New nanotools for the imaging of cancer cells have been synthesized. Two-photon dye-doped 3-aminopropyltriethoxysilane-grafted mesoporous silica nanoparticles (MSN) have been grafted with folic acid (FA) functionalized PEG groups. Amine-PEG groups were first reacted with an activated ester derivative of FA. A mixture of FA- and hydroxyl-PEG has then been reacted with the amino groups at the surface of the particles. Cell culture experiments performed with MCF7 and HeLa cancer cells demonstrated that these functionalized MSN showed a low cytotoxicity even after a 24 hours incubation time at high concentrations. These modified MSN are promising for applications in the field of two-photon imaging and their potentiality for photodynamic therapy is currently being investigated.