Author

Di Sun

Date of Award

December 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Julia X. Zhao

Second Advisor

Diane C. Darland

Abstract

Fluorescent-based nanoparticles have been applied to a broad range of biological applications, as discussed in this dissertation, including bioimaging, gene regulation expression, and photo-induced synergistic cancer therapy. Prior to applications, this dissertation first focused on the development and characterization of several fluorescent-based nanoparticles using different methods. These include 1) Streamlined synthesis of dual-emissive fluorescent-based silicon quantum dots (SiQDs). The SiQDs were generated as a promising, non-toxic labeling tool for bioimaging of a variety of cell types. both in visible and near-infrared (NIR) ranges. 2) Polymer-based nanoparticles - Polymer dots (Pdots) with a strong NIR fluorescence. The Pdots were functionalized as a nanoplatform for small interference RNA (siRNA) delivery. 3) One-pot synthesized porphyrin functionalized silicon nanoparticles (pSiNPs). The pSiNPs showed red-emissive fluorescence to achieve combined photodynamic therapy (PDT) and photothermal therapy (PTT) for potential noninvasive cancer treatment.Following the first chapter of the introduction of nanomaterials, in chapter 2, we reviewed the fluorescent-based silicon quantum dots (SiQDs). We first summarized the various SiQDs synthetic routes including physical and chemical approaches. Physical synthesis methods mainly include laser ablation and plasma synthesis. Chemical synthesis methods generally include electrochemical etching, reduction of anhydrous silicon ionic salt, and decomposition of silicon-based precursor. Then, different bioconjugation reactions for surface modification of SiQDs and a wide variety of bioapplications were discussed. Finally, the remaining challenges and future perspectives of SiQDs in bioapplications were briefly addressed. In Chapter 3, we developed a streamlined and one-pot synthetic route for SiQDs using a hydrothermal method. The silicon precursor, (3-aminopropyl) triethoxysilane (APTES), was used in combination with glucose as a reducing agent for the synthesis reaction. The resulting SiQDs produced potent, stable, potential dual-emissive fluorescence emission peaks in the visible (447 nm) and NIR (844) ranges. The biocompatibility and imaging potential of the SiQDs were tested in mouse brain-derived microvascular cells (BMVEC), neural stem cells (NSC), and RAW 264.7 macrophage cells. The results demonstrated that SiQDs were a promising, non-toxic labeling tool for a variety of cell types. In Chapter 4, NIR fluorescence-based Pdots were developed as a nanoplatform and an indicator for siRNA delivery to regulate the expression of target genes. We then developed strategies to surface functionalize the Pdots (positively charged) so that siRNA (negatively charged) could electrostatically bind to the Pdot. The feasibility of this approach was determined using siRNA targeting specific angiogenesis factors, reference gene targets such as Glyceraldehyde phosphate dehydrogenase (Gapdh), and control (scrambled) siRNA. Gapdh is constitutively expressed in all metabolically active cells and is an ideal first-stage target. Both Pdots and Pdot-siRNA displayed two emission peaks in the visible (588 nm) and NIR emission range (775 nm). We treated primary cultures of BMVEC with Pdot-Gapdh siRNA and observed uniform cellular uptake in BMVEC with reduced intensity of Gapdh immunolabeling. The simple design offered a flexible and novel strategy to inhibit a wide range of mRNA targets with minimal toxicity, high efficiency, and focused cell visualization. In Chapter 5, porphyrin-functionalized SiNPs (pSiNPs) were successfully developed through a streamlined and one-pot synthetic route via the hydrothermal method. This reaction process included hydrolysis, nucleation, and Ostwald ripening steps. By investigation of absorption property, pSiNPs had a wide absorbance range from visible to NIR, and the absorbance peaks were 414 nm, 527 nm, 565 nm, and 651 nm. The optical properties of pSiNPs yielded two distinct emission peaks at 646 nm and 705 nm. The in vitro cell imaging indicated that pSiNPs were valuable imaging tools for cell labeling. The photothermal performance and photodynamic effect showed that pSiNPs did have the ability to generate laser-induced heat generation and produce ROS, highlighting their possibility of achieving PDT and PTT in cancer cells. The in vitro photo-synergistic results indicated that pSiNPs had enhanced PDT/PTT therapeutic performance which potentially can be applied in in vivo studies and clinical trials. In the last chapter, we summarized the previous chapters and gave a brief conclusion for each chapter. Overall, the dissertation covered the development of fluorescent-based nanoparticles and their bioapplications, including in vitro cell imaging as labeling tools, siRNA delivery as a nanoplatform, and photo-synergistic therapy. Looking into the future, nanotechnology will play a substantial role in clinical interventions, making the treatment of human diseases more accurate and effective for improved therapeutic results.

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