Selective and sensitive determination of dopamine by composites of polypyrrole and graphene modified electrodes

A novel method is developed to fabricate the polypyrrole (PPy) and graphene thin films on electrodes by electrochemical polymerization of pyrrole with graphene oxide (GO) as a dopant, followed by electrochemical reduction of GO in the composite film. The composite of PPy and electrochemically reduced graphene oxide (eRGO)-modified electrode is highly sensitive and selective toward the detection of dopamine (DA) in the presence of high concentrations of ascorbic acid (AA) and uric acid (UA). The sensing performance of the PPy/eRGO-modified electrode is investigated by differential pulse voltammetry (DPV), revealing a linear range of 0.1-150 μM with a detection limit of 23 nM (S/N = 3). The practical application of the PPy/eRGO-modified electrode is successfully demonstrated for DA determination in human blood serum.     

一步电沉积纳米铜/石墨烯/壳聚糖复合膜修饰玻碳电极测定邻苯二酚

用一步电沉积法制备了纳米铜/石墨烯/壳聚糖复合膜修饰玻碳电极。用循环伏安法(CV)和差分脉冲伏安法(DPV)对邻苯二酚在该修饰电极的电化学行为进行了研究。实验结果表明,在pH值为7.0的磷酸盐缓冲液(PBS)中,该修饰电极对邻苯二酚具有良好的电催化作用,其电化学信号与邻苯二酚的浓度在1.0×10-6～2.0×10-4mol/L范围内呈良好的线性关系,线性相关系数为0.991。检出限为1×10-7mol/L。结果表明,纳米铜/石墨烯/壳聚糖复合膜修饰电极显著提高了邻苯二酚的电化学响应信号,并表现出良好的选择性和重现性。该方法成功用于水样中邻苯二酚含量的测定。     

TiO2-石墨烯-Nafion复合膜修饰玻碳电极同时测定多巴胺和尿酸

利用在玻碳电极上修饰了TiO2-石墨烯-Nafion复合膜制得的修饰电极进行多巴胺(DA)和尿酸(UA)的同时测定。用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了该修饰电极的电化学行为。在pH为7.0的磷酸盐缓冲液(PBS)中,修饰电极对于DA和UA的电化学氧化具有良好的电催化性能。DA和UA的氧化峰电流分别在2～120和60～300μmol/L浓度范围内呈良好的线性关系,检出限分别为0.066和0.102μmol/L。实验结果表明,TiO2-石墨烯-Nafion复合膜修饰电极显著提高了检测的灵敏度,并表现出良好的选择性和重现性。     

二氧化锰/石墨烯纸电极的制备及其电化学性能

通过电化学法使溶液中的Mn²⁺电解氧化为MnO₂,沉积复合在石墨烯片膜上,形成由MnO₂/石墨烯复合材料构成的纸电极。 采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)、循环伏安(CV)和恒流放电等技术手段对纸电极材料的结构、形貌以及电化学性能进行了研究。 结果表明,MnO₂球形颗粒均匀地沉积在石墨烯片膜上,形成了厚度45 μm的纸电极,经过380 ℃煅烧后,纸电极中的MnO₂晶型由γ-MnO₂转化为β/γ-MnO₂混合晶型,是良好的柔性Li/MnO₂电池的电极材料。 MnO₂/石墨烯纸电极在室温下0.1C放电容量达269 mA·h/g,而且电化学阻抗低、柔韧性好。     

聚多巴胺/多壁碳纳米管/玻璃碳电极上多巴胺的电分析

基于多巴胺（DA）在多壁碳纳米管（MWCNTs）修饰玻璃碳（GC）电极上的电聚合,制得聚多巴胺(PDA)/MWCNTs/GC电极,并对该修饰电极进行了电化学阻抗谱 (EIS)和循环伏安法(CV)表征。 在该修饰电极上,DA呈现良好的电化学行为。在pH=7.4磷酸缓冲溶液中其氧化电流显著高于在裸电极上的响应,且能有效地抑制2.0 mmol/L抗坏血酸(AA)或K4Fe(CN)6的直接电化学响应,表明MWCNTs可增敏信号,且阳离子选择透过性PDA膜可抑制阴离子的电化学干扰。 采用CV实验检测DA,DA氧化的半微分伏安峰高(ipa-sd)与多巴胺浓度在0.08～1.76 μmol/L范围内呈线性关系,在无抗坏血酸和有0.5 mmol/L抗坏血酸共存时的线性回归方程分别为ipa-sd(μA/s1/2)=0.107+0.405c(μmol/L)（r2=0.986）和ipa-sd(μA/s1/2)=0.628+0.649c(μmol/L)(r2=0.992),检测限均为8.0×10-8 mol/L(S/N=3)。 该法用于盐酸多巴胺注射液中多巴胺的快速测定,结果满意。     

Enhanced sensing of dopamine in the present of ascorbic acid based on graphene/poly(p-aminobenzoic acid) composite film

Graphene/p-aminobenzoic acid composite film modified glassy carbon electrode (Gr/p-ABA/GCE) was first employed for the sensitive determination of dopamine (DA). The electrochemical behavior of DA at the modified electrode was investigated by cyclic voltametry (CV), differential pulse voltametry (DPV) and amperometric curve. The oxidation peak currents of DA increased dramatically at Gr/p-ABA/GCE. The modified electrode was used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). The Gr/p-ABA composite film showed excellent electrocatalytic activity for the oxidation of DA in phosphate buffer solution (pH 6.5). The peak separation between DA and AA was large up to 220 mV. Using DPV technique, the calibration curve for DA determination was obtained in the range of 0.05-10 μM. The detection limit for DA was 20 nM. AA did not interfere with the determination of DA because of the very distinct attractive interaction between DA cations and the negatively Gr/p-ABA composite film. The proposed method exhibited good stability and reproducibility.     

多巴胺在聚亚甲基蓝/石墨烯修饰电极上的电化学行为研究

利用电聚合方法在石墨烯修饰的玻碳电极表面制备了聚亚甲基蓝/石墨烯修饰电极(PMB/GH/GCE)。采用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了多巴胺(DA)和抗坏血酸(AA)在该修饰电极上的电化学行为。在pH 6.9的磷酸盐缓冲溶液中,DA和AA分别在0.208 V和-0.108 V处产生灵敏的氧化峰,与其在聚亚甲基蓝和石墨烯单层修饰电极上的电化学行为相比,两者的峰电流明显增加,峰电位差达316 mV。研究表明,电聚合方法使亚甲基蓝牢固地非共价修饰到石墨烯上,并产生协同增效作用,较好地提高了电极的灵敏度和分子识别性能,有利于在大量AA存在下实现对DA的选择性测定。在1.00×10-3mol/L AA的存在下,DA的差分脉冲伏安法峰电流与其浓度在1.00×10-7～5.00×10-3mol/L范围内呈良好的线性关系,检出限达1.00×10-8mol/L。将该方法用于盐酸多巴胺注射液的测定,结果满意。     

Direct electrochemistry-based hydrogen peroxide biosensor formed from single-layer graphene nanoplatelet-enzyme composite film

A novel electrochemical sensing system for direct electrochemistry-based hydrogen peroxide biosensor was developed that relied on the virtues of excellent biocompatibility, conductivity and high sensitivity to the local perturbations of single-layer graphene nanoplatelet (SLGnP). To demonstrate the concept, the horseradish peroxidase (HRP) enzyme was selected as a model to form the SLGnP-TPA (tetrasodium 1,3,6,8-pyrenetetrasulfonic acid)-HRP composite film. The single-layer graphene composite film displayed a pair of well-defined and good reversible cyclic voltammetric peak for Fe(III)/Fe(II) redox couple of HRP, reflecting the enhancement for the direct electron transfer between the enzyme and the electrode surface. Analysis using electrochemical impedance spectroscopy (EIS) revealed that electrostatic attractions existed between graphene monolayers and enzyme molecules. The intimate graphene and enzyme interaction was also observed using scanning electron microscopy (SEM), which resulted in the special properties of the composite film. Ultraviolet visible spectroscopy (UV-vis) indicated the enzyme in the composite film retained its secondary structure similar to the native state. The composite film demonstrated excellent electrochemical responses for the electrocatalytic reduction of hydrogen peroxide (H₂O₂), thus suggesting its great potential applications in direct electrochemistry-based biosensors.     

Sensitive detection of biomolecules and DNA bases based on graphene nanosheets

High surface area electrode materials are of interest for the application of electrochemical sensors. Currently, chemical vapor deposition (CVD) graphene-sensing electrodes are scarce. Herein, for the first time, a graphene based on a Ta wire support was prepared using the CVD method to form a highly electroactive biosensing platform. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were utilized to characterize the morphology and investigate the electrochemical properties of the CVD graphene electrodes. The resulting CVD graphene electrode exhibited good electrocatalytic activity and had a prominent response effect on dopamine, uric acid, guanine, and adenine. Standing graphene nanosheets have rich catalytic sites such as the edges, the defect levels of the plane, and porous network structures between the graphene nanosheets. These catalytic sites prompt the adsorption and resolution for the four species and the strong electron transport capability of the CVD graphene, which effectively improved the electrical signals for response to four species. Moreover, the graphene electrode is a promising candidate in electrochemical sensing and other electrochemical device applications.     

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between ?0.6 and 0.8 V at scan rate of 50 mV s^?1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.     

Electrocatalytic oxidation and voltammetric determination of ciprofloxacin employing poly(alizarin red)/graphene composite film in the presence of ascorbic acid,uric acid and dopamine

A glassy carbon electrode modified with poly(alizarin red)/electrodeposited graphene (PAR/EGR) composite film was prepared and applied to detect ciprofloxacin (CPFX) in the presence of ascorbic, uric acid and dopamine. The morphology and interface property of PAR/EGR films were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electrocatalytic oxidation of CPFX on AR/EGR was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The linearity ranged from 4 × 10⁻⁸ to 1.2 × 10⁻⁴ M with a detection limit (S/N = 3) of 0.01 μM. The modified electrode could be applied to the individual determination of CPFX as well as the simultaneous determination of CPFX, ascorbic acid, uric acid and dopamine. This method proved to be a simple, selective and rapid way to determine CPFX in pharmaceutical preparation and biological media.     

Prussian Blue/Reduced Graphene Oxide Composite for the Amperometric Determination of Dopamine and Hydrogen Peroxide

Prussian blue has significant application for the construction of electrochemical biosensors. In this work, Prussian blue-reduced graphene oxide modified glass carbon electrodes were successfully fabricated using electrochemical deposition. The high surface area of graphene oxide enhanced the deposition of Prussian blue and the resulting electrocatalytic activity. Infrared spectroscopy and scanning electron microscopy showed that the relatively porous Prussian blue was on the surface of reduced graphene oxide. Cyclic voltammetry showed that Prussian blue-coated reduced graphene oxide composite films improved electron transfer compared to Prussian blue films. The Prussian blue-reduced graphene oxide composite film provided higher response for the reduction of hydrogen peroxide and the oxidation of dopamine compared with the Prussian blue film due to synergistic effects between the reduced graphene oxide and Prussian blue particles. The sensitivity of the electrode was 0.1617 µA µM^?1 cm^?2. The linear dynamic range extended from 0.5 µM to 0.7 mM dopamine with a limit of detection equal to 125 nM. This work provided a versatile strategy for the design and construction of sensitive amperometric sensors with robust electrocatalytic behavior.     

Voltammetric Detection of Catechol and Dopamine Based on a Supramolecular Composite Prepared from Multifarene[3,3] and Reduced Graphene Oxide

A selective and sensitive modified‐electrode for catechol and dopamine was presented with supramolecular recognition accomplished by making use of the macrocyclic host multifarene[3,3] that was used as a composite with reduced graphene oxide. The morphologies and electrochemical nature of the composite were characterized by atomic force microscopy, transmission electron microscopy, cyclic voltammetry and differential pulse anodic voltammetry. The modified electrode, best operated at a potential around 0.16 V vs. Ag/AgCl, displayed a differential pulse voltammetric response in the linear concentration range of 10–100 nM within a detection limit of 0.51 nM (at S/N=3). It was further applied to detect dopamine (at a working potential of 0.18 V vs. Ag/AgCl) in the linear concentration range of 10–100 nM with a detection limit of 0.62 nM. The modified electrode also exhibited satisfactory results to the determination of dopamine injections. The constructed modified electrode for dopamine detection was investigated in the presence of the interfering substances including glucose, urea and ascorbic acid, indicating a good selectivity.     

Electrochemical Determination of Dopamine Using a Poly(3,4-Ethylenedioxythiophene)-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant k_s (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM^?1?cm^?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.     

Electrochemical Response of Polyaniline (PANI)/Thiokol Rubber (TR) Films in Cysteine Solution

The electrochemical character of polyaniline/thiokol rubber (PANI/TR) composite film on a Pt electrode was investigated in a cysteine sulphuric acid solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The significant change of the peak current and peak potential in the cyclic voltammograms was observed. The irreversible peaks of cyclic voltammetry for cysteine/cystine redox couple at a platinum electrode have turned into one pair of nearly reversible peaks at the above electrode; the reversibility of the redox couple has been greatly improved. We found that thiokol rubber could improve the electrocatalysis of the PANI film to the electrochemical reaction with S‐S bonds, as well as the adhesion of the PANI film to the Pt substrate. Several effective factors, such as the concentration of thiokol rubber in the nonaqueous electrodeposition solution, different potential scan rate, immersing time of the film electrode in the studied electrolyte were all taken into account.     

Preparation and characterization of PtAu hybrid film modified electrodes and their use in simultaneous determination of dopamine, ascorbic acid and uric acid

A novel biosensor was fabricated by electrochemical deposition of platinum and gold nanoparticles (nanoAu) with l-Cysteine on glassy carbon electrode. It was found that the nanoAu particle size distribution range was (50-80 nm), and the platinum particle size range was (200-300 nm). The hybrid film could be produced on gold and transparent indium tin oxide electrodes for different kind of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) and electrochemical studies. The PtAu hybrid film was applied to the electro catalytic oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at pH 4.0 using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The modified electrode was quite effective not only to detect DA, AA and UA individually but also in simultaneous determination of these species in a mixture. The overlapping anodic peaks of DA, AA and UA were resolved into three well-defined voltammetric peaks in CV and DPV. The catalytic peak currents obtained from CV and DPV increased linearly with concentration. The relative standard deviation (% R.S.D., n = 10) for AA, DA and UA were less than 2.0% and DA, AA and UA can be determined in the ranges of 0.103-1.65, 0.024-0.384 and 0.021-0.336 mM, respectively. In addition, the modified electrode also shows good sensitivity, and stability. Satisfactory results were achieved for the determination of DA, AA and UA in dopamine injection solution, vitamin C tablets and human urine samples.     

Synthesis and Electrochemical Investigation of Tetra Amino Cobalt (II) Phthalocyanine Functionalized Polyaniline Nanofiber for the Selective Detection of Dopamine

A new electrochemical sensing platform based on tetra‐amino cobalt (II) phthalocyanine (TACoPc) ingrained polyaniline (PANI) nanofiber composite (TACoPc/PANI hybrid) has been developed for the selective detection of dopamine. The uniform fibrous network of PANI/TACoPc hybrid was synthesized by a one‐step oxidative polymerization at room temperature. The synthesized nanocomposite was characterized using field emission scanning electron microscopy (FESEM), energy dispersive X‐ray (EDX), fourier transmission infrared spectroscopy (FTIR), raman spectroscopy, X‐ray diffraction (XRD) and UV‐Visible spectroscopy. The electrochemical behavior of the TACoPc/PANI hybrid material was studied by using different electrochemical techniques, including cyclic voltammetry (CV) and chronoamperometry in 0.1 M phosphate buffer solution (PBS) of pH 7 by modifying the glassy carbon electrode (GCE). Due to the synergistic impact of PANI and TACoPc, the suggested altered electrode provided superior catalytic performance for dopamine even in the presence of ascorbic acid. It exhibited a linear reaction with a high sensitivity of 1.212 μA/μM cm^?2 and a low detection limit of 0.064 μM over the 20–200 μM concentration range in 0.1 M PBS. One of the commonly faced problems of interference of ascorbic acid and uric acid in the electrochemical detection of dopamine was completely excluded from this modified electrode which led to an increase in the catalytic activity of the material for the detection of dopamine in the presence of ascorbic acid.     

Voltammetric Determination of Epinephrine in the Presence of Uric Acid Based on Aminated Graphene and Ag NPs Hybrid Membrane Modified Electrode

A hybrid membrane consisted of aminated graphene and Ag nanoparticles（Ag NPs） was prepared on the surface of glassy carbon electrode（GCE） by cyclic voltammetry（CV） with aminated graphene（GR-NH2） as matrix for immobilizing Ag NPs.The morphology and electrochemical properties of this hybrid membrane were characterized by scanning electron microscopy（SEM） and CV,respectively,and on this membrane,the voltammetric behaviors of epinephrine（EP） were studied in detail.The membrane exhibited excellent eletro-catalytic activities for the redox of EP,and could resolve the electrochemical response of EP and uric acid（UA） into two oxidation peaks.The peak current of EP was linear with its concentration in the ranges of 0.916-18.3 μmol/L and 18.3-184 μmol/L.The detection limit was 2.0 nmol/L（S/N=3）.The proposed modified electrode retained the advantages of easy fabrication,high sensitivity and good repeatability for the determination of EP.     

Disposable immunoassay for hepatitis B surface antigen based on a graphene paste electrode functionalized with gold nanoparticles and a Nafion-cysteine conjugate

We report on the modification of a graphene paste electrode with gold nanoparticles (AuNPs) and a Nafion-L-cysteine composite film, and how this electrode can serve as a platform for the construction of a novel electrochemical immunosensor for the detection of hepatitis B surface antigen (HBsAg). To obtain the immunosensor, an antibody against HBsAg was immobilized on the surface of the electrode, and this process was followed by cyclic voltammetry and electrochemical impedance spectroscopy. The peak currents of a hexacyanoferrate redox system decreased on formation of the antibody-antigen complex on the surface of the electrode. Then increased electrochemical response is thought to result from a combination of beneficial effects including the biocompatibility and large surface area of the AuNPs, the high conductivity of the graphene paste electrode, the synergistic effects of composite film, and the increased quantity of HBsAb adsorbed on the electrode surface. The differential pulse voltammetric responses of the hexacyanoferrate redox pair are proportional to the concentration of HBsAg in the range from 0.5–800?ng?mL^?1, and the detection limit is 0.1?ng?mL^?1 (at an S/N of 3). The immunosensor is sensitive and stable.

A facile method for preparation of graphene film electrodes with tailor-made dimensions with Vaseline as the insulating binder

This communication describes a facile but effective method to prepare graphene film electrodes with tunable dimensions with Vaseline as the insulating binder. Cyclic voltammetry (CV) studies reveal that the as-prepared graphene film electrodes have tunable dimensions ranging from a conventional electrode to a nanoelectrode ensemble, depending on the amount of graphene dispersed into the insulting Vaseline matrix. A large amount of graphene (typically, 10.0 μg/mL) leads to the formation of the film electrodes with a conventional dimension, while a small amount of graphene (typically, 1.0 μg/mL) essentially yields the graphene film electrodes like a nanoelectrode ensemble. As one new kind of carbon-based film electrodes with tailor-made dimensions and a good electrochemical activity as well as a high stability, the graphene film electrodes are believed to be potentially useful for fundamental electrochemical studies and for practical applications.