Selective and colorimetric detection of Ba2+ ions in aqueous solutions using 11-mercaptoundecylphosphonic acid functionalized gold nanoparticles

Abstract

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.