Simultaneous determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(p-xylenolsulfonephthalein) modified glassy carbon electrode

A novel poly(p-xylenolsulfonephthalein) modified glassy carbon electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the modified electrode for the electrocatalytic oxidation of EP, AA, and UA in aqueous solutions. The separation of the oxidation peak potentials for AA–EP and EP–UA was about 200 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 10–1343, 2–390, and 0.1–560 μmol L⁻¹, respectively. The detection limits (S/N = 3) were 4, 0.1, and 0.08 μmol L⁻¹ for AA, EP and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation of EP at the modified electrode were calculated as 1.40(±0.10) × 10⁻⁴ cm² s⁻¹ and 1.06 × 10³ mol⁻¹ L s⁻¹, respectively. The present method was applied to the determination of EP in pharmaceutical and urine samples, AA in commercially available vitamin C tablet, and EP plus UA in urine samples.     

Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel sensor for the simultaneous determination of dopamine,ascorbic acid,and uric acid

A novel modified multiwall carbon nanotubes paste electrode with sodium dodecyl sulfate as a surfactant (SDS) has been fabricated through an electrochemical oxidation procedure and was used to electrochemically detect dopamine (DA), ascorbic acid (AA), uric acid (UA), and their mixture by cyclic voltammetry (CV) and differential voltammetry (DPV) methods. Several factors affecting the electrocatalytic activity of the hybrid material, such as the effect of pH, of the scan rate and of the concentration were studied. The bare carbon nanotubes paste electrode (BCNTPE) and SDS-modified carbon nanotubes paste electrode (SDSMCNTPE) were characterized using Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray spectroscopy (EDX). Using the CV procedure, a linear analytical curve was observed in the 1 × 10⁻⁶–2.8 × 10⁻⁵ M range with a detection limit at 3.3 × 10⁻⁷ M in pH 6.5, 0.2 M phosphate buffer solutions (PBS).     

Simultaneous determination of acetaminophen,dopamine and ascorbic acid using a PbS nanoparticles Schiff base-modified carbon paste electrode

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC), dopamine (DA), and ascorbic acid (AA) using a PbS nanoparticles Schiff base-modified carbon paste electrode (PSNSB/CPE). Differential pulse voltammetry peak currents of AC, DA and AA increased linearly with their concentrations within the ranges of 3.30 × 10⁻⁸–1.58 × 10⁻⁴ M, 5.0 × 10⁻⁸–1.2 × 10⁻⁴ M and 2.50 × 10⁻⁶–1.05 × 10⁻³ M, respectively, and the detection limits for AC, DA and AA were 5.36 × 10⁻⁹, 2.45 × 10⁻⁹ and 1.86 × 10⁻⁸ M, respectively. The peak potentials recorded in a phosphate buffer solution (PBS) of pH 4.6 were 0.672, 0.390, and 0.168 V (vs Ag/AgCl) for AC, DA and AA, respectively. The modified electrode was used for the determination of AC, DA, and AA simultaneously in real and synthetic samples.     

Determination of nitrite with the electrocatalytic property to the oxidation of nitrite on thionine modified aligned carbon nanotubes

A thionine modified aligned carbon nanotubes (ACNTs) electrode was fabricated and was used to electrochemically determine nitrite. The thionine modified ACNTs electrode exhibited enhanced electrocatalytic behavior to the oxidation of nitrite. The electrochemical mechanism of the thionine/ACNTs electrode towards the oxidation of nitrite was discussed. The thionine modified ACNTs electrode exhibited fast response towards nitrite with a detection limit of 1.12 × 10⁻⁶ mol  L⁻¹ and a linear range of 3 × 10⁻⁶ – 5 × 10⁻⁴ mol  L⁻¹. The proposed method was successfully applied in the detection of nitrite in real samples.     

Direct electron transfer of cytochrome c and its biosensor based on gold nanoparticles/room temperature ionic liquid/carbon nanotubes composite film

A robust and effective composite film based on gold nanoparticles (GNPs)/room temperature ionic liquid (RTIL)/multi-wall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode was prepared by a layer-by-layer self-assembly technique. Cytochrome c (Cyt c) was successfully immobilized on the RTIL-nanohybrid film modified GC electrode by electrostatic adsorption. Direct electrochemistry and electrocatalysis of Cyt c were investigated. The results suggested that Cyt c could be tightly adsorbed on the modified electrode. A pair of well-defined quasi-reversible redox peaks of Cyt c was obtained in 0.10 M, pH 7.0 phosphate buffer solution (PBS). RTIL-nanohybrid film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis currents increased linearly to the H₂O₂ concentration in a wide range of 5.0 × 10⁻⁵– 1.15 × 10⁻³ M. Based on the multilayer film, the third-generation biosensor could be constructed for the determination of H₂O₂.     

Simultaneous determination of ascorbic acid,dopamine and serotonin at poly(phenosafranine) modified electrode

The oxidation of phenosafranine at glassy carbon electrode gives rise to stable redox active electropolymerized film containing a polyazine moiety (poly(phenosafranine)). The redox response of the poly(phenosafranine) film was observed at the modified electrode at different pH and the pH dependence of the peak potential is 60 mV/pH, which is very close to the expected Nernstian behavior. The apparent diffusion coefficient (D_app) of poly(phenosafranine) film was measured as 2.51 × 10⁻⁹ cm²/s. This film exhibits potent and persistent electron-mediating behavior followed by well-separated oxidation peaks towards ascorbic acid (AA), dopamine (DA) and serotonin with activation overpotential, which is 200 mV lower than that of the bare electrode for AA oxidation. Using differential pulse voltammetry (DPV) studies, the limit of detection of DA in the presence of AA is estimated to be in the submicromolar regime. This method has been used for determining DA and AA concentrations in real samples with satisfactory results.     

Poly(m-ferrocenylaniline) modified carbon nanotubes-paste electrode encapsulated in nafion film for selective and sensitive determination of dopamine and uric acid in the presence of ascorbic acid

A nafion covered carbon nanotubes-paste electrode modified with poly(m-ferrocenylaniline), (Nf/p(FcAni)-CNTsPE), provides a novel voltammetric sensor for the selective determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). We studied the electrochemical activity of Nf/p(FcAni)-CNTsPE toward DA, UA, and AA by differential pulse voltammetry (DPV). DA and UA anodic peaks appear at 0.30 and 0.45 V, respectively while an anodic peak for AA was not observed. DPV oxidation peak values are linearly dependent on DA concentration over the range 1–150 μM (r² = 0.992), and on UA concentration over the range 5–250 μM (r² = 0.997). DA and UA detection limits are estimated to be 0.21 and 0.58 μM, respectively. The modified electrode shows both good selectivity and reproducibility for the selective determination of DA and UA in real samples. Finally, the modified electrode was successfully applied for the determination of DA and UA in pharmaceutical or biological sample fluids.     

Preparation and characterization of 3-[(1H-1,2,4-triazole-3-ylimino)methyl]naphtalene-2-ol film at the platinum surface for selective voltammetric determination of dopamine in the presence of uric acid and ascorbic acid

A [(1H-1,2,4-triazole-3-ylimino)methyl]naphthalene-2-ol (TMN-2-ol) film modified platinum (Pt) electrode has been fabricated by the electrochemical oxidation in acetonitrile solution. The modified surface was characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The prepared Pt electrode can be used as a functional interface to sensitive and selective determination of dopamine (DA) in the presence of uric acid (UA) and ascorbic acid (AA) by square wave voltammetry (SWV) method. The limit of detection (LOD) and limit of quantification (LOQ) of DA were 9.25 × 10⁻⁸ and 2.78 × 10⁻⁷ M, respectively. Linear range of DA was found to be between 3.95 × 10⁻⁷ and 4.19 × 10⁻⁶ M.     

Electrogenerated chemiluminescence aptamer-based biosensor for the determination of cocaine

A novel electrogenerated chemiluminescence aptamer-based (ECL-AB) biosensor for the determination of a small molecule drug is designed employing cocaine-binding aptamer as molecular recognition element for cocaine as a model analyte and ruthenium complex served as an ECL label. A 5′-terminal cocaine-binding aptamer with the ECL label at 3′-terminal of the aptamer was utilized as an ECL probe. The ECL-AB biosensors were fabricated by immobilizing the ECL probe onto a gold electrode surface via thiol-Au interactions. An enhanced ECL signal is generated upon recognition of the target cocaine, attributed to a change in the conformation of the ECL probe from random coil-like configuration on the probe-modified film to three-way junction structure, in close proximity to the sensor interface. The integrated ECL intensity versus the concentration of cocaine was linear in the range from 5.0 × 10⁻⁹ to 3.0 × 10⁻⁷ M. The detection limit was 1.0 × 10⁻⁹ M. This work demonstrates that the combination of a highly binding aptamer to analyte with a highly sensitive ECL technique to design ECL-AB biosensor is a great promising approach for the determination of small molecule drugs.     

Choline biosensors based on a bi-electrocatalytic property of MnO2 nanoparticles modified electrodes to H2O2

An interesting mode of reactivity of MnO₂ nanoparticles modified electrode in the presence of H₂O₂ is reported. The MnO₂ nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H₂O₂. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO₂ nanoparticles onto a glassy carbon (GC) electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0 × 10⁻⁵ –2.1 × 10⁻³ M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed.     

Zirconium(IV) phosphosulphosalicylate-based ion selective membrane electrode for potentiometric determination of Pb(II) ions

Zirconium(IV) phosphosulphosalicylate, a cation exchanger was synthesized by mixing zirconium oxychloride to a mixture of 5-sulphosalicylic acid and phosphoric acid. The material showed good efficiency for the preparation of an ion-selective membrane electrode. The membrane was characterized affinity for Pb(II) ions. Due to its Pb(II) selective nature, the ion-exchanger was used as an electroactive by XRD and SEM analysis. The electrode responds to Pb(II) ions in a linear range from 1 × 10⁻⁵ to 1 × 10⁻¹ M with a slope of 43.8 mV per decade change in concentration with detection limit of 4.78 × 10⁻⁶ M. The life span of electrode was found to be 90 days. The proposed electrode showed satisfactory performance over a pH range of 4.0–6.5, with a fast response time of 15 s. The sensor has been applied to the determination of Pb(II) ions in water samples of different origins. It has also been used as indicator electrode in potentiometric titration of Pb(II) ion with EDTA.     

Direct electrochemistry of hemoglobin and its electrocatalytic effect based on its direct immobilization on carbon ionic liquid electrode

Direct electrochemistry of hemoglobin (Hb) has been achieved by its direct immobilization on carbon ionic liquid electrode (CILE). CILE was immersed in a solution containing Hb and ionic liquid, octylpyridinium chloride ([OcPy][Cl]), to directly immobilize Hb on CILE. Cyclic voltammetry of modified electrode exhibited quasi-reversible peaks corresponding to Hb. The oxidation and reduction peak potentials of immobilized Hb in acetate buffer solution, pH 5.0 and at a scan rate of 0.1 V s⁻¹ were obtained at about –150 mV and –290 mV, respectively. The average surface coverage of the electroactive Hb adsorbed on the electrode surface was calculated as 8.4 × 10⁻¹¹ mol cm⁻². Hb retained its bioactivity on modified electrode and showed excellent electrocatalytic activity towards oxygen, hydrogen peroxide and nitrite. Hydrogen peroxide can be determined in the range of 1.0 × 10⁻⁴–5.0 × 10⁻³ M.     

Photoelectrochemical determination of inorganic mercury ions based on energy transfer between CdS quantum dots and Au nanoparticles

A novel photoelectrochemical (PEC) sensor for mercury ions (Hg^2 +) was fabricated based on the energy transfer (ET) between CdS quantum dots (QDs) and Au nanoparticles (NPs) with the formation of T–Hg^2 +–T pairs. In the presence of Hg^2 + ions, a T-rich single-strand (ss) DNA labeled with Au NPs could hybridize with another T-rich ssDNA anchored on the CdS QDs modified electrode, through T–Hg^2 +–T interactions, rendering the Au NPs in close proximity with the CdS QDs and hence the photocurrent decrease due to the ET between the CdS QDs and the Au NPs. Under the optimal condition, the photocurrent decrease was proportional to the Hg^2 + concentration, ranging from 3.0 × 10^− 9 to 1.0 × 10^− 7 M, with the detection limit of 6.0 × 10^− 10 M.     

New methodology for anodic stripping voltammetric determination of methylmercury

A novel procedure for trace methylmercury determinations by anodic stripping voltammetry at a gold film electrode is presented. Measurements were performed in a flow system. For selective determination of methylmercury, the Hg²⁺ ions were masked by complexation with DTPA. Hg-DTPA complex is not reduced at the gold film electrode at the potential of methylmercury reduction to the metallic state. The calibration graph was linear from 5 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ for an accumulation time 600 s. A detection limit (based on 3σ criterion) for methylmercury was 2.3 × 10⁻⁹ mol L⁻¹. The validation of the proposed procedure was made by analyses of human hair certified reference material.     

Electrospun zirconia-embedded carbon nanofibre for high-sensitive determination of methyl parathion

Carbon nanofibers embedded with ultrafine zirconia nanoparticles (ZrO₂-CNFs) are fabricated via a new methodology. Polyvinylpyrrolidone (PVP) and polymethylmethacrylate (PMMA) binary polymers containing zirconium n-butoxide are first dissolved in dimethylformamide, and the resulting solution is electrospun and heat-treated. The tetragonal zirconia nanoparticles formed, with a size of 5 ± 2 nm in diameter, are uniformly distributed in the carbon nanofibres. Using Nafion as an additive, ZrO₂-CNFs are drop-cast onto the glassy carbon electrode (ZrO₂-CNF/GCE) and the modified electrode is then applied to detect methyl parathion (MP) using differential pulse voltammetry. Two linear relationships are found at the concentration ranges of 1 × 10^− 9–2 × 10^− 8 g/L and 2 × 10^− 8–2 × 10^− 7 g/L, with a detection limit of 3.4 × 10^− 10 g/L (S/N > 3). The electrospun-based ZrO₂-CNF is a very promising coating material for electrochemical sensing of organophosphorus compounds.     

A self-assembled monolayer based electrochemical immunosensor for detection of leukemia K562A cells

A novel strategy to quantify the cell number of leukemia K562A cells using electrochemical immunosensor was developed by effective surface immunoreaction between P-glycoprotein (P-gp) on cell membrane and P-gp mouse monoclonal antibody bound on an epoxysilane monolayer modified glassy carbon electrode. The surface morphologies of the epoxysilane monolayer and the bound antibodies were studied with atomic force microscopy. The binding of target K562A cells onto the immobilized antibodies increased the electron-transfer impedance of electrochemical probe, which depended linearly on the cell concentration in the range of 5.0 × 10⁴–1.0 × 10⁷ cells mL⁻¹. The detection limit of the immunosensor was 7.1 × 10³ cells mL⁻¹. The proposed strategy showed acceptable reproducibility with an RSD of 3.4% for the linear slope and good precision with the RSD of 3.7% and 3.0% examined at the cell concentrations of 2.0 × 10⁶ and 1.0 × 10⁷ cells mL⁻¹.     

Strontium(II) selective PVC membrane electrode based acetophenone semicarbazone (ACS) as an ionophore

A new PVC membrane based strontium(II) ion-selective electrode has been constructed using acetophenone semicarbazone as a neutral carrier. The sensor exhibits a Nerstian response for strontium(II) ion over a wide concentration range 1.0 × 10⁻²–1.0 × 10⁻⁷ M with the slope of 29.4 mV/per decade. The limit of detection was 2.7 × 10⁻⁸ M. It was relatively fast response time (<10 s for concentration ⩾1.0 × 10⁻³ and <15 s for concentration of ⩾1.0 × 10⁻⁶ M) and can be used for 8 months without any considerable divergence in potentials. The proposed sensor revealed relatively good selectivity and high sensitivity for strontium(II) over a mono, di, trivalent cation and can be used in a pH range of 2.5–10.5. It was also successfully used as an indicator electrode in potentiometer titration and in the analysis of concentration in various real samples.     

Voltammetric sensor for buzepide methiodide determination based on TiO2 nanoparticle-modified carbon paste electrode

In this work, we have prepared nano-material modified carbon paste electrode (CPE) for the sensing of an antidepressant, buzepide methiodide (BZP) by incorporating TiO₂ nanoparticles in carbon paste matrix. Electrochemical studies indicated that the TiO₂ nanoparticles efficiently increased the electron transfer kinetics between drug and the electrode. Compared with the nonmodified CPE, the TiO₂-modified CPE greatly enhances the oxidation signal of BZP with negative shift in peak potential. Based on this, we have proposed a sensitive, rapid and convenient electrochemical method for the determination of BZP. Under the optimized conditions, the oxidation peak current of BZP is found to be proportional to its concentration in the range of 5 × 10⁻⁸ to 5 × 10⁻⁵ M with a detection limit of 8.2 × 10⁻⁹ M. Finally, this sensing method was successfully applied for the determination of BZP in human blood serum and urine samples with good recoveries.     

A sensitivity-controlled hydrogen peroxide sensor based on self-assembled Prussian Blue modified electrode

In this communication, a hydrogen peroxide (H₂O₂) sensor based on self-assembled Prussian Blue (PB) modified electrode was reported. Thin film of PB was deposited on the electrode by self-assembly process including multiple sequential adsorption of ferric ions and hexacyanoferrate ions. The as-prepared PB modified electrode displayed sufficient stability for practical sensing application. At an applied potential of ?0.05 V vs. Ag/AgCl (sat. KCl), PB modified electrode with 30 layers exhibited a linear dependence on H₂O₂ concentration in the range of 1 × 10^?6–4 × 10^?4 M (r = 0.9998) with a sensitivity of 625 mA M^?1 cm^?2. It was found that the sensitivity of H₂O₂ sensors could be well controlled by adjusting the number of deposition cycles for PB preparation. This work demonstrates the feasibility of self-assembled PB modified electrode in sensing application, and provides an effective approach to control the sensitivity of PB-based amperometric biosensors.     

Electrochemical oxidation behavior of nitrite on a chitosan-carboxylated multiwall carbon nanotube modified electrode

A novel chitosan-carboxylated multiwall carbon nanotube modified glassy carbon electrode (MC/GCE) was developed to investigate the oxidation behavior of nitrite using cyclic voltammetry and differential pulse voltammetry modes. The electrochemical mechanism of the MC/GCE towards nitrite was discussed. The MC/GCE exhibited fast response towards nitrite with a detection limit of 1 × 10⁻⁷ mol l⁻¹ and a linear range of 5 × 10⁻⁷–1 × 10⁻⁴ mol l⁻¹. The possible interference from several common ions was tested. The proposed method was successfully applied in the detection of nitrite in real samples.