Colorimetric detection of Hg²+ ions in aqueous media using CA-Au NPs

Based on the selective interaction between Hg(2+) ions and cyanuric acid (CA) and the anti-aggregation of CA stabilized gold nanoparticles (CA-Au NPs), a simple colorimetric method was developed for detecting Hg(2+) ions. In a medium of pH 7.4 tris-HCl buffer containing 8×10(-3) M NaCl, the CA-Au NPs solution was red, which was due to CA adsorbed onto the surface of Au NPs, stabilizing Au NPs against aggregation. When CA-Hg(II)-CA complex was formed in the presence of Hg(2+), the stability of CA-Au NPs reduced, and then aggregation of Au NPs occurred. Consequently, the color of the solution changed from red to blue and could easily be measured with a common spectrophotometer. The aggregation of Au NPs was also validated using transmission electron microscopy (TEM). The controlled experiment showed that other ions including Ba(2+), Ca(2+), Zn(2+), Cd(2+), Co(2+), Mn(2+), Cu(2+), Mg(2+), and Ni(2+) ions did not induce any distinct spectral changes, which constituted a Hg(2+)-selective sensor. A dynamic range of 1.6-16×10(-6)M Hg(2+) ions was observed at the optimized reaction condition. This method provides a potentially useful tool for Hg(2+) detection.