Enzymatic Biosensors Based on Carbon Nanotubes Paste Electrodes

The performance of enzymatic biosensors based on the immobilization of different enzymes within a carbon nanotubes paste electrode (CNTPE) prepared by dispersion of multi‐wall carbon nanotubes (MWNT) and mineral oil is reported in this work. The strong electrocatalytic activity of carbon nanotubes towards the reduction of hydrogen peroxide and quinones and the oxidation of NADH have allowed an effective low‐potential amperometric determination of lactate, phenols, catechols and ethanol, in connection with the incorporation of lactate oxidase, polyphenol oxidase and alcohol dehydrogenase/NAD⁺, respectively, within the composite matrix. Compared to the analogous enzymatic CPEs, a great enhancement in the response is observed at the enzymatic CNTPEs. Therefore, highly sensitive lactate, phenols, catechols and alcohols biosensors without using any metal or redox mediator can be obtained with this new composite material.     

Amperometric Cholinesterase Biosensors with Carbon Paste Electrodes Modified with Cobalt Phthalocyanine

Biosensors based on a carbon paste electrode with immobilized cholinesterase and cobalt(II) phthalocyanine as a mediator are studied. Electrochemical characteristics of the biosensors are investigated in relation to the carbon paste composition, the enzyme and mediator immobilization procedures, nature of the protective film and procedure of its application, and also storage conditions of the electrodes. A method is suggested for fabricating a cholinesterase biosensor with cobalt(II) phthalocyanine mediator, providing the maximum electrocatalytic response in electrooxidation of butyrylthiocholine iodide (substrate for cholinesterase).     

Carbon nanotubes paste electrode

The performance of carbon nanotubes paste electrodes (CNTPE) prepared by dispersion of multi-wall carbon nanotubes (MWNT) within mineral oil is described. The resulting electrode shows an excellent electrocatalytic activity toward ascorbic acid, uric acid, dopamine, 3,4-dihydroxyphenylacetic acid (dopac) and hydrogen peroxide. These properties permit an important decrease in the overvoltage for the oxidation of ascorbic acid (230 mV), uric acid (160 mV) and hydrogen peroxide (300 mV) as well as a dramatic improvement in the reversibility of the redox behavior of dopamine and dopac, in comparison with the classical carbon (graphite) paste electrodes (CPE). The substantial decrease in the overvoltage of the hydrogen peroxide reduction (400 mV) associated with a successful incorporation of glucose oxidase (GOx) into the composite material, allow the development of a highly selective and sensitive glucose biosensor without using any metal, redox mediator or anti-interference membrane. No interference was observed at −0.100 V even for large excess of ascorbic acid, uric acid and acetaminophen. A linear response up to 30 mM (5.40 g l⁻¹) glucose with a detection limit of 0.6 mM (0.11 g l⁻¹) were obtained with the CNTPE modified with 10% w/w GOx. Such an excellent performance of CNTPE toward hydrogen peroxide, represents a very good alternative for developing other enzymatic biosensors.     

Bismuth-film-plated carbon paste electrodes

In this preliminary note, carbon paste electrodes (CPEs) plated with a bismuth film are presented. The bismuth film can be generated onto the carbon paste surface either from an external plating solution or in situ; the latter being performed in two ways: (i) as a spike of the Bi³⁺ ions to the solution or (ii) via modifying the carbon paste with solid bismuth oxide (5% m/m). As shown on selected examples, bismuth-film-plated CPEs exhibit a good performance in voltammetric stripping analysis of some heavy metals such as Pb, Cd, and Zn.     

Highly Sensitive and Selective Glucose Biosensing at Carbon Paste Electrodes Modified with Electrogenerated Magnetite Nanoparticles and Glucose Oxidase

This work reports the advantages of carbon paste electrodes modified with electrogenerated magnetite nanoparticles. The nanoparticles present catalytic activity towards hydrogen peroxide reduction. The incorporation of glucose oxidase (GOx) and magnetite in a carbon paste matrix have made possible the development of an efficient glucose biosensor. The effect of the amount of GOx and magnetite present in the composite on the response of the biosensor was critically evaluated. The biosensors demonstrated to be highly selective, with negligible interference of ascorbic acid and uric acid. The proposed biosensor was challenged with human blood serum demonstrating an excellent correlation with the spectrophotometric method.     

Three approaches to the development of selective bilayer amperometric biosensors for glucose by in situ electropolymerization

Three different glucose oxidase biosensors for the enzymatic determination of glucose, based on bilayer polymer coatings consisting of polypyrrole (PPy) and poly(o-phenylenediamine), were developed. The electrode substrates are Pt metal, carbon paste and an organic conducting salt (tetrathiafulvalene-tetracyanoquinodimethane), which introduces appreciable variability in the electrode construction process. The three sensors were compared with one another and with bare and PPy monolayer-coated sensors in terms of performance in the determination of glucose in a synthetic serum sample. These configurations provide improved selectivity against the interferences of electroactive species such as ascorbic acid and uric acid, frequently present in biological samples, and the differences between them can be taken advantage of in application to different kinds of samples.     

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.     

Poly(dimethylsiloxane) cross-linked carbon paste electrodes for microfluidic electrochemical sensing

Recently, the development of electrochemical biosensors as part of microfluidic devices has garnered a great deal of attention because of the small instrument size and portability afforded by the integration of electrochemistry in microfluidic systems. Electrode fabrication, however, has proven to be a major obstacle in the field. Here, an alternative method to create integrated, low cost, robust, patternable carbon paste electrodes (CPEs) for microfluidic devices is presented. The new CPEs are composed of graphite powder and a binder consisting of a mixture of poly(dimethylsiloxane) (PDMS) and mineral oil. The electrodes are made by filling channels molded in previously cross-linked PDMS using a method analogous to screen printing. The optimal binder composition was investigated to obtain electrodes that were physically robust and performed well electrochemically. After studying the basic electrochemistry, the PDMS-oil CPEs were modified with multi-walled carbon nanotubes (MWCNT) and cobalt phthalocyanine (CoPC) for the detection of catecholamines and thiols, respectively, to demonstrate the ease of electrode chemical modification. Significant improvement of analyte signal detection was observed from both types of modified CPEs. A nearly 2-fold improvement in the electrochemical signal for 100 μM dithiothreitol (DTT) was observed when using a CoPC modified electrode (4.0 ± 0.2 nA (n = 3) versus 2.5 ± 0.2 nA (n = 3)). The improvement in signal was even more pronounced when looking at catecholamines, namely dopamine, using MWCNT modified CPEs. In this case, an order of magnitude improvement in limit of detection was observed for dopamine when using the MWCNT modified CPEs (50 nM versus 500 nM). CoPC modified CPEs were successfully used to detect thiols in red blood cell lysate while MWCNT modified CPEs were used to monitor temporal changes in catecholamine release from PC12 cells following stimulation with potassium.     

Evaluation of Immobilization Techniques for the Fabrication of Nanomaterial-Based Amperometric Glucose Biosensors

Eleven glucose biosensors were prepared by cross-linking, entrapment, and layer-by-layer assembly to investigate the influence of these immobilization methods on performance. The effects of separate nanozeolites combined with magnetic nanoparticles and multiwalled carbon nanotubes in the enzyme composition on the performance of glucose biosensors were compared. Cyclic voltammetric studies were carried out on the biosensors. Acrylonitrile copolymer/nanozeolite/carbon nanotube and acrylonitrile copolymer/nanozeolite/magnetic nanoparticle electrodes prepared by a cross-linking method showed the highest electroactivity. These results indicated that a synergistic effect occurred when multiwalled carbon nanotubes, magnetic nanoparticles, and nanozeolites were combined that greatly improved the electron transfer ability of the sensors. Amperometric measurements by the glucose oxidase electrodes were obtained that showed that the acrylonitrile copolymer/nanozeolite/carbon nanotube electrode was the most sensitive (10.959 microamperes per millimolar). The lowest detection limit for this biosensor was 0.02 millimolar glucose, with a linear dynamic range up to 3 millimolar. The response after thirty days was 81 percent of the initial current.     

Design of carbon paste biosensors based on the mixture of ionic liquid and paraffin oil as a binder for high performance and stabilization

This paper reports on the preparation and advantages of novel amperometric biosensors in the presence of hydrophobic ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]). Carbon paste biosensors have been constructed by entrapping heme proteins in carbon + IL mixed with paraffin oil as a binder. The most suitable paste composite was determined according to the catalytic activity of the biosensors to H₂O₂. The simplified preparations of the biosensors display advantages of a high sensitivity, a wide linear range, and a good activity toward H₂O₂. The IL-contained paste enhances high stability (thermal, pH, and operational) onto the immobilized heme proteins. Moreover, the biosensors could still maintain their good activity and the sensitivity after 3-month storage when keeping in the dry state in a refrigerator at 4 °C. The resulting biosensors are suitable for the precise determination of H₂O₂ in actual environment.     

A Novel Molecularly Imprinted Potentiometric Sensor for the Fast Determination of Bisoprolol Fumarate in Biological Samples

In this study, molecularly imprinted polymer (MIP) was prepared and used in the preparation of carbon paste electrode (CPE) for the quantification of bisoprolol fumarate (BF) in pure, pharmaceutical formulation and biological fluids. The selective MIP for BF was synthesized from methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker in dimethyl sulfoxide solution, BF as the template molecule and 2, 2-azobisisobutyronitrile (AIBN) as the initiator. The non-imprinted polymer (NIP) was synthesized by the same procedure, but in the absence of the template molecule then incorporated in the paste of the carbon paste electrodes (CPEs). The prepared MIP for BF and its corresponding NIP were well characterized using scanning electron microscopy (SEM), Fourier transform infrared spectrometer, and thermal gravimetric analysis (TGA). The MIP and NIP based CPEs were further used for the determination of BF and the obtained results indicated that the sensor modified by the MIP have much higher recognition power for the BF molecules than the NIP based sensor where the MIP based CPE exhibited a Nernstian response 29.50±0.55 mV decade⁻¹ within a concentration range of 1.0×10⁻⁷–1.0×10⁻² mol L⁻¹and pH independence in the range 3.50–7.15. The proposed sensor has high selectivity over several possible interfering compounds. The obtained results by the proposed sensor were satisfactory with excellent percentage recovery and relative standard deviation and were comparable with those obtained from HPLC reported method.     

Polypyrrole composites with carbon materials for supercapacitors

Supercapacitors fill the gap between batteries and conventional solid state and electrolytic capacitors. Polypyrrole (PPy) is a very important electrode material for supercapacitors. However, the repeated volume changes usually damage PPy structure and result in PPy poor stability during a long-term charging/discharging process. PPy/carbon material composites were prepared to overcome the defects of pure PPy electrodes, and significant enhancement for the specific capacitance, charging/discharging rate and electrodes stability was demonstrated thereafter. The development of composite electrodes based on PPy and carbon materials is reviewed in this paper.     

New CNT/poly(brilliant green) and CNT/poly(3,4-ethylenedioxythiophene) based electrochemical enzyme biosensors

A combination of the electroactive polymer poly(brilliant green) (PBG) or conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) with carbon nanotubes to obtain CNT/PBG and CNT/PEDOT modified carbon film electrodes (CFE) has been investigated as a new biosensor platform, incorporating the enzymes glucose oxidase (GOx) as test enzyme, alcohol oxidase (AlcOx) or alcohol dehydrogenase (AlcDH). The sensing parameters were optimized for all biosensors based on CNT/PBG/CFE, CNT/PEDOT/CFE platforms. Under optimized conditions, both GOx biosensors exhibited very similar sensitivities, while in the case of AlcOx and AlcDH biosensors, AlcOx/CNT/PBG/CFE was found to give a higher sensitivity and lower detection limit. The influence of dissolved O₂ on oxidase-biosensor performance was investigated and was shown to be different for each enzyme. Comparisons were made with similar reported biosensors, showing the advantages of the new biosensors, and excellent selectivity against potential interferents was successfully demonstrated. Finally, alcohol biosensors were successfully used for the determination of ethanol in alcoholic beverages.     

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.     

Electrocatalytic Activity of Bamboo‐Structured Carbon Nanotubes Paste Electrode Toward Hydrogen Peroxide

Abstract

In this report, we describe the finding that bamboo‐structured carbon nanotubes (CNT) showed superior electrocatalytic activity toward hydrogen peroxide. The slope of the calibration curve for hydrogen peroxide obtained with the bamboo‐structured CNT paste electrode was more than 20 times as large as the slopes obtained with hollow‐structured CNT paste and glassy carbon electrodes at an operating potential of ?0.1 V, with no interfering reactions. Incorporation of glucose oxidase within the bamboo‐structured CNT paste electrode allows the selective detection of glucose in the presence of common interferents without using any permselective membranes. This excellent ability of the bamboo‐structured CNT paste electrode toward hydrogen peroxide is applicable to the development of other enzymatic biosensors.     

A simple and sensitive portable system for a rapid evaluation of bisphenol A contamination in potable and environmental waters using a mesoporous silica-modified carbon paste electrode

In this work, two ordered mesoporous silicas (HMS and SBA-15) were prepared and incorporated into carbon paste electrodes (CPEs) to obtain mesostructured sensors for a rapid determination of bisphenol A (BPA) in waters by voltammetric techniques. The materials were characterised by nitrogen adsorption-desorption measurements, transmission electron microscopy and scanning electron microscopy. The electrochemical properties of the modified carbon paste electrodes were studied by differential pulse voltammetry (DPV) and cyclic voltammetry (CV). Results showed that the sensor modified with HMS (HMS-CPE) exhibited strong adsorption activity toward the oxidation of BPA, with a well-defined voltammetric peak at +0.6 V. Moreover, the HMS-CPE exhibited a wider linearity range, from 0.44 to 3.5 μM BPA, with a detection limit of 61 nM (S/N = 3) and good reproducibility by DPV. The enhanced performance of the HMS-CPE could be attributed to its high surface area, with a 3 D wormhole-like channel structure that favoured an excellent accessibility, high adsorption capacity and faster adsorption rate of BPA. This novel sensor was coupled to a portable system and successfully applied for a rapid determination of BPA in tap, mineral, well and river water samples with good recovery, ranging from 98 ± 12 to 103 ± 7%.     

Electron-transfer properties of different carbon nanotube materials,and their use in glucose biosensors

Different types of carbon nanotube material (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) of different internal diameter) have been used for preparation of CNT-modified glassy-carbon electrodes. Redox reactions involving ferricyanide and hydrogen peroxide were examined at the CNT-modified electrodes. Electrodes modified with SWCNTs usually had better electron-transfer properties than MWCNT-modified electrodes. Glucose biosensors were also prepared with electropolymerized polyphenylenediamine films, CNT materials, and glucose oxidase. Amperometric behavior in glucose determination was examined. SWCNT-modified glucose biosensors usually had a wider dynamic range (from 0.1 to 5.5 mmol L⁻¹) and greater sensitivity in glucose determination. The detection limit was estimated to be 0.05 mmol L⁻¹.     

Characterization and Potential Applications of Immobilized Glucose Oxidase and Polyphenol Oxidase

Pyrrole functionalized polystyrene (PStPy) was copolymerized with pyrrole to obtain a conducting copolymer, P(PStPy‐co‐Py) which is used as the immobilization matrix. Glucose oxidase and polyphenol oxidase enzymes were immobilized via the entrapment method by electrochemical polymerization. Enzyme electrodes were prepared by electrolysis at a constant potential using sodium dodecyl sulfate (SDS) as the supporting electrolyte during the copolymerization of PStPy with pyrrole. Maximum reaction rates (V_max) and enzyme affinities (Michaelis‐Menten constants, K_m) were determined for the enzyme entrapped both in polypyrrole (PPy) and P(PStPy‐co‐Py) matrices. Optimizations of enzyme electrodes were done by examining the effects of temperature and pH on enzymes' activities along with the shelf life and operational stability investigations. Glucose oxidase enzyme electrodes were used for human serum analysis and glucose determination in two brands of orange juices. Polyphenol oxidase enzyme electrodes were used for the determination of phenolics in red wines of Turkey.     

Layer-by-layer electrodeposition of redox polymers and enzymes on screen-printed carbon electrodes for the preparation of reagentless biosensors

Layer-by-layer electrodeposition of redox polymer/enzyme composition films on screen-printed carbon electrodes for fabrication of reagentless enzyme biosensors has been proposed and the resulting films were found to be very stable and rigid.     

Glucose biosensors based on the immobilization of copper oxide and glucose oxidase within a carbon paste matrix

The performance of amperometric glucose biosensors based on the dispersion of glucose oxidase (GOx) and copper oxide within a classical carbon (graphite) paste composite is reported in this work. Copper oxide promotes an excellent electrocatalytic activity towards the oxidation and reduction of hydrogen peroxide, allowing a large decrease in the oxidation and reduction overpotentials, as well as an important enhancement of the corresponding currents. Therefore, it is possible to perform the glucose biosensing at low potentials where there is no interference even in large excess of ascorbic acid, uric acid or acetaminophen. The influence of the copper oxide and glucose oxidase content in the paste on the analytical performance of the bioelectrode is discussed. The resulting biosensor shows a fast response, a linear relationship between current and glucose concentration up to 1.35 × 10⁻² M (2.43 g L⁻¹) and a detection limit of 2.0 × 10⁻⁵ M. The effect of the presence of the enzyme in the composite material on the dispersion of the copper oxide particles is also discussed.