ABSTRACT
This study describes a novel biosensor method for specific determination of nitrate in food and water samples by using nitrate reductase (NR) (EC 1.9.6.1) biosensor based on the detection of oxidation peak current of redox mediator, methyl viologen, related to nitrate concentration. The method was shown to be selective and sensitive to determine the nitrate levels of water samples and processed meat samples. Immobilization procedure and also working conditions of the biosensor were optimized. Dynamic range attained with this method was established as (5.0-90.0 x 10(-9) M) for nitrate concentration with a 10 s response time. Limit of detection (LOD) and quantification (LOQ) of the biosensor were calculated as 2.2 x 10(-9) M and 5.79 x 10(-9) M, respectively. Reproducibility experiments was established on repetitive measurements by using a freshly prepared biosensor for avoiding the memory effect. The RSD was calculated as 1.22% at a nitrate concentration of 4.7 x 10(-8) M (n = 7).
Subject(s)
Biosensing Techniques/instrumentation , Conductometry/instrumentation , Food Analysis/instrumentation , Food Contamination/analysis , Meat/analysis , Nitrates/analysis , Water/chemistry , Animals , Equipment Design , Equipment Failure Analysis , Sensitivity and Specificity , Water Pollutants, Chemical/analysisABSTRACT
Interest in molecular imprinted polymer techniques has increased because they allows for the improvement of some stability characteristics of enzymes. The high stability of molecularly imprinted enzymes for a substrate can make them ideal alternatives as recognition elements for sensors. A bioimprinted mushroom tissue homogenate biosensor was constructed in a very simple way. For this purpose, sulfite was used. The enzyme, polyphenol oxidase, was first complexed by using a competitive inhibitor, sulfite, in aqueous medium and then the enzyme was immobilized on gelatin by crosslinking with glutaraldehyde on a glass electrode surface. Similarly, polyphenol oxidase uncomplexed with sulfite was also immobilized on a glass electrode in the same conditions. The aim of the study was to compare the two biosensors in terms of their repeatability and thermal, pH, and operational stability; also, the linear ranges of the two biosensors were compared with each other.
Subject(s)
Agaricus/chemistry , Biosensing Techniques/methods , Food Analysis/methods , Phenols/analysis , Biosensing Techniques/instrumentation , Catechol Oxidase/antagonists & inhibitors , Catechol Oxidase/metabolism , Catechols/analysis , Cross-Linking Reagents/chemistry , Electrochemistry , Electrodes , Enzyme Inhibitors/pharmacology , Enzymes, Immobilized , Food Analysis/instrumentation , Gelatin/chemistry , Glass/chemistry , Glutaral/chemistry , Hydrogen-Ion Concentration , Reproducibility of Results , Sensitivity and Specificity , Sulfites/pharmacology , Temperature , Water/chemistryABSTRACT
A new amperometric biosensor based on urate oxidase-peroxidase coupled enzyme system for the specific and selective determination of uric acid in urine was developed. Commercially available urate oxidase and peroxidase were immobilized with gelatin by using glutaraldehyde and fixed on a pretreated teflon membrane. The method is based on generation of H(2)O(2) from urine uric acid by urate oxidase and its consuming by peroxidase and then measurement of the decreasing of dissolved oxygen concentration by the biosensor. The biosensor response depends linearly on uric acid concentration between 0.1 and 0.5 muM. In the optimization studies of the biosensor, phosphate buffer (pH 7.5; 50 mM) and 35 degrees C were obtained as the optimum working conditions. In addition, the most suitable enzyme activities were found as 64.9x10(-3) U cm(-2) for urate oxidase and 512.7 U cm(-2) for peroxidase. And also some characteristic studies of the biosensor such as reproducibility, substrate specificity and storage stability were carried out.