Facile Fabrication of a Graphene‐based Electrochemical Biosensor for Glucose Detection

A simple and effective glucose biosensor based on immobilization of glucose oxidase (GOD) in graphene (GR)/Nafion film was constructed. The results indicated that the immobilized GOD can maintain its native structure and bioactivity, and the GR/Nafion film provides a favorable microenvironment for GOD immobilization and promotes the direct electron transfer between the electrode substrate and the redox center of GOD. The electrode reaction of the immobilized GOD shows a reversible and surface‐controlled process with the large electron transfer rate constant (k_s) of 3.42±0.08 s^?1. Based on the oxygen consumption during the oxidation process of glucose catalyzed by the immobilized GOD, the as‐prepared GOD/GR/Nafion/GCE electrode exhibits a linear range from 0.5 to 14 mmol·L^?1 with a detection limit of 0.03 mmol·L^?1. Moreover, it displays a good reproducibility and long‐term stability.     

聚甲基丙烯酸甲酯-牛血清白蛋白核壳纳米粒子在金表面的吸附过程及在传感器中的应用

利用铜离子引发体系, 制备出核层为聚甲基丙烯酸甲酯(PMMA)壳层为牛血清白蛋白(BSA)的PMMA-BSA核壳纳米粒子. 通过透射电子显微镜(TEM)表征, 直接观察到PMMA-BSA纳米粒子的核壳结构.结合X射线光电子能谱(XPS)测试, 分析PMMA-BSA纳米粒子的表面成分, 证明PMMA-BSA纳米粒子的壳层是BSA. 利用带耗散的石英晶体微天平(QCM-D)研究了PMMA-BSA纳米粒子在金片表面的吸附行为. 频率的迅速下降, 耗散因子的快速上升, 说明PMMA-BSA粒子快速地吸附到金片表面. 利用磷酸盐缓冲液反复冲洗时, 频率和耗散没有变化, 表明PMMA-BSA 纳米粒子在金片上吸附较牢固. 以金电极为基底电极, 吸附PMMA-BSA纳米粒子后, 利用戊二醛修饰粒子壳层, 再通过氨基与醛基的反应来固定葡萄糖氧化酶, 制备出电流型葡萄糖传感器. 电化学测试表明该传感器对葡萄糖具有良好的电流响应, 在0.3 V的工作电位下, 响应电流与葡萄糖浓度在0.20-5.85 mmol·L^-1范围内呈现出较好的线性关系, 相关系数为0.989. 传感器的灵敏度高达28.6 μA·L·mmol^-1·cm^-2, 响应时间仅为11 s. 传感器还具有良好的稳定性, 在25℃下储存30 d, 响应电流仅下降了16%.     

An amperometric biosensor based on covalent immobilization of ascorbate oxidase on biocompatiable and low-toxic poly(thiophene-3-acetic acid) matrix

The biocompatiable and low-toxic poly（thiophene-3-acetic acid）（PTAA） matrix was successfully electrosynthesized in ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate（BmimPF₆） in comparison with the electrosynthesis of PTAA matrix in acetonitrile（ACN）.Ascorbate oxidase（AO） was used as a model for the development and application of biosensor.Vitamin C（VC） biosensors were facilely fabricated by the covalent immobilization of AO molecules on PTAA matrices electrosynthesized in ACN containing tetrabutylammonium tetrafluoroborate and BmimPF₆, respectively.Electrochemical impedance spectroscopy,scanning electron microscopy and FTIR spectroscopy indicated that AO molecules were covalently immobilized on PTAA matrices.Parameters of the as-obtained biosensors such as working potential,pH and temperature have been optimized.The amperometric biosensor based on PTAA matrix electrosynthesized in BmimPF₆ exhibited wider linear range,lower detection limit,higher sensitivity and bioaffinity,and better operational and storage stability than that electrosynthesized in ACN under optimal conditions.The as-obtained biosensor based on PTAA matrix electrosynthesized in BmimPF₆ was employed for the detection of VC content in commercial juices,and the result was close to the data given by manufacturers.Excellent results indicate that the PTAA matrix electrosynthesized in ionic liquid is a promising platform for the covalent immobilization of biologically-active species and the development of biosensors.     

Amperometric Biosensor for Hypoxanthine Based on Immobilized Xanthine Oxidase on Iron (III) Meso‐tetraphenylporphyrin Nanoparticles Modified Glassy Carbon Electrode

Abstract

The preparation and performance of hypoxanthine (Hx) electrochemical biosensor, which was based on iron (III) meso‐tetraphenylporphyrin (FeTPP) nanoparticles (NPs), is reported in this work. FeTPP NPs prepared by mixing solvent techniques with diameters ca. 25~45 nm and were used as a mediator. The XOD/FeTPPNP/GC electrode exhibited good amperometric signal for Hx. Based on the consumption of dissolved oxygen during the oxidation process of Hx catalyzed by the immobilized XOD, the biosensor could detect the concentration of Hx up to 0.34 mM with a detection limit of 1.0 µM. The usefulness of this biosensor for the analysis of real sample was also demonstrated by determining Hx in rat brain dialysate coupled with microdialysis.     

PLS Regression in the Spectrophotometric Data for the Simultaneous Determination of Levodopa and Carbidopa in Pharmaceutical Preparations by Using an Enzymatic Stopped‐Flow FIA Technique

Abstract

An enzymatic stopped‐flow‐injection analysis is proposed for simultaneous determination of levodopa and carbidopa in pharmaceutical preparations. The dopaquinones obtained after the oxidation catalized by the enzyme were measured by spectrophotometric method. A reduced calibration matrix based on a central composite experimental design was built and Partial Least Squares (PLS) was applied on the spectral data after reaction with the enzyme. The LOD was 0.015 and 0.0028 mg ml^?1, respectively and the sample throughput was 22.5 h^?1. The proposed method was applied to pharmaceutical preparations and the results are in close agreement with pharmacopeial method. The recovery study and results were satisfactory.     

Electrochemical Determination of Xanthine Oxidase-Catalyzed Oxidation of Xanthine

Abstract

A rapid electrochemical (chronoamperometric) method for the determination of xanthine oxidase catalyzed oxidation of xanthine and hypoxanthine is described. The assay is based on the anodic oxidation of the product, uric acid, at a stationary carbon paste electrode. Metabolism was monitored as reaction proceeded by direct insertion of a three-electrode assembly into incubation mixtures, applying a potential and measuring current after a 7 sec controlled electrolysis. The method requires no sample preparation, nor utilization of external reagents, and is compared with the on-line spectrophotonetric analysis based on monitoring the appearance of uric acid detected as an increase in absorbance at 290 nm.     

Amperometric Choline Sensor with Enzyme Immobilized by Gamma-Irradiation in a Biocompatible Membrane

Abstract

An amperometric choline biosensor was constructed using choline oxidase immobilized on poly(2-hydroxyethylmethacrylate) membranes obtained by gamma radiation-induced polymerization at low temperature. The measurements were carried out by Clark-type oxygen or hydrogen peroxide electrodes. Calibration curves were linear in the 10-200 umol · 1^?1 range for the oxygen probe and 5-250 umol · 1^?1 for the H₂O₂-based probe. Temperature and pH effects on the activity of immobilized enzyme are described and the response characteristics of the sensor are summarized. The immobilized enzyme membranes stored in glycine buffer or in a dry state were very stable and no significant decrease in the electrode response was observed after three months. The biosensor was employed also to analyse a choline-containing pharmaceutical product and the results were compared to those obtained by enzymatic-spectrophotometric detection.     

Determination of Oxalate with Immobilized Oxalate Oxidase in an Enzyme Thermistor

Abstract

This paper describes a rapid enzymic procedure, based on calorimetry, for specific determination of oxalic acid. Oxalate is oxidized by immobilized oxalate oxidase to hydrogen peroxide and carbon dioxide. The heat generated by this reaction is measured in a calorimetric device, the enzyme thermistor. Oxalate concentrations as low as 0.02 mM can be determined. Also described is purification and immobilization of the enzyme, as well as the effect of some of its inhibitors. The urinary oxalate content of 16 persons was determined using the enzyme thermistor. For samples containing a very low concentration of oxalate (less than 0.2 mM) an extraction step with tributylphosphate can be introduced to purify and concentrate the oxalate. The oxalate content in different kinds of food was also determined.     

Argentometric Determination of Cyanide in the Presence of Dithionite

Abstract

Cyanide can be measured in the presence of dithionite and its decomposition products by the method of Liebig-Deniges after treatment of the sample with excess iodine, followed by sulfite. The iodine oxidizes dithionite, sulfite and thiosulfate to sulfate at pH 10. Any cyanide present in the sample will form iodine cyanide. Sulfite reduces excess iodine to iodide and converts cyanogen iodide to iodide and cyanide. A large amount of iodide in the sample shifts the end point of the titration significantly. An appropriate blank must be carried through the procedure to correct for the excess iodide.     

Phosphate Sensor Composed from Immobilized Pyruvate Oxidase and an Oxygen Electrode

Abstract

A phosphate sensor based on amperometric determination was constructed with immobilized pyruvate oxidase and an oxygen electrode. A rapid, simple and sensitive determination of phosphate was performed with the sensor. The determination time was 7min. The linearity range of this sensor was 12 – 80μM.