Fluorescent Porous Silica Microspheres for Highly and Selectively Detecting Hg2+ and Pb2+ Ions and Imaging in Living Cells

Abstract

In this work, SiO₂ microspheres were first prepared by a conventional Stöber method and then etched by NaOH solution to obtain porous ones. By tuning the degree of etching, specific surface area of SiO₂ microspheres could be controlled. Then, small fluorescent molecules are synthesized and incorporated onto the surface and/or pores of the SiO₂ via layer-by-layer reaction to obtain fluorescent microspheres, namely, SiO₂-NH₂-BODIPY (SiNBB), SiO₂-NH₂-BODIPY-indole-benzothiazole (SiNBIT), and SiO₂-NH₂-BODIPY-indole-benzoxazole (SiNBIO). The as-prepared microspheres SiNBB exhibit highly sensitive and selective recognition ability for Hg²⁺ and Pb²⁺. When SiNBB encounters Hg²⁺ and Pb²⁺, the fluorescence intensity of SiNBB is increased up to fivefold. SiNBIT and SiNBIO are solely sensitive to Hg²⁺, and both have a single high sensitivity to recognize Hg²⁺. The adsorption efficiency of Hg²⁺ by the three fluorescent microspheres SiNBB, SiNBIT, and SiNBIO reached 2.91, 0.99, and 0.98 g/g of microspheres, respectively. Experimental results of A549 cells and zebrafish indicate that the fluorescent microspheres are permeable to cell membranes and organisms. The distribution of Hg²⁺ in the brain of zebrafish was obtained by the fluorescence confocal imaging technique, and Hg²⁺ was successfully detected in A549 cells and zebrafish.