Schematic of the measurement of fM concentrations of metal ions, Mn+ (e.g., Co2+, Ni2+, Pb2+), through electrocatalytic amplification. Oxidation of Mn+ to metal oxides (MOx) is accompanied by anodic spikes corresponding to electrocatalytic conversion of reactants, R, to products, P; e.g., water oxidation. Figure adapted from reference 30.