Surface Modification of Hydroxyapatite Nanocrystallite by a Small Amount of Terbium Provides a Biocompatible Fluorescent Probe

Abstract

As the main inorganic component of biological bone and tooth enamel, hydroxyapatite (HAP) is highly biocompatible and bioactive. Our recent work has shown that 20 nm HAP can be readily internalized by living cells. However, HAP nanoparticles are not luminescent so that they are difficult to measure in living cells during in vitro experiments. A novel inorganic biological probe was suggested by doping 20 nm HAP with terbium. The calcium ions on the HAP particle surface could be partially replaced by Tb, which resulted in the 20 nm Tb-HAP particles. The Tb-doped HAP became luminescent and could be observed under a visible excitation of 488 nm. Compared with the usual probes, the modified HAP nanoparticles were more photostable and were almost nontoxic. It was important that the HAP characteristics remained after the surface modification with a small amount of Tb. After incubating with rabbit bone marrow mesenchymal stem cells (MSCs) in culture, the luminescence of the internalized HAP in the living cells was clearly observed under a fluorescent microscope. Transmission electron microscopy analysis also confirmed the uptake of the particles by MSCs. It was demonstrated that the modified HAP was a stable biological probe for cellular research. We suggested that the Tb-doped HAP should have a great potential to trace the evolvement of nanoparticles, which is a key topic in nanobiotechnology.

Nanodimensional and Nanocrystalline Calcium Orthophosphates

“…To conclude this part, the nano-sized particles of apatite might be functionalized and/or doped by various compounds (even by quantum dots [509,510]) to provide new important properties [495,[511][512][513][514][515][516][517][518], e.g., fluorescence[27-29, 515,516] and luminescence [54,60,510,517,518]. Both fluorescence and luminescence can be used as a tracking property for the nano-sized particles to give an observable indication of agent delivery, while the particles are served to protect the agent in vivo until it has reached the destination.…”

Shape-controlled synthesis of F-substituted hydroxyapatite microcrystals in the presence of Na2EDTA and citric acid

“…Artificially synthesized HAp and FHAp are widely used in biomedical fields such as bone regeneration, dental materials and drug delivery system [1][2][3]. They are also used industrially in catalyst, sensors, fluorescence materials, chromatography, and environmental phosphorus recovery [4][5][6][7][8][9]. These applications originate from the unique physical and chemical properties of HAp or FHAp which depend not only on the composition and structure but also on the particle dimension (shape and size) [10][11][12][13][14][15][16].…”

3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite

“…It is of course also possible to introduce guest species into non-porous crystalline hosts, forming traditional solid solutions78. Foreign ions with appropriate size and charge can be exchanged for ions of the parent lattice, and judicious selection of the dopant can create a material with new optical, magnetic and electronic properties.…”