An amperometric lactate biosensor based on lactate dehydrogenase immobilized onto graphene oxide nanoparticles-modified pencil graphite electrode

A novel amperometric lactate biosensor was developed based on immobilization of lactate dehydrogenase onto graphene oxide nanoparticles-decorated pencil graphite electrode. The enzyme electrode was characterized by scanning electron microscopy, Fourier transforminfrared spectroscopy (FTIR), and cyclic voltammetry at different stages of its construction. The biosensor showed optimum response within 5 s at pH 7.3 (0.1 M sodium phosphate buffer) and 35 degrees C, when operated at 0.7 V. The biosensor exhibited excellent sensitivity (detection limit as low as 0.1 mu M), fast response time (5 s), and wider linear range (5-50 mM). Analytical recovery of added lactic acid in serum was between 95.81-97.87% and within-batch and between-batch coefficients of variation were 5.04 and 5.40%, respectively. There was a good correlation between serum lactate values obtained by standard colorimetric method and the present biosensor (r = 0.99). The biosensor measured lactate levels in sera of apparently healthy subjects and persons suffering from lactate acidosis and other biological materials (milk, curd, yogurt, beer, white wine, and red wine). The enzyme electrode lost 25% of its initial activity after 60 days of its regular uses, when stored dry at 4 degrees C.