Preparation And Properties Of Water-soluble Quantum Dots

Semiconductor quantum dots with unique quantum size effect, surface effect quantum confinement effect and macro quantum tunnel effect, show physical and chemical properties different from the macroscopic bulk materials. The special optical properties of quantum dots is that their fluorescent properties can be tailored by changing their size. These particles show great potential in biochemistry, molecular biology, cell biology, genomics, proteomics, medical diagnostics, drug screening, biological macro molecular interactions and so on.Generally, quantum dots should be associated with specific biological molecules firstly and then become a functional unit with targeting. However, due to lots of organic molecules on their surface, quantum dots show hydrophobicity. The quantum dots do not dissolve in water solution and can not be directly coupled to biological molecules. Consequently they must be coated by a layer of hydrophilic materials, and then be connected with biological molecules. Therefore, the water-soluble quantum dots can detect biomolecules. As a result, preparing water-soluble quantum dots is essential.In this work, water-soluble quantum dots which possessed better photostability and better photoluminescence properties were synthesized through ligand exchange between quantum dots and compound or polymer which contained amidogen and different backbone chains. Firstly, QDs/DETA were synthesized through ligand exchange between quantum dots (QDs-1(CdSe/CdS/ZnS) and QDs-2(CdS/ZnS)) and diethylenetriamine (DETA) whose molecular chain was shorter, then were dissolved in aqueous solution of different pH values. The analysis results showed that QDs-1/DETA and QDs-2/DETA self-assembled randomly and they were sensitive to pH of water solution. And fluorescence resonance energy transfer (FRET) occured between QDs-1/DETA and QDs-2/DETA.Secondly, QDs/DADA were synthesized through ligand exchange between quantum dots and1,12-Dodecanediamine (DETA) whose molecular chain was longer than DETA, then were dissolved in aqueous solution of different pH values. The testing results showed that QDs-1’/DADA and QDs-2’/DADA were sensitive to pH of aqueous solution. However, their fluorescent properties were independent from each other. Their fluorescence intensities increased and subsequently decreased gradually with the enhancement of pH values.Finally, QDs/DADA were synthesized through ligand exchange between quantum dots and M2070whose molecular chain is longer than DADA, and were dissolved in aqueous solution with different pH values. The testing results showed that QDs-1’/M2070and QDs-2’/M2070were sensitive to pH of aqueous solution. However, their fluorescent properties were independent from each other. Their fluorescence intensities increased and then decreased gradually when increasing pH values of the solution. At room temperature, QDs/M2070could grow as a result of attachment orientation. After a period of time (two months), the morphology of QDs/M2070changed into rod-like and finally became spherical due to the continuous self-assembly.