Amperometric Glucose Biosensor on Layer by Layer Assembled Carbon Nanotube and Polypyrrole Multilayer Film

An amperometric glucose biosensor on layer by layer assembled carbon nanotube and polypyrrole multilayer film has been reported in the present investigation. Homogeneous and stable single wall carbon nanotubes (SWNTs) and polypyrrole (PPy) multilayer films were alternately assembled on platinum coated Polyvinylidene fluoride (PVDF) membrane. Since conducting polypyrrole has excellent anti‐interference ability, protection ability in favor of increasing the amount of the SWNTs on platinum coated PVDF membrane and superior transducing ability, a layer by layer approach of polypyrrole and carbon nanotubes has provided an excellent matrix for the immobilization of enzyme. The layer‐by‐layer assembled SWNTs and PPy‐modified platinum coated PVDF membrane is shown to be an excellent amperometric sensor over a wide range of concentrations of glucose. The glucose oxidase (GOx) was immobilized on layer by layer assembled film by a physical adsorption method by cross linking through Glutaraldehyde. The glucose biosensor exhibited a linear response range from 1 mM to 50 mM of glucose concentration with excellent sensitivity of 7.06 μA/mM.     

Halloysite clay nanotubes and platinum nanoparticles dispersed in ionic liquid applied in the development of a catecholamine biosensor

Halloysite clay nanotubes were used as a support for the immobilization of the enzyme peroxidase from clover sprouts (Trifolium), and employed together with platinum nanoparticles in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (Pt-BMI·PF(6)) in the development of a new biosensor for the determination of catecholamines by square-wave voltammetry. Under optimized conditions, the analytical curves showed detection limits of 0.05, 0.06, 0.07, 0.12 μM for dopamine, isoproterenol, dobutamine and epinephrine, respectively. The biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (18% decrease in response over 150 days). A recovery study of dopamine in pharmaceutical samples gave values from 97.5 to 101.4%. The proposed biosensor was successfully applied to the determination of dopamine in pharmaceutical samples, with a maximum relative error of ±1.0% in relation to the standard (spectrophotometric) method. The good analytical performance of the proposed method can be attributed to the efficient immobilization of the peroxidase in the nanoclay, and the facilitation of electron transfer between the protein and the electrode surface due to the presence of the Pt nanoparticles and ionic liquid.     

Carbon nanotubes/pentacyaneferrate-modified chitosan nanocomposites platforms for reagentless glucose biosensing

The design, characterization and applicability of a nanostructured biosensor platform are described. The biosensor is developed through the immobilization of three components: a polymeric chitosan network previously modified with a redox mediator (denoted as PCF-Pyr-Ch), an enzyme (glucose oxidase, chosen as a model) and carbon nanotubes onto a solid glassy carbon electrode (C). In order to assess the influence of the nanomaterial in the performance of the resulting analytical device, a second biosensor, free of carbon nanotubes, is developed. The characterization of both biosensing platforms was performed in aqueous phosphate buffer solutions using atomic force microscopy technique. In the presence of glucose, both systems exhibit a clear electrocatalytic activity, and glucose could be amperometrically determined at +0.35 V versus Ag/AgCl. The performance of both biosensors was evaluated in terms of sensitivity, detection limit and linear response range. Finally, the enhancement of the analytical response induced by the presence of carbon nanotubes was evaluated.     

Amperometric Glucose Biosensor Based on Glucose Oxidase Encapsulated in Carbon Nanotube–Titania–Nafion Composite Film on Platinized Glassy Carbon Electrode

A highly sensitive and selective glucose biosensor has been developed based on immobilization of glucose oxidase within mesoporous carbon nanotube–titania–Nafion composite film coated on a platinized glassy carbon electrode. Synergistic electrocatalytic activity of carbon nanotubes and electrodeposited platinum nanoparticles on electrode surface resulted in an efficient reduction of hydrogen peroxide, allowing the sensitive and selective quantitation of glucose by the direct reduction of enzymatically‐liberated hydrogen peroxide at ?0.1 V versus Ag/AgCl (3 M NaCl) without a mediator. The present biosensor responded linearly to glucose in the wide concentration range from 5.0×10^?5 to 5.0×10^?3 M with a good sensitivity of 154 mA M^?1cm^?2. Due to the mesoporous nature of CNT–titania–Nafion composite film, the present biosensor exhibited very fast response time within 2 s. In addition, the present biosensor did not show any interference from large excess of ascorbic acid and uric acid.     

Carbon nanotube-enhanced electrochemical DNA biosensor for DNA hybridization detection

A novel and sensitive electrochemical DNA biosensor based on multi-walled carbon nanotubes functionalized with a carboxylic acid group (MWNTs-COOH) for covalent DNA immobilization and enhanced hybridization detection is described. The MWNTs-COOH-modified glassy carbon electrode (GCE) was fabricated and oligonucleotides with the 5'-amino group were covalently bonded to the carboxyl group of carbon nanotubes. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) analysis using an electroactive intercalator daunomycin as an indicator. Compared with previous DNA sensors with oligonucleotides directly incorporated on carbon electrodes, this carbon nanotube-based assay with its large surface area and good charge-transport characteristics dramatically increased DNA attachment quantity and complementary DNA detection sensitivity. This is the first application of carbon nanotubes to the fabrication of an electrochemical DNA biosensor with a favorable performance for the rapid detection of specific hybridization.     

多壁碳纳米管/纳米Ag-TiO_2膜DNA电化学生物传感器

基于多壁碳纳米管/纳米Ag-TiO2复合膜制备了高灵敏度的DNA电化学生物传感器。将Ag-TiO2复合物与适量分散于N,N-二甲基甲酰胺中的多壁碳纳米管(MWNT)相混合,形成均匀稳定的混合溶液,将其滴涂于裸碳糊电极表面,制得MWNT/Ag-TiO2修饰碳糊电极。碳纳米管大的比表面积和良好的电子传递性能与Ag-TiO2纳米复合物良好的生物相容性和对DNA极好的吸附能力的协同作用,显著提高了DNA探针的固载和DNA杂交的检测灵敏度。应用循环伏安法和电化学交流阻抗谱分别对传感膜的制备和DNA的固定与杂交进行了表征。以电化学交流阻抗谱法对转基因植物外源草丁膦乙酰转移酶基因片段进行了检测,线性范围为1.0×10-11～1.0×10-6mol/L,检出限为3.12×10-12mol/L。     

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。     

The Construction of Glucose Biosensor Based on Platinum Nanoclusters—Multiwalled Carbon Nanotubes Nanocomposites

One-step synthesis method was proposed to obtain the nanocomposites of platinum nanoclusters and multiwalled carbon nanotubes (PtNCs–MWNTs), which were used as a novel immobilization matrix for the enzyme to fabricate glucose biosensor. The fabrication process of the biosensor was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscope. Due to the favorable characteristic of PtNCs–MWNTs nanocomposites, the biosensor exhibited good characteristics, such as wide linear range (3.0 μM–12.1 mM), low detection limit (1.0 μM), high sensitivity (12.8 μA mM⁻¹), rapid response time (within 6 s). The apparent Michaelis–Menten constant ( K_m^\textapp K_m^{\text{app}} ) is 2.1 mM. The performance of the resulting biosensor is more prominent than that of most of the reported glucose biosensors. Furthermore, it was demonstrated that this biosensor can be used for the assay of glucose in human serum samples.     

Applications of Carbon Nanotubes in Electrochemical DNA Biosensors

The discovery of carbon nanotubes (CNTs) about a decade ago has brought fascinating evolutions in electronics, material industry, as well as bio-techniques for DNA analysis, gene therapy, drug delivery etc. It has also dramatically promoted the development of DNA biosensing techniques, especially electrochemical DNA biosensor. The application of CNTs in electrochemical DNA biosensors includes two main aspects: on one hand, using CNTs as a novel substrate not only enables immobilization of DNA molecules but also serves as a powerful amplifier to amplify signal transduction event of DNA hybridization. On the other hand, CNTs can also be employed as a powerful carrier to pre-concentrate enzymes or electroactive molecules for electrochemical sensing of DNA hybridization as a novel indicator. In this review, we place emphasis on recent studies of CNTs-based electrochemical DNA biosensors based on these two aspects, with advantages and disadvantages of each aspect introduced herein.     

A Nitrite Biosensor Based on the Direct Electron Transfer of Hemoglobin Immobilized on Carboxyl‐Functionalized Multiwalled Carbon Nanotubes/Polyimide Composite

The high electrically conductive carboxyl‐functionalized multiwalled carbon nanotubes (COOH‐MWCNTs) were used to combine with nonconducting polyimide (PI) to generate a PI/COOH‐MWCNTs membrane. PI served as a matrix to entrap COOH‐MWCNTs and hemoglobin (Hb). COOH‐MWCNTs can improve the conductivity of the composite. The direct electrochemistry measurement indicated that the PI/COOH‐MWCNTs composite enhanced the immobilization of Hb significantly. Besides, the Hb/PI/COOH‐MWCNTs/GCE biosensor possessed excellent electrocatalytic activity for the detection of nitrite. Therefore, PI is a good matrix for Hb immobilization and it has application in sensor construction. This work is promising in the development of sensitive biosensors based on PI/COOH‐MWCNTs composite film.     

Multi-walled Carbon Nanotubes and Gold Nanorod Decorated Biosensor for Detection of microRNA-126

In this article, we introduced a novel electrochemical biosensor for the detection of microRNA-126. The biosensor utilizes a hybridization assay combined with multi-walled carbon nanotubes and gold nanorod-decorated screen-printed carbon electrodes. For electrode preparation, gold nanorods were first immobilized onto the surface of bare and multi-walled carbon nanotube-modified screen-printed carbon electrodes, and the thiol tagged-capture probe was immobilized on the electrode surface through gold and thiol group interaction. After the immobilization, thiol tagged-capture probe hybridized with the target sequence. Under optimum conditions, we determined limit of detection (LOD) and limit of quantification (LOQ) as high as 11 nM and 36 nM, respectively.     

Multi-walled carbon nanotubes for the immobilization of enzyme in glucose biosensors

A novel biosensor, comprised of electrode of gold/multi-walled carbon nanotubes–glucose oxidase (Au/MWNTs–GOD), has been developed. The MWNTs were produced by microwave plasma enhanced chemical vapor deposition. The enzyme of GOD was immobilized using MWNTs. Performance and characteristics of the fabricated glucose biosensor were assessed with respect to response time, detection limit, pH value and storage stability. The results show that the fabricated biosensor is sensitive and stable in detecting glucose, indicating that MWNTs are a good candidate material for the immobilization of enzyme in glucose biosensor construction.     

Electrochemical DNA biosensors based on platinum nanoparticles combined carbon nanotubes

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. 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 of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10⁻¹¹ mol l⁻¹.     

基于铁氰化镍的非标记型核酸适配体电化学传感器检测凝血酶

在玻碳电极（GCE）表面首先用增敏作用的多壁碳纳米管(MWCNTs)夹心于两层电沉积的铁氰化镍（NiHCF）氧化还原电化学探针之间,然后以金纳米粒子为固定核酸适配体的载体,构建了检测凝血酶的非标记型核酸适配体生物传感器。 利用扫描电子显微镜(SEM)对MWCNTs和NiHCF的形貌进行了表征。 利用电化学阻抗谱对传感器的组装过程进行了监测,用循环伏安法（CV）和差分脉冲伏安法（DPV）对传感器的电化学行为进行了研究。 以铁氰化镍为探针的传感器对凝血酶的检测在1.0 ng/L~1.0 mg/L范围内呈良好的线性关系,相关系数为0.998,检测限为0.2 ng/L(S/N=3)。     

Direct Electrochemistry of Hemoglobin Immobilized on Colloidal Gold‐Hydroxyapatite Nanocomposite for Electrocatalytic Detection of Hydrogen Peroxide

A novel nanocomposite of colloidal gold (GNPs) and hydroxyapatite nanotubes (Hap) was prepared for immobilization of a redox protein, hemoglobin (Hb), on glassy carbon electrode. The immobilized Hb showed fast direct electron transfer and excellent electrocatalytic behavior toward reduction of hydrogen peroxide. A synergic effect between GNPs and Hap for accelerating the surface electron transfer of Hb was observed, which led to a pair of redox peaks with a formal potential of (?340±2) mV at pH 7.0, and a new biosensor for hydrogen peroxide with a linear range from 0.5 to 25 μM and a limit of detection of 0.2 μM at 3σ. Owing to the good biocompatibility of the nanocomposite, the biosensor exhibited good stability and acceptable reproducibility. The as‐prepared nanocomposite film provided a good matrix for protein immobilization and biosensor preparation.     

电化学酶传感器在环境污染监测中的应用

电化学酶传感器是一种应用广泛的生物传感器,它将酶及其底物相互作用的特异性与电化学的强大分析功能相结合,已经被广泛应用于药理学、临床、食品、农业以及环境监测中。制备电化学酶传感器的关键步骤是酶的固定化,选择用于制备电化学酶传感器的合适的酶固定化方法,在传感器电子转移动力学、稳定性和重现性等方面起着主要作用。本文在阐述电化学酶传感器工作原理的基础上,简要介绍了用于电化学酶传感器制备过程中的酶固定化方法,重点讨论了电化学酶传感器在监测环境中广泛存在的有机污染物、无机污染物和重金属等方面的应用,并对电化学酶传感器的发展方向进行了展望。     

Electrochemistry and biosensing of glucose oxidase immobilized on Pt-dispersed mesoporous carbon

A method for immobilizing proteins in a carbon mesoporous material (CMM) containing platinum nanoparticles (Pt-NPs) is demonstrated. Compared to pure CMM or carbon nanotubes, CMM containing Pt-NPs enhances the electron transfer and redox properties of redox enzymes, such as glucose oxidase (GOx), due to a cooperative effect of Pt-NPs and CMM. The quasi-reversible electron transfer of GOx in this system is probed, and the apparent heterogeneous electron transfer rate constants are found to be 66% larger than in pure CMM. The GOx/Pt-CMM based glucose biosensor enables the determination of glucose at a potential of 600 mV (vs. SCE). Its detection limit is 10 times lower, and the sensitivity is 16 times higher than that of the respective biosensor without Pt-NPs.     

A Disposable Biosensor for Organophosphorus Nerve Agents Based on Carbon Nanotubes Modified Thick Film Strip Electrode

A disposable biosensor based on acetylcholinesterase‐functionalized acid purified multi‐wall carbon nanotubes (CNTs) modified thick film strip electrode for organophosphorus (OP) insecticides was developed. The degree of inhibition of the enzyme acteylcholinesterase (AChE) by OP compounds was determined by measuring the electrooxidation current of the thiocholine generated by the AChE catalyzed hydrolysis of acteylthiocholine (ATCh). The large surface area and electro‐catalytic activity of carbon nanotubes lowered the overpotential for thiocholine oxidation to 200 mV (vs. Ag/AgCl) without the use of mediating redox species and enzyme immobilization by physical adsorption. The biosensor detected as low as 0.5 nM (0.145 ppb) of the model organophosphate nerve agent paraoxon with good precision, electrode to electrode reproducibility and stability. Analysis of real water sample using the sensor demonstrated the feasibility of the application of the sensor for on site monitoring of OP compounds.     

Novel electrochemical biosensor based on functional composite nanofibers for sensitive detection of p53 tumor suppressor gene

A novel electrochemical biosensor based on functional composite nanofibers for sensitive hybridization detection of p53 tumor suppressor using methylene blue (MB) as an electrochemical indicator is developed. The carboxylated multi-walled carbon nanotubes (MWNTs) doped nylon 6 (PA6) composite nanofibers (MWNTs–PA6) was prepared using electrospinning, which served as the nanosized backbone for pyrrole (Py) electropolymerization. The functional composite nanofibers (MWNTs–PA6–PPy) used as supporting scaffolds for ssDNA immobilization can dramatically increase the amount of DNA attachment and the hybridization sensitivity. The biosensor displayed good sensitivity and specificity. The target wild type p53 sequence (wtp53) can be detected as low as 50 fM and the discrimination is up to 57.5% between the wtp53 and the mutant type p53 sequence (mtp53). It holds promise for the early diagnosis of cancer development and monitoring of patient therapy.     

An amperometric penicillin biosensor with enhanced sensitivity based on co-immobilization of carbon nanotubes, hematein, and β-lactamase on glassy carbon electrode

An amperometric penicillin biosensor with enhanced sensitivity was successfully developed by co-immobilization of multi-walled carbon nanotubes (MWCNTs), hematein, and β-lactamase on glassy carbon electrode using a layer-by-layer assembly technique. Under catalysis of the immobilized enzyme, penicillin was hydrolyzed, decreasing the local pH. The pH change was monitored amperometrically with hematein as a pH-sensitive redox probe. MWCNTs were used as an electron transfer enhancer as well as an efficient immobilization matrix for the sensitivity enhancement. The effects of immobilization procedure, working potential, enzyme quantity, buffer concentration, and sample matrix were investigated. The biosensor offered a minimum detection limit of 50 nM (19 μg L⁻¹) for penicillin V, lower than those of the conventional pH change-based biosensors by more than two orders of magnitude. The electrode-to-electrode variation of the response sensitivity was 7.0% RSD.