Potentiometric biosensor for urea determination in milk

A potentiometric urea sensitive biosensor, using a NH4+ ion sensitive electrode in double matrix membrane (DMM) technology as the transducer, has been described. Thick film screen printing technique was utilized for the fabrication of the basal conducting track of the potentiometric electrode and also for the development of Ag/AgCl reference electrode. The ion sensitive polymer matrix membrane could be formed in the presence of an electrochemically inert filter paper. The electrochemical response behavior of the NH4+ ion sensitive electrode has been studied initially. Later, a urea biosensor has been developed by immobilizing the urease enzyme, through entrapping, onto the ion sensitive membrane using a polymer matrix of poly(carbamoylsulphonate) (PCS) and polyethyleneimine (PEI). The urea biosensor responded rapidly and in a stable manner to the changes in the test urea concentrations. The sensor exhibited a detection limit of 2.5 × 10−5 mol/L. The average slope in the linear range has been found to be 51.7 ± 0.5 mV/decade. The biosensor system has, then, been tested for the detection of urea levels in the real samples of milk. A good agreement could be observed between the urea concentrations detected by the developed biosensor and the spectrophotometric technique.