally, the proposed modified electrode was successfully used in real sample analysis.