Electrodeposition of PdAu Alloy Nanoparticles on Ionic Liquid Functionalized Graphene Film for the Voltammetric Determination of Oxalic Acid

An ionic liquid functionalized graphene film was prepared and PdAu nanoparticles (NPs) were electrodeposited on it. The PdAu NPs were characterized by various methods and they showed the features of alloys. In 0.2 M H₂SO₄ solution, oxalic acid (OA) exhibited a sensitive anodic peak at the resulting electrode at about 1.1 V (vs. SCE), and the peak current was linear to OA concentration in the range of 5–100 µM with a sensitivity of 45.5 µA/mM. The detection limit was 2.7 µM (S/N=3). The electrode was successfully applied to the determination of OA in real sample.     

Nickel Hydroxide and Intercalated Graphene with Ionic Liquid Nanocomposite‐modified Electrode for Sensing of Glucose

A novel non‐enzymatic glucose sensor based on nickel hydroxide and intercalated graphene with ionic liquid (G‐IL) nanocomposite modified glass carbon electrode was fabricated. Scanning electron microscope, Fourier transform infrared spectra and energy dispersive X‐ray spectroscopy of the nanocomposite confirmed the morphology and ingredient of Ni(OH)₂ as well as G‐IL. Moreover, experimental results of cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry indicated the sensing properties of Ni(OH)₂ at Ni(OH)₂/G‐IL modified electrode towards the typical electrocatalytic oxidation process of glucose at 0.43 V in 0.10 M NaOH. The current response was linearly related to glucose concentration in a range from 0.5 to 500 μM with a detection limit of 0.2 μM (S/N = 3) and sensitivity of 647.8 μA mM^?1 cm^?2. The response time of the sensor to glucose was less than 2 s. This work may be expected to develop an excellent electrochemical sensing platform of G‐IL as a catalysis carrier.     

Electrochemical Behaviors of Ascorbic Acid and Uric Acid in Ionic Liquid

Cyclic voltammetric measurements at platinum electrode have been carried out to investigate the electrochemical oxidation of ascorbic acid and uric acid in ionic liquid, [bmim][BF₄]. It is important that a typical redox couple of ascorbic acid was obtained and it is oxidized to dehydroascorbic acid in [bmim][BF₄]. However, there is no electron-transfer for uric acid and no electrochemical oxidation carried out in the same ionic liquid. It provides a new way to eliminate the interfering between ascorbic acid and uric acid in the study of the electrochemical behaviors for them.     

Electrocatalytic Oxidation and Determination of Hydrazine at an AuCu Nanoparticles – Graphene – Ionic Liquid Composite Film Coated Glassy Carbon Electrode

Gold‐copper alloy nanoparticles (AuCu NPs) were electrodeposited on a graphene – ionic liquid composite film (EGN‐IL). The AuCu NPs showed high electrocatalysis to the oxidation of hydrazine with a catalytic reaction rate constant of about 5.0×10⁴ mol/Ls. In phosphate buffer solutions (pH 6.8) the oxidation current of hydrazine at 0.15 V (vs. SCE) at the resulting electrode (AuCu? EGN‐IL/GCE) was linear to its concentration in the range of 0.2–110 µM with a sensitivity of 56.7 µA/mM, and the detection limit was 0.1 µM (S/N=3). The electrode was successfully applied to the determination of waste water.     

Electro-oxidation of Ascorbic Acid on PVP-stabilized Graphene Electrode

Polyvinylpyrrolidone-stabilized graphene(PVP-graphene) was synthesized and investigated as a modifier for the determination of ascorbic acid(AA).With PVP acting as stabilizer and dispersant,the resulting PVP-graphene material could disperse well into water.And the PVP-graphene modified glassy carbon electrode(PVP-graphene-GCE) showed an obvious electrocatalytical activity toward the oxidation of AA in a phosphate buffer solution(PBS,pH=7.0) with an oxidation potential of AA at 0.052 V vs.Ag|AgCl(sat.KCl).The calibration curve for AA was linear in a concentration range from 1.0×10-5 to 5.0×10-4 mol/L with a correlation coefficient of 0.9998.And the detection limit was found to be 1μmol/L.During the oxidation of AA,the π-π interaction of graphene plane with conjugated hexenoic acid-lactone in AA molecules might play a key role.As a result,an obvious decrease of overpotential was achieved at such a PVP-graphene electrode through a possible adsorption/enrichment process,which will probably trigger potential applications for the electroanalysis of some aromatic and heterocyclic compounds.     

Highly Sensitive Nitric Oxide Sensing Using Three‐Dimensional Graphene/Ionic Liquid Nanocomposite

A nanocomposite gel with a uniform porous structure and well‐controlled compositions prepared by mixing three‐dimensional graphene material with an ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, is used for nitric oxide detection. It shows a fast response of less than 4 seconds, an excellent sensitivity of 11.2 µA cm⁻² (µmol/L)⁻¹ and an extremely low detection limit of 16 nM with a signal‐to‐noise ratio of 3 (S/N=3), a performance superior to that of reported works based on carbon nanotubes and nanoparticles. The high sensitivity is attributed to the large electroactive surface area of the graphene gel nanocomposite towards nitric oxide oxidation. The electrochemical behavior of the gel nanocomposite is investigated and explained.     

石墨烯修饰玻碳电极用于循环伏安法测定抗坏血酸

采用Hummers法制备了纳米石墨烯,并将该纳米材料分散在蒸馏水中得到悬浮液,取5μL的悬浮液滴涂在玻碳电极表面,制备石墨烯修饰电极。用循环伏安法研究了在pH 4.0磷酸盐电解质中,在-0.4～0.8V(vs.Ag/AgCl)电位范围内,抗坏血酸在修饰电极上的电化学行为。结果表明:抗坏血酸在修饰电极上在0.173V处可见明显的氧化峰,且氧化峰电流显著高于在裸玻碳电极上的氧化峰电流;并可有效排除肾上腺素、尿酸、多巴胺等物质的干扰。据此提出了用循环伏安法测定抗坏血酸的方法。抗坏血酸的线性范围为8.00×10-6～1.0×10-3 mol.L-1,检出限(3S/N)为1.0×10-7 mol.L-1。方法用于维生素C片的分析,回收率在96.3%～104.4%之间。     

An Immunosensor for Ultrasensitive Detection of 1‐Pyrenebutyric Acid with Enhanced Electrochemical Performance Based on a Graphene‐Ionic Liquid Doped Chitosan Film Modified Glassy Carbon Electrode

This paper describes a highly sensitive and label‐free electrochemical immunosensor for the detection of 1‐pyrenebutyric acid (PBA) which is based on a graphene (GS), chitosan (CS), and ionic liquid (IL) composite modified glassy carbon electrode (GS‐CS‐IL/GCE). The modification process was monitored by transmission electron microscopy (TEM) and cyclic voltammetry (CV). Due to the synergistic effects of GS, CS, and IL, the biosensor exhibits excellent selectivity to PBA. The current response of the proposed immunosensor decreases linearly at two concentration ranges from 0.01 to 5 and from 5 to 150 ng mL^?1 with a detection limit of 0.01 ng mL^?1.     

Structure of a Mixture of Graphene Plates and Ionic Liquid 1-Octyl-3-methylimidazolium Hexafluoroborate

We reported a molecular dynamics simulation study of a mixture of 1-octyl-3-methylimidazolium hexa-fluoroborate([C₈MIN]⁺[PF₆]^-), an ionic liquid, and pristine graphene. Our simulations were performed under various conditions, including several temperatures and distances between graphene plates. By studying the liquid structure of the ionic-liquid graphene mixture, we found that the transition for the ionic liquids entering the middle of two graphene plates should occur within 1.00 and 1.50 nm in the temperature range studied(300-600 K). We also studied the pair correlations between the graphene plates and the head and tail of the cation and the anion. Our study at the molecular level can aid in understanding the detailed molecular structure of the mixture.     

Selective Detection of Dopamine in the Presence of Uric Acid Using NiO Nanoparticles Decorated on Graphene Nanosheets Modified Screen‐printed Electrodes

A convenient, low cost, and sensitive electrochemical method, based on a disposable graphene nanosheets (GR) and NiO nanoparticles modified carbon screen printed electrode (NiO/GR/SPE), is described for the simultaneous determination of dopamine (DA) and uric acid (UA). The modified electrode exhibited good electrocatalytic properties toward the oxidation of DA and UA. A peak potential difference of 150 mV between DA and UA was large enough to determine DA and UA individually and simultaneously. The anodic peak currents of DA were found to be linear in the concentration range of 1.0–500.0 μM with the detection limit of 3.14×10^?7 M.     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid,at a Graphene Paste Electrode Modified with Functionalized Graphene Sheets

The present study reports the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in phosphate buffer solution (pH 7.0) using graphene paste electrode modified with functionalized graphene sheets (GPE‐MFGSs). The presence of FGS inhibited the adsorption of AA owing to the electrostatic repulsion, but was favorable for the affinity adsorption of DA and UA via the ion exchange and hydrogen bonding mechanisms, respectively. This led to the decrease in the oxidation potential of AA and the significantly enhanced oxidation peak currents of DA and UA at the GPE‐MFGSs. By cyclic voltammetry and differential pulse voltammetry, the oxidation potentials of AA, DA, and UA, at the GPE‐MFGSs in a ternary mixture were found to be well resolved so that their simultaneous determination could be achieved. Furthermore, the influence of some experimental variables such as graphene paste composition, working solution pH, scan rate and pulse amplitude was studied. In addition, by differential pulse voltammetry, the linear dependence of peak current on the concentration was obtained in the ranges of 0.05–9.0, 0.03–13, and 0.03–5.5 µM with the lowest detection limits of 0.02, 0.01, and 0.01 µM for AA, DAand UA, , respectively.     

Electrochemical Study of Indium in a Water‐Stable 1‐Ethyl‐3‐Methylimidazolium Chloride/Tetrafluoroborate Room Temperature Ionic Liquid

The electrochemistry of indium species was investigated at glassy carbon, tungsten and nickel electrodes in a basic 1‐ethyl‐3‐methylimidazolium chloride/tetrafluoroborate ionic liquid. Amperometric titration experiments suggest that In(III) chloride is complexed as [InCl₅]^2? in this ionic liquid. The electrochemical reduction of [InCl₅]^2? to indium metal is preceded by overpotential driven nucleations. The effective anodic dissolution of indium to indium(III) requires, however, the presence of sufficient chloride ions at the electrode surface. The electrodeposition of indium at glassy carbon and tungsten electrodes proceeds via three‐dimensional instantaneous nucleation with diffusion‐controlled growth of the nuclei. At the nickel electrode, the deposition proceeds via three‐dimensional progressive nucleation with diffusion‐controlled growth of the nuclei. Raising the deposition temperature decreases the average radius of the individual nuclei, r. Scanning electron microscopic and x‐ray diffraction data indicated that bulk crystalline indium electrodeposits could be prepared on nickel substrates within a temperature range between 30 and 120 °C.     

金纳米粒子-石墨烯修饰玻碳电极的制备及对多巴胺、抗坏血酸和尿酸的同时检测

采用三步法制备了金纳米粒子-石墨烯层层组装的复合材料,并将其修饰在玻碳电极上,制备成一种新型的同时检测抗坏血酸(AA)、多巴胺(DA)和尿酸(UA)的电化学传感器。采用扫描电子显微镜(SEM)对复合材料进行了表征,并研究了传感器对AA、DA、UA电催化性能。结果表明:该传感器对AA、DA和UA的氧化具有很好的催化和分离效果,可实现AA、DA和UA的同时测定。在三者共存体系中,AA-DA、DA-UA、AA-UA的氧化峰电位差分别为152mV、161mV和313mV。线性范围分别为1.996×10-5~5.580×10-3、1.996×10-6~5.478×10-3和1.000×10-6~1.000×10-3 mol/L,检出限分别为1.200×10-5、1.030×10-7和4.100×10-7 mol/L。该修饰电极选择性好、稳定性高,有望用于实际样品中AA、DA和UA的同时检测。     

Electrochemical Behavior of Caffeic Acid Assayed with Gold Nanoparticles/Graphene Nanosheets Modified Glassy Carbon Electrode

A gold nanoparticle (AuNP) and graphene nanosheet (GN) modified glassy carbon electrode (GCE) is proposed as voltammetric sensor for caffeic acid assay. The sensor exhibits a surface‐confined and reversible process for oxidation of caffeic acid revealed by cyclic voltammetry. The results show more favorable electron transfer kinetics than the bare GCE. The linear response of the sensor is from 5×10^?7 to 5×10^?5 M with a detection limit of 5×10^?8 M (S/N=3). The AuNP/GN nanocomposite shows more favorable electrochemical activity and should be a kind of more robust and advanced functional material, which provides a promising platform for electrochemical sensors and biosensors. The method was successfully applied to detect caffeic acid in pharmaceutical tablets with satisfactory results.     

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

A room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF₆) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (k_s) as 0.87 and 0.800 s^?1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10^?5 to 3.0×10^?3 mol/L with the linear regression equation as I_p (μA)=?2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10^?6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.     

Synthesis and Esterification of 3‐Ferrocenyl Acrylic Acid in Ionic Liquid

3‐Ferrocenyl acrylic acid, synthesized from ferrocenecarboxaldehyde and propandioic acid in water‐insoluble ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate, [BMIM]PF₆) at 85 °C in high yield, was transformed to a series of 3‐ferrocenyl acrylate of alcohols and phenols in water‐soluble ionic liquid (1,3‐dimethylimidazolium dimethylphosphate, [DMIM]Me₂PO₄) at room temperature in the presence of dicyclohexylcarbodiimide (DCC) and 4‐dimethylaminopyridine (DMAP).     

Electropolymerization of Methylene Blue on Carbon Ionic Liquid Electrode and Its Electrocatalysis to 3,4‐Dihydroxybenzoic Acid

In this paper an ionic liquid modified carbon paste electrode (CILE) was prepared and methylene blue (MB) was electropolymerized on the CILE by using the cyclic voltammetric technique in the potential range from −1.0 V to 0.8 V (vs. SCE). A stable polymer film was obtained and exhibited a pair of redox peaks. The morphology and characteristics of poly(methylene blue) (PMB) film was studied by the techniques such as scanning electron microscopy and electrochemical impedance spectroscopy. This PMB modified CILE (PMB/CILE) showed excellent electrocatalytic response to 3,4‐dihydroxybenzoic acid with the increase of the electrochemical responses. The oxidation peak current had a linear relationship with 3,4‐dihydroxybenzoic acid concentration in the range of 5.0 × 10⁻⁴ ∼ 3.0 × 10⁻² mol L⁻¹ and the detection limit was 1.72 × 10⁻⁴ Mol L⁻¹ (3 σ).     

MWCNTs/Ionic Liquid/Graphene Quantum Dots Nanocomposite Coated with Nickel‐Cobalt Bimetallic Catalyst as a Highly Selective Non‐enzymatic Sensor for Determination of Glucose

In this work, a glassy carbon electrode (GCE) was modified with multiwall carbon nanotubes/ionic liquid/graphene quantum dots (MWCNTs/IL/GQDs) nanocomposite. Then, the nanocomposite was decorated with nickel‐cobalt nanoparticles (Ni?Co NPs), and it was used as a non‐enzymatic glucose sensor. Field emission scanning electron microscopy, X‐ray diffraction spectroscopy, and energy dispersive spectroscopy were employed to prove the electrodeposition of the Ni?Co NPs on the surface of MWCNTs/IL/GQDs/GCE. Also, cyclic voltammetric and amperometric methods were utilized for the investigation of the electrochemical behaviour of the Ni?Co NPs/MWCNTs/IL/GQDs/GCE for glucose oxidation. The novel amperometric sensor displayed two linear ranges from 1.0 to 190.0 μmol L^?1 and 190.0 to 4910 μmol L^?1 with a low detection limit of 0.3 μmol L^?1 as well as fast response time (2 s) and high stability. Also, the sensor showed good selectivity for glucose determination in the presence of ascorbic acid, citric acid, dopamine, uric acid, fructose, and sucrose, as potential interference species. Finally, the performance of the proposed sensor was investigated for the glucose determination in real samples. Ni?Co NPs/MWCNTs/IL/GQDs/GCE showed good sensitivity and excellent selectivity.     

聚乙烯亚胺功能化石墨烯修饰电极同时测定抗坏血酸、 多巴胺、尿酸和色氨酸

制备了聚乙烯亚胺(PEI)功能化的石墨烯(G)修饰电极以实现抗坏血酸(AA)、 多巴胺(DA)、 尿酸(UA)和色氨酸(Trp)的分离及同时测定. 采用红外光谱(FTIR)、 紫外-可见吸收光谱(UV-Vis)、 X射线粉末衍射仪(XRD)和透射电子显微镜(TEM)对电极修饰材料进行了表征, 并优化了该修饰电极同时测定AA, DA, UA和Trp的实验条件. 在聚乙烯亚胺功能化石墨烯修饰的玻碳电极(PEI-G/GCE)上实现了AA, DA, UA 和Trp氧化峰的分离, AA-DA, DA-UA和UA-Trp的氧化峰电位差分别为298, 130和350 mV. 该修饰电极对AA, DA, UA和Trp的检测线性范围分别为50~5800, 30~2570, 0.05~400和6~1000 μmol/L; 检出限分别为16.67, 10, 0.017和2 μmol/L.     

Preparation of MoS2‐graphene Hybrid Nanosheets and Simultaneously Electrochemical Determination of Levodopa and Uric Acid

MoS₂ nanoflakes were prepared by exfoliating commercial MoS₂ powders with the assistance of ultrasound and graphene foam was synthesized by chemical vapor deposition using nickel foam as the template. MoS₂‐graphene hybrid nanosheets were developed through the combination of MoS₂ nanoflakes and graphene nanosheets by ultrasonic dispersion. The hybrid nanosheets were sprayed onto the ITO coated glass, which acts as an electrode for the simultaneously electrochemical determination of levodopa and uric acid. The MoS₂‐graphene hybrid nanosheets were characterized by scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. The results show that the hybrid nanosheets are composed of MoS₂ and graphene with a sheet‐like morphology. The sensitivity of the electrode for levodopa and uric acid is 0.36 μA μM⁻¹ and 0.39 μA μM⁻¹, respectively. The electrode also shows low limit of detection, good selectivity, reproducibility and stability. And it is potential for use in clinical research.