Selective and sensitive biosensor for theophylline based on xanthine oxidase electrode.

Milk and microbial xanthine oxidases (XOs) were used for the construction of amperometric enzyme electrodes. Substrate specificity differences of these enzymes were studied. Of the two enzymes, only the microbial XO was found to oxidize theophylline, but not theobromine and caffeine. The substrate specificity of microbial XO was affected by pH, where the optimum for xanthine was 5.5, while for theophylline it was in the range from 6.5 to 8.5. The theophylline biosensor showed a low detection limit of 2 x 10(-7) M and signal linearity up to 5 x 10(-5) M. The sensitivity of the microbial XO electrode to theophylline could be selectively eliminated by immersion in alkaline phosphate solution, thus allowing for the construction of a blank electrode for differential measurements. The feasibility of this approach has been demonstrated by the determination of free (unbound) and total theophylline in blood samples. The biosensor exhibited good operational (>6 h) and shelf (>3 months) stability when trehalose was used as a stabilizer of the biocatalytic layer.

Amperometric biosensors based on solid binding matrices applied in food quality monitoring.

Solid binding matrix (SBM) based composite transducers have been used for development of series of multibiosensor systems applicable in various fields. Here we present two hybrid three-channel multibiosensors for simultaneous amperometric operation in food quality control, i.e. glucose/fructose/ethanol multibiosensor, based on glucose oxidase/fructose dehydrogenase/alcohol dehydrogenase surface-modified enzyme electrodes and L-lactate/L-malate/sulfite multibiosensor, based on L-lactate dehydrogenase/L-malate dehydrogenase/sulfite oxidase surface-modified enzyme electrodes. Different parameters have been studied in order to optimize the response of the multibiosensor systems. The multibiosensor showed a good sensitivity, linear range and storage stability. The multibiosensors were used for the determination of glucose, fructose, ethanol, L-lactate, L-malate and sulfite in samples of wine, resulting in a good agreement with data certified by the supplier. Comparison of various designs, surface-modified, bulk-modified and thick-cover, of SBM based biosensors is studied on the example of fructose biosensor.

Composite transducers for amperometric biosensors. The glucose sensor.

A new concept of a composite transducer for amperometric biosensors based on the use of a solid substance with amphiphilic character (called a solid binding matrix, SBM) is presented. The electrochemical properties of the transducers prepared with five different SBMs and the characteristics and performance of SBM-based glucose sensors prepared by three different methods are described. Biosensor stability is evaluated and discussed. The biosensor was used for the determination of glucose in wine, yielding results which were consistent with those obtained with the commercially available Glucose Enzyme Photometric Kit. The average accuracy was 6% for the whole range of analyzed concentrations (0.2-47 g/L) using the same sample dilution in a buffer.

Hybrid biosensor for the determination of lactose.

Genetically manipulated bacteria Escherichia coli K-12 recombinant PQ-37 and glucose oxidase (EC 1.1.3.4) were used for the construction of a hybrid lactose sensor because of the hyperproduction of beta-galactosidase (EC 3.2.1.23) by E. coli effected by a genotoxic agent. The biocatalytic layer was prepared by coimmobilization of the E. coli cells with glucose oxidase on the nylon network via glutardialdehyde and fixed to the Clark oxygen electrode. The influence of pH, temperature, and concentration of activators of beta-galactosidase on the sensor response was tested. Analyses of milk products were completed without any special pretreatment of the samples. The contents of lactose determined by hybrid sensor agree with conventional photometric measurements. Standard relative deviation is less than 3% for all samples. The half-life of operational stability is 30 days.

The SOS chromotest study on cisplatin: the genotoxicity evaluation and analytical determination in human urine.

Mechanism of action of cis-diamminedichloroplatinum (II) (cis-DDP) was studied using genetically manipulated bacteria Escherichia coli K-12, recombinant PQ 37 (so-called SOS chromotest). Basic characteristics, namely strength of cis-DDP genotoxicity, influence of chloride ions on genotoxicity and dependence of genotoxicity versus time of cis-DDP aquation reaction were tested. The rate constant has been found to be 0.91 +/- 0.03 x 10(-4)s-1. Possibilities of the use of SOS chromotest in the determination of cis-DDP were found. The detection limit has been 0.09 mg/l in water as well as in urine. The amount of cis-DDP was determined in urine of patients after drug treatment. Analysis of clinical samples have been completed without any preseparation.

[The "crescent sign" in older children (author's transl)]. / Das "Crescent sign" bei älteren Kindern.

The "crescent sign", a dense, convex line parallel to the surface of the kidney, has only been reported in small children with obstructive uropathy during urograms. Two patients (aged 13 and 14 years) with this sign are described. The cause of this appearance is discussed and related to the striations seen on late films in adults with urinary obstruction. The practical value of the "crescent sign" is the possibility of diagnosing obstructive uropathies in the absence of contrast filling of the upper urinary tracts. According to the literature available to us, this is the first time the sign has been reported in older children.