Au nanoparticle-hydrogel nanozyme-based colorimetric detection for on-site monitoring of mercury in river water

A sensitive on-site mercury sensing platform was developed for simple and effective monitoring of mercury levels in the field. The simple and practical mercury detection system was designed by integrating an Au nanoparticle-PEG hydrogel block nanozyme (Au-HBNz) into a polymer film-based colorimetric device. Upon addition of Hg²⁺ ions, Au-HBNz exhibited excellent peroxidase-like activity, catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine into a blue-colored product, which has a maximum absorbance at 652 nm. The resulting color intensity change was evaluated using a smartphone for simple and rapid Hg²⁺ detection with a broad detection range (0.008-20 μg∙mL^-1) and a linear concentration-response relationship (R² = 0.96). The detection limit (1.10 ng∙mL^-1) was lower than the maximum permissible Hg²⁺ levels in drinking water set by the World Health Organization (6 ng∙mL^-1) and U.S. Environmental Protection Agency (2 ng∙mL^-1). The recoveries of Hg²⁺ determination in river water by spiking Hg²⁺ samples ranged from 92 to 106%, which indicated high validity and applicability of the Hg²⁺ detection system for field measurements. Thus, the developed sensor enables highly selective and efficient real-time monitoring of Hg²⁺.