Luminescent lanthanide-doped calcium phosphate from oyster shell waste: an example of bright recycling

This research explores the transformation of biogenic CaCO3 microparticles (& Oslash; < 45 mu m) from oyster shell waste into luminescent Eu- or Tb-doped calcium phosphate (apatites), using a sustainable "one-step" and eco-friendly method. The full transformation was achieved at 200 degrees C via a dissolution-precipitation mechanism. Precipitates were composed of Eu- or Tb-doped apatite particles, with average sizes L = 163 +/- 7 nm and anisometric shapes for the former, and 41 +/- 8 nm and more isometric shapes for the latter. Alongside these, particles of either EuPO4nH(2)O or TbPO4nH(2)O (rhabdophane) were present. The physicochemical and electrokinetic analysis revealed the A- and B-carbonate substitutions and labile CO32- species in the apatite particles, and zeta-potentials approaching zero in the aqueous suspensions at physiological pH levels, indicating a tendency for particle aggregation. The luminescence properties, such as relative luminescent intensity and luminescence lifetimes, were dependent on the lanthanide content and the presence of the rhabdophane phase. The Ap-Ln samples demonstrated cytocompatibility, with cell viability exceeding 85% when incubated with murine pancreatic endothelial cells (MS1) and murine mesenchymal stem cells (m17.ASC), regardless of the lanthanide type or the particle dosage used (ranging from 0.1 to 100 mu g mL(-1)).