br Acknowledgments This work was funded

Acknowledgments This work was funded by the Basque Government within the framework of the Etortek Program (Grant No. IE14-391), the Spanish Ministerio de Economía y Competitividad Research Projects, CTQ2015-64402-C2-1-R, and CTQ2011–24355 and the NANOAVANSENS Program from the Comunidad de Madrid (S2013/MT-3029). U. Eletxigerra acknowledges Fundación Centros Tecnológicos Iñaki Goenaga for a PhD. grant. R. Villalonga acknowledges Ramón y Cajal contract from the Spanish Ministry of Science and Innovation. Rodrigo Barderas is supported by the Ramón y Cajal Program of the MINECO. The authors would also like to acknowledge Dr. J.M. Sánchez-Puelles for kindly providing the MDA-MB-436 cell line.
Introduction The analytical monitoring of mercury in environmental, industrial and food samples is extremely important because of the high toxicity of this metal both in its inorganic and organic compounds (e.g., methyl mercury). The ability of living organisms to convert inorganic mercury to organic mercury compounds, which are more toxic and accumulate to a greater extent in living organisms, additionally increases the danger of mercury exposure even at trace levels [1]. Numerous highly sensitive and selective spectroscopic methods for the determination of mercury compounds at low concentrations have been developed, the majority of them employ expensive and large instrumentation (e.g., neutron activation analysis [2], atomic fluorescence spectrometry [3], atomic used the survey spectrometry [4] and inductively coupled plasma atomic emission spectrometry [5]. The electrochemical methods [6,7] provide an alternative platform for the detection of mercury at trace level due to the ease of miniaturization, low cost, timesaving, high sensitivity, and in situ determination [8]. Several solid electrodes, such as gold electrodes [9–13], platinum electrodes [14], graphite electrodes [15] and glassy carbon electrode (GCE) [13,16], have been employed. Gold electrodes are recently gaining confidence the detection for mercury [17]. The later have reported the methodology for the anodic stripping voltammetric determination of methyl mercury and inorganic mercury. Recently graphene-based materials have been highly concerned for constructing electrochemical sensors. Gong et al. [18] described a method for the preparation of a sensor with a monodispersed gold nanoparticles assembled on graphene nanosheet matrix for Hg(II) determination. Moreover, the recent trend to replacement of conventional electrodes by screen-printed electrodes (SPEs) is making possible to explore other options in this field [19]. The great versatility presented by the SPEs is based on the wide range of ways in which the electrodes may be modified (directly modifying the composition of printing ink or just depositing the substances on the surface) as demonstrated in recent published papers for Hg(II) determination [20–23]. Few papers concerning the use of silver nanoparticles-modified glassy carbon electrodes in electrochemical analysis of ion and molecule charge positive (lead, cadmium, lamotrigine) were published [24–26] and described the development of a procedure for the determination of molecules at a homemade silver nanoparticle electrode focusing in the study of the instrumental variables involved and the applicability for this molecules detection in pharmaceutical samples. Hg(II) and Au(III) ions represent the most critical element sin the frame work of interference studies within the electro-chemistry of Ag(I) ions [27]. However, the most common problem in applying the bare-type silver electrode is the formation of undesirable silver amalgam, which may destroy the surface feature of the electrode. In addition, silver-based electrodes often suffer from the interference effect for several metal ions such as mercury, copper and bismuth. An effective way to overcome these barriers is protection of surface of silver particles to inhibit the formation of amalgam mercury(II).