Graphene Oxide/ZnO Nano Composite for Sensitive and Selective Electrochemical Sensing of Levodopa and Tyrosine Using Modified Graphite Screen Printed Electrode

Determination of levodopa and tyrosine as two important species for treatment of Parkinson's disease is described. A novel electrochemical sensor involving graphene oxide/ZnO nanorods (GR/ZnO) nano composite and the graphite screen‐printed electrodes (GSPE) was developed for the simultaneous detection of levodopa and tyrosine. The screen‐printed electrodes with several advantages, including low cost, versatility and miniaturization were employed. On the other hand, the graphene oxide/ZnO nanorods nano composite was casted on the surface of GSPE to obtain GR/ZnO/SPE. The proposed nano sensor has excellent performance such as high sensitivity, good selectivity and analytical application in real samples. The combination of graphene oxide/ZnO nanorods nano composite with the screen‐printed electrode is favorable for amplifying electrochemical signals. Under optimized conditions square wave voltammetry (SWV) exhibited linear dynamic ranges from 1.0×10^?6 to 1.0×10^?3 M and 1.0×10^?6 to 8.0×10^?4 M with detection limits of 4.5×10^?7 M and 3.4×10^?7 M for levodopa and tyrosine respectively.     

Electrochemical Sensor for Arabinose Based on Template‐free Pb/Cd Branched Nanorods on Glassy Carbon Electrode

In this paper, the electrochemical behavior of glassy carbon electrodes modified with Cd/Pb (GC/Cd/Pb) branched nanorodes (NRs) was studied using cyclic voltammetry technique. The obtained results showed that the branched nanorods of Cd/Pb can be readily prepared without any templates. The modified electrode was characterized using scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDAX) and electrochemical impedance spectroscopy (EIS) techniques. The electrocatalytic behavior of GC/Cd/Pb electrode showed an increase in oxidation signal of arabinose by increasing its concentration. The catalytic current was linearly related to arabinose concentration in the range of 0.6 to 6.8 μM with a limit of detection 0.2 μM.     

Determination of Nicotine in Tobacco by Capillary Electrophoresis with Electrochemical Detection

A sensitive, simple and low-cost method based on capillary electrophoresis(CE) with electrochemical(EC) detection at a carbon fiber microdisk electrode(CFE) was developed for the determination of nicotine. Effects of detection potential, concentration and pH value of the phosphate buffer, and injection time as well as separation voltage were investigated. Under the optimized conditions: a detection potential of 1.20 V, 40 mmol/L phosphate buffer(pH 2.0), a sample injection time of 10 s at 10 kV and a separation voltage of 16 kV, the linear range obtained was from 5.0×10^-7 mol/L to 1.0×10^-4 mol/L with a correlation coefficient of 0.9989 and the limit of detection(LOD, S/N=3) obtained was 5.0×10^-8 mol/L. The method was also used to determine the nicotine in cigarettes. Nicotine amount ranged from 0.211 mg/g to 0.583 mg/g in the pipe tobacco of seven brands of cigarette and the amount in one cigarette varied from 0.136 mg/cigarette to 0.428 mg/cigarette.     

A Novel Electrochemical Sensor for Simultaneous Determination of Hydroquinone,Catechol, and Resorcinol Using a Carbon Paste Electrode Modified by Zn-MOF,Nitrogen-doped Graphite,and AuNPs

In this work, the carbon paste electrode was modified with a composite of a metal-organic framework, nitrogen-doped graphite, and gold nanoparticles and used as an electrochemical sensor for dihydroxybenzene isomers. The morphology and characteristics of the modifiers were found by SEM and FT-IR. Electrochemical techniques showed the specific surface of the electrode to be significantly enhanced. The outcome achieved shows that this novel sensor displays an excellent electro-catalytic activity towards the oxidation of these isomers. The sensor was applied to the simultaneous determination of each three isomers using DPV with a linear response in the concentration range of 5–10⁵ nM.     

分子印迹电化学传感器测定L-色氨酸的研究

报道了一种由溶胶-凝胶法制备的分子印迹电化学传感器,并用于L-色氨酸的测定.印迹聚合物是由四乙氧基硅烷、甲基三甲氧基硅烷、苯基三甲氧基硅烷等聚合而成,L-色氨酸为模板分子.通过循环伏安法验证了印迹膜与模板分子的结合和去除.该传感器对L-色氨酸具有良好的选择性以及高的灵敏度,线性范围为1.0×10-9～1.0×10-5m...     

盐酸金霉素分子印迹电化学传感器的研制

构建了一种选择性检测盐酸金霉素(CTC)的分子印迹电化学传感器。在NaClO4溶液中,以邻氨基酚(OAP)为功能单体,盐酸金霉素(CTC)为模板,通过循环伏安法在玻碳电极表面上聚合制备了CTC印迹敏感膜(MIPs)。在含0.005 mol/L K3[Fe(CN)6]及0.1 mol/L KCl的磷酸盐缓冲液(PBS)中,应用差分脉冲伏安法(DPV)研究了传感器的响应性能。DPV峰电流差与CTC浓度在2.0×10!8~6.1×10!7mol/L范围内呈线性关系,检出限为1.5×10!8mol/L(3σ)。实验表明,用甲醇/H2SO4混合洗脱溶液可以使传感器再生,对CTC的测定具有良好的重现性,并具有良好的储存稳定性。传感器对于干扰物氯霉素及青霉素没有响应,结构相似的四环素、土霉素有微弱的响应,显示了良好的选择性。在牛奶和鸡肉实际样品中所测得的CTC加标回收率为86.4%~96.9%。与文献报道的CTC检测方法相比,本传感器具有低的检测限,操作简便,整个过程无需衍生化处理,响应快,成本低。     

Simultaneous Trace Electrochemical Determination of Xanthine Theophylline and Theobromine with a Novel Sensor Based on a Composite Including Metal Oxide Nanoparticle Multi-walled Carbon Nanotube and Nano-Na-montmorillonite Clay

We report the simultaneous determination of purine molecules with biological significance on pencil graphite electrode (PGE) modified with a composite solution including NiO nanoparticles, multi-walled carbon nanotube (MWCNT), and natural nano-Na-montmorillonite clay (NNaM) using DPV technique. The novel sensor, NiO/MWCNT/NNaM/PGE, achieved simultaneous determination of xanthine, theophylline, and theobromine at the detection limits 0.077 μM, 0.361 μM, and 0.458 μM with the linear working ranges 0.5–150 μM, 5–200 μM, and 5–250 μM in Britton-Robinson buffer at pH 2.0, respectively. The sensor revealed excellent performance for the simultaneous determination of XT, TP, and TB in three real-world samples.     

First Report for Electrochemical Determination of Levodopa and Cabergoline: Application for Determination of Levodopa and Cabergoline in Human Serum,Urine and Pharmaceutical Formulations

The electrochemical oxidation of levodopa on the surface of a carbon paste electrode modified with graphene nanosheets, 1‐(4‐bromobenzyl)‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole (1,4‐BBFT) and hydrophilic ionic liquid (n‐hexyl‐3‐methylimidazolium hexafluoro phosphate) as a binder is studied. It has been found that the oxidation of levodopa at the surface of a modified electrode occurs at a potential of about 210 mV less positive than that of an unmodified carbon paste electrode (CPE). The prepared modified electrode exhibits a very good resolution of the voltammetric peaks of levodopa and cabergoline. The electrode has been applied successfully for the determination of levodopa and cabergoline in some real samples.     

Fe2V4O13 Nanoparticles Based Electrochemical Sensor for the Simultaneous Determination of Guanine and Adenine at Nanomolar Concentration

A simple strategy has been proposed for the simultaneous quantification of guanine (GU) and adenine (AD) using Fe₂V₄O₁₃ nanoparticles (Fe₂V₄O₁₃ NPs) modified carbon paste electrode (Fe₂V₄O₁₃NPs/CPE) in phosphate buffer solution (PBS). The Fe₂V₄O₁₃ NPs were prepared by a simple solution combustion method where sucrose was used as a fuel. The electrochemical behavior of GU and AD at the electrochemical interface has been studied by using cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The results illustrate that the Fe₂V₄O₁₃ NPs shows enhanced electrocatalytic activity and voltammetric response towards GU and AD. The proposed sensor showed linearity between the concentration 0.5 and 60 μM with limit of detection (LOD) 32 and 37 nM for GU and AD respectively. The sensitivity towards GU and AD were respectively found to be 1.393 and 1.851 μA/μM. Further, the proposed electrochemical sensor has been successfully employed to determine GU and AD contents in milk powder and calf thymus DNA samples.     

Electrochemical Sensor for Ultrasensitive Determination of Doxorubicin and Methotrexate Based on Cyclodextrin‐Graphene Hybrid Nanosheets

In this work, an electrochemical sensor based on a cyclodextrin‐graphene hybrid nanosheets modified glassy carbon electrode (CD‐GNs/GCE) was proposed for the ultrasensitive determination of doxorubicin and methotrexate. The peak currents of doxorubicin and methotrexate on the CD‐GNs/GCE increased 26.5 and 23.7 fold, respectively, compared to the results obtained on the bare GCE. Under optimized conditions, the linear response ranges for doxorubicin and methotrexate are 10 nM–0.2 µM and 0.1 µM–1.0 µM, with detection limits of 0.1 nM and 20 nM, respectively. The sensor showed the advantages of simple preparation, low cost, high sensitivity, good stability and reproducibility. These properties make the prepared sensor a promising tool for the determination of trace amounts of doxorubicin and methotrexate in biological, clinical and pharmaceutical fields.     

Tape Casting of Graphite Material: A New Electrochemical Sensor

Tape casting is a feasible method for preparing ceramic tapes with different electrical and magnetic properties for multilayer ceramic devices. This paper describes the tape casting process for the preparation of a new kind of self‐standing carbon electrodes (SSCE) using different ratios of graphite and the organic additives generally used in the non‐aqueous tape casting process.     

基于Ag@C@Ag核壳型纳米材料电化学传感器的制备及对邻苯基苯酚的测定

本文通过一种简单的水热反应合成出核壳型纳米材料Ag@C,然后再利用Ag@C表面丰富的功能基团均匀地负载一层Ag纳米颗粒,得到了大小均一、形貌良好的三层Ag@C@Ag核壳型纳米材料。实验结果表明,该Ag@C@Ag核壳纳米材料对邻苯基苯酚的电化学测定有良好的催化活性。据此,成功构建了一种简单、快速检测邻苯基苯酚的新型电化学传感器。该电化学传感器测定邻苯基苯酚的线性范围为0.08~35μmol/L,检出限为13.6nmol/L。     

Determination of Bisphenol A Using an Electrochemical Sensor Based on a Molecularly Imprinted Polymer-Modified Multiwalled Carbon Nanotube Paste Electrode

A novel electrochemical sensor for bisphenol A was developed through the combination of a molecular imprinting technique with a multiwalled carbon nanotube paste electrode. A molecularly imprinted polymer and nonimprinted polymer were synthesized in the presence and absence of bisphenol A, and then used to prepare the electrode. The bisphenol A imprinted polymer was applied as a selective recognition element in the electrochemical sensor. Differential pulse voltammetry was used to characterize the electrochemical behavior of bisphenol A at the modified electrodes. The results showed that the imprinted sensor had highest response for bisphenol A. Parameters including the carbon paste composition, pH, and adsorption time for the imprinted sensor were optimized. Under the optimized conditions, the differential pulse voltammetry peak current was linear with the concentration of bisphenol A from 0.08 to 100.0 µM, with a detection limit of 0.022 µM. The imprinted sensor for bisphenol A exhibited good selectivity, stability, and reproducibility. This sensor was successfully used for the determination of bisphenol A in real water samples.     

基于石墨烯的毒死蜱分子印迹电化学传感器的制备及对毒死蜱的测定

利用分子印迹技术,以马来松香丙烯酸乙二醇酯为交联剂,使用自由基热聚合法在石墨烯修饰的玻碳电极表面合成毒死蜱( CPF)分子印迹聚合膜,制得了CPF分子印迹电化学传感器。采用循环伏安法、线性扫描伏安法和电化学交流阻抗法等,考察了此CPF分子印迹膜的电化学性能。在最佳检测条件下,传感器的峰电流与CPF浓度在2.0×10-7~1.0×10-5mol/L范围内呈线性关系,线性方程为Ip(μA)=-7.1834-0.2424C (μmol/L),相关系数r2=0.9959,检出限为6.7×10-8 mol/L(S/N=3)。构建了CPF分子印迹电化学传感器的动力学吸附模型,测得印迹传感器的印迹因子β=2.59,结合速率常数k=12.2324 s。传感器表现出良好的重现性和稳定性,并成功用于实际水样和蔬菜样品中CPF的测定,加标回收率为94.1%~101.4%。     

Organic Phase Cyclopentadienylnickelthiolate Sensor System for Electrochemical Determination of Sulfur Dioxide

A series of cyclopentadienylnickelthiolate complexes, [Ni(PBu₃)(η⁵‐C₅H₅)(SC₆H₄X‐4)] (X=F, Cl, Br, NH₂), were shown to express stable reversible electrochemical properties even after formation of SO₂ adducts in organic phase consisting of argon purged CH₂Cl₂/0.1 M [n‐Bu₄N][BF₄]. The formal potentials (E°′) values of the compounds ranged from 265 to 431 mV/Ag‐AgCl depending on the para substituent of the benzene thiolate ligand. Electrochemical, UV‐vis and ¹H NMR spectroscopic analyses show that the formation of SO₂ adducts causes the perturbation of the electronic density of the nickel metal center, indicated by shifts in the E°′ values of the Ni^II/III redox couple that is dependent on SO₂ concentration. The detection limits of the resulting organic phase electrochemical gas sensor system was as low as 0.56 ppm SO₂ for the fluoro complex, while the linear range was as high as 700–2000 ppm SO₂ for the amino complex.     

Polydopamine-modified MWCNTs-glassy Carbon Electrode,a Selective Electrochemical Morphine Sensor

An electrochemical sensor based on a glassy carbon electrode was prepared using f-MWCNTs and polydopamine. Several techniques were used to investigate the surface features. Voltammetric techniques were used to evaluate the electrocatalyst efficiency, and it was used for morphine determination using differential pulse voltammetry. Different parameters affecting the method‘s sensitivity and selectivity were optimized. The linear dynamic range was 0.075–75.0 μM with a detection limit of 0.06 μM morphine. Also, the method‘s selectivity was tested, which was proved to be satisfactory. Finally, the sensor was successfully used for morphine determination in human plasma and urine samples with acceptable results.     

A Novel Electrochemical Sensor for Detection of Molinate Using ZnO Nanoparticles Loaded Carbon Electrode

In this work, electrochemical detection of molinate herbicide was studied by developing a novel sensor based on carbon paste incorporated with zinc oxide (ZnO) nanoparticles using cyclic (CV) and square wave voltammetric (SWV) techniques. Molinate exhibited one well resolved peak at pH of 3.0 phosphate buffer solution (PBS), which was irreversible. The lowest possible detection limit of 1.0×10^?8 M was achieved in the concentration range of 0.002 μM to 0.25 μM. The modifying ability of ZnO nanoparticles was responsible for such a low level sensing in water and soil samples.     

Fabrication of Electrochemical Sensor Modified with Porous Graphene for Determination of Trace Calycosin

In this study, the porous graphene (PG) with excellent structure was successfully prepared by a simple pyrolysis process, and applied to construct electrochemical sensor (PG@GCE) for detection of calycosin (CYS). PG was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Also, the electrochemical properties of the proposed sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results indicated that sensors had relatively large specific surface area and higher electron transport rate. Based on all those characteristics, CYS, a traditional Chinese medicine (TCM) active ingredient, displayed a great response on the surface of PC@GCE. Under the optimized conditions, the sensors displayed a good linear relationship between the peak current and the CYS concentration in the range of 1.8 × 10^–7–4.4 × 10^–5 M with the detection limit of 5.8 × 10^–8 M (S/N = 3). This study provided a novel analytical method for detection of CYS, rapid identification of Radix Hedysari and Radix Astragali, and gave another way for the trace analysis of CYS in biological samples. Furthermore, it would also deepen the application of PG in the field of pharmaceutical analysis.     

An Electrochemical Sensor Based on Nitrogen‐doped Carbon Nanofiber for Bisphenol A Determination

In this paper, bisphenol A was determined by electrochemical method at a nitrogen‐doped carbon nanofiber modified carbon paste electrode (NCNF/CPE) with high sensitivity and good selectivity. NCNF was obtained by a simple electrospinning followed by carbonization procedure, in which polyacrylonitrile (PAN) as precursor and nitrogen doping was realized by re‐utilizing the tail gas that produced in the thermal pretreatment process. Good reproducibility and high stability were obtained for BPA detection at NCNF modified CPE. Current response plotted with BPA concentration was linear in the range of 0.1–60 μM with LOD of 0.05 μM. The proposed electrochemical sensor was employed for BPA determination with satisfactory recoveries for real water samples, indicating the practical applicability of NCNF/CPE.     

Fabrication of a Nanostructure Based Electrochemical Sensor for Voltammetric Determination of Epinephrine,Uric Acid and Folic Acid

A carbon paste electrode (CPE) was modified by incorporation of graphene nano sheets and a ferrocene derivative. The modified electrode showed an excellent electrocatalytic effect on the oxidation of epinephrine. In phosphate buffer solution (PBS) of pH 7.0, the oxidation current increased linearly with concentration of epinephrine in the range of 0.05–550.0 µM and a detection limit (3σ) 27.0 nM was obtained for epinephrine. Then the modified electrode was used to determine epinephrine in an excess of uric acid and folic acid by SWV.