Porous Ag-Chitosan Nanospheres Bridged by Cysteine Residues for Colorimetric Sensing of Trace Hg<sup>2+</sup>
Lin Xing, Qi Zhao, Xiaoyu Zheng, Mingwei Hui, Yalin Peng, Xiao Zhu, Lei Hu, Wenli Yao, Zhengquan Yan
Abstract
To enhance the sensing performance of precious metal nanomaterials, porous Ag-chitosan nanospheres (AgNPs-cys-CS) were developed for the first time in this work. There was a strong coordination bonding interaction between the Ag nanospheres and the −SH groups in cysteine, accompanied by hydrogen bonds or esterification between the −OH groups in chitosan and the −COOH groups in cysteine. Porous Ag nanospheres and chitosan chains were bridged by cysteine residues. After its structure and properties were characterized in detail, we found that the AgNPs-cys-CS material expressed exclusive colorimetric recognition of Hg2+ with a color change from yellow to colorless. Under the optimized conditions, the partitioned linear range of cHg2+ was quite wide from 8.0 to 14 000.0 × 10–8 mol·L–1 and the detection limit was 1.2 × 10–9 mol·L–1, far below the restricted limit for the presence of Hg2+ in drinking water set by the World Health Organization. After detection, more than 92.8% of the Hg2+ in the samples was separated by a simple filtration process. The secondary pollution caused during the detection process was eliminated accordingly. The action mechanism was proposed to form silver amalgam on the surface of the AgNPs-cys-CS by virtue of the reducibility of chitosan.