Enzymatic Biosensor Based on Carbon Paste Electrodes Modified with Gold Nanoparticles and Polyphenol Oxidase

The results presented here demonstrate the important catalytic effect of a carbon paste electrode modified by dispersion of gold nanoparticles towards different electroactive compounds. The oxidation of hydrogen peroxide starts at potentials 400 mV less positive than at bare carbon paste, while the reduction, almost negligible at bare carbon paste, starts at 0.100 V. The influence of the size and amount of gold nanoparticles in the composite matrix on the response of the electrode is discussed. The incorporation of albumin within the carbon paste facilitates the dispersion of gold nanoparticles, improving substantially the catalytic effects. At carbon paste modified with gold nanoparticles and albumin, the peak potential separation for hydroquinone decreases from 0.385 V to 0.209 V while the reduction current increases from 16.6 to 75.2 μA. The immobilization of polyphenol oxidase within the carbon paste electrode modified with nanoparticles has allowed us to obtain a very sensitive biosensor for dopamine even in the presence of large excess of ascorbic acid.     

Comparison of the Electrochemical Reactivity of Carbon Nanotubes Paste Electrodes with Different Types of Multiwalled Carbon Nanotubes

Carbon nanotubes (CNTs) are widely used in electrochemical studies. It is reported that CNTs with different source and dispersed in different agents [1] yield significant difference of electrochemical reactivity. Here we report on the electrochemical performance of CNTs paste electrodes (CNTPEs) prepared by multiwalled carbon nanotubes (MWNTs) with different diameters, lengths and functional groups. The resulting electrodes exhibit remarkable different electrochemical reactivity towards redox molecules such as NADH and K₃[Fe(CN)₆]. It is found that CNTPEs prepared by MWNTs with 20–30 nm diameter show highest catalysis to NADH oxidation, while CNTPEs prepared by MWNTs with carboxylate groups have best electron‐transfer rate (The peak‐peak separation (ΔE_p) is +0.108 V for MWNTs with carboxylate groups, +0.155 V for normal MWNTs, and +0.174 V for short MWNTs) but weak catalysis towards oxidation of NADH owing to the hydrophilicity of carboxylate groups. The electrochemical reactivity depends on the lengths of CNTs to some extent. The ‘long’ CNTs perform better in our study (The oxidation signals of NADH appear below +0.39 V for ‘long’ CNTs and above +0.46 V for the ‘short’ one totally). Readers may get some directions from this article while choose CNTs for electrochemical study.     

Glassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in Polylysine

We report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT‐Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0 mg/mL MWCNT in 1.0 mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT‐Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self‐assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self‐assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT‐Plys as polycationic layers for further adsorption of GOx is also evaluated.     

基于碳纳米管的化学修饰电极及电化学生物传感器的研究进展

综述了碳纳米管的结构、合成、纯化、功能化、分散及基于碳纳米管的化学修饰电极和电化学生物传感器的研究进展。     

Bioanalytical Application of the Ordered Mesoporous Carbon Modified Electrodes

An ordered mesoporous carbon modified electrode (OMCE) was prepared by film forming method. The electrochemical behavior of the OMCE was evaluated in connection with the electrochemistry of some electroactive biospecies, such as ascorbic acid (AA), acetaminophenol (AP), cysteine (CySH), dopamine (DA), epinephrine (EP), uric acid (UA), β‐nicotinamide adenine dinucleotide (reduced disodium salt hydrate, NADH), and hydrogen peroxide (H₂O₂) with cyclic voltammetry. Compared with the conventional carbon nanotubes (CNT) and graphite powder (GP) modified electrodes, the OMCE provided the best electrochemical reactivities in all cases associated with decreased over potential, better‐defined peak shape, and higher sensitivity. In addition, the OMC, CNT, and GP modified electrodes were employed as sensitive sensors for H₂O₂ and NADH quantification and as stable platforms for the fabrication of glucose and ethanol biosensors on which the enzymes were immobilized.     

Amperometric Glucose Biosensors Based on Integration of Glucose Oxidase onto Prussian Blue/Carbon Nanotubes Nanocomposite Electrodes

Nanosized Prussian blue (PB) particles were synthesized with a chemical reduction method and then the PB nanoparticles were assembled on the surface of multiwall carbon nanotubes modified glassy carbon electrode (PB/MWNTs/GCE). The results showed that the PB/MWNTs nanocomposite exhibits a remarkably improved catalytic activity towards the reduction of hydrogen peroxide. Glucose oxidase (GOD) was immobilized on the PB/MWNTs platform by an electrochemically polymerized o‐phenylenediamine (OPD) film to construct an amperometric glucose biosensor. The biosensor exhibited a wide linear response up to 8 mM with a low detection limit of 12.7 μM (S/N=3). The Michaelis–Menten constant K_m and the maximum current i_max of the biosensor were 18.0 mM and 4.68 μA, respectively. The selectivity and stability of the biosensor were also investigated.     

Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube‐Modified Electrodes

The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)‐modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH 7.4 phosphate buffer solutions (PBS) with the formal potential of about ?455 mV (vs. Ag/AgCl) and shows a surface‐controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0 mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD.     

Biosensors Based on Aligned Carbon Nanotubes Coated with Inherently Conducting Polymers

The use of multiwalled aligned carbon nanotubes provides a novel electrode platform for inherently conducting polymer based biosensors. The example used here to highlight the usefulness of such a platform is the polypyrrole based glucose oxidase system for detection of glucose. The use of these three dimensional electrodes offers advantages in that large accessible enzyme loadings can be obtained within an ultrathin layer. It has also been found that the detection of H₂O₂ at these new electrode structures containing iron loaded nanotube tips can be achieved at low anodic potentials. The result is a sensitive and selective glucose sensor.     

New Strategy for Dehydrogenase Amperometric Biosensors Using Surfactant to Enhance the Sensitivity of Diaphorase/Ferrocene Modified Carbon Paste Electrodes for Electrocatalytic Oxidation of NADH

A carbon paste electrode (CPE) modified with diaphorase (DAP) and ferrocene (FcH) has been developed for determination of NADH at low working potential. The sensitivity and operational stability, towards the detection of the reduced form of the nicotinamide adenine dinucleotide (NADH) in flow injection analysis (FIA), were greatly improved (5 times) upon adding Tween 20 into the electrode matrix. The magnitude of the amperometric signal was dependent on DAP, FcH and surfactant loading, into the modified carbon paste electrode. A rapid and repeatable response was observed to the variation of NADH concentration in the vicinity of the electrode surface. Such advantages of the DAP/FcH/Tween 20 modified carbon paste were successfully used in the construction of L ‐lactate dehydrogenase modified electrodes. The use of this new approach can be generalized to other dehydrogenases and represents a decisive step for a versatile preparation method of amperometric biosensors.     

Nanomolar Detection of Glutamate at a Biosensor Based on Screen-Printed Electrodes Modified with Carbon Nanotubes

The amperometric glutamate biosensor based on screen-printed electrodes containing carbon nanotubes (CNT), and its integration in a flow injection analysis system, is described herein. The sensor was fabricated by simply adsorbing enzyme glutamate oxidase (GlutOx) on a commercial substrate containing multi-wall CNT. The resulting device displayed excellent electroanalytical properties toward the determination of L-glutamate in a wide linear range (0.01-10 μM) with low detection limit (10 nM, S/N≥3), fast response time (≤5 s), and good operational and long-term stability. The CNT modified screen-printed electrodes have a potential to be of general interest for designing of electrochemical sensors and biosensors.     

Ordered Mesoporous Carbon Paste Electrodes for Electrochemical Sensing and Biosensing

Surface renewable ordered mesoporous carbon paste electrodes (OMCPE) were prepared by mechanical mixing ordered mesoporous carbon (OMC) and mineral oil. Electrochemical behavior of the composite electrode was evaluated and compared with the conventional graphite paste (GPE) and carbon nanotubes paste (CNTPE) electrodes. The OMCPE provided improved electron transfer kinetics and catalytic capabilities in connection with oxidation and/or reduction of different redox systems, such as ferricyanide and some biological species, e. g. ascorbic acid (AA), uric acid (UA), β‐nicotinamide adenine dinucleotide (NADH), dopamine (DA), epinephrine (EP), acetaminophenol (AP) and hydrogen peroxide. The substantial decrease in the over voltage of the hydrogen peroxide oxidation along with the facile incorporation of glucose oxidase (GOD) into the composite matrix allowed us successfully to fabricate a sensitive and selective glucose biosensor. A linear response up to 15 mM glucose was obtained for the OMCPE modified with 10% GOD (w/w) with a detection limit of 0.072 mM. In addition, we also successfully applied the OMCPE to the anodic stripping voltammetric analysis of heavy metal ions with improved sensitivities in comparison with CNTPE and GPE. The excellent experimental results implicate that the new developed paste electrode holds great promise in the design of electrochemical devices, such as sensors and biosensors.     

Fabrication of a Highly Sensitive Glucose Biosensor Based on Immobilization of Osmium Complex and Glucose Oxidase onto Carbon Nanotubes Modified Electrode

In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxygen and H₂O₂ in physiological pH solutions. Electroless deposition at a short period of time (60 s), was used for strong and irreversible adsorption of 1,4,8,12‐tetraazacyclotetradecane osmium(III) chloride (Os(III)LCl₂) ClO₄ onto single‐walled carbon nanotubes (SWCNTs) modified GC electrode. The modified electrode shows a pair of well defined and reversible redox couple, Os(IV)/Os(III) at wide pH range (1–8). The glucose biosensor was fabricated by covering a thin film of glucose oxidase onto CNTs/Os‐complex modified electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The fabricated biosensor shows high sensitivity, 826.3 nA μM^?1cm^?2, low detection limit, 56 nM, fast response time <3 s and wide calibration range 1.0 μM–1.0 mM. The biosensor has been successfully applied to determination of glucose in human plasma. Because of relative low applied potential, the interference from electroactive existing species was minimized, which improved the selectivity of the biosensor. The apparent Michaelis‐Menten constant of GOx on the nanocomposite, 0.91 mM, exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this glucose biosensor.     

Electrochemical DNA Biosensors Based on Palladium Nanoparticles Combined with Carbon Nanotubes

Palladium nanoparticles, in combination with multi‐walled carbon nanotubes (MWCNTs), were used to fabricate a sensitivity‐enhanced electrochemical DNA biosensor. MWCNTs and palladium nanoparticles were dispersed in Nafion, which were used to modify a glassy carbon electrode (GCE). Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement using methylene blue (MB) as an indicator. Due to the ability of carbon nanotubes to promote electron‐transfer and the high catalytic activities of palladium nanoparticles for electrochemical reaction of MB, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.2×10^?13 M.     

碳纳米管用作超级电容器电极材料

碳纳米管由于具有化学稳定性好、比表面积大、导电性好和密度小等优点,是很有前景的超级电容器电极材料。本文介绍了碳纳米管用作超级电容器电极材料的研究现状,总结了单纯碳纳米管电极材料和碳纳米管复合物电极材料的特点与性能,并探讨了今后碳纳米管电极材料的发展方向。     

基于多壁碳纳米管和氧化锌纳米棒复合物的葡萄糖生物传感器(英文)

利用多壁碳纳米管(MWCNTs)和氧化锌(ZnO)纳米棒复合物膜构建了一种新的电流型葡萄糖生物传感器。MWCNTs-ZnO复合物在超声协助下通过静电配位的方式产生。其中,ZnO纳米棒的存在加强了该复合物催化氧化H2O2的能力,增加了响应电流。与单一的MWCNTs和ZnO相比,这种纳米复合物显示了更为有效地电催化活性。在此基础上,我们以MWCNTs-ZnO复合物膜为基底,用戊二醛交联法固定葡萄糖氧化酶,电聚合邻苯二胺(PoPD)膜为抗干扰层,构建了抗干扰能力强,稳定性好,灵敏度高,响应快的葡萄糖传感器。在+0.8V的检测电位下,该传感器对葡萄糖响应的线性范围为5.0×10-6~5.0×10-3mol·L-1(R=0.997),检测限为3.5×10-6mol·L-1(S/N=3),响应时间小于10s的葡萄糖生物传感器,常见干扰物质如抗坏血酸和尿酸不影响测定。     

Dehydrogenase‐Based Reagentless Biosensors: Electrochemically Assisted Deposition of Sol‐Gel Thin Films on Functionalized Carbon Nanotubes

Multiwalled carbon nanotubes (MWCNT) have been functionalized, for the electrocatalytic detection of NADH, by microwave treatment, electrochemical deposition of poly(methylene green) or wrapping with an Os‐complex modified polymer. Sol‐gel thin films have been then electrodeposited on the carbon nanotube layers for co‐immobilization of D ‐sorbitol dehydrogenase and diaphorase when necessary and NAD⁺ via covalent linkage using glycidoxypropyltrimethoxysilane. The comparison of these systems shows that the electrodeposited sol‐gel matrix can significantly affect the operational behavior of functionalized MWCNT. Only MWCNT wrapped with the Os‐complex modified polymer and covered with a sol‐gel biocomposite allowed the electrochemical detection of D ‐sorbitol in a reagentless configuration.     

基于碳纳米管修饰电极的胆碱电化学发光生物传感器研制

在碳纳米管(CNTs)和K3Fe(CN)6修饰的铂电极上吸附固定胆碱氧化酶,以鲁米诺为发光试剂,研制了胆碱电化学发光(ECL)生物传感器。CNTs可有效提高电极表面的电荷传输能力、提高电极表面的生物相容性和对酶分子的固载能力;K3Fe(CN)6对酶活性具有激活作用,同时对H2O2增敏的鲁米诺ECL有增强作用,均有利于提高传感器的检测灵敏度。研究表明,将CNTs分散液与K3Fe(CN)6混合,滴涂修饰在Pt电极上,吸附固定胆碱氧化酶,制备传感器。此传感器在含有8×10-6mol/L鲁米诺的磷酸盐缓冲液(pH7.4)、30℃条件下产生的ECL强度与胆碱浓度在1×10-7～4×10-3mol/L范围内呈线性关系,相关系数为0.994,检出限为1.2×10-8 mol/L。此生物传感器应用于鼠血样中胆碱的测定,测得结果为2.68 mg/L,平均回收率为101.1%。传感器具有快速、稳定和重现性好等特点,有望应用于常规分析。     

Comparison of the Electrochemical Reactivity of Electrodes Modified with Carbon Nanotubes from Different Sources

The electrochemical activity of five different commercial carbon nanotubes (CNT), prepared by the ARC discharge and chemical vapor deposition (CVD) methods, has been assessed and compared. The various multi‐walled CNT were immobilized onto a glassy carbon electrode using three different dispersing agents (Nafion, concentrated nitric acid and dimethylformamide (DMF)) and their voltammetric response to ferricyanide, NADH and hydrogen peroxide examined. SEM was used to characterize the surface morphology. The corresponding cyclic voltammetry and amperometric data showed that the electrocatalytic activity, the background current and the electroanalytical performance are strongly depended on the preparation of the CNT and on the dispersing agent used. The most favorable amperometric detection of NADH and hydrogen peroxide is observed at the NanoLab CVD‐produced CNT in connection to a DMF‐surface dispersion. ARC‐produced CNT display a smaller capacitance, particularly in connection to the DMF dispersion. Such differences in the electrochemical reactivity are attributed to the different surface chemistries (primarily defect densities) of the corresponding CNT layers, associated with the different production and dispersion protocols.     

Use of Cationic Surfactants Film Carbon Paste Electrodes Modified with Multiwalled Carbon Nanotubes in Electrochemical Analysis of dsDNA

Direct electrochemistry of dsDNA based on the enhancement effect of cationic surfactants such as dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) was achieved by using a carbon paste electrode modified with multiwalled carbon nanotubes (MWCNTs/CPE) as the basal electrode. The results indicated that the dsDNA molecules have been adsorbed quite strongly on the cationic surfactants’ film and very well developed peaks which were attributed to the oxidation of guanine residues on the dsDNA molecule structure were obtained from both electrodes. The electrochemical behavior of dsDNA at the surface of the modified electrodes was also evaluated. Based on the signal of guanine, under the optimal conditions, very low levels of dsDNA were detected following short accumulation times with detection limits of 0.650 mg L^?1 and 0.119 mg L^?1 for DTAB/MWCNTs/CPE and TTAB/MWCNTs/CPE, respectively.     

基于碳纳米管修饰电极的甲醛生物传感器

利用甲醛脱氢酶和羧基化多壁碳纳米管修饰的丝网印刷电极,制备了基于还原型辅酶Ⅰ检测的甲醛生物传感器,并优化了传感器的检测条件.结果表明,此传感器对甲醛有较好的电催化氧化作用,显著降低了甲醛的氧化峰电位.在0.001～11nmol/L范围内,响应电流与甲醛的浓度线性相关,其线性回归方程为z(μA)=0.944c(mmol/L,) +0.0623,相关系数为0.9934,响应时间约为20 s,检出限为0.2 μmol/L( S/ N=3).