Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In this work, the activation of 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) in situ is proposed, for L-cysteine electrooxidation at low overpotentials. The redox mediator was immobilized in an nanostructured platform containing multi-walled carbon nanotubes (MWCNTs), polyethylenimine (PEI) and gold nanoparticles (GNPs). The optimization of the interface was performed monitoring the R-NO/R-NHOH redox couple in which was electrogenerated in situ by cycling the potential between 0.1 and -0.7 V versus SCE at 100 mV s(-1) The kinetic parameters such as the apparent electron transfer rate constant (k(s)) and the rate constant of the reaction between L-cysteine and DTNB (k(obs)) were evaluated. The electrocatalytic oxidation oft-cysteine was studied by means of cyclic voltammetry, chronoamperometry and amperometry. The sensor presented a linear response range for CyS from 9.0 up to 250 mu molL(-1) with sensitivity of 21 nA mu mol(-1), detection and quantification limits of 2.7 and 9.1 mu mol L(-1) respectively, with a response time of 0.12 s at an applied potential of 0 mV versus SCE. (c) 2010 Elsevier By. All rights reserved.1461213220Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2009/08508-8]