102,348 research outputs found
3,3′,5,5′-Tetramethylbenzidine as electrochemical substrate for horseradish peroxidase based enzyme immunoassays. A comparative study
No full textThe use of 3,3′,5,5′-tetramethylbenzidine (TMB) as an electrochemical substrate for horseradish peroxidase (HRP) was investigated. HRP activity has been detected using flow injection analysis at a glassy carbon working electrode polarised at +100 mV versus Ag/AgCl in 0.1 mol l-1 citrate-phosphate buffer (pH 5.0). The optimum concentrations were 2 × 10-4 mol l-1 TMB and 10-3 mol l-1 H2O2. The detection limit obtained after 15 min of incubation was 8.5 × 10-14 mol l-1 HRP with the amperometric method. This limit was lower than that obtained using hydroquinone as HRP substrate and comparable to that with the p-aminophenyl phosphate-alkaline phosphatase system. Better performance was achieved with amperometric than spectrophotometric detection using TMB in a competitive ELISA for rabbit immunoglobulin G as a model analyte
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).[...
FLOW-THROUGH ANALYSIS OF GLUTATHIONE IN HUMAN ERYTHROCYTES WITH AN AMPEROMETRIC BIOSENSOR
No full textA flow-through system for the determination of glutathione was developed using the enzyme glutathione oxidase covalently immobilized on an Immobilon AV membrane assembled on a Clark type oxygen electrode. A calibration curve for glutathione, was obtained in the range 10(-5) - 10(-3) mol/L with a detection limit of 5 . 10(-6) mol/L and a relative standard deviation of 4.5%.[...
Electrochemical probe for polyamines detection in biological fluids
No full textThe enzyme polyamine oxidase from maize has been purified and covalently immobilized onto polymeric supports to assemble a polyamine electrochemical biosensor. The enzyme has been used in conjunction with either an O-2 or a H2O2 electrode. The analytical behaviour of this enzyme electrode has been studied with respect to sensitivity, selectivity, optimum pH and buffer, response time and lifetime. Recovery studies performed on urine samples demonstrated that the polyamine biosensor developed can be successfully used to measure polyamines in biological fluids.[...
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.[...
Rapid amperometric determination of magnesium(II) ions
No full textAn amperometric procedure for the measurement of magnesium(II) has been developed using the enzyme hexokinase in solution and glucose oxidase immobilized onto a preactivated polymeric support. The reaction of hexokinase was monitored following the decrease in current due to the glucose consumption by the enzyme in the presence of the ATP-Mg2+ complex. The reaction rate was dependent on the concentration of magnesium(II) in solution. Concentrations of hexokinase and ATP were optimised. Measuring the current change in the 1-3 min interval after the start of the reaction magnesium(II) can be determined in the 4 x 10(-5) to 10(-3) M range. Other divalent cations tested showed no interference. The magnesium(II) content of 5 pharmaceutical products was measured with the amperometric and compared to a spectrophotometric procedure. The results correlated well.[...
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