In this study, luminescent upconversion nanoparticles (UCNPs) Y2O3 and Gd2O3 co-doped with Yb3+ and Er3+ were prepared by the sol-gel method (SG). These NPs are able to absorb near infrared photons and upconvert them into visible radiation with a direct application in bioimaging, as an important tool to diagnose and visualize cancer cells. The UCNPs were coated with a thin silica shell and functionalized with amino groups for further folic acid conjugation to allow their interaction with folate ligands on the cell surface. Their physical properties were analysed by Transmission Electron Microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) measurements. The PL results revealed excellent luminescence properties on all core-shell UCNPs. Cytotoxicity experiments with concentrations of bare and aminosilane coated/functionalized UCNPs between 0.001 μg/mL to 1 μg/mL were tested on two different cell lines from human cervix carcinoma (HeLa) and human colorectal adenocarcinoma (DLD-1) with a colorimetric assay based on the reduction of MTT reagent (methy-134-thiazolyltetrazolium). The assays show that some concentrations of bare UCNPs were cytotoxic for cervical adenocarcinoma cells (HeLa); however, for human colorectal adenocarcinoma all UCNPs are non-cytotoxic. After UCNPs functionalization with silica-aminosilane (APTES/TEOS), all of the nanoparticles tested were found to be non-cytotoxic for both cell lines. The UCNPs functionalized in this work can be further conjugated with specific ligands and used as biolabels for detection of cancer cells.
Keywords: Aminosilane Functionalization; Biolabels; Nanoparticles; Sol-gel; Upconversion.