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Biomedical subjects

F W Scheller

Publications and source records attributed to F W Scheller.

11 recordsLinked to original sources
PubMed1996

Zeptomole-detecting biosensor for alkaline phosphatase in an electrochemical immunoassay for 2,4-dichlorophenoxyacetic acid.

A bienzyme substrate-recycling biosensor in a flow injection analysis system is described for the sensitive measurement of alkaline phosphatase (ALP) and applied to the fast readout of a competitive immunoassay for the widely used pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). The phenol-indicating biosensor consists of a Clark-type electrode covered by a membrane with coentrapped tyrosinase and quinoprotein glucose dehydrogenase. ALP dephosphorylates phenyl phosphate to phenol (K(m) = 36 microM) outside the flow system. Phenol is oxidized in the sensor membrane by the oxygen-consuming tyrosinase via catechol to o-quinone. The quinone is reconverted to catechol by glucose dehydrogenase. This substrate cycling results in a 350-fold amplified sensor response to phenol. The oxygen consumption of the enzyme couple in the presence of phenol is monitored as a decrease in current. A total of 3.2 fM ALP (320 zmol/ 100 microL) has been detected after a 57.5 min incubation with phenyl phosphate. All involved reagents are stable over the time of measurement. The sensor does not produce any measurable blank signals. The immunoassay detects 0.1 microgram/L 2,4-D, the maximum concentration for pesticides allowed in drinking water by European Community regulations. The applicability of this biosensor for fast immunoassay readout is demonstrated by a 2 min incubation. By comparison, a standard photometric method (p-nitrophenyl phosphate) requires overnight incubation.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1996

Label-free observation of DNA-hybridisation and endonuclease activity on a wave guide surface using a grating coupler.

Hybridisation of nucleic acid oligomers to an immobilised target has been observed in real time using evanescent field technology. A biotinylated 24-mer with random sequence including the EcoRI recognition site was immobilised via streptavidin onto a grating coupler wave guide surface. Hybridisation of 22-mer, 15-mer and 8-mer was observed. Activity of restriction endonuclease EcoRI was visualised by measurement of the loss of bound DNA after incubation.

Base Sequence↗
PubMed1993

Enhancing biosensor performance using multienzyme systems.

Enhancing the performance of biosensors, in terms of increasing the range of analytes that may be detected, and the sensitivity and specificity of the detection event, would improve the prospects for commercializing this technology. Coupling the catalytic activities of several enzymes is one approach being used to address these issues. Sequences of enzymes, where ligand binding triggers the activation of enzymes, or where biocatalytic pre-concentration of intermediates permits augmentation of the signal, may be used. In addition, enzymatic recycling of the analyte can be used to increase the sensitivity by several orders of magnitude.

Animals↗
PubMed1993

Enzyme activation for activator and enzyme activity measurement.

A new sensing principle of enzyme activation is demonstrated for the determination of glycogen phosphorylase b and its allosteric effector AMP. As the indicator of the phosphorylase catalysed glycogen phosphorolysis, glucose-1-phosphate formation has been detected with an enzyme sequence comprising coentrapped alkaline phosphatase, mutarotase and glucose oxidase on a hydrogen peroxide indicating electrode. The optimized three-enzyme sensor was useful for the determination of 0.005-0.2 U.ml-1 glycogen phosphorylase a and b. A biosensor for AMP and inorganic phosphate has been developed by coupling glycogen entrapped phosphorylases to the three-enzyme indicator membrane. The measurement of AMP is based on the modulation of the phosphorylase b catalysed glycogen phosphorylating activity. The proposed sensor responds to AMP between 5 and 150 microM. The calibration graph of the reagentless phosphate sensor is linear between 0.05 and 1 mM.

Adenosine Monophosphate↗
PubMed1991

Second generation biosensors.

Enzyme-membrane electrodes using glucose oxidase in combination with peroxide detection dominate in the field of laboratory analyzers for diluted samples. Using the same indication principle, extremely fast responding glucose sensors have been fabricated by covering thin metal electrodes with a porous enzyme layer. In the second generation auxiliary enzymes and/or co-reactants are coimmobilized with the analyte converting enzyme in order to improve the analytical quality and to simplify the performance. Following this line oxidizable interferences are suppressed by using a glucose oxidase/peroxidase complex which communicates with the electrode at a low working potential. Furthermore, fluctuations of pH or buffer capacity are ineffective when using a glucose oxidase/peroxidase layer covered fluoride FET in the potentiometric glucose determination. Enzymatic recycling of the analyte and/or accumulation of intermediates increase the sensitivity by several orders of magnitude. Inclusion of NAD bound to PEG in the glucose dehydrogenase layer allows a reagentless glucose measurement.

Biosensing Techniques↗
PubMed1990

Amperometric bi-enzyme based biosensor for the detection of lactose--characterization and application.

Based on the glucose oxidase-beta-galactosidase sequence an enzyme probe for the specific determination of lactose has been developed. beta-Galactosidases from different sources have been compared, the sensor containing beta-galactosidase from Curvularia inaequalis has been characterized in respect of optimal pH, enzyme loading, apparent activity and functional stability. The response of the bi-enzyme probe depends linearly on lactose concentration between 0.02 and 3.00 mmol dm-3. The application to different milk and foodstuff samples resulted in good correlations toward enzymatic photometric (y = (0.956x-1.67) mmol dm-3) and infrared detection (y = (1.0772x-0.3909)%). Using a measuring frequency of 100 h-1 the serial imprecision is about 2% for diluted milk, urine, or foodstuff samples.

Animals↗
PubMed1989

Glucose measurement in diluted blood.

The sensitivity, measuring range and lifetime of enzyme electrodes using glucose oxidase sandwiched between dialysis membranes or alternatively in a polyurethane layer directly on the surface of a platinum electrode are compared. The GOD modified electrode exhibits the highest sensitivity. However, the signal depends strongly on the stirring rate. Using the sandwich membranes up to 120 diluted blood samples per hour with a serial coefficient of variation below 1% can be analyzed.

Biosensing Techniques↗