1,720,990 research outputs found
Assay of phospholipase D activity by an amperometric choline oxidase biosensor
Full text linkA novel electrochemical method to assay phospholipase D (PLD) activity is proposed based on the employment of a choline biosensor realized by immobilizing choline oxidase through co‐crosslinking on an overoxidized polypyrrole film previously deposited on a platinum electrode. To perform the assay, an aliquot of a PLD standard solution is typically added to borate buffer containing phosphatidylcholine at a certain concentration and the oxidation current of hydrogen peroxide is then measured at the rotating modified electrode by applying a detection potential of + 0.7 V vs. SCE. Various experimental parameters influencing the assay were studied and optimized. The employment of 0.75% (v/v) Triton X‐100, 0.2 mM calcium chloride, 5 mM phosphatidylcholine, and borate buffer at pH 8.0, ionic strength (I) 0.05 M allowed to achieve considerable current responses. In order to assure a controlled mass transport and, at the same time, high sensitivity, an electrode rotation rate of 200 rpm was selected. The proposed method showed a sensitivity of 24 (nA/s).(IU/mL)−1, a wide linear range up to 0.33 IU/mL, fast response time and appreciable long-term stability. The limit of detection, evaluated from the linear calibration curve, was 0.005 IU/mL (S/N = 3). Finally, due to the presence of overoxidized polypyrrole film characterized by notable rejection properties towards electroactive compounds, a practical application to real sample analysis can be envisaged
Sensitive Quantification of Iodide by Ion-Exchange Chromatography with Electrochemical Detection at a Modified Platinum Electrode
No full textA rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a. owing solution 300 mg/ L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. < 6%). Using a mixture of 25 mM HNO3 and 50 mM NaNO3 as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 mu g/L (S/N= 3) with an injection volume of 50 mu L. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels
Permselective and enzyme-entrapping behaviours of an electropolymerized, non-conducting, poly(o-aminophenol) thin film-modified electrode: A critical study
No full textNon-conducting polymeric films synthesised by the electrooxidation of o-aminophenol on a platinum
electrode in acetate or phosphate buffer displayed an interesting permselective behaviour, which proved
valuable in minimising the electrochemical interferences from ascorbate, acetaminophen, cysteine and
urate sample molecules in amperometric detection mode. The electrosynthesis of poly(o-aminophenol)
(p(oAP)) film showed also useful as permselectivemembrane for enzyme immobilization as demonstrated
by the production of an interference-free glucose oxidase biosensor. In this respect, the glucose response
time, t0.95, evaluated in batch addition experiments, was lower than 5 s while the calibration curve was
linear up to 10mM of glucose with a sensitivity of 69.7 nA/mM. Both the permselective behaviour and
the enzyme-entrapping property of the film were critically compared with the relevant studies until
now reported. With respect to the sophisticated but complex approaches described elsewhere, this study
shows that simply a proper optimization of p(oAP) electrosynthesis and its permselective behaviour is
the key to improve significantly the selectivity of the resulting analytical devices
The kinetic and analytical behaviours of an l-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by co-crosslinking
No full textAn improved L-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by glutaraldehyde co-crosslinking with bovine serum albumin is described. A thoroughly optimization of the enzyme immobilization procedure permitted the fabrication of a fast-response biosensor with high sensitivity and improved stability. Moreover, the relevant electrochemical study showed the possibility to tune the overall kinetic control of biosensor from merely diffusive to enzymatic or mixed by switching the pH from weakly alkaline to weakly acid values, respectively, as well as by controlling its hydrodynamic behaviour. The response time, t(0.95), evaluated in batch addition experiments, was lower than 6 s. Linear lysine responses up to 0.6 M were observed with a sensitivity of 4.4 mu A mM(-1), while detection limit at S/N = 3 was 1 mu M. The sensor has been tested for lysine determination of a pharmaceutical sample obtaining a good agreement with the expected values
Pulsed electrochemical detection of orotic acid by an activated potential waveform at a gold working electrode following anion-exchange chromatography
No full textAn improved L-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by glutaraldehyde co-crosslinking with bovine serum albumin is described. A thoroughly optimization of the enzyme immobilization procedure permitted the fabrication of a fast-response biosensor with high sensitivity and improved stability. Moreover, the relevant electrochemical study showed the possibility to tune the overall kinetic control of biosensor from merely diffusive to enzymatic or mixed by switching the pH from weakly alkaline to weakly acid values, respectively, as well as by controlling its hydrodynamic behaviour. The response time, t(0.95), evaluated in batch addition experiments, was lower than 6 s. Linear lysine responses up to 0.6 M were observed with a sensitivity of 4.4 mu A mM(-1), while detection limit at S/N = 3 was 1 mu M. The sensor has been tested for lysine determination of a pharmaceutical sample obtaining a good agreement with the expected values
Electrosynthesized poly(o-aminophenol) films as biomimetic coatings for dopamine detection on Pt substrates
Full text linkDopamine (DA) is a neurotransmitter, and its levels in the human body are associated with serious diseases. The need for a suitable detection method in medical practice has encouraged the development of electrochemical sensors that take advantage of DA electroactivity. Molecularly imprinted polymers (MIPs) are biomimetic materials able to selectively recognize target analytes. A novel MIP sensor for DA is proposed here based on a thin film of poly(o-aminophenol) electrosynthesized on bare Pt. A fast and easy method for executing the procedure for MIP deposition has been developed based on mild experimental conditions that are able to prevent electrode fouling from DA oxidation products. The MIP exhibited a limit of detection of 0.65 μM, and appreciable reproducibility and stability. The high recognition capability of poly(o-aminophenol) towards DA allowed for the achievement of notable selectivity: ascorbic acid, uric acid, serotonin, and tyramine did not interfere with DA detection, even at higher concentrations. The proposed sensor was successfully applied for DA detection in urine samples, showing good recovery
Permselective Behaviour of an Electrosynthesized, Nonconducting Thin Film of poly(2-Naphthol) and Its Application to Enzyme Immobilization
No full textDetection of choline in biological fluids from patients on haemodialysis by an amperometric biosensor based on a novel anti-interference bilayer
No full textA new and highly selective amperometric biosensor able to analyse choline in clinical samples from patients suffering from renal diseases and receiving repetitive haemodialysis treatment is described. The proposed biosensor is based on choline oxidase immobilized by co-crosslinking onto a novel anti-fouling and anti-interferent membrane. Between the several polymeric films electrosynthesized on a Pt electrode whose permselective behaviours were here investigated, those based on overoxidized polypyrrole/poly(o-aminophenol) bilayer revealed the most effective in rejecting common interferents usually present in biological fluids. The so realized biosensor showed notably analytical performances, displaying linear choline responses up to 100 μM, a sensitivity of 156 nA mM−1 mm−2 and a limit of detection, calculated at a signal-to-noise ratio equal to 3, of 1 μM; further, the within-a-day coefficients of variation for replicate (n = 3) were 2.7% and 1.2% at 100 μM and 10 μM choline levels, respectively. The remarkable performances and anti-interference behaviour allowed us the use of the proposed biosensor for the selective and fouling-free detection of choline in dialysate coming from patients on haemodialysis and even in their unpretreated human sera. Preliminary results gave choline levels in good agreement with the expected values
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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