Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH

Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for β-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.     

辅酶NADH与色氨酸共振能量转移的荧光动力学研究

采用时间相关单光子计数技术, 结合紫外-可见吸收光谱和稳态荧光光谱, 对不同环境下的色氨酸和辅酶还原型烟酰胺腺嘌呤二核苷酸(NADH)之间的共振能量转移荧光动力学进行了研究. 单体色氨酸、 牛血清白蛋白以及乳酸脱氢酶蛋白与NADH之间相互作用的光谱数据表明, 只有存在NADH结合位点的乳酸脱氢酶和NADH之间发生了荧光共振能量转移. 进一步通过加入丙酮酸来阻断乳酸脱氢酶和NADH之间的荧光共振能量转移通道, 时间分辨荧光光谱和衰减相关光谱(DAS)证实, 蛋白结合位点的存在是NADH和色氨酸之间发生荧光共振能量转移的前提条件. DAS揭示了乳酸脱氢酶平均荧光寿命的减小主要是源于色氨酸中7.35 ns的荧光寿命成分与NADH之间的荧光共振能量转移, 同时给出了NADH和色氨酸之间的能量转移效率, 为研究NADH和蛋白之间的相互作用提供了新思路.     

6-Vinyl coenzyme Q0: Electropolymerization and electrocatalysis of NADH oxidation exploiting poly-p-quinone-modified electrode surfaces

6-Vinyl coenzyme Q₀ serves as a convenient starting material for the formation of electropolymerized coenzyme Q₀ on glassy carbon electrodes and the modified electrodes displays electrocatalytic activity toward NADH (β-nicotinamide adenine dinucleotide) oxidation. The detection of NADH was measured by differential pulse voltammetry, which reveals that the peak current is linear to the concentration of NADH within the range of 10–100 μM. This would be helpful for the understanding of the interaction between coenzyme Q₀ and NADH in the biological process.     

Au‐TiO2/Graphene Nanocomposite Film for Electrochemical Sensing of Hydrogen Peroxide and NADH

We describe a simple method for preparing Au‐TiO₂/graphene (GR) nanocomposite by deposition of Au nanoparticles (NPs) on TiO₂/GR substrates. The as‐prepared Au‐TiO₂/GR was characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The presence of Au NPs on TiO₂/GR surface remarkably improves the electrocatalytic activity towards the oxidation of hydrogen peroxide (H₂O₂) and β‐nicotinamide adenine dinucleotide (NADH). The Au‐TiO₂/GR modified glassy carbon (GC) electrode exhibits good amperometric response to H₂O₂ and NADH, with linear range from 10 to 200 µM and 10 to 240 µM, and detection limit of 0.7 and 0.2 µM, respectively.     

Determination of Reduced Nicotinamide Adenine Dinucleotide Based on Immobilization of Tris(2,2′‐bipyridyl) Ruthenium(II) in Multiwall Carbon Nanotubes/Nafion Composite Membrane

Abstract

An electrochemiluminescence (ECL) method for reduced nicotinamide adenine dinucleotide (NADH) was proposed by immobilizing tris(2,2′‐bipyridyl) ruthenium(II) (Ru(bpy)₃ ²⁺) in multiwall carbon nanotubes (MWCNTs)/Nafion composite membrane that was formed on glassy carbon electrode surface. The electrochemical and ECL behaviors of the immobilized Ru(bpy)₃ ²⁺ were investigated. The cyclic votammogram of the modified electrode in pH 7.0 phosphate buffer solution showed a couple of redox peaks at +1190 and +1060 mV at 100 mV/s. The composite film had a more open structure and a large surface area allowing faster diffusion of Ru(bpy)₃ ²⁺. The presence of MWCNTs resulted in the improved ECL sensitivity and longer‐term stability of the modified electrode. The modified electrode showed a linear response to NADH in the concentration range of 1.0×10^?6 to 1.6×10^?5 M with a detection limit of 8.2×10^?7 M.     

Highly Stable Bioluminescence-Based Fiber-Optic Sensor Using Immobilized Enzymes from Vibrio Harveyi

Abstract

The properties of the bioluminescent enzymatic systems from V. fischeri and V.harveyi immobilized on preactivated polyamide membranes, as well as the characteristics of a fiber-optic biosensor equipped with such membranes, have been studied. Particular attention has been paid to the stability of the bioactive matrices under working conditions, since this remains a key-point for designing operational biosensors of practical use. Whatever the origin of the bioluminescent system, the microdetermination of NADH could be performed at the nanomolar level with detection limits of 2 nM and 0.3 nM with the systems from V. harveyi and V. fischeri, respectively. the use of polyethyleneglycol (PEG 600) improves the operational stability of the bi-enzymatic system from V. fischeri, but a recalibration must be carried out every ten assays. Although the immobilized system from V. harveyi exhibited a lower activity than the enzymes from V. fischeri, its excellent operational stability (100 assays performed within a day without loss in activity) makes it more suitable in designing a truly operational bioluminescence-based NADH sensor.     

A NADH Sensor Based on 1,2‐Naphththoquinone Electropolymerized on Multi‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

A new carbon nanotubes modified electrode (poly‐Nq‐MWCNTs/GCE) was fabricated by electropolymerization of 1,2‐naphththoquinone to the surface of multi‐walled carbon nanotubes modified electrode by casting method. The morphology of the nanocomposite was characterized by scanning electron microscopy. Cyclic voltammetry and chronoamperometry were applied to investigate the electrochemical properties of the poly‐Nq‐MWCNTs nanocomposite modified electrode. The result of electrochemical experiments showed that such modified electrode had a favorable catalytic ability to oxidation of β‐nicotinamide adenine dinucleotide (NADH). The resulted sensor was sensitiveness to NADH and achieved 95β of the steady‐state current within 5s. Furthermore, the anodic peak current was linear to the concentration of NADH for the range from 1.0 μM to 0.14 mM. The linear equation was: I(μA) = 0.3987 + 0.1035c (μmol/L), the correlation coefficient r = 0.9962, the detect limit is down to 1 × 10^?7 M (S/N = 3) and the sensitivity is 0.1035 μA/mmol. The well catalytic activity of the sensor was ascribed to the synergistic effect role played by MWCNTs and poly‐Nq. Moreover, the based sensor possesses good stability and reproducibility.     

Multi‐walled Carbon Nanotubes Non‐covalently Functionalized with Polyarginine: A New Alternative for the Construction of Reagentless NAD+/Dehydrogenase‐based Ethanol Biosensor

This work reports for the first time the development of a reagentless enzymatic amperometric biosensor for ethanol based on the use of a glassy carbon electrode (GCE) modified with multi‐walled carbon nanotubes (MWCNTs) non‐covalently functionalized with polyarginine (Polyarg) as platform for the robust immobilization of alcohol dehydrogenase (ADH) and NAD⁺. The new strategy allows to obtain an integrated GCE/MWCNTs‐Polyarg/NAD⁺‐ADH ethanol biosensor with important advantages compared to the existing ethanol biosensors: avoids the external addition of the cofactor for each measurement, ensures a fast and sensitive quantification of ethanol due to the intimate interaction of the components, and allows the detection at considerably lower potentials due to the catalytic activity of the carbon nanostructures. These unique properties have made possible a very efficient ethanol quantification with a sensitivity of (1487±6) μA M^?1, detection limit of 0.65 μM, response time of 8 s, and reproducibility of 5.5 % with a very successful application for the quantification of ethanol in different commercial beverages.     

Electrochemical investigations of the reaction mechanism and kinetics between NADH and riboflavin immobilised on amorphous zirconium phosphate

Electrochemical investigations of the reaction mechanism and kinetics between riboflavin immobilised on zirconium phosphate (ZPRib) in carbon paste and NADH showed results yielding reliable information about aspects on the mechanism of the electron transfer reaction between the flavin and NADH. The formal potential (E°′) of the adsorbed riboflavin was −220 mV versus SCE at pH 7.0. A shift about 250 mV towards a more positive potential compared with its value in solution was assigned to the interaction between the basic nitrogen of riboflavin and the acid groups of ZP. The invariance of the E°′ with the pH of the contacting solution and the effect of different buffer constituents were attributed to the protection effect of ZP over the riboflavin. The electrocatalytic oxidation of NADH at the electrode was investigated using cyclic voltammetry and rotating disk electrode methodology using a potential of −50 mV versus SCE. The heterogeneous electron transfer rate constant, k _obs, was 816 M⁻¹ s⁻¹ and the Michaelis-Menten constant, K _M, was 1.8 mM (confirming a charge transfer complex intermediate in the reaction) for an electrode with a riboflavin coverage of 6.8 × 10⁻¹⁰ mol cm⁻². This drastic increase in the reaction rate between NADH and the immobilised riboflavin was assigned to the shift of the E°′. A surprising effect with addition of calcium or magnesium ion to the solution was also observed. The E°′ was shifted to −150 mV versus SCE and the reaction rate for NADH oxidation increased drastically. Received: 22 February 1999 / Accepted: 10 March 1999