An ultrasensitive amperometric determination of lactate by lactate dehydrogenase nanoparticles immobilized onto Au electrode.

The nanoparticles (NPs) of commercial lactate dehydrogenase (LDH) from rabbit muscle were prepared, characterized and immobilized covalently onto Au electrode to construct an improved amperometric lactate biosensor. The biosensor showed optimum response within 2.5 s at an applied potential of 0.10 V, pH 7.0 and 35 °C. The biosensor had a wider working range linear (0.01 μM to 55 mM) with a higher sensitivity (3.45 ± 0.02 μA cm-2  mM-1 ) and a lower detection limit (0.01 μM) compared to earlier biosensors. The analytical recovery of added lactate in sera was 98.61% and within and between batches coefficients of variations (CVs) were 1.38% and 1.03%, respectively. A good correlation coefficient (R2  = 0.99) was observed between sera lactate values as measured by the standard enzymatic colorimetric method and the present biosensor. The biosensor measured lactic acid in the sera of apparently healthy subjects and persons suffering from cardiogenic shocks. There was a 10% loss in the initial activity of LDHNPs/Au electrode after its regular use over a period of 210 days, while being stored dry at 4 °C.