A self-assembling luminescent lanthanide molecular nanoparticle with potential for live cell imaging.

Four luminescent 32-metal Cd-Tb nanoclusters, [Tb8Cd24(L1)12(OAc)48] (1), [Tb8Cd24(L2)12(OAc)48] (2), [Tb8Cd24(L3)12(OAc)48] (3) and [Tb8Cd24(L2)12(1,4-BDC)4(OAc)38(OH)2] (4), were constructed from three specially designed chain-like Schiff base ligands H2L1-3 with flexible carbon-carbon backbones containing 5, 6 and 10 methylene units, respectively. The clusters exhibit drum-like structures and can be imaged using transmission electron microscopy (TEM). In addition to the Schiff base ligands (the primary energy transfer donors), four 1,4-BDC bridging units were successfully introduced into the structure of 4. In addition to providing increased structural stability, the 1,4-BDC units act as secondary energy transfer donors providing extra energy for lanthanide luminescence, which results in improved luminescence properties when compared to those of the related Cd-Ln nanoclusters without 1,4-BDC units. In vitro investigations on 4 with SGC and PANC cancer cells revealed an accumulation of the molecular nanoparticles in the cells, as confirmed by confocal microscopy. The cytotoxicity of 4 toward the SGC and PANC cells is moderate (IC50 values of 4 lie in the range of 15-60 μM). ICP-MS analysis reveals that cellular uptakes of 4 in 1000 SGC and PANC cells after treatment for 3 hours are 0.0094 pmol and 0.015 pmol, respectively.