An amperometric sensor for l-cysteine based on nanostructured platform modified with 5,5′-dithiobis-2-nitrobenzoic acid (DTNB)

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 (ks) and the rate constant of the reaction between l-cysteine and DTNB (kobs) were evaluated. The electrocatalytic oxidation of l-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 μmol L−1 with sensitivity of 21 nA L μmol−1, detection and quantification limits of 2.7 and 9.1 μmol L−1 respectively, with a response time of 0.12 s at an applied potential of 0 mV versus SCE.