טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGryaznova Anna
SubjectStability and Flow Study of Water-Soluble PbSe
Semiconductor Nanocrystals
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors Professor Efrat Lifshitz
Ms. Rina Tannenbaum
Full Thesis textFull thesis text - English Version


Abstract

In recent decades, infrared-emitting PbSe nanocrystal quantum dots (NQDs) have been studied in both fundamental research and various applications, such as bioimaging, lasers and solar cells. PbSe NQDs exhibit size-dependent broad-band absorption, sharp photoluminescence (PL) emission in near infra-red region, and large Stokes shift, which makes them excellent materials for biological imaging, as compared to organic dyes. Moreover, the biomedical applications require agent stability, which is very poor in organic dyes. The main reason that stability of PbSe NQDs is crucial is the release of lead ions that tend to accumulate in living organisms, causing various health problems. This chemical degradation and size reduction of the nanocrystals can be tracked by the changes of their optical properties (absorption and PL spectra). In addition, application of PbSe NQDs in biosciences requires their targeting to the desired area. One of the targeting methods is the conjugation of PbSe NQDs to magnetic nanoparticles (NPs), such as γ-Fe2O3, which assist in transporting the fluorescent agent to the aim. The γ-Fe2O3 NPs could be manipulated by external magnetic field gradient.

In this work, the stability of optical properties under various conditions, such as ligand concentration, particle size, temperature and light exposure was tested. It was revealed that most of the oxidation of the nanocrystal surface occurs during the phase transfer, weakening the optical properties of the NQDs. Stokes shift was significantly increased upon ligand exchange rendering the NQDs even more suitable for bioapplication. The temporal investigation of optical properties of the water-soluble NQDs showed their reduced sensibility to the ambient environment. The absorption spectra of water-soluble PbSe NQDs showed energy peak (Epeak) shifts, which were less significant compared to the analogue parameters of the PbSe NQDs in organic solution. In addition, the flow behavior of the conjugated nanostructures consisting of PbSe NQDs and γ-Fe2O3 NPs under viscous flow and an external magnetic field was studied. The γ-Fe2O3 component was used to control the trajectories of the nanoplatforms under an external magnetic field in polymer fluids mimicking the bloodstream viscosity. The trajectories of the conjugated nanostructures were investigated under various fluid flow rates and magnetic field application, in the presence of polystyrene (PS) microparticles, mimicking the various blood constituents. It was shown that the trajectories of the nanoplatforms can be controlled by an external magnetic field gradient, indicating the application possibility of the conjugate nanostructures as a vehicle for targeted delivery of tags or drugs.