Cytotoxicity, genotoxicity and uptake detection of folic acid-functionalized green upconversion nanoparticles Y2O3/Er3+, Yb3+ as biolabels for cancer cells

Upconversion nanoparticles (UCNPs) have been used as biolabels for cancer cells due to their ability to absorb near-infrared photons and upconvert them into visible radiation. We reported the synthesis of UCNPs Y2O3/Yb3+, Er3+ (1, 1 mol%), which upon excitation with infrared photons (lambda = 980 nm) emit green color with a maximum peak centered at lambda = 550 nm. UCNPs were functionalized with folic acid (UCNPs-NH2-FA) and analyzed by transmission electron microscopy, Fourier transform infrared spectroscopy, XRD, DLS and photoluminescence measurements. UCNPs-NH2-FA had a particle size of 70 +/- 10 nm and exhibit a good luminescence spectrum in comparison with bare UCNPs. Cytotoxicity of different concentrations of bare and functionalized UCNPs was measured with the MTT assay in three cancer cell lines: human cervical adenocarcinoma (HeLa) and human breast adenocarcinoma cells (MDA-MB-231 and MCF-7). Some concentrations of bare UCNPs were cytotoxic for cells; however, after been functionalized, UCNPs resulted to be non-cytotoxic. Genotoxicity of bare and functionalized UCNPs was performed by the comet assay, and no DNA damage was found for any concentration. The internalization of UCNPs-NH2-FA into cancer cells was confirmed by confocal microscopy showing a cytoplasmic fluorescence signal. UCNPs-NH2-FA were used to detect cancer cells in suspension by flow cytometry, with a specific green fluorescent signal for effective detection of cells. These results confirm that functionalized UCNPs can be used without any cytotoxic or genotoxic effects for bioimaging to detect and visualize cancer cells.