A method was developed for Hg2＋ quantitative determination using the Hg2＋ aptamer to modify gold nanoparticles (AuNP). The aptamer would adsorb onto the AuNP and help to enhance the AuNP stability against salt-induced aggregation. But this attraction was weaker than the affinity between the target (Hg2＋) and the aptamer. So if the proper Hg2＋ and aptamer were put into the AuNP solution, addition of salt resulted in aggregation of AuNP that led to red-to-blue color change. And the maximum absorption wavelength would change from 520 to 620 nm. Before detecting Hg2＋, the concentrations of NaCl and aptamer were optimized, and the appropriate pH was chosen. Under optimal conditions, the absorption ratio A620/A520 was proportional to the concentration of Hg2+ in the range of 5.0×10－9 to 7.2×10－7 mol•L－1 and the detection limit was 3.3×10－10 mol•L－1. Interferences from selected inorganic ions were investigated and the proposed method was simple and sensitive.

Key words: gold nanoparticle, aptamer, Hg2＋, UV-Vis spectra