Sensitive Colorimetric Hg2+ Detection via Amalgamation-Mediated Shape Transition of Gold Nanostars

Dong Xu; Shufang Yu; Yueqin Yin; Suyan Wang; Qinlu Lin; Zhiqin Yuan

doi:10.3389/fchem.2018.00566

Sensitive Colorimetric Hg²⁺ Detection via Amalgamation-Mediated Shape Transition of Gold Nanostars

Front Chem. 2018 Nov 27:6:566. doi: 10.3389/fchem.2018.00566. eCollection 2018.

Authors

Dong Xu^{1

2}, Shufang Yu^{1

2}, Yueqin Yin^{1

2}, Suyan Wang^{1

2}, Qinlu Lin^{1

2}, Zhiqin Yuan³

Affiliations

¹ National Engineering Laboratory for Rice and By-Products Further Processing, College of Food Science and Engineering, Central South University of Forestry and Technology, Changsha, China.
² Hunan Key Laboratory of Processed Food for Special Medical Purpose, College of Food Science and Engineering, Central South University of Forestry and Technology, Changsha, China.
³ State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, China.

Abstract

Reliable and sensitive methods to monitor mercury levels in real samples are highly important for environment protection and human health. Herein, a label-free colorimetric sensor for Hg²⁺ quantitation using gold nanostar (GNS) has been demonstrated, based on the formation of Au-Hg amalgamate that leads to shape-evolution of the GNS and changes in its absorbance. Addition of ascorbic acid (AA) to GNS solution is important for quantitation of Hg²⁺, mainly because it can reduce Hg²⁺ to Hg to enhance amalgamation on the GNSs and stabilize GNSs. In addition to transmission electron microscopy images, the distribution of circular ratios of GNSs in the presence of 2 mM AA and various concentrations of Hg²⁺ are used to show the morphology changes of the GNSs. Upon increasing the concentration of Hg²⁺, the average circular ratio of GNSs decreases, proving GNS is approaching to sphere. The morphology change alters the longitudinal localized surface plasmonic resonance (LSPR) absorbance of the GNSs significantly. Under the optimum conditions, our sensor exhibits a dynamic response for Hg²⁺ in the range of 1-4,000 nM with a detection limit of 0.24 nM. Upon Increasing Hg²⁺ concentration, the solution color changes from greenish-blue, purple to red, which can be distinguished by the naked eye when the Hg²⁺ concentration is higher than 250 nM. Owing to having a high surface-to-volume ratio and affinity toward Hg⁰, the GNS is sensitive and selective (at least 50-fold over tested metal ions like Pb²⁺) toward Hg²⁺ in the presence of AA. Practicality of this assay has been validated by the analysis of water samples without conducting tedious sample pretreatment.

Keywords: Hg2+ quantification; LSPR sensing; amalgamation; gold nanostar; morphological transformation.