Direct Electrochemistry of Glucose Oxidase Immobilized on Titanium Carbide‐Au Nanoparticles‐Fullerene C60 Composite Film and Its Biosensing for Glucose

The direct electrochemistry of glucose oxidase (GOD) immobilized on the designed titanium carbide‐Au nanoparticles‐fullerene C₆₀ composite film modified glassy carbon electrode (TiC‐AuNPs‐C₆₀/GCE) and its biosensing for glucose were investigated. UV‐visible and Fourier‐transform infrared spectra of the resulting GOD/TiC‐AuNPs‐C₆₀ composite film suggested that the immobilized GOD retained its original structure. The direct electron transfer behaviors of immobilized GOD at the GOD/TiC‐AuNPs‐C₆₀/GCE were investigated by cyclic voltammetry in which a pair of well‐defined, quasi‐reversible redox peaks with the formal potential (E^0′) of ‐0.484 V (vs. SCE) in phosphate buffer solution (0.05 M, pH 7.0) at the scan rate of 100 mV·s^?1 were obtained. The proposed GOD modified electrode exhibited an excellent electrocatalytic activity to the reduction of glucose, and the currents of glucose reduction peak were linearly related to glucose concentration in a wider linearity range from 5.0 × 10^?6 to 1.6 × 10^?4 M with a correlation coefficient of 0.9965 and a detection limit of 2.0 × 10^?6 M (S/N = 3). The sensitivity and the apparent Michaelis‐Menten constant (K_M^app) were determined to be 149.3 μA·mM^?1·cm^?2 and 6.2 × 10^?5 M, respectively. Thus, the protocol will have potential application in studying the electron transfer of enzyme and the design of novel electrochemical biosensors.     

Influence of Metal Nanoparticles on the Electrocatalytic Oxidation of Glucose by Poly(NiIIteta) Modified Electrodes

Conductive polymeric [Ni^II(teta)]²⁺ (teta=C‐meso‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetra‐azacyclotetradecane) films (poly(Ni)) have been deposited on the surface of glassy carbon (GC), Nafion (Nf) modified GC (GC/Nf) and Nf stabilized Ag and Au nanoparticles (NPs) modified GC (GC/Ag‐Nf and GC/Au‐Nf) electrodes. The cyclic voltammogram of the resulting electrodes, show a well defined redox peak due to oxidation and reduction of poly(Ni) system in 0.1 M NaOH. They show electrocatalytic activity towards the oxidation of glucose. AFM studies reveal the formation of poly(Ni) film on the modified electrodes. Presence of metal NPs increases electron transfer rate and electrocatalytic oxidation current by improving the communication within the Nf and poly(Ni) films. In the presence of metal NPs, 4 fold increase in current for glucose oxidation was observed.     

Electrochemical Behavior of Glucose Oxidase Immobilized on Pd‐Nanoparticles Decorated Ionic Liquid Derived Fibrillated Mesoporous Carbon

Pd nanoparticles with an average diameter of 5 nm were decorated on the surface of ionic liquid derived fibrillated mesoporous carbon (IFMC) to prepare a novel nano‐hybrid material (Pd@IFMC). Thereafter, glucose oxidase was immobilized on Pd@IFMC modified glassy carbon electrode to fabricate an enzymatic glucose biosensor. A pair of well‐defined redox peaks was recorded for direct electron transfer of the immobilized glucose oxidase at the formal potential of ? 0.418 V with a peak to peak separation of 25 mV. Electron transfer rate constant of was calculated to be 14.6 s^?1. The response of fabricated biosensor was linear towards glucose concentration.     

Steering the Selectivity of Electrocatalytic Glucose Oxidation by the Pt Oxidation State

Electrocatalytic glucose oxidation can produce high value chemicals, but selectivity needs to be improved. Here we elucidate the role of the Pt oxidation state on the activity and selectivity of electrocatalytic oxidation of glucose with a new analytical approach, using high-pressure liquid chromatography and high-pressure anion exchange chromatography. It was found that the type of oxidation, i.e. dehydrogenation of primary and secondary alcohol groups or oxygen transfer to aldehyde groups, strongly depends on the Pt oxidation state. Pt⁰ has a 7-fold higher activity for dehydrogenation reactions than for oxidation reactions, while PtO_x is equally active for both reactions. Thus, Pt⁰ promotes glucose dialdehyde formation, while PtO_x favors gluconate formation. The successive dehydrogenation of gluconate is achieved selectively at the primary alcohol group by Pt⁰, while PtO_x also promotes the dehydrogenation of secondary alcohol groups, resulting in more complex reaction mixtures.     

Properties of Dendrimer‐Encapsulated Pt Nanoparticles Doped Polypyrrole Composite Films and Their Electrocatalytic Activity for Glucose Oxidation

A type of novel electroanalytical sensing nanobiocomposite material was prepared by electropolymerization of pyrrole containing poly(amidoamine) dendrimers‐encapsulated platinum nanoparticles (Pt‐PAMAM), and glucose oxidase (GOx). The Pt nanoparticles encapsulated in PAMAM are nearly monodisperse with an average diameter of 3 nm, and they provide electrical conductivity. Polypyrrole acts as a polymer backbone to give stable and homogeneous cast thin films, and it also defines the electrical conductivity. Both Polypyrrole and PAMAM can provide a favorable microenvironment to keep the bioactivity of enzymes such as glucose oxidase. The homogeneity of GOx/Pt‐PAMAM‐PPy nanobiocomposite films was characterized by atomic force microscopy (AFM). Amperometric biosensors fabricated with these materials were characterized electrochemically using cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and amperometric measurements in the presence of hydrogen peroxide or glucose. All those show the resultant biosensor sensitivity was strongly enhanced within the nanobiocomposite film. The optimized glucose biosensor displayed a sensitivity of 164 μA mM^?1 cm^?1, a linear range of 0.2 to 600 μM, a detection limit of 10 nM, and a response time of <3 s.     

葡萄糖在纳米金修饰金电极上电化学行为研究

利用电还原氯金酸制备了纳米金(Nano-gold,NG)修饰Au电极。该电极对葡萄糖有催化作用,可能是由于纳米金降低了OH-表面吸附能,增加了OH-在电极表面的吸附量。通过循环伏安法研究了扫描速度、温度、本体浓度和溶液pH值对葡萄糖氧化的影响。     

A Flexible Nafion Coated Enzyme‐free Glucose Sensor Based on Au‐dimpled Ti Structures

The detection of glucose at low concentrations using electrochemical sensors is of great importance due to the possibility of using different human body fluids than blood, such as e. g. urine, saliva, sweat or tears. The interest behind those biofluids is related to their utility in non‐invasive sugar determination. In this work, we present flexible, fully biocompatible electrode material based on Au nanoparticles immobilized onto titanium dimples. Au?Ti heterostructures were obtained via electrochemical anodization of titanium foil in presence of fluoride anions followed by chemical etching, magnetron sputtering of gold and subsequent thermal dewetting in continuous regime. In the last step of fabrication, electrodes were modified by permselective Nafion membrane. The selection of the best electrode material among different configurations was carried out basing on the electrochemical activity in the contact with 5 mM glucose dissolved in neutral air‐saturated 0.1 M PBS. For the 10 nm Au dewetted gold film, limit of detection of 30 μM and high sensitivity of 93 mA cm^?2 mM^?1 were achieved. Application of Nafion membrane caused complete inhibition of the impact of various interference species onto the glucose detection. Good selectivity and repeatability combined with the resistance to prolonged mechanical stress suggest that prepared material can be used in non‐invasive glucose sensing.     

A Novel Glucose Biosensor Based on Glucose Oxidase Immobilized on AuPt Nanoparticle – Carbon Nanotube – Ionic Liquid Hybrid Coated Electrode

A novel amperometric glucose biosensor is presented in this article, which is based on the adsorption of glucose oxidase on gold‐platinum nanoparticle (AuPt NP)‐multiwalled carbon nanotube (MWNT) – ionic liquid (i.e., 1‐octyl‐3‐methylimidazolium hexafluorophosphate, [OMIM]PF₆) composite. The gold‐platinum nanoparticles is prepared through direct electrodeposition. Owing to the synergistic action of AuPt nanoparticle, MWNT and [OMIM]PF₆, the biosensor shows good response to glucose, with wide linear range (0.01 to 9.49 mM), short response time (3 s), and high sensitivity (3.47 μA mM⁻¹). With the biosensor the determination of glucose in human serum is performed.     

Direct Electrochemistry of Glucose Oxidase Immobilized at a Novel Composite Material β‐Cyclodextrin/poly(4‐aminothiophenol)/Au Nanoparticle Modified Electrode

A novel complex material was fabricated by three steps. In the first step, gold nanoparticle (Au_nano) was prepared with the method of chemistry and dialysis. In the second step, 4‐aminothiophenol (AT) was encapsulated in the cavity of β‐cyclodextrin and formed inclusion complex, cyclodextrin/4‐aminothiophenol (CD/AT). And then inclusion complex was adsorbed to the surface of Au_nano based on the bond of Au‐S interaction. In the last step, a complex material, cyclodextrin/poly(4‐aminothiophenol)‐Au nanoparticles (CD/PAT‐Au_nano) was obtained by the polymerizing in the acid solution initiated by chlorauric acid. The CD/PAT‐Au_nano has spherical nanostructure with the average diameter of 55 nm. Glucose oxidase (GOx) was anchored with this complex material and direct electrochemistry of GOx was achieved. A couple of stable and well‐defined redox peaks were observed with the formal potential (E^0′) of ‐0.488 V (vs. SCE) in a pH 6.98 buffer solution. The GOx modified electrode also exhibited an excellent electrocatalytic activity to the reduction of glucose, a linearity range for determination of glucose is from 0.25 mM to 16.0 mM with a detection limit of 0.09 mM (S/N = 3). This protocol had potential application to fabricate the third‐generation biosensor.     

Gold Decorated Graphene by Laser Ablation for Efficient Electrocatalytic Oxidation of Methanol and Ethanol

A well‐known limitation in the fabrication of metal‐graphene composite has been the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. We demonstrate here a novel one‐pot synthesis of gold nanoparticles by laser ablation of gold strip and in‐situ decoration on graphene substrate. Not only the impregnation of nanoparticles was linker free, but also the synthesis by itself was surfactant‐free. The composite materials were well characterized morphologically and functionally using electron microscopy, X‐ray and electron diffraction, Raman spectroscopy, Zeta potential, electrochemical measurements and UV‐Visible spectroscopic techniques. This linker‐free gold‐graphene based composite has been employed for catalytic applications pertaining to electrooxidation. We have explored the use of this composite as a binder‐free electrode in electrocatalytic oxidation of methanol and ethanol in alkaline medium. Additionally, the onset potential for ethanol oxidation was found to be more negative, ?100 mV, an indication of its promising application in direct ethanol fuel cells.     

Amperometric Glucose Determination by Means of Glucose Oxidase Immobilized on a Cellulose Acetate Film: Dependence on the Immobilization Procedures

Glucose microelectrodes were prepared by immobilizing glucose oxidase onto a cellulose acetate film coating a platinum wire. Hexamethylenediamine (HMDA) and Glutaraldehyde (GA) were employed as spacer and coupling agent, respectively. Sensitivities and linear response ranges were studied as a function of the relative amounts of HMDA and GA. The best sensitivity was found when HMDA and GA were 5% and 2.5% in aqueous solutions, respectively. Taking as a reference the functioning of this biosensor, the roles of HMDA and GA percentages appear to be opposed when the extension of the linear response range is considered. Indeed, an increase of one unit in HMDA percentage (from 5 to 6 %) induces an increase in the extension of the linear response range equal to that obtained with a decrease of one unit of GA percentage (from 2.5 to 1.5%).     

Electrocatalytic Oxidation of Carbohydrates Mediated by Nitroxyl Radical‐modified Electrodes in Aqueous Solution

The electrocatalytic activity of a 2,2,6,6‐tetramethylpipridine‐N‐oxyl (TEMPO)‐modified electrode toward the oxidation of carbohydrates in phosphate buffer solution was investigated under neutral aqueous solution conditions at 25 °C. The modified electrode was prepared on the surface of a glassy carbon electrode by the electrochemical polymerization of a TEMPO precursor containing a pyrrole side chain. Cyclic voltammetric studies showed that the anodic peak current increased with the concentration of carbohydrates in a dose‐dependent manner.     

Electrocatalytic Oxidation of Glucose at Carbon Nanotubes Supported PtRu Nanoparticles and Its Detection

PtRu nanoparticles were supported on multiwall carbon nanotubes (MWNTs), which were further fabricated as an electrode for nonenzymatic glucose sensing. Transmission electron microscope and X‐ray diffraction patterns were used for characterization of the PtRu nanoparticles on MWNTs. Cyclic voltammetry and chronopotentiometry were applied to investigate the performance of the PtRu/MWNTs nanocomposite electrode for nonenzymatic oxidation of glucose. The PtRu/MWNTs electrode shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution and thus can be used to selectively detect glucose. Under the optimal potential (+0.55 V vs. Ag/AgCl), the biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), dopamine (DP) and uric acid (UA). Wide linear calibration ranging from 1 mM to 15 mM, high sensitivity of 28.26 μA cm^?2 mM^?1, low detection limit of 2.5×10^?5 M, and fast response time of 10 s were achieved for the detection of glucose at the PtRu/MWNTs electrode.     

Facile Synthesis of Leaf‐Like CuO Nanoparticles and Their Application on Glucose Biosensor

An efficient amperometric biosensor based on well‐crystallized leaf‐like CuO nanoparticles for detecting glucose has been proposed. The leaf‐like CuO nanoparticles, synthesized by a simple one‐step hydrothermal method, were characterized by X‐ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. Under the optimal condition, the electrochemical behaviour of the leaf‐like CuO nanoparticles modified electrode for detection of glucose exhibited high sensitivity of 246 µA/mM/cm², short response time (within 5 s), linear dynamic range from 1.0 to 170 µM (R²=0.9995), and low limit of detection (LOD) (S/N=3) of 0.91 µM. The high sensitivity, good reproducibility, stability, and fast amperometric sensing towards oxidation of glucose, make this biosensor promising for future application.     

Size‐Dependent Electrocatalytic Activity of Free Gold Nanoparticles for the Glucose Oxidation Reaction

Understanding the fundamental relationship between the size and the structure of electrode materials is essential to design catalysts and enhance their activity. Therefore, spherical gold nanoparticles (GNSs) with a mean diameter from 4 to 15 nm were synthesized. UV/Vis spectroscopy, transmission electron microscopy, and under‐potential deposition of lead (UPD_Pb) were used to determine the morphology, size, and surface crystallographic structure of the GNSs. The UPD_Pb revealed that their crystallographic facets are affected by their size and the growth process. The catalytic properties of these GNSs toward glucose electrooxidation were studied by cyclic voltammetry, taking into account the scan rate and temperature effects. The results clearly show the size‐dependent electrocatalytic activity for glucose oxidation reactions that are controlled by diffusion. Small GNSs with an average size of 4.2 nm exhibited high catalytic activity. This drastic increase in activity results from the high specific area and reactivity of the surface electrons induced by their small size. The reaction mechanism was investigated by in situ Fourier transform infrared reflectance spectroscopy. Gluconolactone and gluconate were identified as the intermediate and the final reaction product, respectively, of the glucose electrooxidation.     

Construction of a Novel Glucose Biosensor Based on Covalent Immobilization of Glucose Oxidase on Poly(glycidyl methacrylate‐co‐vinylferrocene)

A novel glucose biosensor was constructed via direct covalent attachment of glucose oxidase onto epoxy group containing polymeric electron transfer mediator, Poly(glycidyl methacrylate‐co‐vinylferrocene). A copolymer of glycidyl methacrylate (GMA) and vinylferrocene (VFc) with different molar ratios has been prepared by free radical copolymerization. These copolymers have been utilized as polymeric mediators for amperometric glucose sensing. The catalytic electrochemistry of the enzyme electrode with the copolymer was investigated. Copolymer acts as an electron transfer mediator between the redox center of Glucose oxidase (GOx) and the electrode. The stability, reusability, pH and temperature response of the biosensor as well as its kinetic parameter have also been studied.     

Ni纳米催化剂的制备及其对葡萄糖电催化氧化的研究

采用等体积浸渍和程序升温还原的方法制备了不同Ni含量的Ni/AC纳米催化剂,并对其进行了形貌和结构表征。采用三电极体系和循环伏安法在碱性溶液中进行了其对葡萄糖催化氧化的电化学测试。结果表明,Ni/AC/GCE(修饰在玻碳电极上的Ni/AC)催化剂对葡萄糖有较强的电催化氧化作用。其中,20%的Ni/AC/GCE对葡萄糖电催化氧化作用最强,且随着葡萄糖浓度增加,响应电流显著增大,二者呈线性相关。20%Ni/AC/GCE催化剂对葡萄糖催化氧化的线性响应范围为0.2~6.5 mmol/L,相关系数为0.999,响应灵敏度是13.15μA/(mmol/L),最低检测限为35μmol/L。稳定性测试结果表明,20%Ni/AC/GCE有着良好的稳定性,每隔两天测试,运行三周后其响应电流仍能维持在95%以上。     

固载于壳聚糖-纳米金复合膜修饰玻碳电极上的葡萄糖氧化酶的直接电化学研究及其生物传感应用

通过将葡萄糖氧化酶固载于壳聚糖-纳米金复合膜内所构置的传感器,实现了葡萄糖氧化酶的直接电化学,并采用循环伏安法与电化学阻抗法对修饰电极进行了表征。研究表明：在除氧缓冲溶液中,葡萄糖氧化酶-壳聚糖-纳米金复合膜修饰电极表现出一对良好的氧化还原峰,这对峰归因于葡萄糖氧化酶的氧化还原,证明葡萄糖氧化酶被成功固载于复合膜内。电子传递速率常数为15.6 s-1,说明葡萄糖氧化酶的电活性中心与电极之间的电子传递很快。将壳聚糖与纳米金相结合还提高了葡萄糖氧化酶在复合膜内的稳定性并保持其生物活性,并可以用于葡萄糖检测。计算得到其表观米氏常数为10.1 mmol·L-1。而且,该生物传感器可以用于血样中葡萄糖含量的测定。     

Fabrication of Au‐Nanoparticle/TiO2‐Nanotubes Electrodes Using Electrochemical Methods and Their Application for Electrocatalytic Oxidation of Hydroquinone

Gold nanoparticle (Au‐NPs)‐Titanium oxide nanotube (TiO₂‐NTs) electrodes are prepared by using galvanic deposition of gold nanoparticles on TiO₂‐NTs electrodes as support. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy results indicate that nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm diameters and gold nanoparticles are well‐dispersed on the surface of TiO₂‐NTs support. The electrooxidation of hydroquinone of Au‐NPs/TiO₂‐NTs electrodes is investigated by different electrochemical methods. Au‐NPs/TiO₂‐NTs electrode can be used repeatedly and exhibits stable electrocatalytic activity for the hydroquinone oxidation. Also, determination of hydroquinone in skin cream using this electrode was evaluated. Results were found to be satisfactory and no matrix effects are observed during the determination of hydroquinone content of the “skin cream” samples.     

Direct Electrocatalytic Oxidation and Simultaneous Determination of 5‐Methylcytosine and Cytosine at Electrochemically Reduced Graphene Modified Glassy Carbon Electrode

Direct electrocatalytic oxidation and simultaneous determination of 5‐methylcytosine (5‐mC) and cytosine(C) were realized in alkaline solutions by differential pulse voltammetry (DPV) based on an electrochemically reduced graphene oxide (er‐GO) modified glassy carbon electrode (er‐GO/GCE). The as‐prepared er‐GO/GCE exhibited good electrocatalytic activity towards the oxidation of 5‐mC and C. Under optimum conditions, the er‐GO/GCE was applied to the simultaneous determination of 5‐mC and C with a significantly improved peak potential resolution (about 150 mV), and a linear relationship can be obtained in the range of 6–200.0 µmol/L and 8–250.0 µmol/L, respectively. In addition, the proposed method was further successfully applied to the analysis of methylation status in short CpG oligonucleotides with satisfactory results.