ABSTRACT
The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.
Subject(s)
Biosensing Techniques/methods , Electrochemical Techniques/methods , Nanotubes, Carbon/chemistry , Phenazines/chemistry , Polymers/chemistry , Trityl Compounds/chemistry , Biosensing Techniques/instrumentation , Catalysis , Electric Conductivity , Electrochemical Techniques/instrumentation , Electrodes , Molecular Structure , Oxidation-ReductionABSTRACT
Poly(brilliant green) (PBG) and poly(thionine) (PTH) films have been formed on carbon film electrodes (CFEs) modified with carbon nanotubes (CNT) by electropolymerisation using potential cycling. Voltammetric and electrochemical impedance characterisation were performed. Glucose oxidase and uricase, as model enzymes, were immobilised on top of PBG/CNT/CFE and PTH/CNT/CFE for glucose and uric acid (UA) biosensing. Amperometric determination of glucose and UA was carried out in phosphate buffer pH 7.0 at -0.20 and +0.30 V vs. SCE, respectively, and the results were compared with other similarly modified electrodes existing in the literature. An interference study and recovery measurements in natural samples were successfully performed, indicating these architectures to be good and promising biosensor platforms.
Subject(s)
Biosensing Techniques , Electrodes , Glucose/analysis , Nanotubes, Carbon/chemistry , Phenothiazines/chemistry , Quaternary Ammonium Compounds/chemistry , Uric Acid/analysis , Coloring Agents/chemistry , Electrochemistry , Enzymes, Immobilized/chemistry , Enzymes, Immobilized/metabolism , Glucose/chemistry , Glucose Oxidase/chemistry , Glucose Oxidase/metabolism , Uric Acid/chemistryABSTRACT
A new type of modified electrode sensor for ascorbic acid has been prepared by deposition of multi-walled carbon nanotubes (MWCNT) and poly(Nile blue A) on the surface of glassy carbon electrodes. Nile blue A was electropolymerised either beneath (directly on glassy carbon) or onto the MWCNT layer by potential cycling in phosphate buffer solution at pH 6.0. Characterisation of the modified electrodes was carried out by cyclic voltammetry and electrochemical impedance spectroscopy. Quantitative determination of ascorbate was achieved by cyclic voltammetry and fixed potential amperometry in phosphate buffer solution at pH 5.3. The modified electrodes exhibited good sensitivity, wide linear range, a detection limit of 1.6 µM and good stability, showing that they can be used as sensors for ascorbic acid. There is no interference from compounds commonly found in clinical and pharmaceutical samples and the determination of ascorbic acid in commercial tablet samples was successfully performed.
Subject(s)
Ascorbic Acid/analysis , Dielectric Spectroscopy/methods , Electrochemical Techniques/methods , Nanotubes, Carbon/chemistry , Oxazines/chemistry , Ascorbic Acid/chemistry , Calibration , Dielectric Spectroscopy/instrumentation , Electrochemical Techniques/instrumentation , Electrodes , Hydrogen-Ion Concentration , Polymers/chemistry , Reproducibility of Results , Surface Properties , Tablets/analysis , Tablets/chemistryABSTRACT
A new and simple-to-prepare hypoxanthine biosensor has been developed using xanthine oxidase (XOD) immobilised on carbon electrode surfaces. XOD was immobilised by glutaraldehyde cross-linking on carbon film (CF) electrodes and on carbon nanotube (CNT) modified CF (CNT/CF). A comparison of the performance of the two configurations was carried out by the current response using amperometry at fixed potential; the best characteristics being exhibited by XOD/CNT/CF modified electrodes. The effects of electrolyte pH and applied potential were evaluated, and a proposal is made for the enzyme mechanism of action involving competition between regeneration of flavin adenine dinucleotide and reduction of hydrogen peroxide. Under optimised conditions, the determination of hypoxanthine was carried out at -0.2 V vs. a saturated calomel electrode (SCE) with a detection limit of 0.75 µM on electrodes with CNT and at -0.3 V vs. SCE with a detection limit of 0.77 µM on electrodes without CNT. The applicability of the biosensor was verified by performing an interference study, reproducibility and stability were investigated, and hypoxanthine was successfully determined in sardine and shrimp samples.
Subject(s)
Biosensing Techniques/instrumentation , Cultured Milk Products/enzymology , Enzymes, Immobilized/chemistry , Hypoxanthine/analysis , Nanotubes, Carbon/chemistry , Xanthine Oxidase/chemistry , Carbon/chemistry , Electrodes , Limit of Detection , Models, MolecularABSTRACT
Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H(2)O(2), the product of the oxidase enzymatic reaction, at 0.0 V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1 microM and an apparent Michaelis-Menten constant of 0.20mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples.
