Hydroxyapatite nanomaterials co-doped with Gd3+ and Eu3+ for luminescent imaging and targeted drug delivery

Nanomaterials have been extensively investigated for diagnostic and therapeutic applications in various diseases. Among them, hydroxyapatite (HAp) stands out due to its bioactivity and chemical similarity to the inorganic component of bone, as well as its ability to accommodate ionic substitutions that confer new functional properties. Doping with rare earth elements is preferred because their atomic radii are like that of calcium (Ca2+), allowing efficient incorporation into the crystal structure. Europium (Eu3+) is widely used due to its luminescent properties, making it suitable for various imaging applications. However, high concentrations may induce cytotoxic effects, while low concentrations can result in insufficient luminescence for high-performance biomedical applications. To overcome this limitation, gadolinium (Gd3+) is introduced as a second dopant, acting as a sensitizer ion that promotes energy transfer between rare earth ions, enhancing luminescence without compromising biocompatibility. Additionally, Gd3+ exhibits paramagnetic behavior and is widely used as a contrast agent in magnetic resonance imaging (MRI). In this study, Eu3+/Gd3+ co-doped HAp was synthesized via hydrothermal treatment and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), vibrating sample magnetometry (VSM), and photoluminescence analyses. Drug incorporation and release studies using ciprofloxacin were conducted to evaluate the potential of these nanocomposites for controlled drug delivery. The results confirmed suitable luminescent and magnetic properties, demonstrating the potential of these systems for imaging applications and targeted therapies.