Mesoporous
silica nanoparticles functionalized by surface hyperbranching polymerization of
poly(ethylene imine), PEI, were further modified by introducing both fluorescent and targeting moieties, with the aim of specifically targeting
cancer cells. Owing to the high abundance of
folate receptors in many
cancer cells as compared to normal cells,
folic acid was used as the targeting
ligand. The internalization of the particles in cell lines expressing different levels of
folate receptors was studied. Flow cytometry was used to quantify the mean number of nanoparticles internalized per cell. Five times more particles were internalized by
cancer cells expressing
folate receptors as compared to the normal cells expressing low levels of the receptor. Not only the number of nanoparticles internalized per cell, but also the fraction of cells that had internalized nanoparticles was higher. The total number of particles internalized by the
cancer cells was, therefore, about an order of magnitude higher than the total number of particles internalized by normal cells, a difference high enough to be of significant
biological importance. In addition, the biospecifically tagged hybrid PEI-
silica particles were shown to be noncytotoxic and able to specifically target
folate receptor-expressing
cancer cells also under coculture conditions.