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)