Enhanced voltammetric determination of dopamine using a glassy carbon electrode modified with ionic liquid-functionalized graphene and carbon dots

The authors describe a dopamine (DA) sensor based on a glassy carbon electrode modified with a composite film composed of carbon dots (C-dots) and graphene functionalized with an ionic liquid. The C-dots were functionalized with carboxy groups whose negative charge promotes electrostatic attraction to the protonated amino groups in DA. The presence of an imidazole cation in the IL facilitates interaction with the C-dots and DA via electrostatic interactions and π-stacking forces. Under optimal conditions, the modified GCE display improved electrochemical response to DA compared to a bare GCE, or a GCE modified with C-dots or IL-graphene only. The oxidation current, measured best at a potential of 0.22 V (vs. Ag/AgCl) is linearly related to the DA concentration in the 0.1 to 600 μM range, with a 30 nM detection limit at a signal-to-noise ratio of 3. Ascorbic acid does not interfere even in large excess, and the sensor is stable for at least a month. The modified GCE was applied to the determination of DA in spiked fetal bovine serum and gave satisfactory results.     

Voltammetric sensing of paracetamol, dopamine and 4-aminophenol at a glassy carbon electrode coated with gold nanoparticles and an organophillic layered double hydroxide

A differential pulse voltammetric method was developed for the simultaneous determination of paracetamol, 4-aminophenol and dopamine at pH 7.0 using a glassy carbon electrode (GCE) coated with gold nanoparticles (AuNPs) and a layered double hydroxide sodium modified with dodecyl sulfate (SDS-LDH). The modified electrode displays excellent redox activity towards paracetamol, and the redox current is increased (and the corresponding over-potential decreased) compared to those of the bare GCE, the AuNPs-modified GCE, and the SDS-LDH-modified GCE. The modified electrode enables the determination of paracetamol in the concentration range from 0.5 to 400???M, with a detection limit of 0.13???M (at an S/N of 3). The sensor was successfully applied to the stimultaneous determination of paracetamol and dopamine, and of paracetamol and 4-aminophenol, respectively, in pharmaceutical tablets and in spiked human serum samples.

Highly selective dopamine quantification using a glassy carbon electrode modified with a melanin-type polymer

A highly selective dopamine quantification at a new polymer-modified electrode in the presence of large excess of ascorbic acid and 3,4-dihydroxyphenyl acetic acid (dopac) is described. The electrochemical detection was performed at a glassy carbon electrode modified with a melanin-type polymer obtained by polymerization of 3.0×10⁻³ M -dopa in 0.050 M phosphate buffer solution pH 7.40 by applying 1.00 V for 60 min. The polymeric film exhibits attractive permselectivity excluding anionic species such as potassium ferricyanide, ascorbic acid, dopac and uric acid. Cationic species such as epinephrine, norepinephrine and dopamine and neutral ones such as catechol and hydrogen peroxide can be oxidized at the polymer-modified electrode. The use of ascorbic acid in the measurement solution allows the amplification of dopamine oxidation signal due to the reduction of the electrochemically generated dopaminequinone. By using 1.0×10⁻³ M ascorbic acid, the detection limit for dopamine is 5.0 nM. The interference for the maximum physiological concentrations of ascorbic acid and dopac in nervous centers, i.e. 500 μM ascorbic acid and 50 μM dopac is 8.1 and 1.4%, respectively.     

聚精氨酸修饰玻碳电极上多巴胺的电化学特性及其检测

用循环伏安法制备了聚精氨酸修饰玻碳电极,研究了神经递质多巴胺在该聚合物薄膜修饰电极上的电化学行为及其检测。在pH7.0的磷酸盐缓冲溶液中,多巴胺在聚精氨酸修饰电极上于0.19V和0.16V处出现一对灵敏、可逆的氧化还原峰。在最佳测试条件下,氧化峰电流与多巴胺的浓度在3.0×10-7~8.0×10-4mol/L范围内呈良好的线性关系,线性回归方程为Ipa(μA)=86.063C(mmol/L) 20.183,相关系数r=0.9993,最低检测限(3σ)5.0×10-8mol/L。用于多巴胺针剂含量的测定,结果满意。     

双层纳米金修饰电极对多巴胺的测定及应用研究

利用含有连续腺嘌呤碱基模块的DNA(CA DNA)构建了双层纳米金,在此基础上制备了由聚番红花红和双层三维分布的纳米金修饰的玻碳电极,并研究了多巴胺(DA)在此修饰电极上的电化学行为,发现对于DA的氧化,CA DNA构建的电极比巯基DNA构建的电极能够起到更明显的电催化作用。利用差分脉冲法(DPV)考察了DA测定的优化条件,并发现其浓度在8.0×10-9~1.2×10-6mol·L-1范围内与氧化峰电流呈良好的线性关系。该电极用于实际样品的测定,结果满意。     

Nafion-graphene composite film modified glassy carbon electrode for voltammetric determination of p-aminophenol

A Nafion-graphene (Nafion-GR) nanocomposite film modified glassy carbon electrode was fabricated by a simple drop-casting method, and used in the electrochemical detection of p-aminophenol (4-AP). Owing to the large surface area, good conductivity of GR and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of 4-AP. The electrochemical behaviors of 4-AP on Nafion/GR film modified glassy carbon electrodes were investigated by cyclic voltammetry and differential pulse voltammetry. A calibration curve is constructed in the same matrix, urine, as the unknown samples to be analyzed. The Nafion-GR film modified electrode was linearly dependent on the 4-AP concentration and the linear analytical curve was obtained in the ranges of 0.5–200 μM with differential pulse voltammetry (DPV) and the detection limit was 0.051 μM. The Nafion-graphene nanocomposite modified electrode exhibited good reusability than pure graphene modified GCE. This procedure can be used for the determination of p-aminophenol in the presence of its degradation products and paracetamol. Finally, the proposed method was successfully used to determine p-aminophenol in local tap water samples in urine samples and pharmaceutical preparations.     

Enhanced sensing of ascorbic acid, dopamine and serotonin at solid carbon paste electrode with a nonionic polymer film

A nonionic poly(2-amino-5-mercapto-thiadiazole) film was electrodeposited on a solid carbon paste electrode via a potential scanning procedure, and used for amperometric sensing of ascorbic acid (AA), dopamine (DA) and serotonin (ST). The highly electrocatalytic activity of the sensor to the three analytes was demonstrated from the sensitive and well separated voltammetric signals. The polymer film did not show significant accumulation effect on all the three species, reducing the fouling and deactivation of the electrode surface as well as the mutual interference among the analytes. The sensor achieved amperometric sensitivities of 1.92 nA (nmol L⁻¹)⁻¹ cm⁻² to AA in the linear range of 0.025-1.95 μmol L⁻¹, 3.76 nA (nmol L⁻¹)⁻¹ cm⁻² to DA and 7.00 nA (nmol L⁻¹)⁻¹ cm⁻² to ST both in the linear range of 0.02-1.56 μmol L⁻¹. The lowest detection limits were found to be 1.5, 0.7 and 0.4 nmol L⁻¹ for AA, DA and ST, respectively. This sensor was successfully employed for the successive determination of AA, DA and ST in pharmaceutical samples. The good antifouling property and reproducibility of the proposed sensor can be attributed to the nonionic polymer film without electrostatic attraction to the ionized species in the solutions.     

Chemically modified glassy carbon electrode for electrochemical sensing paracetamol in acidic solution

Different organic molecules were covalently grafted on glassy carbon electrodes (GCEs) by an electrochemical reduction or potentiostatic process of several in situ-generated diazonium cations in acidic aqueous solution containing NaNO₂. The cyclic voltammetry implemented in 0.1?M KCl aqueous solution containing 5?mM Fe(CN) ₆ ^3? or Ru(NH₃) ₆ ³⁺ confirmed the blocking properties of the modified GCEs. The electrochemical impedance spectroscopy (EIS) performed in 0.1?M KCl aqueous solution containing 5?mM Fe(CN) ₆ ^3?/4? was used to measure the surface coverage of the modifiers on GCE; the results showed that the modified layers on GCEs are very compact. The linear sweep voltammetry (LSV) was employed to investigate the electrochemical sensing properties of the bare and modified GCEs toward paracetamol (PCT) in sulfuric acid solution of pH?1.02, and the corresponding calibration plots were obtained, respectively. The results indicated there is an oxidation peak of PCT in the linear sweep voltammograms on the bare and modified GCEs with the active terminal groups such as ?OPO₃H₂, ?SO₃H, ?COOH, and so on, but do not appear on GCEs modified with the inert terminal groups such as ?NO₂ and ?Br. These imply that the GCEs modified with the active terminal groups display an electrochemical behavior like bulk GCE; however, those with the inert terminal groups present an electrochemical behavior like microelectrode. The varying electrochemical sensitivity of all the electrodes toward PCT was explained according to electronegativity and pK _a of the terminal groups of the modifiers on the electrodes and hydrogen bond between the modifiers and PCT. Apparent standard rate constants of PCT oxidation reaction on the bare and modified GCEs were obtained from the Laviron’s approach.     

Electrochemical sensor using glassy carbon electrode modified with acylpyrazolone-multiwalled carbon nanotube composite film for determination of xanthine

In this work, an electrochemical sensor 1-phenyl-3-methyl-4-(2-furoyl)-5-pyrazolone/multiwalled carbon nanotubes/glassy carbon electrode (GCE) was prepared for the determination of xanthine (XN) in the presence of an excess of uric acid. Cyclic voltammetry and differential pulse voltammetry were used to characterize the electrode. The oxidation of XN occurred in a well-defined peak having E _p 0.73 V in phosphate buffer solution of pH 6.0. Compared with the bare GCE, the electrochemical sensor greatly enhanced the oxidation signal of XN with negative shift in peak potential about 110 mV. Based on this, a sensitive, rapid, and convenient electrochemical method for the determination of XN has been proposed. Under the optimized conditions, the oxidation peak current of XN was found to be proportional to its concentration in the range of 0.3~50 μM with a detection limit of 0.08 μM. The analytical utility of the proposed method was demonstrated by the direct assay of XN in urine samples and was found to be promising at our preliminary experiments.     

A glassy carbon electrode modified with a film composed of cobalt oxide nanoparticles and graphene for electrochemical sensing of H2O2

We have prepared a graphene-based hybrid nanomaterial by electrochemical deposition of cobalt oxide nanoparticles (CoO_xNPs) on the surface of electrochemically reduced graphene oxide deposited on a glassy carbon electrode (GCE). Scanning electron microscopy and cyclic voltammetry were used to characterize the immobilized nanoparticles. Electrochemical determination of H₂O₂ is demonstrated with the modified GCE at pH 7. Compared to GCEs modified with CoO_xNPs or graphene sheets only, the new electrode displays larger oxidative current response to H₂O₂, probably due to the synergistic effects between the graphene sheets and the CoO_xNPs. The sensor responds to H₂O₂ with a sensitivity of 148.6 μA mM^?1 cm^?2 and a linear response range from 5 μM to 1 mM. The detection limit is 0.2 μM at a signal to noise ratio (SNR) of three. The method was successfully applied to the determination of H₂O₂ in hydrogen peroxide samples.

多巴胺在牛磺酸修饰玻碳电极上的电化学行为及其分析应用

采用电化学聚合法制备了牛磺酸修饰玻碳电极,研究了多巴胺在聚牛磺酸修饰电极上的电化学行为,建立了测定痕量多巴胺的新方法.在pH 7.2的磷酸盐缓冲溶液中,多巴胺在修饰电极上产生一对灵敏的氧化还原峰,采用差分脉冲伏安法测定,其氧化峰电流与多巴胺浓度在8.0×10-8～1.0×10-4 mol/L范围内呈良好的线性关系,检出限为1.0×10-8 mol/L.     

Simultaneous determination of dopamine and serotonin using a carbon nanotubes-ionic liquid gel modified glassy carbon electrode

An electrochemical sensor based on carbon nanotubes (CNTs)-ionic liquid (IL) composite has been developed for the simultaneous determination of serotonin (5-HT) and dopamine (DA). The CNTs-IL composite modified electrode presents excellent selectivity and sensitivity towards 5-HT and DA and eliminates the interference of ascorbic acid. The parameters which influence the determination of 5-HT and DA have been investigated. Under optimized conditions, linear calibration graphs were obtained in the range from 20 nM to 7 µM, with a detection of limit of 8 nM, for 5-HT, and in the range from 0.1 to 12 µM, with a detection of limit of 60 nM, for DA. The electrode has been applied to the assay of 5-HT and DA in human blood serum with good results.     

Voltammetric sensing of sulfamethoxazole using a glassy carbon electrode modified with a graphitic carbon nitride and zinc oxide nanocomposite

A voltammetric sensor is described for the determination the antibiotic sulfamethoxazole (SMZ). It is based on the use of a glassy carbon electrode (GCE) modified with a nanocomposite prepared from graphitic carbon nitride and zinc oxide (g-C₃N₄/ZnO). The nanorod-like ZnO nanostructure were synthesized sonochemically. The g-C₃N₄/ZnO nanocomposite was then prepared by mixing g-C₃N₄ with ZnO, followed by ultrasonication. The morphology and structure of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy and transmission electron microscopy. Under the optimal conditions, the response of the electrode, typically measured between 0.8 and 0.9 V (vs. Ag/AgCl), increases linearly in the 20 nM to 1.1 mM SMZ concentration range, and the lower detection limit is 6.6 nM. This is better than that of many previously reported sensors for SMZ. The modified electrode is highly selective, well reproducible and maintains its activity for at least 4 weeks. It was applied to the determination of SMZ in spiked human blood serum samples in with satisfactory results.

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Graphical abstract Schematic presentation of the voltammetric sensor for sulfamethoxazole. It consists of a glassy carbon electrode modified with a nanocomposite prepared from graphitic carbon nitride (g-C₃N₄/ZnO) that was supported with zinc oxide nanorods.

     

Docosyltrimethylammonium chloride modified glassy carbon electrode for simultaneous determination of dopamine and ascorbic acid

A glassy carbon electrode (GCE) modified with docosyltrimethylammonium chloride (DCTMACl) is used for simultaneous determination of dopamine (DA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) technique in 0.10 mol·L^?1 phosphate buffer solution of pH 5.0. The cationic surfactant DCTMACl modified film has a positive charge. DA exists as the positively charged species, whereas AA is the negatively charged one in the solution. Thus, at DCTMACl film-modified GCE, the oxidation peak potential of AA shifts toward less negative potential and the peak current of AA increases a little, while the oxidation peak potential of DA shifts toward more positive potential and peak current decreases greatly in comparison with that on bare electrode. The two anodic peaks are separated around 200 mV. Under optimal conditions, the catalytic peak currents obtained from DPV increase linearly with concentrations of DA and AA in the ranges of 1.0?×?10^?5 to 1.0?×?10^?3?mol·L^?1. This electrode has good reproducibility, high stability in its voltammetric response, and low detection limit (micromolar) for both AA and DA. The modified electrode has been applied to the determination of DA and AA in injection.     

Electrochemical oxidation behavior of bisphenol A at surfactant/layered double hydroxide modified glassy carbon electrode and its determination

Electrochemical behavior of bisphenol A (BPA) at glassy carbon electrode-modified with layered double hydroxide (LDH) and anionic surfactant (sodium dodecyl sulfate) is investigated by electrochemical techniques. Compared with the bare electrode and LDH-modified electrode, the oxidation peak potential of BPA shifted negatively and the peak current increased significantly due to the enhanced accumulation of BPA via electrostatic interaction with LDH at the hydrophobic electrode surface. Some determination conditions such as LDH loading, pH, scan rate, accumulation potential, and accumulation time on the oxidation of BPA were optimized. And some kinetic parameters were investigated. Under the optimized conditions, the oxidation current was proportional to BPA concentration in the range of 8 × 10⁻⁹ to 2.808 × 10⁻⁶ M with the detection limit of 2.0 × 10⁻⁹ M by amperometry. The fabricated electrode showed good reproducibility, stability, and anti-interference. The proposed method was successfully applied to determine BPA in water samples, and the results were satisfactory.     

用磷钨杂多酸-聚吡咯-氧化铝薄膜修饰玻碳电极测定废水中的对苯二酚

利用草酸电解液一步阳极氧化法在高纯铝表面制得纳米孔阳极氧化铝(AAO)薄膜;随后通过纳米孔阳极氧化铝模板电聚合,将磷钨杂多酸(PW12)掺杂吡咯(Py)溶液修饰到玻碳电极(GCE)表面,制得高灵敏的纳米微粒修饰电极(PW12-PPy/AGCE);研究了PW12-PPy/AGCE的伏安行为,考察了其影响因素;并将该电极应用于废水中对苯二酚的测定.结果表明,所制备的PW12-PPy/AGCE可以用于测定废水中的对苯二酚.     

Amperometric nitrite biosensor based on a gold electrode modified with cytochrome c on Nafion and Cu-Mg-Al layered double hydroxides

An amperometric biosensor for nitrite was prepared by immobilizing cytochrome c (Cyt c) on a gold electrode that was modified with Nafion and a Cu-Mg-Al layered double hydroxide (Cu-LDH). The Cu-LDH was characterized by Fourier transform infrared spectroscopy and powder X-ray diffraction. The UV-visible spectrum suggests that Cyt c retains its native conformation in the modified film. The direct electrochemical investigation indicated that the composite film represents a good platform for the immobilization of Cyt c as well as an excellent promoter for the electron transfer between Cyt c and the gold electrode. Moreover, the biosensor showed a remarkable bioelectrocatalytic activity for the oxidation of nitrite with a linear range from 0.75 to 123 μM. The detection limit is 2?×?10^?7 M (S/N?=?3). The biosensor was successfully applied to the determination of nitrite in food samples.