Correlating surface growth of nanoporous gold with electrodeposition parameters to optimize amperometric sensing of nitrite

The electrochemical deposition of nanoporous gold (NPG) on a solid substrate has been an intensive area of research in recent years. Such facile technique offers a fine control over the growth and nucleation mechanism, which determines the grain size and the morphology of the deposited NPG, which in turn strongly influences its electrochemical activity[1]. Accordingly, a systematic study was performed in the present work to fabricate NPG modified gold electrodes using the Dynamic Hydrogen Bubble Template (DHBT) method[2], which were subsequently tested for the electrooxidation of nitrite. Two sets of experiments were carried out: a) NPG were electrodeposited at applied potentials of -1 V, -2 V, -3 V and -4 V at a fixed time of 100 s; and b) at constant applied potential of -4 V varying the deposition time (100 s, 200 s, 400 s and 600 s). NPG modified electrodes ware characterized using profilometry, SEM, XRD and EDXRF. The porous gold nanostructures electrodeposited on a solid gold substrate are strongly dependent on electrodeposition parameters, especially the applied potential and time of deposition, influencing the electrocatalytic activity towards nitrite oxidation. Based on results of surface characterization experiments, it was established that the film gets denser with more negative potential, while a more porous morphology was achieved, including nanodendrite formation, as the deposition time increased. Changes in the gold surface were correlated with different growth models and nucleation processes. Based on electrochemical and surface characterization studies, an NPG platform prepared at -4 V for 100 s was found to be the most suitable for electrochemical nitrite sensing applications because of a potential shift towards less positive potentials with enhanced sensitivity. The sensor was employed for amperometric detection of nitrite and sensitivity and limit of detection values were found to be 0.2 µA µM-1 and 10 nM, respectively. The modified electrode exhibited good reproducibility and shelf-life stability in experiments carried out for a prolonged time (two months). Finally, the applicability of the proposed NPG modified electrode was successfully confirmed by measuring nitrite in real samples including processed meat and lake and tap water, whose results were validated by the spectrophotometric Griess method. To further understand the growth mechanism of NPG, electrodeposition on a single crystal gold substrate has been envisaged.