Regenerable Multifunctional Mesoporous Silica Nanocomposites for Simultaneous Detection and Removal of Mercury(II)

Abstract

Mercury (Hg²⁺) is a highly toxic and widespread environmental pollutant. Herein, a regenerable and highly selective core–shell structured magnetic mesoporous silica nanocomposite with functionalization of thymine (T) and T-rich DNA (denoted as Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposite) has been developed for simultaneous detection and removal of Hg²⁺. In this work, the thymine and T-rich DNA were immobilized onto the interior and exterior surface of outermost mesoporous silica, respectively. The detection mechanism is based on Hg²⁺-mediated hairpin structure formed by T-rich DNA functionalized on the exterior surface of the nanocomposites, where, upon addition of SYBR Green I dye, strong fluorescence is observed. In the absence of Hg²⁺, however, addition of the dye results in low fluorescence. The limit of detection for Hg²⁺ in a buffer is 2 nM by fluorescence spectroscopy. Simultaneously, the Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposite features a selective binding with Hg²⁺ between two thymines immobilized at the interior surface of the mesopores and exhibits efficient and convenient Hg²⁺ removal by a magnet. Kinetic study reveals that the Hg²⁺ removal is a rapid process with over 80% of Hg²⁺ removed within approximately 1 h. The applicability of the developed nanocomposites is demonstrated to detect and remove Hg²⁺ from samples of Xiangjiang river water spiked with Hg²⁺. In addition, distinguishing aspects of the Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposites for Hg²⁺ detection and removal also include the regeneration using a simple acid treatment and resistance to nuclease digestion. Similar process can be used to functionalize the Fe₃O₄@nSiO₂@mSiO₂ nanocomposites with other nucleic acids and small molecules for environmental and biomedical applications