A colorimetric probe for the detection of aluminum ions based on 11-mercaptoundecanoic acid functionalized gold nanoparticles

Abstract

An easy, simple and selective colorimetric method for aluminum ions has been developed using 11-mercaptoundecanoic acid functionalized gold nanoparticles (MUA–AuNPs). The MUA–AuNPs could be induced to aggregate in the presence of Al³⁺ ions according to the chelation effect between the carboxyl group and Al³⁺, and a color change from red to purple with increasing Al³⁺ ion concentration was observed. The plasmon absorbance of the MUA–AuNPs allows the quantitative detection of Al³⁺ ions. A sensitive linear correlation existed between the ratio of absorbance at 650 nm to that at 520 nm and the Al³⁺ ion concentration ranging from 10⁻⁶ M to 10⁻⁴ M. The detection limit was 5.7 × 10⁻⁷ M, which is below the maximum recommended contamination level of the World Health Organization (WHO) for the aluminum content (7.4 μM) in drinking water. The MUA–AuNPs chelated with Al³⁺ showed excellent selectivity in the presence of EDTA compared to other metal ions (Ag⁺, Ba²⁺, Ca²⁺, Cd²⁺, Cr³⁺, Cu²⁺, Fe²⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺ and Zn²⁺). The proposed method can offer the additional advantage of the efficient determination of Al³⁺ ions in drinking water, and the recovery was in the range of 98.5–101.6% with a relative standard deviation below 2%.