Lanthanum-Doped Hydroxyapatite Nanoparticles as Biocompatible Fluorescent Probes for Cellular Internalization and Biolabeling

Abstract

Rod-shaped nanoparticles of lanthanum-doped hydroxyapatite (LA-HAp) were synthesized by a modified sol– gel method at a low temperature of 100 C. The (La+Ca):P ratio was maintained at 1.67 and the La/Ca+La ratio was varied as x= 0.02, 0.06 and 0.1. XRD, FTIR, EDAX and TEM analysis indicated that pure, crystalline La-incorporated HAp rod-shaped nanoparticles of 15–25 nm diameter and 100–120 nm length, were obtained. On increasing the concentration of La, from x= 0.02 to 0.1, an increase in crystallinity and crystallite size was achieved. These particles were internalized by human embryonic kidney and human adenocarcinoma cells and exhibited fluorescence when observed under TRITC and FITC filters using epifluorescence microscopy. La-HAp nanoparticles with x = 0.02 exhibited the highest internalization, maximum intracellular fluorescence and no cytotoxicity. The cell viability and internalization decreased with increases in La concentration. Nanoparticles corresponding to x= 0.1 exhibited spindle-shaped morphology with filopodia and the presence of stress granules.