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[Optimal conditions for the functioning of a urease-based biosensor and pH-sensitive field transistors. Determination of urea in solution].

The article deals with the optimal conditions of urea determination in solution by the enzyme sensor based on pH-sensitive field effect transistor. The dependence of response level on temperature, pH, ionic strength, buffer capacity were investigated. 10 mM phosphate buffer, pH 7.4 containing 200 mM NaCl is optimal for possible measurements of urea in diluted blood. Temperature change in the measured samples from 15 degrees to 30 degrees C does not affect the sensor signal value. Stability of immobilized ureas was investigated at storage under different conditions. In the presence of 1 mM EDTA activity of immobilized enzyme does not change during one month storage at 4 degrees C.

Biosensing Techniques↗
PubMed2001

New immunoassay for the detection of Helicobacter pylori infection compared with urease test, 13C breath test and histology: validation in the primary care setting.

Helicobacter pylori plays a major role in peptic ulcer disease and, as a result, testing for H. pylori infection among patients with dyspepsia has often been advocated. The aim of the study was to determine the diagnostic accuracy, the analytical performance, and optimal cut-off point of a new serological assay, the Pyloriset EIA-G III for the detection of H. pylori infection in the primary care setting. For 113 primary care patients with dyspepsia urea breath test, CLO test, histology and serology tests were performed. Diagnostic accuracy of the Pyloriset EIA-G III was evaluated against a reference standard of a carbon urea breath test (CUBT), CLO test and histology (from gastric biopsies). Precision, linearity and correlation of the serological assay with the CUBT and former Pyloriset were also determined. At the optimal cut-off level of 40 U/ml, the positive predictive value was 92.1%, negative predictive value 96.3%, sensitivity 87.5%, and specificity 93.9%. The within-run precision was high. The recovery data were good. The correlation of both CUBT and the former Pyloriset EIA-G and the Pyloriset EIA-G III was high. At the cut-off level of 40 U/ml, the new Pyloriset EIA-G III is a reliable method to detect H. pylori infection in the primary care setting.

Adult↗
PubMed2002

Amperometric urea biosensor based on urease and electropolymerized toluidine blue dye as a pH-sensitive redox probe.

The electropolymerized toluidine blue film deposited on the glassy carbon electrode show amperometrically detectable pH sensitivity. This feature of polytoluidine blue (PTOB) film was used for a construction of an amperometric urea biosensor. We have observed a linear shift of the formal redox potential with increasing pH value between 4 and 8 giving the slope of 81 mV(Delta) pH(-1). Polytoluidine blue film has had a significantly increased stability and higher electrochemical activity compared to the adsorbed monomeric dye. The polytoluidine blue urea biosensor has been operating at a working potential of -200 mV vs. SCE. The sensitivity of the biosensor was 980 nA mM(-1) cm(-2). The biosensor showed linearity in concentration range up to 0.8 mM with the detection limit of 0.02 mM (S/N=3).

Biosensing Techniques↗
PubMed2002

Diagnosis and monitoring of inborn errors of metabolism using urease-pretreatment of urine, isotope dilution, and gas chromatography-mass spectrometry.

To diagnose inborn errors of metabolism, it would be desirable to simultaneously analyze and quantify organic acids, purines, pyrimidines, amino acids, sugars, polyols, and other compounds using a single-step fractionation; unfortunately, no such method currently exists. The present article will be concerned primarily with a practical yet comprehensive diagnostic procedure of inborn errors of metabolism (IEM). This procedure involves the use of urine or eluates from urine on filter paper, stable isotope dilution, and gas chromatography-mass spectrometry (GC-MS). This procedure not only offers reliable and quantitative evidence for diagnosing, understanding and monitoring the diseases, but also provides evidence for the diagnosis of new kinds of IEM. In this review, the differential diagnosis for hyperammonemia are described; deficiencies of ornithine carbamoyl transferase, argininosuccinate synthase (citrullinemia), argininosuccinate lyase and arginase, lysinuric protein intolerance, hyperammonemia-hyperornithinemia-homocitrullinemia syndrome, and citrullinemia type II. The diagnosis of IEM of purine and pyrimidine such as deficiencies of hypoxanthine-guanine phosphoribosyl transferase, adenine phosphoribosyl transferase, dihydropyrimidine dehydrogenase, dihydropyrimidinase and beta-ureidopropionase are described. During the pilot study for newborn screening, we found neonates with diseases at a rate of 1 per 1,400 including propionic acidemia, methylmalonic acidemia, orotic aciduria, beta-ureidopropionase deficiency, lactic aciduria and neuroblastoma. A rapid and reliable prenatal diagnosis for propionic acidemia is also described.

Adult↗

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