A reagentless, disposable biosensor for lactic acid based on a screen-printed carbon electrode containing Meldolaʹs 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% Meldolaʹs Blue (by weight of carbon). Sensor construction was optimised, the final biosensor contained 10 units of LDH, 60 μg 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 °C. The relative standard deviation for a single batch of electrodes was found to be 8.7%.