Calcium phosphate nanoparticles : colloidally stabilized and made fluorescent by a phosphate-functionalized porphyrin

Calcium phosphate nanoparticles were prepared by precipitation and colloidally stabilized by surface functionalization with 5,10,15,20-tetrakis(4-phosphonooxyphenyl)porphine (p-TPPP). No other stabilizing agents were necessary, and all dissolved counter-ions and excess porphyrin were removed by ultracentrifugation. The resulting porphyrin-functionalized nanoparticles were spherical with a diameter of about 250 nm. The adsorption of porphyrin on the calcium phosphate surface was confirmed by IR spectroscopy and quantified by elemental analysis (the loading was about 4-5 wt% porphyrin). In a cell culture with NIH 3T3 fibroblast cells, the particles showed excellent biocompatibility (confirmed by an MTT test), and their uptake into the cells could be followed by confocal laser scanning microscopy. Hence, these biocompatible nanoparticles may be used as biocompatible fluorescing agents or for the delivery of fluorescing molecules.