Urease-based biosensor for mercuric ions determination

Urease immobilized into Nafion film on the surface of an ion sensitive field effect transistor (ISFET) has been used for heavy metal salt measurement. Enzyme immobilization into a negatively charged polymer seems to cause an increase in the effect of heavy metal inhibition due to cation accumulation in the polymeric matrix. Fifty percent urease inactivation was observed with 0.2 mu M Ag (I), 1.5 mu M Hg (II) or 5 mu M Cu (II). To make the urease-based biosensor sensitive only to mercuric ions, it is proposed to add small amounts (up to 100 mu M) of NaI into the sample (to suppress sensitivity to Ag ions) and to rewash the sensor in 100 mM solution of EDTA for 5 min to remove Cu ions. Restoration of enzyme activity after Hg (II) inhibition can be obtained by sensor rewashing in a 300 mM solution of NaI for-5 min. (C) 1997 Elsevier Science S.A.