Label-free colorimetric sensing of cobalt(ii) based on inducing aggregation of thiosulfate stabilized gold nanoparticles in the presence of ethylenediamine

摘要

As a sensitive and selective analytical technique, gold nanoparticles-based colorimetric sensing was characterized by its simplicity and cost-effectiveness. Specific methods have been extensively developed for different targets in diverse samples. In this study, a label-free method for sensing Co ~(2+) in aqueous solutions was described. The target was achieved by the induced aggregation of thiosulfate (S _2O _3 ~(2-)) stabilized gold nanoparticles (AuNPs) in the presence of ethylenediamine (en). Co ~(2+) first reacted with en and formed complexes of Co(en) _3 ~(2+) in aqueous solutions, which was followed by the oxidation of Co(en) _3 ~(2+) to Co(en) _3 ~(3+) by dissolved oxygen. Co(en) _3 ~(3+) then attacked S _2O _3 ~(2-) ligands adsorbed on the AuNPs' surfaces, forming positively charged (en) _2CoS _2O _3 ~+ on the AuNPs' surfaces, which reduced the surface charges of AuNPs and induced the aggregation of AuNPs. The process was accompanied by a red-shift in the adsorption spectrum and a visible colour change from wine red to blue. Potential effects of relevant experimental conditions, including pH, concentrations of S _2O _3 ~(2-) and en, and incubation time were evaluated for optimization of the method. The proposed method is sensitive (LOD = 0.0 4 μM or 2.36 ppb) and selective (by at least 100-fold over other metal ions except for Cu ~(2+)) toward Co ~(2+) with a linear range from 0.1 to 0.7 μM. The cost-effective method allows rapid and simple determination of the concentrations of Co ~(2+) ions in drinking water.