Visible light sensitized attapulgite-based lanthanide composites: microstructure, photophysical behaviour and biological application

Abstract

Attapulgite, an extremely stable fibrillar mineral present in nature, is a promising new carrier of luminescent lanthanide complexes for further applications. A europium complex Eu(DBM)₃(H₂O)₂ (HDBM = dibenzoylmethane) was covalently coupled onto modified attapulgites (or silica nanoparticles) via a ligand exchange reaction, generating attapulgite-based ternary europium complexes. The composites were characterized by CHN elemental analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for Eu³⁺ content, powder X-ray diffraction (XRD), thermogravimetry (TG) and UV-vis absorption spectra. The results indicate that the Eu³⁺ complex was grafted covalently to the outer surfaces of attapulgites (or silica nanoparticles) and modifications by coupling agents containing different alkoxide groups (aminopropyltriethoxysilane (APTES) or aminopropylmethyldiethoxysilane (APMDES)) led to different grafting ratios. The structures of these composites were further evidenced by the determination of photophysical behaviours and coordinated water molecules of the complexes linked to matrices. Attapulgite-based lanthanide composites linked by APTES can be excited by visible light, with a wide excitation wavelength range from UV to visible light (a maximum at 398 nm), long luminescence lifetime (503 μs), high quantum yield (48%) and improved exposure durability. When incubated with HeLa cells at 37 °C, the fluorescence of matrix-APTES-cpa-Eu(DBM)₃ is observed on the cell membrane. Moreover, the low cytotoxicity of our present system results in potential applications for cell imaging in biological systems.