L-Cysteine Determination Based on Tyrosinase Amperometric Biosensors without Interferences from Thiolic Compounds

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.

Keywords:

• L-Cysteine
• Quinone-thiol adduct
• Thiolic compound
• Tyrosinase biosensors
• Tyrosinase inhibition

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.