FLOW-INJECTION DETERMINATION OF CATECHOL WITH A NEW TYROSINASE DNA BIOSENSOR/

Biosensors find application in Bow analysis due to their high selectiv ity and sensitivity. Decrease in the response during extended use, ori ginated by degradation, inhibition or structural changes of the enzyme or leaching of active components by the how, is the prevailing proble m. As an alternative to additives and preparation techniques cited in the literature, it is proposed to use DNA as a matrix for improving pr eservation of the activity of a diphenol-sensor-based tyrosinase, Tyr, (EC 1.14.18.1). The Tyr-DNA mixture was incorporated into carbon past e, CP-DNA-Tyr, or applied on glassy carbon, GC-DNA-Tyr. The CP-DNA-Tyr , covered by a membrane -of Cuprophan, presented superior performance in amperometric operation under Bow conditions (electroreduction of th e products of the enzymatic oxidation of diphenols in the presence of O-2) In comparison with paste electrodes without DNA, CP-Tyr, a curren t increase of one order of magnitude was observed for catechol FIA pea ks, with good repeatability during several hours of operation. The res ponse decayed ca. 50% after every 3 to 3 days of use (with dry storage at 4 degrees C overnight). Original performance was recovered by simp ly substituting the used paste for a new portion of stock paste, stabl e for 2 months under refrigeration. Evaluation of 18 different substra tes and potential interferents indicated that, at the adopted potentia l of -0,15 V vs. Ag/AgCl, only p-cresol gives a response comparable to catechol. Flow-injection determination of catechol samples was conduc ted at a frequency of 30 injections/h, with linear response from the d etection limit of 1x10(-6) up to 5x10(-5) mol l(-1). (C) 1998 Elsevier Science B.V.