Upconversion Nanoparticles Used In Nanomedicine

Lanthanide-based upconversion nanoparticles (UCNPs) that emit high-energyphotons under excitation by near-infrared (NIR) low-energy light have been widelyexplored in recent years for their potential applications in nanomedicine. Comparedwith traditional down-conversion fluorescent dyes and quantum dots (QDs), UCNPspossess of many advantages, such as low toxicity, high chemical and optical stability,deep light-penetration under NIR excitation, minimal photodamage to living organisms,and nearly-zero background auto-fluorescence.In this dissertation, we synthesize various kinds of UCNPs, which arefunctionalized with hydrophilic polymers to acquire water solubility andbiocompatibility, for applications in biomedical imaging. The in vivo behaviors andtoxicology of those UCNPs are studied as well. On the other hand, multifunctionalnanoparticles based on UCNPs are designed and fabricated, and used for multimodalimaging, imaging guided cancer therapy, as well as in vivo stem cell tracking andmanipulation. Besides UCNPs, as a side project, we have also developed organicnanoparticles for photothermal treatment of cancer. The main results are as following:Chapter1: Recent research progresses of using UCNPs for biomedicalapplications are reviewed in details in this chapter.Chapter2: We synthesize a series of UCNPs with different emission colors andfunctionalize them with an amphiphilic polymer to confer water solubility. Multicolor invivo upconversion luminescence (UCL) imaging is demonstrated by imagingsubcutaneously injected UCNPs and applied in multiplexed in vivo lymph nodemapping. We also use UCNPs for multicolor cancer cell labeling and realize in vivo celltracking by UCL imaging. Moreover, for the first time we compare the in vivo imagingsensitivity of QD-based fluorescence imaging and UCNP-based UCL imaging side byside, and find the in vivo detection limit of UCNPs to be at least one order of magnitudelower than that of QDs in our current non-optimized imaging system. Our data suggestthat UCNPs have great potential for use in highly-sensitive multiplexed biomedicalimaging.Chapter3: UCNPs based on sodium yttrium fluoride (NaYF4) nanocrystals are synthesized, functionalized with an amphiphilic polymer, and loaded with fluorescent orquenching molecules by physical adsorption. The as-synthesized supramolecularUCNP-dye complexes show tuned visible emission spectra owing to the luminescenceresonance energy transfer (FRET) from nanoparticles to the organic dyes undernear-infrared (NIR) excitation, and can be well separated in multi-color imaging afterspectral decovolution. Our work provided a facile and flexible method to modulate theUCL spectra of UCNPs for in vivo multi-color UCL imaging in animals.Chapter4: NaFY4based UCNPs with the unique multi-photon excitationphotoluminescence properties have gained significant interest in the areas of biomedicalimaging and photo therapies. UCNPs functionalized by two different polymers,polyacrylic acid (PAA) and polyethylene glycol (PEG), are synthesized and tested invivo. It is found that PEG coated UCNPs (UCNP-PEG) exhibit prolonged bloodcirculation half-lives than UCNP-PAA. The biodistribution of two types of UCNPsshow dominate accumulations of nanoparticles in the reticuloendothelial system (RES)for long periods of time. We further carry out blood biochemistry tests, hematologyanalysis, and histological examinations to look for potential toxicity of UCNPs to thetreated mice. No noticeable toxic side effect is found for either UCNP-PAA orUCNP-PEG in our toxicology study.Chapter5: In this chapter, utilizing a layer-by-layer (LBL) assembly approach, wesynthesize a novel class of multifunctional nanoparticles (MFNPs) by adsorbing ofsuperparamagnetic iron oxide nanoparticles (IONPs) on UCNPs, forming aUCNP-IONP nanocomposite, on top of which a thin gold shell is grown. The obtainedUCNP-IONP-Au MFNPs are then coated with polyethylene glycol and used for in vitrotargeted UCL, magentic resonance (MR), and dark-field scattering multimodal imagingof cells. The NIR optical absorption offered by the gold shell of MFNPs also enablesmolecular and magnetic dual-targeted photothermal destruction of cancer cells. In vivodual-model UCL and MR imaging of tumors and lymph nodes using MFNPs are furtherdemonstrated in mice.Chapter6: The same MFNPs developed in the previous chapter show highlyintegrated functionalities including upconversion luminescence, superparamagnetism,and strong optical absorption in the near-infrared (NIR) region. In vivo dual modaloptical/magnetic resonance imaging of mice uncover that by placing a magnet nearbythe tumor, MFNPs tend to migrate towards the tumor after intravenous injection andshow high tumor accumulation, which is⁸folds higher than that without magnetictargeting. NIR laser irradiation is then applied to the tumors grown on MFNP-injected mice under magnetic tumor-targeting, obtaining an outstanding photothermaltherapeutic efficacy with100%of tumor elimination in a murine breast cancer model.To our best knowledge, this work is the first that the in vivo dual modal imaging alonewith photothermal therapy targeted by the magnetic filed has ever been achieved inanimal experiments. Our work presents a unique strategy for multi-modal imagingguided, magnetically targeted physical cancer therapy and highlights the promise ofusing multifunctional nanostructures for novel cancer theranostics.Chapter7: Beside therapeutic applications of UCNP-based MNFPs, we alsoutilize those multi-functional nanoprobes for stem cell research. It is uncovered thatafter being labeled with MFNPs, mouse mesenchymal stem cells (mMSCs) are able tomaintain their viability, and more importantly, their ability to proliferate anddifferentiate. In vivo UCL imaging of MFNP-labeled mMSCs transplanted into animalsis carried out, achieving ultra-high tracking sensitivity with as few as¹0cellsdetectable in a mouse. We further track MFNP-labeled mMSCs after intraperitonealinjection under magnetically targeted field, and observe the translocation of mMSCsfrom the middle of abdominal to the wound site nearby the magnet. Our resultshighlight the promise of using MFNPs as a new type of multi-functional probes forlabeling, in vivo tracking and manipulation of stem cells.Chapter8: We synthesize a new class of ultraviolet emitting UCNPs, which arecoated with a layer of SiO₂and then another layer of TiO₂step-by-step. TheUCNP@SiO₂@TiO₂nanoparticles are able to efficiently generate reactive oxygenspecies under980nm NIR laser irradiation and could serve as a photosensitizing agentfor NIR-induced photodynamic therapy of cancer. This part of work is still in progress.Chapter9: UCNPs attached with gold nanoparticle (AuNPs) are further coatedwith a thin layer of gold. By attaching Raman molecules onto the surface of AuNPs, aunique class of Raman-UCL dual functional imaging nanoprobes are developed, formulti-color multiplexed imaging of biological samples. This part of work is also inprogress.Chapter10: Besides UCNPs, as a side project, we have also developed organicnanoparticles for photothermal treatment of cancer. PEGylated organic nanoparticlesbased on PEDOT:PSS conductive polymers are fabricated and used for highly effectivein vivo PTT treatment of cancer in animal experiments. Using the LBL method,PEDOT:PSS polymeric nanoparticles are step-by-step coated with charged polymersand then conjugated to PEG, obtaining PEDOT:PSS-PEG with excellent compatibilityin physiological environments. With an ultra-long blood circulation half-life, the PEDOT:PSS-PEG nanoparticles show surprisingly high in vivo tumor uptake by theEPR effect after intravenous injection, and appear to be an excellent PTT agent fortumor ablation, without rendering any obvious toxicity to the treated animals. To ourbest knowledge, this is the first time to explore the in vivo behaviors, applications, andpotential toxicity of conductive polymers in animal models, and most importantly,realize in vivo photothermal therapy in animals with excellent therapeutic efficacy undera low laser power.In summary, this thesis illustrates a comprehensive investigation of UCNPs andUCNP-based composite nanostructures for applications in biomedical imaging, novelcancer physical therapies, and stem cell research. Our results greatly promise furtherexplorations of those functional nanomaterials in biomedical research.