Modified glassy carbon electrode with Nafion/MWNTs as a sensitive voltammetric sensor for the determination of paeonol in pharmaceutical and biological samples

A simple, highly sensitive method was reported for directly voltammetric determination of paeonol in drug samples and human biological samples. Nafion/multi-wall carbon nanotubes’ (MWNTs) composite film was coated on the glassy carbon electrode. The adsorptive voltammetric behavior of paeonol on the Nafion/MWNTs-modified electrode was investigated using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The results indicated that the Nafion/MWNTs-modified electrode could remarkably enhance electrocatalytic activity toward the oxidation of paeonol, and showed an excellent resistance capability toward the electrode passivation. A highly sensitive voltammetric sensor was developed for the detection of paeonol in pharmaceutical and biological samples. Under the optimum conditions, the anodic peak current was proportional to paeonol concentration in the range of 6.0 × 10⁻⁷–6.0 × 10⁻⁵ M with a detection limit of 4.0 × 10⁻⁷ M. Some kinetic parameters were determined, and multi-step mechanism for oxidation of paeonol was proposed.     

Preparation of poly(9‐aminoacridine)‐modified electrode and its application in the determination of dopamine and ascorbic acid simultaneously

A novel modified electrode was fabricated with 9‐aminoacridine by electropolymerization in the phosphate buffer solution (PBS) (pH 7.4) and was characterized by cyclic voltammetry (CV). The modified electrode showed excellent electrocatalytic effect and high stability toward the electrochemical oxidation of dopamine (DA) and ascorbic acid (AA). Also, it showed a high stability for the determination of DA and AA simultaneously. Well‐separated voltammetric peaks were observed for DA and AA on the modified electrode. The separation of two anodic peaks was 170 mV, which was large enough to eliminate the interference of AA and determine DA. The differential pulse voltammograms (DPV) were used for the measurement of DA by means of the poly(9‐aminoacridine)‐modified electrode in PBS at pH 7.4. A linear response toDA was observed in the concentration range from 1.5 × 10^?6 to 3.5 × 10^?3 mol L^?1 with a correlation coefficient of 0.9998 and a detection limit (S/N = 3) of 1.0 × 10^?7mol L^?1. The proposed method was used to determine DA in DA‐hydrochloride injection and showed excellent sensitivity and recovery. The ease of fabrication, good reproducibility, high stability, and low cost of the modified electrode are the promising features of the proposed sensor. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3864–3870, 2007     

Simultaneous detection of ascorbic acid, uric acid and homovanillic acid at copper modified electrode

The copper was deposited on glassy carbon (GC) and indium tin oxide (ITO) electrodes by electrochemical method. The copper structures on electrode were characterized by atomic force microscope, X-ray diffractometeric pattern and differential pulse voltammetric studies. Optimal conditions for uniform growth of copper structures on the electrode were established. Voltammetric sensor was fabricated using the copper deposited GC electrode for the simultaneous detection and determination of uric acid (UA) and homovanillic acid (HVA) in the presence of excess concentrations of ascorbic acid (AA). The voltammetric signals due to AA and UA oxidation were well separated with a potential difference of 400 mV and AA did not interfere with the measurement of UA and HVA at the GC/Cu electrode. Linear calibration curves were obtained in the concentration range 1-40 μM for AA and 20-50 μM for UA at physiological pH and a detection limit of 10 nM of UA in the presence of 10-fold excess concentrations of AA was achieved. The simultaneous detection of submicromolar concentrations of AA, UA and HVA was achieved at the GC/Cu electrode. The practical utility of the present GC/Cu modified electrode was demonstrated by measuring the AA content in Vitamin C tablet, UA content in human urine and blood serum samples with satisfactory results.     

杯芳烃衍生物修饰电极的电化学性能研究

采用5,11,17,23-四叔丁基-25,27-二羟基-26,28-二(乙氧羰基甲氧基)杯[4]芳烃(酯-杯[4]芳烃)-PVC膜修饰玻碳电极,研究了其对Pb2+的电化学行为。研究表明:该修饰电极在碱性条件中为不可氧化过程,在酸性条件下具有良好的电化学活性,对Pb2+具有很高的响应,在3.65×10-6～4.83×10-3mol.L-1范围内线性扫描溶出伏安峰电流与Pb2+浓度具有良好的线性关系,检测限为1.28×10-6mol.L-1。     

Poly(taurine)/MWNT-modified glassy carbon electrodes for the detection of acetaminophen

A novel dye-polymer/CNT, poly(taurine)/MWNT-modified glassy carbon electrode was fabricated. This electrode is based on an electrochemically polymerized taurine layer coated on a MWNT film. The application of this electrode for voltammetric detection of acetaminophen is described. The electroactive surface area of the modified electrode was calculated to be 0.37 cm². Acetaminophen is oxidized at 0.38 V and then reduced at 0.27 V on the modified electrode. The irreversible oxidation process is due to the conversion of acetaminophen into imidogenquinone; the reduction process is ascribed to the reverse electrode reaction. The adsorption-controlled anodic peak current is proportional to the acetaminophen concentration (from 1.0 μM to 0.1 mM) with a detection limit of 0.5 μM. The detection of acetaminophen in drugs was conducted.     

Comparison of electrochemical oxidation of epinephrine in the presence of interfering ascorbic and uric acids on gold electrodes modified with S-functionalized compounds and gold nanoparticles

Mercaptopropionic acid (MPA), gold nanoparticles (Au-NPs) and cystamine (CA) modified gold bare electrodes have been applied in voltammetric sensors for simultaneous detection of epinephrine (EP), ascorbic (AA) and uric (UA) acids. Modification of the electrode surface by self-assembled layers (SAMs) improves the reactivity of a gold electrode for EP oxidation remarkably. A linear relationship between the epinephrine concentration and the current response is obtained in the range of 0.1–700 μM with the detection limit ≥0.042 μM for the electrodes modified at 2D template and in the range of 0.1–800 μM with the detection limit ≥0.040 μM for the electrodes modified at 3D template. The results have shown that the overlapping voltammetric response of epinephrine, ascorbic and uric acids is well resolved at modified electrodes. The modified SAMs electrodes show high selectivity, sensitivity, reproducibility and stability.     

Hybrid Plasticizers Enhance Specificity and Sensitivity of an Electrochemical-Based Sensor for Cadmium Detection

In addition to their use as an additive to improve physical properties of solvent polymeric membranes, plasticizers have a considerable impact on the specificity and sensitivity of membrane-modified electrochemical sensors. In this work, we aim at the hybridization of two different plasticizers using the electropolymerization technique in the development of a cadmium(II)-selective electrochemical sensor based on screen-printed gold electrode along with cyclic voltammetric measurement. At this point, we first screen for the primary plasticizer yielding the highest signal using cyclic voltammetry followed by pairing it with the secondary plasticizers giving rise to the most sensitive current response. The results show that the hybridization of DOS and TOTM with 3:1 weight ratio (~137.7-μm-thick membrane) renders a signal that is >26% higher than that from the sensor plasticized by DOS per se in water. The solution of 0.1 mM hydrochloric acid (pH 4) is the optimal supporting electrolyte. In addition, hybrid plasticizers have adequate redox capacity to induce cadmium(II) transfer from bulk solution to the membrane/water interfaces. Conversion of voltammetric signals to semi-integral currents results in linearity with cadmium(II) concentration, indicating the irreversible cadmium(II) transfer to the membrane. The DOS:TOTM hybrid sensor also exhibits high sensitivity, with a limit of detection (LOD) and limit of quantitation (LOQ) of 95 ppb and 288 ppb, respectively, as well as greater specificity towards cadmium(II) than that obtained from the single plasticizer sensor. Furthermore, recovery rates of spiked cadmium(II) in water samples were higher than 97% using the hybrid plasticizer sensor. Unprecedentedly, our work reports that the hybridization of plasticizers serves as ion-to-electron transducer that can improve the sensor performance in cadmium(II) detection.     

A novel amperometric sensor for peracetic acid based on a polybenzimidazole–modified gold electrode

We have developed a peracetic acid (PAA) sensor based on a polybenzimidazole–modified gold (PBI/Au) electrode. Fourier transform infrared and X-ray photoelectron spectroscopy indicated that PAA oxidized 69.4% of the imine in PBI to form PBI N-oxide, increasing the electrochemical reduction current during cyclic voltammetry. The chemical oxidation of the PBI/Au electrode by PAA, followed by its electrochemical reduction, allowed PAA to be detected directly and consecutively by assessing its reduction current. The PAA sensor had a broad linear detection range (3.1 μM–1.5 mM) and a rapid response time (3.9 s) at an applied potential of −0.3 V. Potentially interfering substances, such as hydrogen peroxide, acetic acid, and oxygen, had no effect on the ability of the probe to detect PAA, indicating high selectivity of the probe. Furthermore, the detection range, response time, and sensitivity of the sensor could all be improved by modification of the smooth planar electrode surface to a porous three-dimensional configuration. When compared to the analytical characteristics of other PAA sensors operating under optimal conditions, the three-dimensional PBI/Au electrode offers a rapid detection time, a usable linear range, and a relatively low detection limit.     

Maltose-Containing Polyurethane Films: Synthesis,Characterization, and Their Use for Determination of Dopamine in the Presence of the Electroactive and Nonelectroactive Interferents

A series of polyurethanes were prepared from the maltose-ethylene glycol-diphenylmethane diisocyanate and used to construct a novel polyurethane electrode for the detection of dopamine. The polyurethanes were characterized by FT-IR, differential scanning calorimetry, and thermogravimetric analysis. The intrinsic viscosity and adhesive properties were also evaluated. Selectivity behaviour of films prepared from polyurethane solutions containing 1%, 3%, 5%, and 10% maltose to electroactive and nonelectroactive substances was examined by DPV. The results demonstrated that polymer electrode by 2 µL polyurethane solutions containing 3% maltose was allowed penetration of dopamine while blocking the permeation of ascorbic acid and uric acid through film.     

Application of thionine-nafion supported on multi-walled carbon nanotube for preparation of a modified electrode in simultaneous voltammetric detection of dopamine and ascorbic acid

A modified carbon-paste electrode (CPE) is prepared by incorporating thionine-nafion supported on multi-walled carbon nanotube (MWCNT). The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) on the surface of the modified electrode is investigated by cyclic voltammetry (CV). The results show that thionine effectively immobilized in the matrix of the paste by using an appropriate mixture of nafion/MWCNT under the ultrasonic condition. On the other hand, presence of nafion enhances the stability of the thionine supported by MWCNT in the composite electrode and improves the reproducibility of the surface of the modified electrode under renewing process by polishing. The results of cyclic and differential pulse voltammetric investigations show that the modified electrode possesses an efficient electrocatalytic activity for the electrochemical oxidation of DA and AA and a peak potential separation nearly 379 mV is resulted for two compounds. The prepared modified electrode does not show any considerable response toward the electro-oxidation of sulfhydryl compounds, such as, cysteine, penicillamine and glutathione, revealing a good selectivity for voltammetric response to AA and DA in clinical and pharmaceutical preparations. The effective electrocatalytic property, excellent peak resolution and ability for masking the voltammetric responses of the other biologically reducing agents, make the modified electrode suitable for simultaneous and sensitive voltammetric detection of sub-micromolar amounts of AA and DA.     

Amperometric hydrogen peroxide biosensor based on a modified gold electrode with silver nanowires

A novel amperometric biosensor for the detection of hydrogen peroxide (H₂O₂) was prepared by immobilizing horseradish peroxidase (HRP) on highly dense silver nanowire (Ag-NW) film. The modified electrode was characterized using UV–Vis spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical performances of the electrode were studied by cyclic voltammetry and chronoamperometry. The HRPs immobilized on the surface of Ag-NWs exhibited an excellent electrocatalytic response toward reduction of H₂O₂. The resulting Ag-NW modified sensor showed a sensitivity of ~2.55 μA μM⁻¹ (correlation coefficient r = 0.9969) with a linear range of 4.8 nM–0.31 μM. Its detection limit was 1.2 nM with a signal-to-noise ratio of 3. The Michaelis–Menten constant K_M^app and the maximum current density I _max of the modified electrode were 0.0071 mM and 8.475 μA, respectively. The preparation process of the proposed biosensor was convenient, and the resulting biosensor showed high sensitivity, low detection limit and good stability.     

Glassy carbon electrodes modified with a film of nanodiamond-graphite/chitosan: Application to the highly sensitive electrochemical determination of Azathioprine

A novel modified glassy carbon electrode with a film of nanodiamond-graphite/chitosan is constructed and used for the sensitive voltammetric determination of azathioprine (Aza). The surface morphology and thickness of the film modifier are characterized using atomic force microscopy. The electrochemical response characteristics of the electrode toward Aza are investigated by means of cyclic voltammetry. The modified electrode showed an efficient catalytic role for the electrochemical reduction of Aza, leading to a remarkable decrease in reduction overpotential and enhancement of the kinetics of the electrode reaction with a significant increase of peak current. The effects of experimental variables, such as the deposited amount of modifier suspension, the pH of the supporting electrolyte, the accumulation potential and time were investigated. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of Aza in the range of 0.2-100 μM with a detection limit of 65 nM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, excellent catalytic activity in physiological conditions and good reproducibility. The modified electrode can be successfully applied to the accurate determination of trace amounts of Aza in pharmaceutical and clinical preparations.     

Simultaneous voltammetric detection of ascorbic acid and uric acid at a carbon-paste modified electrode incorporating thionine-nafion ion-pair as an electron mediator

The electrochemical behavior of ascorbic acid (AA) and uric acid (UA) at the surface of a carbon-paste electrode modified with incorporate thionine-nafion ion-paired was thoroughly investigated. The results show the presence of nafion inside the matrix of modified electrode, because of the effective ion-pairing and hydrophobic interactions, significantly enhances the stability of thionine as an electron mediator inside the modified electrode. A high reproducibility in voltammetric response to analyte species results because of this enhancement. The cyclic voltammetric studies using the prepared modified electrode show the best electrocatalytic property for the electro-oxidation of AA and noticeable decrease in anodic overpotential. Although the catalytic effect is observed to some extent for UA, the property cannot be seen for other biologically reducing agents such as cysteine. The voltammetric studies using the thionine-nafion modified electrode show two well-resolved anodic peaks for AA and UA, revealing the possibility of the simultaneous electrochemical detection of these compounds in the presence of biological thiols. The detection limits of 5 × 10⁻⁸ and 5 × 10⁻⁷ M were obtained in differential pulse voltammetric (DPV) measurements for UA and AA, respectively. Spectrophotometric investigations were used to confirm the selective catalytic effect of thionine in oxidation of AA and to some extent, UA. The detection system is stable (R.S.D. for the slope of the calibration curves was less than 4% for six measurements in one month) and is of high selectivity for electro-oxidation of AA and UA in complex biological and clinical matrices. The prepared modified electrode is applied for the DPV measurement of AA in pharmaceutical preparations. Also, the electrode is used to determine UA in human urine and serum samples and recovery of the amounts of UA added to these complex samples.     

Electrocatalytic oxidation of thioglycolic acid at carbon paste electrode modified with cobalt phthalocyanine: application as a potentiometric sensor

The voltammetric behavior of thioglycolic acid (TGA) was studied at a carbon paste electrode modified with cobalt phthalocyanine (CoPc). The CoPc-modified electrode shows high electrocatalytic activity toward oxidation of TGA, lowering substantially the overpotential of anodic reaction. Results of the cyclic voltammetry show that TGA undergoes a two-step oxidation (each step with one electron) resulting the dimer of thiol. Enhancement of the rate of electron transfer results in a near-Nernstian behavior of modified electrode to the concentration of TGA and makes it as a suitable potentiometric sensor for the detection of this compound. This electrode shows a near-Nernstian response in a wide linear range of the concentration TGA (4 orders of magnitude). The modified electrode was used successfully for the determination of TGA and its salts in hair-treatment products and also in culture media. The modified electrode exhibited a fast response time (<10 s), very good stability, and had an extended lifetime.     

Simultaneous determination of dopamine and uric acid on nafion/sodium dodecylbenzenesulfonate composite film modified glassy carbon electrode

A novel electrochemical sensor has been constructed by using a glassy carbon electrode (GCE) coated with nafion/sodium dodecylbenzenesulfonate (SDBS). Differential pulse voltammetry (DPV) was used to study the electrochemical behaviors of dopamine (DA) and uric acid (UA). An optimum of 5 mM SDBS together with 0.05 wt% of nafion was used to improve the resolution and the determination sensitivity successfully. In 0.1 M phosphate buffer solution (pH 6.5), the modified electrode exhibited high electrocatalytical activity toward the oxidation of DA and UA with obvious reduction of overpotential. Compared with bare GCE, the modified electrode resolved the voltammetric response of DA and UA into two well-defined voltammetric peaks by DPV, which can be used for simultaneous determination of these species in mixture. The peak currents obtained from DPV were linearly related to the concentrations of DA and UA in the ranges of 4.0 × 10⁻⁷–8.0 × 10⁻⁵ M and 4.0 × 10⁻⁶–8.0 × 10⁻⁴ M, respectively. The detection limit of DA and UA (signal-to-noise ration was 3) were 5.0 × 10⁻⁸ and 4.0 × 10⁻⁷ M, respectively.     

Silver nanoparticles/poly(2-(N-morpholine) ethane sulfonic acid) modified electrode for electrocatalytic sensing of hydrogen peroxide

A sensitive amperometric hydrogen peroxide (HP) sensor was constructed based on silver nanoparticles/poly(2-(N-morpholine) ethane sulfonic acid) (PMES) modified glassy carbon electrode. PMES and silver nanoparticles were orderly introduced to the surface of the electrode by electrochemical methods and characterized by cyclic voltammetry, scanning electron microscopy, and X-ray powder diffraction. The fabricated electrode showed a good electrocatalytic activity toward the reduction of HP with a line range from 0.6 ??M to 0.54 mM and a detection limit of 0.18 ??M. In addition, the sensor exhibited favorable reproducibility and good long-term stability, and was applied to determine HP in real sample with satisfactory result.     

Selective determination of norepinephrine in the presence of ascorbic and uric acids using an ultrathin polymer film modified electrode

This paper reports the selective determination of norepinephrine (NEP) in the presence of very important interferences, ascorbic acid (AA) and uric acid (UA) using electropolymerized film of 2-amino-1,3,4-thiadiazole (p-ATD) modified glassy carbon (GC) electrode in 0.20 M phosphate buffer solution (pH 5.0). The bare GC electrode does not separate the voltammetric signals of AA, NEP and UA. However, p-ATD modified GC electrode not only resolved the voltammetric signals of AA, NEP and UA with potential differences of 150 and 130 mV between AA–NEP and NEP–UA, respectively but also dramatically enhanced the oxidation peak currents of them when compared to bare GC electrode. The modified electrode showed an excellent selectivity towards NEP even in the presence of 100-fold excess of AA and UA. The amperometric current was linearly increased from 40 nM to 25 μM for NEP and the lowest detection limit was found to be 0.17 nM (S/N = 3). The practical application of the modified electrode was demonstrated by determining NEP in norepinephrine hydrochloride injection.     

Electrochemical Biosensor Based on surfactant doped polypyrrole (PPy) matrix for lactose determination

Lactose biosensor based on surfactant doped polypyrrole (PPy) was developed. Galactose oxidase and β‐galactosidase was coimmobilized in PPy matrix during electropolymerization process with the presence of sodium dodecylbenzene sulphonic acid as surfactant. Bi‐enzyme entrapped PPy was characterized with Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The response of the enzyme electrode was measured by CV in the range of ?0.1 to 1.0 V versus Ag/AgCl which was due to the electrooxidation of enzymatically produced H₂O₂. The effect of lactose concentration was investigated. Response time of biosensor was found to be 8–10 s (the time required to obtain the maximum peak current) and upper limit of the linear working portions was found to be 1.22 mM lactose concentration with a detection limit of (2.6 × 10^?6 M). The apparent Michaelis–Menten constant was found to be 0.117 mM lactose. The effects of interferents (ascorbic acid and uric acid) were determined. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40200.     

Effect of Eleven Antioxidants in Inhibiting Thermal Oxidation of Cholesterol

Eleven antioxidants including nine phenolic compounds (rutin, quercetin, hesperidin, hesperetin, naringin, naringenin, chlorogenic acid, caffeic acid, ferulic acid), vitamin E (α‐tocopherol), and butylated hydroxytoluene (BHT) were selected to investigate their inhibitory effects on thermal oxidation of cholesterol in air and lard. The results indicated that the unoxidized cholesterol decreased with heating time whilst cholesterol oxidation products (COPs) increased with heating time. The major COPs produced were 7α‐hydroxycholesterol, 7β‐hydroxycholesterol, 5,6β‐epoxycholesterol, 5,6α‐epoxycholesterol, and 7‐ketocholesterol. When cholesterol was heated in air for an hour, rutin, quercetin, chlorogenic acid, and caffeic acid showed a strong inhibitory effect. When cholesterol was heated in lard, caffeic acid, quercetin, and chlorogenic acid demonstrated inhibitory action during the initial 0.5 h (p < 0.05), with caffeic acid being the best inhibitor. Hesperetin, naringenin, caffeic acid, ferulic acid, vitamin E, and BHT could decrease the peroxide value during the initial 0.5 and 1 h (p < 0.05) in lard. It seemed that 200 ppm antioxidant could not obviously retard the long‐term oxidation of cholesterol and lard under high temperature, but caffeic acid, quercetin, and chlorogenic acid displayed great untapped potential to prevent thermal oxidation of cholesterol 0.5 h at least. For the sake of health and flavor, fast stir‐frying over a high flame is recommended. If baking or deep fat frying food in oil, it is best to limit cooking time to within 0.5 h.     

Effects of capacitance and resistance of MWNT-film coated electrodes on voltammetric detection of acetaminophen

The active electrode area, capacitances, and resistances of MWNT-film coated glassy carbon electrodes with different amount of MWNTs have been characterized by cyclic voltammetry and chronoamperometry. They are varied by controlling the amount of MWNTs dispersed on the electrode surface and affect the voltammetric responses of analytes in liquids. The redox current of acetaminophen is enhanced on the MWNT-film coated electrodes due to the enlarged active electrode area. The oxidation of acetaminophen occurs at 0.34 V and the reduction occurs at 0.27. Two electrons and two protons participate in the reversible redox reaction. The diffusion-controlled anodic peak current is proportional to the concentration of acetaminophen from 5.0 to 0.1 mM with a detection limit of 2.4 μM. The determination of acetaminophen in pharmaceutical formulations was also conducted.