Hydroxyapatite nano particles doped with Gd3+, Yb3+/Tm3+ and Eu3+ as lumino-magnetic multimodal contrast agents

Abstract

Hydroxyapatite (HAp) has been widely used as bone reconstruction materials due to their similarity to bone tissue. The improvement of HAp properties was achieved by doping its crystal lattice with different ions. Lanthanides, i.e. Rare Earth Elements (RE) are also suitable for doping HAp. The aim of the presented research was to investigate the possibility of creating lumino-magnetic particles of HAp doped with gadolinium (Gd3+) ions and co-doped with ytterbium/thulium (Yb3+/Tm3+) or europium (Eu3+) ions for potential use in multimodal imaging (MI). Pure HAp (Ca5(PO4)3(OH)), magnetic HAp:Gd (Ca4.85Gd0.15(PO4)3(OH)), and lumino-magnetic HAp:Gd/Yb/Tm (Ca4.85Gd0.03Yb0.1Tm0.02(PO4)3(OH)) and HAp:Gd/Eu (Ca4.94Gd0.02Eu0.04(PO4)3(OH)) particles were synthesized using emulsification process and hydrothermal processing. All synthesized particles had an elongated shape and exhibited a paramagnetic behavior. Reduction of the unit cell volume as a result of replacement of Ca2+ ions by ions with a smaller ionic radius (Gd3+, Yb3+, Tm3+, Eu3+) confirmed by using XRD and Rietveld refined plots. The energy band gap values of the synthesized samples range from 4.93 to 3.18 eV and decrease in the following order: HAp:Gd >HAp>HAp:Gd/Eu>HAp:Gd/Yb/Tm. The results of photoluminescence emission spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu particles showed characteristic transitions of Tm3+ and Eu3+, respectively.