Cyclodextrin Modified CdTe Quantum Dots As Fluorescence Probe For Molecular Recognition

The vital movement of life in nature is usually the molecular recognition process associated with nanoscale interface, the study of recognition mechanism will thus contribute to better understand of the biological phenomena. As a novel type of fluorescent nanomaterials, quantum dots (QDs) possess excellent size-tuned optical properties such as broad absorption spectra and narrow emission spectra. Cyclodextrins (CD) are advantageous for their unique structure and molecular recognition ability as host molecule. In This thesis, fluorescent probes based on β-CD modified CdTe QDs have been developed, and their recognition performance for achiral and chiral molecules is demonstrated in the aqueous phase as follows.At first, Monodispersed and high quantum yield water-soluble CdTe QDs have been prepared by using 3-mercaptopropionic acid as ligands in water phase. Reaction parameters including total concentration of the reactants (Cd2+), the pH value, the precursor (Te) content, mercaptopropionic acid ligand content and ligand types have been optimized for QDs by tracing PL intensity. The optimal conditions,3 mM of Cd2+, pH of 10, the molar ratio of Cd:MPA:Te of 1:1:0.2 with MPA as the surface ligand was thus obtained.Then, Nano-fluorescent probes 6A-thiol-(3-CD functional ized CdTe QDs was successfully prepared via the as-optimized condition in the water phase. The obtained nano-fluorescent probes possess small particle size (3-4 nm) and high fluorescence quantum efficiency (65%, Rhodamine B as a reference). Under pH 7.7 phosphate buffer solution, the detection limit of o-, m-,p-nitrophenol isomer reached 0.05 μM,0.3 μM and 0.05 μM, respectively. In the concentration range of 0-100 μM, linear fluorescence quenching was observed for all isomers due to the electron transfer with the aid of inclusion complexes of CD. The results proved the fluorescent probe to be sensitive for the detection of isomers.At last, CdTe QDs encapsulated with CD clicked silica via layer-by-layer modification was proposed to prepare a novel hybrid molecular recognition platform. The fluorescent probe exhibited different response behaviors towards four racemic amino acids with enhanced or slightly decreased fluorescent intensity, amongst of them, tryptophan and histidine enantiomers presented relatively higher fluorescence enhancement. The behavioral differences between enantiomers can be attributed to the different stable inclusion complexation constants with CD, as revealed using density-functional theory calculation. Meanwhile, the behavior of D- and L-histidine within 0-50 μM and 0-8 μM, respectively, concentration range was consistent with a linear relationship as the Langmuir isotherm equation.