Luminescent Tb³⁺/Sm³⁺ co-doped hydroxyapatite nanoparticles as an imaging probe in N2a cells

This work reports the synthesis of hydroxyapatite (HAp) nanoparticles co-doped with trivalent terbium (Tb³⁺) and samarium (Sm³⁺) ions by a surfactant free chemical precipitation method. Co-doping enables to combine the optical properties of Tb³⁺ and Sm³⁺ ions. Characterization techniques like X-Ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), energy dispersive X-ray spectroscopy (EDX) were used to determine the crystalline and structural properties. These studies confirmed that the lanthanide ions Tb³⁺ and Sm³⁺ were successfully doped onto the HAp lattice. The photoluminescence emission spectra exhibited intense emissions from both the lanthanide ions. The Sm³⁺ photoluminescence spectra showed enhanced emission,indicating that energy is being transferred from the Tb³⁺ to Sm³⁺ ions. To examine the cell viability, N2a cellswere subjected to the MTT cytotoxicity assay. As demonstrated by the cell imaging on N2a cells, the synthesised nanoparticles are ideal candidates for fluorescent labelling using lanthanide ions. Furthermore, thestrong cytocompatibility of Tb³⁺/Sm³⁺ co-doped hydroxyapatitesuggests that it is a promising nanoscale biomaterial.