Application of a long shelf-life biosensor for the analysis of l-lactate in dairy products and serum samples

An l-lactate biosensor using an enzyme-immobilised eggshell membrane and an oxygen electrode for l-lactate determination has been developed. An ionotropic gelatinous solution of l-lactate oxidase and chitosan was deposited on an eggshell membrane and subsequently covered the surface of the oxygen electrode. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to l-lactate solution. The decrease in oxygen concentration was monitored by the oxygen electrode which was connected to a datalogging system for data acquisition and processing. The effects of pH, dissolved oxygen content, salt concentration, temperature and potential interferants have been studied in detail. The relative standard deviation (n = 10) of the response was 5% for a 0.10 mM l-lactate standard. The t95 response time is ≈60 s and the recovery time is ≈90 s. A linear calibration curve, decrease in dissolved oxygen concentration = 11.67[l-lactate] + 0.039; r2 = 0.9998, where dissolved oxygen concentration is in mg L−1 and [l-lactate] is in mM, was obtained from the biosensor. The limit of detection was calculated to be 8.6 μM. The response of the membrane to l-lactate was reversible and fast. The l-lactate biosensor demonstrated long shelf-life of at least 1 year and it maintained its activity above 80% after being kept at 4 °C for a year. The biosensor has been successfully applied to the determination of l-lactate content in dairy products and serum samples.