Laser-induced fluorescence with hyperspecral imaging of europium-doped hydroxyapatite: a novel photoluminescent bioactive ceramic material with minimal cytotoxicity on astrocyte primary cell cultures and RAW 264.7 cell line

Abstract

The virtue development of photo-luminescent material for biomedical imaging and drug delivery systems has become a vital need for diagnosis and treatment purposes. Hydroxyapatite (HA) demonstrates a flexible structure that could accommodate different ions. The proper integration of rare earth elements into the HA structure could offer novel photoluminescence properties with minimal cytotoxicity. In the present study, Europium was precisely integrated into the HA structure via a hydrothermal-assisted co-precipitation technique. Highly crystalline mono-dispersed europium-hydroxyapatite (Eu-HA) nanorods of 80 nm length were developed. Eu-HA maintained the crystalline structure of HA with minimal change. XPS spectroscopy confirmed the partial replacement of calcium with europium ions. Whereas HA demonstrated Ca/P ratio of 1.405, Eu-HA demonstrated Ca/P ratio of 0.118. The atomic percent of Europium was reported to be 6.91%. Eu-HA nanorods exhibited strong fluorescence at 686 nm when stimulated with a UV laser source at 390 nm. Hyperspectral imaging and K-Means clustering enabled high discrimination and delineation of Eu-HA, highlighting its potential for biomedical imaging. Cytotoxic MTS and MTT assays were conducted to evaluate the cytotoxicity of Eu-HA nanocomposite on astrocytes cultured from male and female Sprague-Dawley rat pups, as well as the mouse leukaemic monocyte macrophage (RAW 264.7) cell line. Eu-HA was incubated in the cell in concentrations ranging from 6.25 to 100 µg/ml. Eu-HA nanocomposite demonstrated minimal cytotoxicity; Eu-HA did not alter cell viability in male or female astrocyte primary cell cultures, nor in the RAW 264.7 cell line. The developed Eu-HA nanorods demonstrated consistent product quality, superior photo-luminescent properties, and minimal cytotoxicity.