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Biosensori in Biochimica Clinica. Determinazione di AST, ALT, salicilato, alanina e glutatione
No full textRecent advances in NADH electrochemical sensing design
No full textNADH electrochemical sensor development has been one of the most studied areas of bioelectroanalysis because of the ubiquity of NAD(P)H based enzymatic reactions in nature. The different solutions proposed are still far from the realisation of the "ideal" NADH sensor and the research area is still challenging. The principles and the recent approaches in NADH electrochemical sensing design are reported in this review. An overview of selected examples and novel sensor materials for the electrocatalysis of NADH is given with emphasis on the appropriate design to obtain improved performances. The literature data taken in consideration has been grouped depending on the strategy used in: surface modified electrodes for NADH sensing, surface redox mediated NADH probes, and bulk modified electrodes for the electrocatalytic oxidation of NADH. A list of already reported dehydrogenase-based biosensors is also given. (C) 2009 Elsevier B.V. All rights reserved.[...
Glucose oxidase/hexokinase electrode for the determination of ATP
No full textA hydrogen peroxide based enzyme electrode for the determination of ATP has been developed by the immobilization of glucose oxidase and hexokinase. Competition between the enzymes for the substrate glucose allowed the measurement of ATP. Different immobilization procedures and different types of hexokinase have been tested. Using a BSA-glutaraldehyde procedure and hexokinase from an overproducing strain of bakers' yeast, ATP was measured in the 0.05-0.5 mmol l(-1) range with a detection limit of 0.01 mmol l(-1). ATP concentrations comparable to those reported in the literature and a good recovery were obtained when the enzyme electrode was used with human erythrocyte hemolysate.[...
NONINVASIVE BIOSENSORS FOR INVIVO AND EXVIVO ANALYSIS
No full textMeasurements of metabolites in media other than blood are becoming increasingly important because of the growing demand for non-invasive analysis, especially for patients who require daily monitoring of such parameters as glycemia and urea and, generally, for people from whom it is difficult to collect blood (including hemophiliacs, neonates and the elderly).[...
Amperometric ammonium ion and urea determination with enzyme-based probes
No full textAmperometric enzyme probes for ammonium and urea have been assembled and evaluated using immobilized glutamate dehydrogenase and urease enzymes coupled with platinum electrodes. Analytical parameters such as pH, buffer, temperature, probe life-time, enzyme immobilization, cofactor concentration and response time have been optimized. Ammonium was detected in the range 10(-5)-3 x 10(-4) mol l(-1). Better reproducibility and stability were achieved using the enzyme GLDH type III and NADH at a concentration of 10(-3) mol l(-1). Urea has been determined in the range 10(-5)-3 x 10(-4) mol l(-1) using the enzyme urease first in solution and then immobilized on nylon net. The analysis was based on an amperometric measurement which gives a linear relationship between current and analyte concentration. This considerably improved the sensitivity of the analysis when compared with the potentiometric-based procedures. Moreover, this method does not suffer from the potassium ion interference which affects the potentiometric nonactin-based NH4+ electrodes. Analysis of ammonium and urea were carried out in standard solutions and in saliva samples. Results compared with a spectrophotometric reference procedure correlated well.[...
ELECTROCHEMICAL SENSORS FOR THE DETERMINATION OF METAL-IONS
No full textAn electrochemical method for the determination of the metal ions Fe3+, Cu2+ and Hg2+ has been developed. It is based on organic chelators changing their electrochemical behaviour as a function of metal ion concentration in solution. Amperometric measurements of the metal ions are performed by cyclic voltammetry using a glassy carbon or a modified carbon paste as working electrodes. Fe3+ is determined in the range 6-60 ppb using two chelators synthesized by the British Technology Group (UK Patent Nos. GB 2118176B and GB 2136807B), Cu2+ is determined in the range 0.35-4 ppm with bis-cyclohexanone oxalyldihydrazone and Hg2+ is determined in the range 20-200 ppm using glyoxal dithiosemicarbazone.[...
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