NaYbF@NaYF Nanoparticles: Controlled Shell Growth and Shape-Dependent Cellular Uptake.

This study presents a controlled synthesis of NaYbF@NaYF core-shell upconversion nanoparticles using the hot-injection technique. NaYF shells with tunable morphologies including long-rod, short-rod, and quasi-sphere are grown on identical NaYbF core nanoparticles by controlled injection of acetate or trifluoroacetate precursors. Mechanistic investigations reveal that anisotropic interfacial strain accounts for the preferential growth of shell layers along the -axis. However, the strain effect can be offset by the fast injection of shell precursors, leading to nearly isotropic growth of NaYF shells over the NaYbF core nanoparticles. The core-shell nanoparticles are further modified with DNA molecules and incubated with adenocarcinomic human alveolar basal epithelial cells. Based on a combination of characterizations by flow cytometry and confocal microscopy, favorable cellular uptake and DNA delivery are observed for the quasi-sphere nanoparticles, owing to the high dispersibility and easy membrane wrapping. The method described here could be extended to synthesize other types of functional nanostructures for the study of morphology-dependent properties.