AMPEROMETRIC DETERMINATION OF LACTATE-DEHYDROGENASE BASED ON A CARBON-FIBER MICROCYLINDER ELECTRODE MODIFIED COVALENTLY WITH TOLUIDINE-BLUE-O BY ACYLATION

A method has been developed for the modification of a carbon fiber mic rocylinder electrode with acylation. The stability and surface coverag e of the Toluidine Blue O-modified microelectrode were studied by cycl ic voltammetry. The modified electrode showed significant activity for the electrocatalytic oxidation of NADH in pH 6.8-7.8 solution. The ca talytic current increased linearly with increasing concentration of NA DH from 4.0 x 10(-5) to 1.5 x 10(-3) M. A simple amperometric determin ation based on electrochemical detection of NADH produced from the enz ymatic reaction of lactate with NAD(+) under the catalysic effect of l actate dehydrogenase (LDH) is reported. The experimental factors which had primary influence on the analytical performance were studied. The sensor had a linear response over a range of LDH concentrations from 5.0 U l(-1) to 200 U l(-1) at -0.2 V vs. SCE under optimum conditions. A satisfactory result was obtained for the determination of LDH in cl inical blood samples.