Luminescent Lanthanide Complexes and Nanoparticles for Biological Applications
This dissertation focuses on the design, synthesis, and photocharacterization of new water-soluble lanthanide-based complexes and nanoparticles for potential use in biological environments. Trivalent lanthanide (Ln(III)) are attractive for bioimaging and sensing applications because of their long emission lifetimes, sharp emission bands, color purity, resistance to photobleaching, and enhanced signal-to-noise ratios. Their practical use in aqueous and biological systems requires organic chromophores or other organic ligands that provide water solubility while minimizing quenching from high-energy vibrational oscillators. To address these challenges, several classes of Ln(III) materials were developed and investigated. Carbazole-based ligands were synthesized and coordinated to Eu(III) and Tb(III) to produce visible emitting complexes designed for viscosity and temperature sensing. These complexes were isolated to perform both one- and two-photon absorption experiments. This enables their potential use in biological imaging where deeper tissue penetration and reduced photodamage and scattering are desired. Additionally, these studies demonstrated that carbazole effectively sensitized Eu(III) and Tb(III) emission while also providing sensitivity to changes in viscosity and temperature. Triple-decker sandwich complexes were isolated and explored as up-conversion (UC) emitters. These systems were designed to enable efficient energy transfer and direct excitation processes that enable near-infrared (NIR) excitation to produce emission in the visible region. The isolated complexes exhibited Er(III)-centered up-conversion luminescence in solution and demonstrated detectable emission in HeLa cells. These findings highlight the potential of molecular up-conversion systems for biological imaging applications. Sensitizer-capped Eu2O3 nanoparticles (NPs) were synthesized and functionalized with different aromatic ligands to enhance Eu(III)-centered emission and excited state lifetimes in aqueous solutions and tissue lysate. A family of common aromatic ligands was investigated for its ability to sensitize Eu(III) emission while maintaining water solubility and enabling longer emission lifetimes. These experiments led to the isolation of a co-sensitizer-capped nanoparticle system, which demonstrated an extended excited-state lifetime of over 1 ms. Furthermore, time-delayed photoluminescence measurements demonstrated improved detection of the metal centered emission. The studies mentioned above demonstrate various approaches for developing Ln(III)-based luminescent materials that perform well for bio-imaging or photosensing applications in aqueous solutions. The results offer insight into ligand design, environmentally responsive Ln(III) probes, low energy sensitization, and modification of nanoparticle surface strategies that enhance Ln(III) emission and lifetimes. These findings contribute to the broader development of luminescent Ln(III) materials for applications in bioimaging and sensing.
bioimaging, lanthanide, luminescent, time-gated, two-photon, up-conversion
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