Multifunctional NaYF4:Yb/Er/Gd nanocrystal decorated SiO2 nanotubes for anti-cancer drug delivery and dual modal imaging

Silica nanotubes (SNTs) functionalized with magnetic and up-conversion luminescent (UCL) NaYF4:Yb/Er/Gd nanocrystals (NCs) (denoted as MUCNCs@SNTs) have been prepared by single-nozzle electrospinning based on a phase separation effect without any templates. Monodisperse and hydrophilic cubic alpha-NaYF4:Yb/Er/Gd NCs decorated with polyethyleneimine (PEI) were fabricated in a facile hydrothermal route. Then, the Gd3+-doped alpha-NaYF4:Yb/Er NCs were dispersed into the electrospinning precursor solution containing polyvinylpyrrolidone (PVP) and tetraethylorthosilicate (TEOS), followed by the preparation of precursor nanotubes via electrospinning process. Finally, after annealing at 600 degrees C, pure MUCNCs@SNTs were obtained. The biocompatibility test on L929 fibroblast cells using MTT assay reveals low cytotoxicity of the composites. Doxorubicin hydrochloride (DOX), a typical anti-cancer drug, was introduced into MUCNCs@SNTs to evaluate the loading and sustained release behaviours. The composite carriers provide pH-dependent drug release behaviour owing to abundant Si-OH active bonds of silica and its interactions with DOX. The in vitro cytotoxicity and cell uptake behaviour of the MUCNCs@SNTs for HeLa cells were evaluated. For in vitro magnetic resonance imaging (MRI), the composites show the promising spin lattice relaxation time (T-1) weighted effect and could potentially apply as a T-1-positive contrast agent. In addition, the composites show near-infrared UC luminescence and were successfully applied in the bioimaging of HeLa cells. Considering the good biocompatibility, high drug releasing content and pH-dependent drug release of the materials, these magnetic and luminescent composite nanotubes have potential applications in drug sustained release and magnetic resonance/UC luminescence modality imaging.