WEB Lanthanide-based (NaLnF4) Nanoparticles for Biomedical Applications: The Role of Materials CrystallinityTuesday (22.09.2020) 15:40 - 16:10 B: Biomaterials Part of:
Bioimaging is a powerful tool that is used in clinics and labs for diagnosis and to unveil biomedical processes, whereas bioprobes are used to increase contrast. Sub-10nm sized nanoparticles are particularly appealing for biomedical applications as their size approaches that of biological features and due to their tunable optical or magnetic properties. Magnetic resonance imaging (MRI) allows for deep-tissue imaging; yet, spatial resolution is limited to the millimeter realm. Optical imaging offers spatial resolution at the micrometer scale, but common probes rely on UV/visible light with limited tissue penetration, risk of autofluorescence and phototoxicity. Near-infrared (NIR) light can overcome these issue, and NIR-emitting lanthanide-based nanoparticles (Ln-NPs) – also exhibiting magnetic properties – are strong candidates for deep-tissue high-resolution imaging. Our favorite nanomaterials are based on MLnF4 (M = alkali metal, Ln = lanthanides and Yttrium), and our research addresses challenges in their synthesis and the establishment of structure-property relationships.
This presentation will address the role of host material crystallinity, NaLnF4 being known to crystallize in either the cubic or the hexagonal crystalline phase. This intrinsic materials property has a huge impact on the synthesis of nanoscalic NaLnF4 particles of controlled size and phase as well as their optical and magnetic properties. For instance, while the hexagonal crystalline phase is generally favored to endow these nanoparticles with optical – NIR-emitting and upconverting – properties, we demonstrated the superior magnetic performance of cubic-phase NaGdF4 nanoparticles over their hexagonal counterparts, interesting findings with respect to possible MRI applications. Seeking such biomedical applications dispersibility in aqueous media is key. This can be achieved by acidic treatment rending as-prepared hydrophobic nanoparticles hydrophilic. Yet, in stark contrast to the generally considered good chemical stability of NaLnF4, acidic conditions were observed to pose a risk to phase transformation of sub-10 nm NaLnF4 nanoparticles into larger LnF3 particles, depending on crystalline phase and Ln-ion choice. These findings serve as an alert to the community working with small NaLnF4-type nanoparticles, emphasising the importance of carefully choosing the procedure used to achieve water-dispersibility.