Rare earth element doped hydroxyapatite luminescent bioceramics contrast agent for enhanced biomedical imaging and therapeutic applications

The design and synthesis of alternative biocompatible, luminescent bioimaging agent for application in diagnostics imaging and preventive medicine is very important for the future of biomedicine. With an advanced flexible structure of hydroxyapatite (HAp), rare earth ions (Gd3+, Eu3+) were doped to achieve an enhanced luminescent optical property. A facile wet co-precipitation method was employed to dope Gd3+, and Eu3+ on host HAp structure (Eu-x-Gd-x-HAp). Different sophisticated characterization instruments, such as powder X-Ray diffraction, Fourier transformed infrared (FTIR) spectroscopy, micro Raman spectroscopy, Thermogravimetric-differential thermal analysis (TG-DTA), Brunauer-Emmett-Teller (BET) surface area analysis confirms the hexagonal crystal structure, functional groups, high thermal stability, with large surface area and average pore size. The optical properties were measured by diffusive reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and fluorescence imaging. The enhanced luminescence could be observed due to "Gd-Eu" co-doping, which causes energy transfer (I-6(J) of Gd3+-> H-5(J) of Eu3+) under 273 nm excitation with possible combination effect of the cooperative up-conversion and subsequent energy transfer under 394 nm excitation respectively. The in vitro study confirms the intracellular nontoxic behavior of Eu-x-Gd-x-HAp nanocrystals with good biocompatibility. Further in vivo studies with Eu-x-Gd-x-HAp nanocrystals confirms the cell labelling and in vivo imaging capabilities. The synthesized biocompatible, nontoxic Eu-x-Gd-x-HAp nanomaterials has the potential to act as a luminescence enhanced contrast agent for biomedical fluorescent imaging applications.