Determination of caffeic acid in wine using PEDOT film modified electrode.

A novel method using PEDOT (poly(3,4-ethylenedioxy) thiophene) modified electrode was developed for the determination of caffeic acid (CA) in wine. Cyclic voltammetry (CV) with the additions standard method was used to quantify the analyte at PEDOT modified electrodes. PEDOT films were electrodeposited on Platinum electrode (Pt) in aqueous medium by galvanostatic method using sodium poly(styrene-4-sulfonate) (PSS) as electrolyte and surfactant. CV allows detecting the analyte over a wide concentration range (10.0nmoll(-1)-6.5mmoll(-1)). The electrochemical method proposed showed good statistical and analytical parameters as linearity range, LOD, LOQ and sensitivity.

Pt based enzyme electrode probes assembled with Prussian Blue and conducting polymer nanostructures.

Conductive polymer nanotubules of 1,2-diaminobenzene (1,2-DAB) were prepared using a porous polycarbonate membrane template, placed on a Pt foil and used to support the polymer, then, the electropolymerisation was performed by chronocoulometry. The obtained conductive polymer nanostructures were then placed on Pt electrode and used to support highly dispersed prussian blue (PB), which acts as the active component for H2O2 detection. The observed good stability of PB as catalyst of H2O2 was related to the presence of organic non-conventional conducting polymers in a composite nanostructured film. These nanostructured polymer/PB composite films were also characterised by scanning electron microscopy (SEM) and Raman spectroscopy. The non-conventional conducting polymer nanotubules/PB modified Pt electrodes were tested by cyclic voltammeter for stability at different pH values, then, by amperometry, for hydrogen peroxide, ascorbic acid, acetaminophen, uric acid and acetylcholine. Glucose oxidase (GOD), lactate oxidase (LOD), L-amino acid oxidase (L-AAOD), alcohol oxidase (AOD), glycerol-3-phosphate oxidase (GPO), lysine oxidase (LyOx), and choline oxidase (ChOx) were immobilised on PB layer supported on 1,2-diaminobenzene (1,2-DAB) nanotubules onto the Pt electrodes. Different strategies for enzyme immobilisation were performed and used. Analytical parameters such as reproducibility, interference rejection, response time, storage and operational stability of the sensors have been studied and optimised. Results provide a guide to design high sensitive, stable and interference-free biosensors. The glucose biosensors assembled with nanostructured poly(1,2-DAB) showed a detection limit of 5 x 10(-5) mol l(-1), a wide linearity range (5 x 10(-5) to 5 x 10(-3) mol l(-1)), a high selectivity, a stability of 3 months at 4 degrees C, and at least 4 weeks at room temperature. Similar analytical parameters and stability were also studied for L-(+)-lactic acid, L-leucine, ethanol, glycerol-3-phosphate, lysine, and choline biosensors.

Chemical reversibility and stable low-potential NADH detection with nonconventional conducting polymer nanotubule modified glassy carbon electrodes.

Studies of the oxidation of beta-nicotinamide adenine dinucleotide (NADH) at glassy carbon (GCEs) electrode surfaces, modified with nonconventional conducting polymer nanotubules, are reported. In contrast to the situation with conventional carbon electrodes, chemical reversibility of the NADH oxidation reaction was achieved by means of poly(1,2-diaminobenzene) conducting nanotubule coatings. A Delta E(p) of 425 mV (vs Ag/AgCl; pH 7.0) was observed. The NADH amperometric response of the conducting nanotubule modified GCEs was shown to be extremely stable, with 98% of the initial response remaining after 48 h of stirring in the presence of 1 x 10(-4) M NADH solutions (compared to 14% at the poly(1,2-diaminobenzene) modified GCEs). The nonconventional conducting polymer nanotubule-coated electrodes, when tested in amperometric mode for NADH electrochemical oxidation at an applied potential of 450 mV, showed a sensitivity of 99 nA/mM, an operational stability for 2 days, a storage stability of 2 weeks at 4 degrees C, a linearity from 5 x 10(-5) to 1 x 10(-3) M, and good NADH chemical reversibility, all of which make them useful tools for dehydrogenase enzyme probe assembly.

A new interference-free lysine biosensor using a non-conducting polymer film.

An electrochemical biosensor for the determination of lysine to be used for rapid evaluation of food quality has been developed. Platinum electrodes have been coated by electropolymerisation with 1,2-diaminobenzene (1.2-DAB) using cyclic voltammetry. The reduction in the oxidation of interferents compared with the bare platinum electrode was 100% for ascorbic acid, 99% for acetaminophen and 99% for cysteine. The enzyme L-lysine-alpha-oxidase was then immobilised onto the polymer layer by passive adsorption and a calibration curve for lysine constructed. This gave a linear range of 1 x 10(-5) mol/l to 1 x 10(-3) mol/l and a limit of detection of 2 x 10(-7) mol/l.

Assembling and evaluation of new dehydrogenase enzyme electrode probes obtained by electropolymerization of aminobenzine isomers and PQQ on gold, platinum and carbon electrodes.

Pt, Au and graphite electrodes have been coated by electropolymerization of 1,2-, 1,3-, 1,4-diaminobenzene (DAB) and 4-aminobiphenyl in the presence of PQQ using cyclic voltammetry. The activity of the modified electrodes for the oxidation of paracetamol, ascorbic and uric acid was reduced by approximately 90% as compared to the bare electrodes. Polymerization in the presence 4,5-dihydro-4,5-dioxo-1H-pyrrolo(2,3-f)quinoline-2,7,9-tricarboxilic+ ++ acid, pyrroloquinolinequinone (PQQ) led, after optimization, to electrodes capable of catalysing the electrooxidation of beta-nicotinamide adenine dinucleotide, reduced form (NADH), in the range 10(-4)-10(-2) mol/l with a detection limit of 5 x 10(-5) mol/l. Amperometric measurements of NADH have been carried out at +0.2 V and the efficiency of different electrodes based on different materials has been studied. By co-entrapment of dehydrogenase highly selective enzymes, electrodes for glucose, L-lactate and L-glutamate were obtained. Dehydrogenase substrates such as glucose, lactate and glutamate were measured in the range 5 x 10(-5)-1 x 10(-2) mol/l, with detection limits of 10(-5) and 5 x 10(-6) mol/l, respectively. Probe stability under non-dynamic conditions was evaluated over 2 months. All the probes showed a decrease of 10% over 1 month and a residual activity of 50% over 2 months.

Enzyme electrode probes obtained by electropolymerization of monomers with PMS and selected dehydrogenase enzymes.

5-methylphenazonium methylsulphate, (commonly named phenazine methosulphate, PMS) mediated electroxidation of beta-nicotinamide adenine dinucleotide (phosphate), reduced form, (NAD(P)h), on platinum, gold and carbon electrodes has been studied by electropolymerization of 1,2-, 1,3-, 1,4-diaminobenzene (DAB), pyrrole-2-carboxylic acid (PY-2-COOH) and 4,4'-dihydroxybenzophenone (DHB) in presence of PMS using cyclic voltammetry. The electroxidation of ascorbic acid has been evaluated on the electrodes electropolymerized in absence and in presence of PMS. The same experiments have been carried out with NAD(P)H in solution. Results showed that the NAD(P)H is oxidised by PMS coimmobilized with the polymer film on the electrode surface. NAD(P)H has been measured in the range 10(-6)-10(-2)mol l(-1) with a detection limit of 5 x 10(-7) mol 1(-1). Amperometric measurements of NAD(P)H have been carried out at -0.10 V and the efficiency of different elecrodes based on different materials has been studied. The electropolymerization has been also carried out in presence of PMS and selected dehydrogenase enzymes. The activity of these enzymes has been tested amperometrically at -0.1 V. Enzyme substrates such as glucose, lactate and glutamate have been measured in the range 5 x 10(-6)-1 x 10(-2) mol 1(-1) with a detection limit 1 x 10(-6) mol 1(-1). Also the stability of these probes during time has been evaluated.