Gold or silver modified carbon electrodes for trace detection

Trace analysis [1] (i.e. the analysis of analytes in concentration low enough to cause difficulty, generally under 1 ppm) albeit very challenging, in the last years has shown a tremendous growth, prompted by the urgent need of many International Organizations (US Environmental Protection Agency EPA, U.S. Food and Drug Administration FDA, European Food Safety Authority EFSA, World Health Organization WHO) looking for new analytical techniques for the detection of different molecules in different and increasingly more complex matrixes. The determination of trace analytes requires reliable and robust analytical methods characterized by high level of sensitivity, precision, accuracy, selectivity and specificity. Among different analytical techniques suitable for this purpose, such as mass spectrometry, which is characterized by high accuracy and sensitivity and low limits of detection, electroanalytical techniques and particularly those based on pulsed voltammetry, seem to be a promising independent alternative in terms of very high precision, accuracy and sensitivity. Advantages in using these latter systems lie on simplicity of use, portability, easy automation and possibility of on-line and on-site monitoring without sample pre-treatments and low costs. In this context, the use of nanosized and/or nanostructured materials for the modification of electrodes is growing in importance, with the aim of increasing the affinity for the analyte, increasing sensitivity, lowering the limits of detection and minimizing or completely avoiding interferences, i.e. increasing their selectivity. Carbon nanomaterials coupled with metal nanoparticles [2, 3] present unique peculiar properties, dependent on metal nanoparticle size and shape and therefore are extensively employed in electroanalysis as tunable materials. In this communication, we will present the electrochemical characterization (by Cyclic Voltammetry and Electrochemical Impedance Spectroscopy) and the electroanalytical application of modified electrodes based on gold or silver nanoparticles on carbon nanotubes. In particular, the synergic effect of both metal and carbon nanomaterials was investigated highlighting the importance of the co-presence of both nanomaterials. Gold/CNT electrodes offer the best results in terms of higher peak currents, thus allowing the possibility of reaching lower detection limits. On the other hand, silver/CNT electrodes, although maintaining the same peak currents of the bare electrodes, allow an opening of the electrochemical cathodic window, thus permitting the analysis of compounds which reduce less favorably. The optimized electrodes were then tested for the determination of relevant or toxic analytical substances for environmental monitoring such as glycerol and chlorinated compounds, with interesting promising results. [1] D.T. Pierce, J.X. Zhao, Trace Analysis with Nanomaterials, Wiley-VCH, Weinheim (Germany), (2010). [2] L. Rassaei, M. Amiri, C.M. Cirtiu, M. Sillanpaa, F. Marken, M. Sillanpaa, Trends in Analytical Chemistry 30(11) (2011) 1705-1715. [3] V. Pifferi, V. Marona, M. Longhi, L. Falciola, Electrochimica Acta 109 (2013) 447-453.