POTENTIOMETRIC ENZYME ELECTRODE FOR UREA BASED ON ELECTROCHEMICALLY PREPARED POLYPYRROLE MEMBRANES

Potentiometric enzyme electrodes for urea were prepared by the covalen t attachment of urease to a functionalized polypyrrole film. In partic ular, a polypyrrole film was first deposited on the surface of a glass y-carbon electrode and then functionalized to incorporate nitro groups that were later electrochemically reduced to amine groups. The enzyme urease was attached to the film's amino groups through its carboxyl f unctionalities (i.e., C-terminus, aspartic and glutamic acid residues) by a carbodiimide reaction. The pH response of the polypyrrole film a fter incorporation of the enzyme was evaluated potentiometrically, res ulting in a slope of -54+/-1 mV/pH, Urease catalyzes the hydrolysis of urea, which causes a change in pH that can be detected by the polypyr role film. The film containing the immobilized enzyme was tested for r esponse to urea, typically showing detection limits of 1.4 x 10(-4) +/ - 1 x 10(-5) M (n = 3). Interference studies with N-methylurea and hyd roxyurea were also conducted. The electrodes exhibited no response to the non-competitive inhibitor N-methylurea. The response characteristi cs of the electrodes towards urea remained unaffected after N-methylur ea additions. In the case of hydroxyurea, the electrodes responded sli ghtly, but urea response was not restored afterwards.