Highly selective and quantitative colorimetric detection of mercury(II) ions by carrageenan-functionalized Ag/AgCl nanoparticles

The natural algal polysaccharide carrageenan was used for the greener synthesis of silver/silver chloride nanoparticles (Carr-Ag/AgCl NPs) without any toxic chemicals. We report the robust, highly selective, and sensitive colorimetric sensing of Hg2+ ions using Carr-Ag/AgCl NPs without any further surface modification. The dark-brown color of a solution of Carr-Ag/AgCl NPs turned to white in a concentration-dependent manner with the addition of Hg2+ ions, confirming the interaction of Carr-Ag/AgCl NPs with Hg2+ ions. The plot of the extinction ratio of absorbance at 350 nm to 450 nm (A350/A450) for Carr-Ag/AgCl NPs against the concentration of [Hg2+] ions was linear, and the calibration curve was A350/A450 = 1.05254 + 0.00318 × CHg with a lower detection limit of 1 μM. This portable and cost-effective method for mercury(II) ion sensing is widely applicable in on-field qualitative and quantitative measurements of [Hg2+] ions in environmental or biological samples.