Fluorophore-doped calcium phosphate nanoparticles for non-toxic biomedical applications

We report the synthesis of optically doped calcium phosphate nanoparticles (CPs), with and without surface coating with the biocompatible polymer chitosan. Trisilanol was used to restrict the size of calcium phosphate in the nano-dimension. The diameter of the nanoparticles was found to be less than 200 nm. A powder X-ray diffraction (XRD) study demonstrated the crystalline nature of the nanoparticles, largely matching with the XRD pattern of hydroxyapatite, which is the most common crystalline form of calcium phosphate. Upon fluorophore encapsulation in these nanoparticles, the optical properties of the fluorophore not only remained preserved, but also had enhanced stability against chemical quenching in comparison to its free form. In vitro analysis showed that these nanoparticles are taken up by cells, the uptake being enhanced upon coating with chitosan. No sign of in vitro cytotoxicity was observed in the dosages tested. Preliminary in vivo studies showed that oral administration of these nanoparticles in healthy Wistar rats, at a dose of 2000 mg kg(-1), did not result in any visible sign of acute toxicity. These results highlight the potential for CPs to be used as safe and efficient agents for optical bioimaging and drug delivery.