Abstract
This paper presents an enzymatic analysis method for selective detection of L-cysteine (L-Cys) without interferences from other thiols like cysteamine (CA) and mercaptoacetic acid (MAC). The amperometric biosensors are based on tyrosinase (Tyr) that converts catechol to o-quinone. The L-Cys detection is based on the fact that all thiols (including L-Cys) react with o-quinone producing electroinactive compounds and only interfering thiols (CA and MAC) inhibit Tyr. One sample was analyzed twice: with Tyr immobilized on WE surface to quantify enzyme inhibition by thiolic interferents and with Tyr free in solution to investigate the reactions between quinone and all thiolic compounds.
This work was supported by the Romanian Ministry of Education and Research through Grants MICROSEN 11049/2007 and SAFEFOOD 61/2007. The screen-printed electrodes were a generous gift from Prof. Jean-Louis Marty (University of Perpignan, France). Ovidiu Ilie Covaci is a Ph.D. student with AMPOSDRU scholarship. Paper revision by dr. Mihaela Badea is kindly acknowledged.