Thiol terminated chitosan capped silver nanoparticles for sensitive and selective detection of mercury (II) ions in water

In this paper, we report a simple method for the optical detection of environmentally toxic mercury (II) ions (Hg2+) in water using chitosan capped silver nanoparticles (Ch–Ag NPs). The yellow colored aqueous solution of Ch-Ag NPs instantly (10 s) became colorless with addition of Hg2+ ions. Cu2+, and Fe3+ ions also produced colorless solution after 1 min. To overcome the Cu2+ and Fe3+ interference, thiol terminated chitosan was synthesized via amide coupling formation between amine group of chitosan and carboxylic acid group of 3-Mercaptopropanoic acid (3-MPA). The detailed study of selectivity, sensitivity, effect of interfering radicals, and response time confirmed that thiol terminated chitosan capped silver nanoparticles (Mod-Ch-Ag NPs) are highly selective and speedy for Hg2+ ions detection. The limit of detection was found to be 5 ppb. Furthermore, since the change in color with addition of mercury can be observed by naked eye, the developed nanosensor can also be utilized for real field applications. Hydrogel of Mod-Ch–Ag NPs was successfully synthesized and it was also found highly specific for Hg2+ ions. It was observed that separation of Hg2+ ions is also possible by simply changing the pH of the solution containing colorless Hg2+ with Mod-Ch-Ag NPs.