Nanotoxicological Assesment and Cell Internalization for Cancer Cells of Luminescent Nanoparticles

The detection of cancer cells by bioimaging with luminescent nanoparticles instead of usual dyes is being eagerly investigated. In this study we prepared upconversion (UCNPs) and downconversion (DCNPs) nanoparticles (NPs) by sol-gel method. The UCNPS uses a near infrared beam (NIR λ=980 nm) as the excitation source to upconvert the energy into light in the visible region. The present study used UCNPs: Y₂O₃/Gd₂O₃:Yb³⁺/Er³⁺ capable of emitting red or green photons of 660 nm and 550 nm wavelength. The DCNPs were: Y2O3:Eu³⁺ and Eu³⁺/Bi³⁺ excited at λ=250 nm and 330 nm with red emission at 660 nm. The functionalization was done by aminosilanes and folic acid (FA-UCNPs and FA-DCNPs). Folic acid binds to the folate receptor on the surface of certain types of cancer cells, and this binding promotes internalization of the NPs via endocytosis. The NPs were characterized by TEM, EDS, and FTIR. Cytotoxicity was also analyzed using the MTT (methy-134 thiazolyltetrazolium) colorimetric assay. Finally, cellular uptake of FA-UCNPs was determined using flow cytometry and epifluorescence microscopy; we also did a comparison between cellular uptake of spheroidal NPs and two-dimensional (2D) cell culture models, also known as monolayers, finding that the architectural arrangement of 3D cell cultures allowed up to 20% more internalization of FA-UCNPs than in 2D cell arrangements.