Luminescent lanthanide-doped nano- and microparticles and hybrid materials towards biomedical applications

Luminescent lanthanide materials are of great interest not only for biomedical applications due to their tuneable emission wavelengths that extend from the
ultra-violet region into the near-infrared region. These materials are known to be non-toxic and resistant to photobleaching unlike traditional organic dyes. In this Thesis,
the focus was laid on the synthesis of nanoscale and microscale fluoride containing luminescent lanthanide materials, such as (LaF₃:Ce³⁺Tb³⁺, TiO₂@SiO₂@LaF₃:Ce³⁺Tb³⁺, and KSmF₄:Ln³⁺ (Ln = Ce, Tb, Eu), which promise unique optical properties, as fluoride containing lanthanide materials are recognized for their strong luminescence and good optical stability due to their low phonon energies. To harness these properties for potential bioimaging applications, this Thesis thus focused on developing and optimizing synthetic routes for producing monodisperse lanthanide doped particles that bridge the length scales from the nano- (< 10 nm) to the microscale (> 1 µm). Furthermore, to enhance their scope by exploiting their surface features, these particles were incorporated into hydrogels and were modified with polymer brushes.
The results confirm the successful synthesis of monodisperse particles with sizes ranging from < 10 nm to 15 µm with intense red and green luminescence due to Eu3+ and Tb3+ ions. Among the particles studied, the (LaF₃:Ce³⁺Tb³⁺) nanoparticles were investigated in cell toxicity tests, while the MgF2 microbeads were tailor made for application in digital holography microscopy. The toxicity tests indicated that the NPs are non-toxic at concentrations below 0.0023 mg/mL in cell medium. These NPs were also incorporated into a biocompatible sodium alginate hydrogel matrix and the influence on the mechanical properties of the hydrogels was investigated. Rheological measurements revealed that nanoparticle inclusion significantly enhances the hydrogels’ structural stability, supporting their potential use in drug delivery and bioimaging. The tomography phase microscopy results of spherical MgF2 microparticles hinted at a very similar refractive index compared to human cells (1.360 ± 0.004). These particles were shown to provide the structural parameters required for precise calibration in digital holography, which enhances the accuracy and reliability of label-free live cell imaging. In addition, antibacterial tests with E. coli showed enhanced antibacterial activity compared to commercially purchased MgF2. These results suggest that lanthanide-based particles can be further exploited in future biomedical applications.