LAUSR

In this paper we describe a simple colorimetric method for the sensitive and selective detection of Ba2+ ions, using 11-mercaptoundecylphosphonic acid functionalized gold nanoparticles (AuNPs–MPA) in aqueous solution. With increasing concentration, Ba2+ ions induced aggregation of AuNPs–MPA, causing a change in color of the colloidal solution from pink to blue. The detection result was monitored using the naked eye and UV-Vis spectroscopy. The maximum absorption was located at 625 nm. The stability of AuNPs–MPA and detection of Ba2+ by AuNPs–MPA was investigated at different pH values (pH = 3, 4, 5, 6, 7, 8, 9, 10, 11, 12). Results indicated that AuNPs–MPA at pH 6 were the optimal choice for detecting Ba2+ ions. The detection limit for Ba2+ was found to be 43.27 μmol L−1 (R2 = 0.9901) within a range of 20–120 μmol L−1. In addition, the selectivity of this method was investigated using other metal ions. The AuNPs–MPA was selective for Ba2+ compared with other metal ions (Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Sb3+, Bi3+) leading to a remarkable color change. Moreover, the developed cost-effective probe has been successfully applied to real drinking and tap water samples which demonstrated the potential for field applications.