Voltammetric sensing of silver nanoparticles on electrodes modified with selective ligands by using covalent and electropolymerization procedures. Discrimination between silver(I) and metallic silver

New electrochemical sensors are described for the rapid quantification of silver nanoparticles (AgNPs). They are based on the immobilization of L-cysteine on a glassy carbon electrode (GCE) and on the formation of electropolymerized oligomers on the GCE. Ligands with amino, sulfur and carboxy functional groups are used that are capable of selectively retaining AgNPs. The experimental conditions for electropolymerizations were optimized for each of four monomers studied: L-lysine, thiophene-3-carboxamide, thionin, and o-phenylene-diamine. The best retention capabilities and conditions for quantification of AgNPs were found for immobilized nanoparticle voltammetry. This method is more sensitive than others based on the sorption of AgNPs from dispersions. These ligands also retain ionic silver species. Hence, Ag(I) and Ag0 can be discriminated, and the total silver content can be quantified by stripping voltammetry. The best analytical properties (for dispersions of AgNPs of 40 nm diameter) were found with GCEs carrying electropolymerized L-lysine. Figures of merit include (a) sensitivity of 4.329 ± 0.031 μA μg−1 mL cm−2, (b) a detection limit of 0.010 μg mL−1, and (c) a relative standars deviation of about 7.2% (for n = 4). The poly-L-lysine sensors can also evaluate the size of the AgNPs in the range 20 to 80 nm diameter, owing to displacements of the maximum potential of the voltammetry peaks.