Production of enzyme based amperometric lactate biosensor and determination of limit of detection

Lactate (lactic acid) is naturally produced by lactic acid bateria, which is found in fermented foods such as yogurt, pickle and wine. Thus, it is a very important parameter for monitoring foods, determining their shelf life, freshness and quality characteristics. Also, lactate is a main metabolite of anaerobic metabolism and indicator of fatigue and hydration in humans, multiple organ failure and death in septic shock patients, stroke and lactic acidosis. Therefore, determining and monitoring the lactate level; is of a great importance to ensure food safety in terms of sustainable agriculture in the food industry and monitoring of patient health and rapid intervention in the field of health. For this aim; biosensors which are quick, easy to apply, sensitive and economic analytical devices for the determination and monitoring of lactate levels, are pretty preferred instead of conventional methods. The commercial and laboratory-scale biosensors used for lactate determination are commonly enzyme-based and amperometric transducer biosensors. In the light of these information, the enzyme-based amperometric transducer lactate biosensor, with a determination range of 31-350 µM which can detecte too low lactate amount, and suitable for use in the food and health field, has been produced within the scope of this thesis. For this purpose, the biosensor was designed after determination of the optimum conditions with preliminary trials, for determination of lactate amount according to oxidation the lactate by lactate oxidase enzyme immobilised with nafion (5% wt) on working electrode was resulted an electron to flow from the H2O2, then there was been a current. Furthermore, the biosensor has been triple electrode system which contented glassy carbon electrode, Ag / AgCl reference electrode and platinum counter electrode. After these; lactate amount produced by 23 lactic acid bacteria, which were isolated from samples of cheese, Turkish sausage and kefir that were provided by different area in Ankara and determined of Gram positive, were measured with the produced biosensor. HPLC analyzes were performed for the same samples and the results were compared with the results of the biosensor's and measurement results of the biosensor in the real samples were examined.