Microwave-assisted synthesis of dual responsive luminomagnetic rare earth metal ions (Nd3+, Dy3+) co-doped nanohydroxyapatite for biomedical applications

The existing demand for the development of innovative multimodal imaging nanomaterial probes for biomedical applications stems from their unique combination of dual response modalities, i.e., photoluminescence (PL) and magnetic resonance imaging (MRI). In this study, for the first time, neodymium (Nd3+) and dysprosium (Dy3+) rare earth (RE) metal ions were co-doped into a hydroxyapatite (HAp) crystal lattice using a simple microwave-assisted synthesis technique to incorporate the essential properties of both the lanthanides in HAp. Theoretical as well as experimental studies were performed on novel Nd:Dy:HAp nanoparticles (NPs) to understand their photoluminescence and magnetic behaviour. Through co-precipitation, RE (Nd3+, Dy3+) ions were effectively integrated into the HAp crystal lattice, where they preferentially occupied the calcium ion (Ca2+) sites. The as-synthesized HAp, Nd:HAp, Dy:HAp, and Nd:Dy:HAp samples were characterized using different analytical tools. The PL and magnetic characteristics of Nd:Dy:HAp were dependent on the RE dopant ion type and concentration. In comparison with the pure HAp, the RE co-doped (Nd:Dy:HAp) NPs displayed multimodal features due to efficient energy transfer from the Nd3+ (sensitizer) to the Dy3+ (activator) ions. Furthermore, Nd:Dy:HAp NPs had good antimicrobial properties and they also displayed low cell toxicity effects. Hence, Nd:Dy:HAp NPs are attractive biomaterials for PL and MRI applications (e.g. permanent bone and tooth implants) and they can effectively be utilized in the biomedical industry for target-specific drug delivery, bioimaging, functional antimicrobial coatings etc. due to their tunable PL, magnetic, antimicrobial, and biocompatible capabilities.