Lanthanide (=Ce, Pr, Nd and Tb) ions substitution at calcium sites of hydroxyl apatite nanoparticles as fluorescent bio probes: Experimental and density functional theory study

An interesting property of hydroxyl apatite is the ability to undergo cationic and anionic substitution. In this study, nano hydroxyl apatite(nHAp) substituted with four different lanthanide ions(LnO)(Cerium,Praseodymium,Neodymium and Terbium) is prepared by co-precipitation method and characterized by X-Ray Diffraction, Fourier Transform Infrared, Fluorescence and UV‐Visible Spectroscopy and Transmission Electron Microscopy, and Magic Angle Nuclear Magnetic Resonance techniques. Rietveld refinement and computational study using Density Functional Theory has provided information about the effect of LnO substitution on nHAp phase. These studies reveal changes in lattice parameters and preferential calcium sites for LnO substitution in apatite structure. Experimental results have shown that LnO substituted particles have shown an intense fluorescent emission under UV‐Visible excitation. The ability of prepared LnO substituted nHAp particles to inhibit oxidative stress in terms of reduction of hydrogen peroxide is also demonstrated. In- vitro biocompatibility has been assessed via adsorption of human plasma/serum proteins on the surface of nHAp. Adsorption of the protein on nHAp also leads to passivation against corrosion. Particles have shown excellent cell viability and better proliferation of MG-63 cell lines. These results may open new avenues for the development of bioactive materials for bone regeneration and smart fluorescent probes for bio imaging applications.