Synthesis and Biological Applications of Upconverting Nanoparticles: Observations of Intracellular and Intercellular Dynamics

Abstract

Upconverting nanoparticles (UCNPs) are promising imaging probes due to their advantages such as no auto-fluorescence from biological samples, low photo-toxicity, deep penetration depth, and photostability because of the NIR excitation. However, as-synthesized UCNPs cannot be directly used in bio-imaging. For upconversion emission efficiency, core/shell structure UCNPs should be required due to quenching effect in core only UCNPs. Also, the surfaces of UCNPs are hydrophobic by their capping surfactants such as oleic acid and oleylamine. Thus, surface modification with hydrophilic groups should be required. The modified UCNPs by ligand exchange or ligand attraction, they can be used in bio-imaging and bio-tracking. In Chapter II, cellular uptake efficiency depending on surface charges and TAT peptide were researched with UCNPs-PEG-COOH, UCNPs-PEG-NH2, and UCNPs-TAT as probes. TAT peptide is cell-penetrating peptide, thus, UCNPs-TAT showed the most uptake efficiency. Also, after 24 h, they were remained in cells, whereas other types of UCNPs were not by exocytosis. In Chapter III, with two types of UCNPs (Er-doped UCNPs and Tm-doped UCNPS), cell-cell communications were observed. There are two types for cell-cell communications, contact-dependent communications and contact-independent communications. One group of cell were incubated with Er-doped UCNPs, and the other group of cells were incubated with Tm-doped UCNPs. After that, two groups of the cells were mixed and incubated. Through endocytosis and exocytosis of UCNPs between cells, cell-cell communications could be reserached.