Mercury(II) Trace Detection Using a Glassy Carbon Electrode Functionalized by Chemically Prepared Gold Nanoparticles. Influence of Coating Process on Surface Reactivity and Analytical Performances

Abstract

An electrochemical sensor dedicated to Hg(II) trace detection was elaborated based on a gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode. AuNPs were prepared using the Turkevich method and deposited on GC by drop casting. Different protocols including suspension filtration and evaporation temperature control were tested and their influence both on coating morphology and electrochemical activity assessed. From structural characterization, it can be concluded that neither the filtration step nor the drop evaporating temperature have a significant impact on coating morphology at the mesoscale level. However, regarding to the electrochemical activity of the functionalized electrodes, results showed that when some heterogeneities due to (AuNPs) aggregation were present in the coating, the electrochemical activity was reduced. Contrary to what was observed in our previous studies dealing with electrodeposited AuNPs, cycling an AuNPs-GC electrode in H 2 SO 4 lead in all cases to a decrease in active surface area and in a higher density of surface defects, thus revealing a higher surface reactivity of chemically-synthesized AuNPs. The electrochemical activation procedure was found to influence the analytical performances of the functionalized electrode with respect to Hg(II) assay in the picomolar range, but not in the nanomolar range, as a consequence of a saturated concentration effect. A linear concentration range was obtained between 2 and 12 pM with a normalized sensitivity of 0.296 µA pM -1 min -1 using square wave anodic stripping voltammetry (SWASV) as the detection mode. A limit of detection (LOD) down to 1 pM was reached.

Study of an AuNPs functionalized electrode using different diazonium salts for the ultra-fast detection of Hg(II) traces in water

“…3). As presented in a previous study [24], star and pyramidal geometric arrangements were observed (Fig. 3a).…”

“…On the other hand, this peak decreased all along the scanning for each electrode, showing a decrease of the AuNPs active surface. This trend was already observed in several studies including one of our previous work with drop-casted AuNPs [24,55,56]. It is the consequence of a dissolution-redeposition mechanism of the AuNPs during the cycling in H 2 SO 4 : during the oxidation scan the smallest AuNPs dissolve in the solution and redeposited on the remaining AuNPs during the reduction scan, leading to NPs growth and to a subsequent decrease in active surface area.…”

“…However, this procedure was still done on every interface before any other electrochemical measurement because it proved to be efficient for the homogenization of the crystals faces of the AuNPs. It is interesting to point out that this behavior was not observed in our past studies with electrodeposited [22,23] and filtered drop-casted AuNPs [24], possibly because of a different structure configuration and reactivity of the AuNPs.…”

“…Hg(II) detection was achieved on GC/AuNPs, GC/NBD/AuNPs and GC/SH/AuNPs interfaces by recording SWASV in 0.01 mol l À1 HCl following a previously reported procedure [22,24] which used a typical preconcentration time of 300 s. In such conditions and whatever the considered interface, an unexpected behavior of the sensor towards Hg(II) detection was noticed, illustrating the peculiar reactivity of the drop-casted AuNPs. First, the functionalized electrode failed at recording a proper blank, i.e.…”

“…Because chloride ions were shown to play an important role in the detection, a desorption step was added to the detection process and a concentration of mercury of 19 pmol l À1 was reached for a submarine groundwater discharge sample [23]. In an alternative way, chemically prepared AuNPs were used to functionalize a GC electrode reaching a LOD of 1 pmoll À1 [24]. However, the remaining sensor suffered a poor stability over time and electrochemical treatments.…”