Synthesis, Biological Effects And Photodynamic Therapy Of Water-soluble Quantum Dots

With the development of quantum dots (QDs) in the chemical, biological, medicine, medical diagnosis, and other applications, the high quality and multifunctional QDs of water-phase synthesis has been extensively developed. In addition, the biological effects of QDs have also been studied greatly by researchers. In this thesis, valuable explorations have been carried on the green, one-step hydrothermal, and one-step refluxing route synthesis of water-soluble QDs. This thesis is focused on studing the effects of QDs on DNA, BSA, and Escherichia coli (E. coli) cells, and then proposing a possible mechanism of action. Owing to large two-photon absorption cross sections, the photodynamic therapy of QDs has been explored.This thesis consists of seven chapters:Chapter1:This chapter introduced a more comprehensive overview of quantum dots, progress in synthesis, fluorescence (FL) mechanism, opatic properties, biological effects, application in biomedical areas and toxicity.Chapter2:A simple method was developed for preparing CdSe QDs using a common protein (bovine serum albumin (BSA)) to sequester QD precursors (Cd2+) in situ. FL and absorption spectra showed that the chelating time between BSA and Cd2+, the molar ratio of BSA/Cd2+, temperature, and pH are the crucial factors for the quality of QDs. With Fourier transform infrared spectra (FTIR) and thermogravimetric (TG) analysis, an interesting mechanism was discussed for the formation of the BSA-CdSe QDs. In addition, FL imaging suggests that the QDs we designed can successfully label E. coli cells, which gives us a great opportunity to develop biocompatible tools to label bacteria cells.Chapter3:Bifunctional fluorescence (CdSe QDs)-protein (Lysozyme, Lyz) nanocomposites were synthesized at room temperature by a protein-directed, solution-phase, green-synthetic method. FL and absorption spectra showed that CdSe QDs were prepared successfully with Lyz. With attenuated total reflection-fourier transform infrared (ATR-FTIR) spectra and TG analysis, an interesting mechanism was discussed for the formation of the Lyz-CdSe QDs. FL polarization was measured and FL imaging was done to monitor whether QDs could be responsible for possible changes in the conformation and activity of Lyz. Interestingly, the results showed Lyz still retain the biological activity after formation of QDs. And the advantage of this synthesis method is producing excellent fluorescent QDs with specifically biological function.Chapter4:A one-step, rapid, cost-efficient and convenient method has been developed for synthesis of water-soluble CdTe/CdS QDs using N-acetyl-L-cysteine (NAC) as the stabilizer via hydrothermal route. NAC not only acts as a stabilizer but also undergoes gradual thermal decomposition to release free S2-, forming a CdS shell on the CdTe core, and resulting in low cytotoxicity. The QDs was charactered by FL spectra, absorption spectra, TEM, XRD, XPS, EDS, and FTIR. The formation mechanism of core/shell QDs is also discussed in detail. Furthermore, the result of microcalorimetric technique showed our as-prepared CdTe/CdS QDs exhibit lower cytotoxicity than previous synthesized QDs (e.g.:MPA-capped CdTe QDs).Chapter5:A one-step and convenient method has been developed for synthesis of water-soluble glutathione (GSH)-capped and Zn+-doped CdTe QDs via refluxing route. Due to the addition of Zn ions and the epitaxial growth of a CdS layer, the prepared QDs exhibit superior properties, including strong fluorescence, minimal cytotoxicity and enhanced biocompatibility. The QDs was charactered by FL spectra, absorption spectra, TEM, XRD, XPS, AAS, EDS, and FTIR. Furthermore, the low cytotoxicity of the prepared QDs was proved by microcalorimetric technique and inductively coupled plasma-atomic emission spectrometry (ICP-AES).Chapter6:The interaction of CdSe/CdS QDs with DNA (dsDNA and ssDNA) was studied by using a direct absorption spectroscopic technique and an indirect electrochemical method The apparent association constant has been deduced from the absorption spectral changes of the dsDNA-QDs and ssDNA-QDs. The results of dissociation method suggest there are strong interaction of QDs with hs-DNA and the binding force of QDs with dsDNA is stronger than ssDNA. The interaction of CdTe QDs with different size ((green-emitting QDs, GQDs),(yellow-emitting QDs, YQDs) and (red-emitting QDs, RQDs)) and modifier (mercaptopropanoic acid (MPA), L-cysteine (L-cys), and glutathione (GSH)) with bovine serum albumin (BSA) was investigated. FL, UV-vis absorption, ATR-FTIR, and circular dichroism (CD) spectra methods were used. The Stern-Volmer quenching constant (Ksv), corresponding thermodynamic parameters (ΔH, AG and AS), and information of the structural features of BSA were gained. Using E. coli cells as model, we found that CdTe QDs exhibited a dose-dependent inhibitory effect on cells growth by a microcalorimetric technique. The mechanism of cytotoxicity of QDs was also studied through ATR-FTIR spectra, FL polarization, and SEM. he results indicated that CdTe QDs have cytotoxic effects on E. coli cells, and this effects might attribute to the damaged structure of the cell out membrane, and QDs and by-products (free radicals, reactive oxygen species (ROS), and free Cd2+) which might enter the cells.Chapter7:We have used two-step reverse microemulsion method to synthesize nanocomposites with QDs/SiO2or QDs/RITC-SiO2core and a photosensitizer (HP)-doped mesoporous silica shell (HP-mSiO2). These biocompatible nanoparticles (QDs/SiO2/HP-mSiO2and QDs/RITC-SiO2/HP-mSiO2) not only could efficiently generate’O2for PDT through TPE of the QDs by energy transfer and increase biocompatible, but also acts as a carrier for the photosensitizers and a nanoreactor to facilitate the photo-oxidation reaction. The nanocomposites would be good for "see and treat" photodynamic therapy to tumor tissue in vivo when controlling the molar ratio of other materials quenching QDs.