Colorimetric detection of Hg2+ using thioctic acid functionalized gold nanoparticles

Abstract

This paper describes the sensing application of water-dispersible thioctic acid functionalized gold nanoparticles (TA-GNPs) as sensors for the colorimetric detection of Hg2+ ion in water samples. The state and stability of thioctic acid decorated gold nanoparticles in pH range (pH = 4–11) were evaluated by UV/vis spectra. The thioctic acid modified GNPs could be induced to aggregate quickly in the presence of Hg2+, especially after adding a solution of 0.05 M NaCl. The detection of Hg2+ by TA-GNPs at different pH values (pH = 5, 7, 9, 11) was also investigated to optimize the experimental conditions in detail. The result indicated that the TA-GNPs at pH 5 were the most optimal choice for detecting Hg2+. The detection results of Hg2+ could be determined by the naked eye or a UV-vis spectrophotometer. The detection of Hg2+ could be realized with a detection limit of 10 nM over a long range (10 nM to 20 μM). Additionally, the selectivity of this method has been investigated using other metal ions. The TA-GNPs can selectively bind Hg2+ over other metal ions (Pb2+, Mg2+, Zn2+, Ni2+, Cu2+, Co2+, Ca2+, Mn2+, Fe2+, Cd2+, Ba2+, Ag+ and Cr3+), leading to prominent color change. This will provide a simple and effective colorimetric sensor (no DNA) for on-site and real-time Hg2+ ion detection. More importantly, this probe was also applied to determine the Hg2+ in lake samples, and the results demonstrate low interference and high sensitivity.