Surface PEGylation and biological imaging of fluorescent Tb3+-doped layered double hydroxides through the photoinduced RAFT polymerization

Tb3+-doped layered double hydroxides (LDHs) exhibit excellent optical characteristics, uniform size and uniform morphologies when synthesized through a hydrothermal method. However, due to their lack of functional groups and poor dispersibility, applications of these fluorescent Tb3+-doped LDHs have been largely impeded especially in the biomedical fields. In this work, a novel strategy was developed for the surface modification of these fluorescent Tb3+-doped LDHs using photoinduced surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with hydrophilic poly(ethylene glycol) methacrylate (PEGMA) as the monomer. The final products were obtained via the metal free surface-initiated RAFT polymerization with light irradiation. Successful preparation of these fluorescent LDHs polymer composites (LDH-PEG) was confirmed by a number of analytical technologies, such as transmission electron microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. In addition, laser scanning confocal microscope was employed to examine the cell uptake behavior of the LDH-PEG composites and evaluate their potential for biomedical applications. We demonstrated that the hydrophilic monomer PEGMA could be facilely grafted on the surface of Tb3+-doped LDHs through metal free photoinduced surface-initiated RAFT polymerization. The resultant LDH-PEG composites displayed high water dispersibility, strong fluorescence, low cytotoxicity and a desirable cell uptake performance. These features of the LDH-PEG composites indicated their great potential for biomedical applications. More importantly, photoinduced RAFT polymerization has the advantages of a conventional controlled living radical polymerization, which could overcome drawbacks such as toxicity, the fluorescence quenching effects of metal catalysts and the complex synthesis of chain transfer agents. Therefore, this method could be an alternative tool for the surface modification of materials and fabrication of multifunctional fluorescent nanomaterials based polymer composites. (C) 2018 Elsevier Inc. All rights reserved.