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

In this work, SiO2 microspheres were first prepared by a conventional Stober 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.