Selective and sensitive colorimetric determination of cobalt ions using Ag-Au bimetallic nanoparticles

Abstract

Plasmonic nanoparticle-based colorimetric sensing has gained wide attention due to its advantages including rapidity, simplicity and expensive instrument-free characters. In the present study, Ag-Au bimetallic nanoparticles were proposed as novel optical probes to determine cobalt ion (Co2+) concentration. The sensing mechanism is based on the fact that Co2+ can react with ethylenediamine (en) and S2O32− to form (en)2CoS2O3+ on the nanoparticle surface, which can decrease the negative charge of the nanoparticle, reduce the repulsion between adjacent nanoparticles, and subsequently induce nanoparticle aggregation, was verified by dynamic light scattering. The effects of several parameters on the detection sensitivity, including the concentration of S2O32− and en, pH value and incubation time, were investigated. The assay demonstrated high selectivity toward Co2+ in the presence of K+, Cu2+, Pb2+, Ag+, Zn2+, Ba2+, Mn2+, Fe2+, Fe3+, Ni2+ and Hg2+. Under optimal conditions, the absorbance ratio of A600/A434 showed a linear relationship versus Co2+ concentration from 0 to 0.6 μM with a correlation coefficient (R2) of 0.980, and the detection limit was calculated to be 0.02 μM. The practical application of the proposed nanoprobes was evaluated with river and tap water samples.