Development and evaluation of a glassy carbon electrode modified with silver and mercury nanoparticles for quantification of cysteine rich peptides

A glassy carbon electrode,covered with a Nafion film, on which nano-structured bimetallic particles of Ag-Hg were deposited; from now on “the AgHgNpNf/GC electrode”, was used for the indirect determination of cysteine, glutathione and metallothioneins by measuring the catalytic hydrogen evolution signal according to the Brdička reaction using cobalt as a catalyst. Upon successful formation and deposition of the Ag-Hg bimetallic nanoparticles cyclic voltammetry (CV), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the electrode for that specific task. The results showed the electrode to be mechanically resistant even under sonication, stable in its performance, porous, sensitive in its response and of low cost to be built. Differential pulse voltammetry signals for cysteine and glutathione obtained using the AgHgNpNf/GC electrode were qualitatively similar to those reported using a hanging mercury drop electrode, (HMDE), dropping mercury electrode (DME) and static mercury drop electrode (SMDE). Detection limits based on the variability of a blank solution, (3 s criterion) calculated for those tests were 0.463 μg L⁻¹ and 0.064 μg L⁻¹, for cysteine and glutathione, respectively. Based on the Brdička procedure and considering the particular characteristics of the new electrode, some analytical tests were carried out for the indirect determination of the metallothioneins content of samples of blood serum of rats exposed to lead by measuring the evolution of the catalytic hydrogen signal. An average accuracy value around 102%, n = 6, and a precision of 0.87% ± 0.09 were obtained for these tests.