A REAGENTLESS, DISPOSABLE BIOSENSOR FOR LACTIC-ACID BASED ON A SCREEN-PRINTED CARBON ELECTRODE CONTAINING MELDOLAS-BLUE AND COATED WITH LACTATE DEHYDROGENASE, NAD+ AND CELLULOSE-ACETATE

A disposable amperometric biosensor for lactic acid has been constructed based on the immobilisation of the enzyme L-lactate dehydrogenase (LDH) and its cofactor nicotinamide adenine dinucleotide (NAD) using a cellulose acetate (CA) membrane cast in situ. These components were deposited onto a screen-printed carbon electrode containing 2% Meldola's Blue (by weight of carbon). Sensor construction was optimised, the final biosensor contained 10 units of LDH, 60 mu g of NAD(+) and used a membrane cast from a 1% CA solution. The optimum solution for lactate measurement was found to consist of 0.5 mol dm(-3) phosphate buffer, pH 8. The optimum temperature was 32 degrees C. The relative standard deviation for a single batch of electrodes was found to be 8.7%.