An immunoreaction-based method was investigated for the detection of aflatoxin M1 (AFM1), which is the hydroxylated metabolite of aflatoxin B1 (AFB1). This mycotoxin may be found in milk and milk products obtained from livestock that have ingested contaminated feed. Quantitative analysis of AFM1 was carried out using indirect (competitive) immunoassay method, which can be used for low weight molecules. The real-time measurement was done with Optical Waveguide Lightmode Spectroscopy (OWLS) technique. After the optimization of the chemical and biochemical parameters (determination of the optimal concentration of the immobilized AFM1-protein conjugate, determination of the AFM1 antibody content of the samples, etc.) real samples were also examined. Three kinds of milk sample preparation methods (filtration, centrifugation, size exclusion centrifugation) and two dilution rates (100 and 200 fold) were compared. The presented competitive immunoassay method showed the best results when 100 fold diluted filtered or centrifuged milk samples were examined. The dynamic measuring ranges for AFM1 were 0.001–0.1 ng ml−1 and 0.0005–0.01 ng ml−1, respectively.
Authors:N. Adányi, E. E. Szabó, M. Váradi, and J. Szamos
To explore new possibilities of enzyme immobilization, we investigated bioactive layers prepared by a new procedure based on three-phase partitioning (TPP) of proteins. By this method a third phase or midlayer as a protein layer can be developed at the interface of a protein system containing two phases (organic solvent/aqueous salt solution). Proteins of meat origin partitioned together with bioselective material (e.g. an enzyme) after centrifugation resulted in excellent bioactive layers.In the newly developed sensor, glucose oxidase was immobilized in a layer, which was fixed on the surface of a platinum ring electrode. The biosensor was built in a flow injection analyzer (FIA) system, where the hydrogen peroxide generated during the enzymatic reactions was determined by an amperometric cell. The parameters for biochemical and electrochemical reactions (ion concentration and pH of buffer, flow rate) were optimized. The linear range of analysis by the newly developed sensor was from 0.5 to 10 mmol l–1 glucose. The biosensor could be used for more than 300 analysis.
Authors:G. Csiffáry, P. Nagy, A. Kiss, and N. Adányi
An amperometric biosensor for the detection of organophosphorus and carbamate type pesticides was developed. Acetylcholinesterase enzyme (electric eel) was immobilized in a thin-layer enzyme cell, and acetylthiocholine chloride (AcTCh) was used as substrate. Amperometric detection with glassy carbon electrode was performed in a stopped-flow FIA system. The inhibition effect of dichlorvos (DDVP), carbofuran, methomyl, and pirimicarb were examined: the linear measuring ranges were 0.001–0.1 μmol l−1, 0.001–0.1 μmol l−1, 0.2-1 μmol l−1, and 0.1–10 μmol l−1, respectively. Soil extract and apple juice were measured with spiking method. It was concluded that the biosensor can be used for screening pesticide residues in food and environmental samples.
Authors:N. Adányi, M. Váradi, I. Sziklai-László, P. Snyder, R. D. Snyder, and M. Á. Cser
Total daily Se intake was determined by duplicate diet collection, venous blood samples were taken and urine was collected over 24 h in order to measure selenium input and output in healthy, American and Hungarian children aged 8 to 17 living in Budapest. The American children consumed not only locally processed food. Food samples were weighed, mixed, homogenised and the Se content was determined by Instrumental neutron activation analysis (INAA). The Se concentration of blood, plasma and urine samples was determined by atomic absorption spectrometry-hydride generation (AAS-HG) after wet digestion. Se intake calculated for wet weight was 62±18.5 mg/day in American children. In the Hungarian children the mean Se intake was about 35% less than in the Americans. Se concentrations in plasma were 0.84±0.16, in whole blood 1.13±0.17 mmol l-1 in the Americans, higher than those in healthy Hungarian children (0.64±0.10 and 0.83±0.12 mmol l-1, respectively) of similar age and gender. Urinary Se output calculated for creatinin was higher in the children from abroad (27.0±9.5 mg Se/day/g creatinin) compared to Hungarians (11.0±5.0 mg Se/day/g creatinin).