Construction of L-lysine biosensor and its characterisation

In man and the other mammals, L-lysine is one of the essential amino acid and it must be intaken with foods. Lysine deficiency can cause severe diseases therefore it is often added as dieatary supplement to foods and drugs. Owing to this, lysine content of foods can be used as an index of nutritional quality or the evaluation of food processing techniques as it is easily damaged by heat treatment and storage conditions. The biosensors consisting of enzyme as biologically active material, basically including electrodes transducing electrochemical signals and an enzyme or enzymes immobilised onto these electrodes. It becomes widespread recently to use different substrate detection by using ion selective electrodes immobilised with one or more enzymes. The biosensors used to determination of organic materials like vitamins, antibiotics, metabolites, for determination of inorganic compounds, enzymes, viruses and micro-organism as well as it finds application in biotechnology and food industry. The aim of this thesis the construction of a L-lysine biosensor on ammonium-selective poly (vinylchloride) (PVC) membrane containing palmitic acid electrode. The construction procedure occurs two stage: the first stage is preparation of ammonium-selective poly (vinylchloride) (PVC) membrane electrode and the second stage is chemically immobilisation of lysine oxidase (LOx) on this by using glutaraldehyde. Ammonium ions produced after enzymatic reaction were determined potentiometrically with the biosensor. The sensitivity of the lysine biosensor against ammonium ions and lysine studied separately. The response time, linear working range, repeatibility, life time of the biosensor studied, optimum pH, buffer concentration and optimum temperature of biosensor determined. The interfering effects of other amino acids and ascorbic acid on the biosensor performance is also studied. Although lysine oxidase enzyme specifically catalyse α-oxidation of lysine, it shows reaction towards a few amino acids as L-phenyalanine, L-arginin, L-histidine slowly. In this study ascorbic acid and alot of amino acids that can present in some real samples didn't show any important interference. Additionally, lysine assay in commercial lysine tablets and capsules were also succesfully carried out. The results were good agreement with reported value.