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

Abstract

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 H₂L^1–3 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.