Luminescent
europium(III)-doped nanoporous
silica nanospheres (Eu:NPS) were successfully synthesized, and a
folate N-hydroxysuccinimidyl
ester (FA-NHS) molecule as a targeting
ligand for
cancer cells was immobilized on the
nanosphere surfaces through mediation of the
3-aminopropyltriethoxysilane (APTES) adlayer. The ordered nanopores were preserved by the immobilization, and the specific surface area decreased only with the APTES immobilization, suggesting that the FA-NHS was predominantly immobilized on the outer surface of the nanopores. The photoluminescence of the
nanospheres functionalized with
folic acid (FA) exhibited a characteristic peak due to the interactions (e.g., energy transfer) between FA and Eu(3+), and further the orange luminescence could be clearly detected by fluorescence microscopy in air and water. Furthermore, the
nanospheres highly dispersed in cell culture medium exhibited nontoxicity in the cellular proliferation stages of the Hela
cancer cells and NIH3T3 fibroblasts and specifically bind to the Hela cells. The
nanospheres after the binding and uptake also showed intense luminescence from the outer/inner cell surfaces for the culture time of 4 days. Therefore, the luminescent FA-functionalized Eu:NPS
nanospheres could be used for specific targeting and imaging abilities for
cancer cells.