טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentLioz Etgar
SubjectThe Development and the Investigation of PbSe Quantum
Dots - Gamma-Fe2O3 Nanoparticles Conjugate
Structures for Biological Application
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors Full Professor Lifshitz Efrat
Ms. Tannenbaum Rina
Full Thesis textFull thesis text - English Version


Abstract

This research deals with the development and characterization of a unique conjugated structure comprised of γ-Fe2O3 nanoparticles (NPs) and PbSe quantum dots (QDs), bonded via chemical functional groups. The conjugate nanostructure can be considered as a useful medical platform. The magnetic NPs may serve as transport vehicles (nanoplatforms) that could be manipulated by an external magnetic field gradient, and the QDs may act as fluorescence tags in the near-infrared regime, thereby allowing for an optical window for in vivo cancer cell detection.

 The compatibility with an aqueous environment was rendered by exchanging the organic surfactants of the PbSe QDs and γ-Fe2O3 NPs with 2-aminoethanethiol and polyhedral silsesquioxane hydrate octakis ligands, respectively.  Comparison of the transmission electron microscopy (TEM) images of the PbSe QDs and γ-Fe2O3 NPs capped with either organic or water soluble ligands, highlights the preservation of the morphology and size of both types upon the ligand exchange.  The absorbance, photoluminescence and Fourier transform infrared spectra of the PbSe QDs, revealed that the optical properties of the QDs were retained during the surfactant exchange.  High-resolution TEM images of the conjugated structure and Nuclear Magnetic Resonance validate the presence of the coupling between the PbSe QDs and the γ-Fe2O3 NPs.

Moreover the optical and magnetic properties of these unique conjugate nanostructures were investigated.  The results exhibit retention of the QDs’ emission quantum efficiency and radiative lifetime and only a small red-shift of its band energy, upon conjugation to the dielectric surrounding of γ-Fe2O3 NPs. The study also shows sustainability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic-superparamagnetic transition temperature with respect to that of the individual NPs. 

In addition the flow behavior of the nanoplatforms has been investigated. The nanoplatforms’ flow was characterized by visualizing their trajectories within a viscous fluid (mimicking a blood stream), using an optical imaging method, while the trajectories pictures were analyzed by a specially-developed processing package.  The trajectories were examined under various flow rates, viscosities and applied magnetic field strengths.  The results revealed a control of the trajectories even at low magnetic fields (~1 Tesla), validating the use of similar nanoplatforms as active targeting constituents in personalized medicine.   Thus, the conjugate nanostructure can be considered as a useful medical platform, when PbSe QDs act as fluorescence tags, while the γ-Fe2O3 NPs are used as a vehicle driven by an external magnetic field for targeted delivery of drugs.