RGDS- and TAT-Conjugated Upconversion of NaYF₄:Yb³⁺/Er³⁺&SiO₂ Nanoparticles: In Vitro Human Epithelioid Cervix Carcinoma Cellular Uptake, Imaging, and Targeting

Starting NaYF4:Yb(3+)/Er(3+) nanoparticles with size tuned from 24 to 33 nm were prepared by high-temperature coprecipitation of lanthanide chlorides in high-boiling organic solvents. To enhance colloidal stability in aqueous medium, an aminosilica shell was introduced on the surface by hydrolysis and condensation of tetramethyl orthosilicate and (3-aminopropyl)trimethoxysilane using a reverse microemulsion technique; to form alkyne groups, reaction with 4-pentynoic acid followed. Finally, the cell adhesive and cell penetrating azidopentanoyl-GGGRGDSGGGY-NH2 (RGDS) and azidopentanoyl-GGGRKKRRQRRR-NH2 (TAT) peptides were conjugated to the upconversion particles via Cu(I)-catalyzed alkyne-azide cycloaddition. The concentrations of the peptides bound to the nanoparticle surfaces and amount of adsorbed residual Cu(I) catalyst were determined using an (125)I-radiolabeled RGDS peptide and a (64)Cu(I)-doped catalyst, respectively. Targeting and uptake of the RGDS- and TAT-conjugated NaYF4:Yb(3+)/Er(3+)&SiO2 nanoparticles by human cervix carcinoma HeLa cells were monitored by confocal microscopy. RGDS-conjugated nanoparticle probes were mainly localized on the cell plasma membrane due to specific binding of the peptide to the corresponding integrins. In contrast, the TAT-conjugated nanoparticles were able to cross the cell membrane and accumulate in the cell cytoplasm. Thus, this new peptide bioconjugation approach supported both extra- and intracellular nanoparticle uptake, enabling targeting and imaging of the specific tumor phenotypes.