Aqueous Synthesis Of CdTe/CdSe And CdS/ZnS Quantum Dots For Cell Imaging And Biosensing

Colloid semiconductor quantum dots (QDs) are promising lumophores for bioimaging and biosensors because QDs offer many advantages over conventional organic fluorophores. such as high photoluminescence efficiency, size-dependent emission wavelengths, and sharp emission profile. QDs have been widely explored for detecting either ions or molecules, and for tracing biorecognition events or biocatalytic transformations. However, to our knowledge, much less attentions have been paid to near-infrared (NIR) fluorescent QDs and non-thiol functionalized QDs based markers and probes. This dissertation focused on the preparation, characterization and application of NIR CdTe/CdSe QDs and polyethyleneimine (PEI) capped CdS/ZnS QDs for bioimaging and biosensing. A layer-by-layer colloidal epitaxial growth of L-cysteine-capped CdTe/CdSe type-II core/shell QDs (CYS-CdTe/CdSe QDs) in aqueous solution was developed. The fluorescence emissions of the prepared CYS-CdTe/CdSe QDs are tunable between 600 and 800 nm. A quantum yield of 12% was achieved without any post-preparative treatment. In addition, the prepared CYS-CdTe/CdSe QDs in this work are only 4-5 nm in diameter, much smaller than the CdTe/CdSe QDs prepared via organometallic routes. HgTe and PbS QDs synthesized in water. The CYS-CdTe/CdSe QDs kept their emission intensity for months in the growth solution and for more than 24 h in biological media. To demonstrate the availability of their stable NIR fluorescence and small dimensions for bioimaging applications. CdTe/CdSe QDs were employed in cell staining for fixed human cervical carcinoma (Hela) cells. CYS-CdTe/CdSe quantum dots (QDs) was photoactivated as a novel NIR fluorescent probe for biothiols. This assay is based on both the superior photoactivity of CdTe/CdSe QDs and the strong affinity of thiols to photoactivated CdTe/CdSe QDs. The addition of thiols into the photoactivated CdTe/CdSe QDs improved the passivation of the illumination-induced traps, meanwhile reduced most of Se(Ⅳ) and Te(Ⅳ) on the surface of photoactivated CdTe/CdSe QDs so as to improve the fluorescence property. The probe offered good sensitivity and selectivity for detecting cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) in the presence of 20 other amino acids, main relevant metal ions, and some other molecules in biological fluids. The recovery of spiked 5.0μM thiols in human urine, plasma, and cell extracts ranged from 90% to 109%. The precision for nine replicate measurements of the thiols at 5.0μM is in the range of 1.6-1.8%. The detection limits (3s) for Cys, Hcy, and GSH are 131,26, and 20 nM, respectively. PEI capped CdS/ZnS QDs were prepared, characterized, and applied as a reproducible, sensitive and selective fluorescent probe for folic acid (FA). The PEI capped CdS/ZnS QDs were stable in several buffers, and the fluorescence of QDs kept constant especially in Tris buffer of pH 6.5-10.0. The PEI capped CdS/ZnS QDs did not aggregate or photo-oxidized in pH 7.4 Tris for more than 5 months. The probe offered good selectivity for detecting FA in the presence of main relevant metal ions and some other coexisting molecules in pharmaceutics. The recovery of spiked 2.0μM FA in samples of pharmaceutical tablet ranged from 99% to 104%. The detection limit (3s) for FA is 35 nM.