Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Jin Zhang

Abstract

Colloidal inorganic nanoparticles (NPs) have been attracting considerable interest in biomedicine, from drug and gene delivery to imaging, sensing and diagnostics. It is essential to modify the surface of nanoparticles to have enhanced biocompatibility and functionality for the in vitro and in vivo applications, especially in delivering locally and recognizing biomolecules. Herein, the goal of this research work is to develop advanced NPs with well-tailored surface functionalities and/or bio-functionality for the applications in cell tracking and analytes detection.

In the first project, quantum dots incorporating with gelatin nanoparticles (QDs-GNPs) have been developed for bioimaging applications. Two different approaches have been developed, i.e. directly encapsulating QDs with gelatin polymer (QDs-GNP1) and layer-by-layer (LBL) adsorption of QDs approach (QDs-GNP2), respectively. The special hybrid structures of two QDs-GNPs nanosystems were investigated by transmittance electron microscopy, scanning electron microscopy, X-ray energy dispersion, Fourier Transform Infrared spectroscopy, fluorometer, and confocal fluorescent microscopy. Both nanosystems exhibit high intensive luminescence and good biocompatibility. Compared to free QDs, QDs-GNP2 shows improved quantum yield and longer lifetime, due to multiple layers of polyelectrolytes protection. Furthermore, QDs-GNP2 demonstrates the proton-resistant properties in term of PL intensity and lifetime. The bright and stable photoluminescence (PL) allows the QD-GNP2 for labeling living 3T3 cells in vitro, which may indicate the QDs-GNP2 are able to be a suitable candidate for bio-imaging application.

In the second project, fluorescent magnetic nanoparticles (FMNPs) were bioconjugated with gentamicin (Gm) for rapid capture, detection and decontamination of bacteria. The Gm-FMNPs consist of a fluorescent silica shell and an iron oxide magnetic core. Initially, we prepared the core-shell NPs through a one-pot reaction. The antibacterial efficiency is found 20 % higher than that of the free antibiotic. We further improved NPs stability and capture efficiency by a two-step thermal decomposition method to produce the fluorescent magnetic core-shell nanoparticles. It is noted that one mg of gentamicin conjugated FMNPs are able to capture both gram-negative bacteria Escherichia coli and gram-positive bacteria Staphylococcus aureus as low as 1x104 colony-forming unit/mL (cfu/mL) in less than one minute. It is expected that the Gm-FMNPs could be a promising multifunctional platform for disease control in clinic and wastewater treatment.

In addition, a nanosensor for detecting human thrombin has been designed and developed. A recombinant luciferase was covalently conjugated to gold nanoparticles (Au NPs) through 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediated reaction. The conjugation enables Au NPs to quench the bioluminescence produced by luciferase. Recovery of bioluminescence has been studied as a function of the concentration of thrombin. The results indicate that the designed nanosensor can efficiently detect a protease thrombin in both buffer and human urine spiked buffer. A linear assay response is found between 300 ng/mL to 300 μg/mL, with limit of detection (LOD) of 3 ng/mL in both buffer and human urine spiked samples. The assay time can be less than 15 min. The nanosensor can thus be a promising tool for clinical diagnostic of thrombin related diseases.

In summary, different strategies have been explored to engineer the surface of hybrid NPs with good water stability, biocompatibility and enhanced chemical and physical properties. The thesis addresses that engineered hybrid NPs in biomedicine and how the biofunctionalized NPs can find applications in imaging and diagnostics indistinctly.