Decorated silica particles with terbium complexes as luminescent biomarker for cell imaging

Most commercially available fluorescent dyes used for cellular images are toxic and their luminescence is often outshined by the intrinsic autofluorescence of the biological medium, the use of long emission lifetime inherent of the lanthanide compounds is a viable alternative. This paper reports the development of a luminescent hybrid based on silica nanoparticles decorated with Tb3+ complexes suitable for use in exploratory tests as biomarkers in the visualization of CHO-k1 cells by microscopy techniques. To achieve this aim, spherical/spheroidal (∼125 nm) functionalized silica particles were prepared by the sol-gel method and had their surface functionalized covalently with Schiff base ligands. Tb3+ Complexes were bonded onto the particles surface by a step-by-step methodology approach. By zeta potential, it was possible to investigate the particles surface charge after each synthesis step, reaching a negative value for the final hybrid, which showed intense luminescence in the green region, where the Tb3+ 5D4 → 7FJ transitions were observed in the emission spectrum. After the benzoic acid ligand (BzAc) addition, there was an intensification of Tb3+ emission, as well as an increase in the emission lifetime. Concerning the biological application of the material, the CHO-k1 cell viability was evaluated by the MTT method in the presence of the SiO2-[Tb(SB)(BzAc)y] hybrid, and high biocompatibility was observed. The absorption process of particles by the cells was investigated by TEM, suggesting an endocytosis mechanism as a probable uptake process. The confocal images indicated a green emission of the biomarker due to the Tb3+, distributed through the cytoplasm, mainly closely to the cell nuclei. Therefore, the silica particles decorated with Tb3+ complexes proved to be suitable to act as biomarkers in biological assays and cellular imaging.