Direct colorimetric visualization of mercury (Hg) based on the formation of gold nanoparticles

It is critical to be able to detect and quantify Hg²⁺ ions under aqueous conditions with high sensitivity and selectivity. The technique presented herein provides a direct way for simple colorimetric visualization of Hg²⁺ ions in aqueous solution, based on the formation of gold nanoparticles through the Hg²⁺ catalyzed HAuCl₄/NH₂OH reaction. The outstanding selectivity and sensitivity result from the well-known amalgamation process that occurs between mercury and gold. The entire procedure takes less than 20 min. The limit of detection (2 ppb) shows excellent potential for monitoring ultralow levels of mercury in water samples.