Controlling Size and Surface Property of Lanthanide-Doped Luminescent Nanoparticles for Bio-applications


Student thesis: Doctoral Thesis

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Awarding Institution
Award date13 Sep 2018


Lanthanide-doped luminescent nanoparticles have attracted increasing research interests in the past decades, owing to their outstanding upconversion and downshifting luminescent properties. With appropriate doping and excitation, lanthanide-doped luminescent nanoparticles exhibit a full-spectrum range emission including ultraviolet (UV), visible, near infrared (NIR), and mid infrared (MIR). When compared to semiconductor quantum dots, organic dyes and lanthanide chelates, lanthanide-doped luminescent nanoparticles display distinct advantages including large anti-Stokes shifts, sharp emission bandwidths, long excited-state lifetimes, high photochemical stability, and low cytotoxicity. Therefore, lanthanide-doped nanoparticles with desired size distribution, and suitable surface coating are appealing for biological research and biomedical applications, such as bioimaging, biodetection, drug delivery, and photodynamic therapy (PDT). This thesis reports new developments in controlling size and surface functionality of lanthanide-doped nanoparticles, as well as biodetection using these nanoparticles.

In Chapter 4, we describe a controlled synthesis of NaYbF4 nanoparticles through co-precipitation in a ternary solvent mixture of oleylamine (OM), oleic acid (OA), and 1-octadecene (ODE). The synthetic approach is modified from a literature protocol by inclusion of oleylamine as a cofactor. We investigate the role of oleylamine in controlling the cubic-to-hexagonal phase transformation and Ostwald ripening of NaYbF4 nanoparticles. By optimizing oleylamine composition and experimental variables, we demonstrate rational control of nanoparticle phase, size, and core–shell structure.

In Chapter 5, we report a facile and versatile ligand exchange protocol for displacing native oleate ligands on upconversion nanoparticles with a diversity of hydrophilic molecules. In our protocol, removal of oleate ligands and attachment of new ligands were conducted in separate operations, which is beneficial for reliable attachment of different ligands at mild and consistent experimental conditions. Notably, functional biomolecules such as biotin can be directly attached to the nanoparticles by this means for quick and effective biodetection through affinity interactions.

In Chapter 6, we describe a new class of DNA sensing system by using lanthanide-doped nanoparticles as both energy donor and acceptor. We also investigate the effects of nanoparticle size and concentration on the detection performance. The nanocrystals are functionalized with oligonucleotides that specifically bind to STAT3, the activation of which is tumour-specific and may represent a novel molecular target for the therapy and early diagnosis of tumours. This study not only promotes the applications of lanthanide-doped nanocrystals in biosensing, but also provides a promising mean for the early diagnosis of tumours.

    Research areas

  • Lanthanide, Doping, Upconversion Luminescence, Controlled synthesis, Ostwald Ripening, Ligand Exchange, Biosensing