Turning metals cations into catalytic nanoparticles on modified electrode: a general strategy for their electrochemical quantification

We present an innovative electrochemical sensing method for the detection of heavy metal cations that departs from conventional pulsed electroanalytical techniques. The keystone of this approach is the nanostructuring of trace amounts of preconcentrated metal on a functionalized electrode, thereby exploiting the heterogeneous catalytic properties of the resulting metal nanodeposits. Rather than introducing a new selective sensing interface, this work focuses on a general detection strategy. In this approach, a diazonium modified graphite electrode is used as a robust platform to demonstrate that sparsely pre accumulated metal cations can be reduced into nanodeposits, which behave as a nanoelectrode array. The macroscopic electrochemical response of this array towards the hydrogen evolution reaction depends on the size of the nanoelectrodes: higher metal concentrations in the incubation solution lead to more extensive metal deposition and larger nanostructures, which shift the hydrogen evolution reaction catalytic peak potential positively in cyclic voltammetry. This shift continues until the metal becomes detectable by standard pulsed analytical methods. As an illustration, the proposed approach enables the detection of copper and iron with improved sensitivity compared to the corresponding reference pulsed techniques. Moreover, this gain in sensitivity does not rely on a specific surface chemistry. Therefore, the more affine a given accumulation layer is for its target metal, the lower the detection limits that can be achieved with this method. This study points toward a promising route for next generation electrochemical sensors for trace metal detection, offering sensitivity beyond that of traditional faradaic detection schemes.