A New Type Of Quantum Dot Fluorescence Probe-based Design, Assembly And Biological Applications

Semiconductor nanoparticles (NPs) or quantum dots (QDs) as the new generation of fluorescent probes have unique photophysical properties that offer significant advantages. Accordingly, increasing research efforts have been devoted to the nanoprobes for bioimaging, biolabeling, as well as for biosensing. These functional QDs allow the secondary tethering of ligands or receptor units to the surface of the QDs, thus yielding QD–ligand conjugates in which the NP acts as an optical transducer for recognition of sensing events occurring at the surfaces of the NPs. Furthermore, the incorporation of the biomaterial/QDs hybrid nanostructures into cellular environments could combine the targeting functions of the biomolecules with the superior photophysical properties of QDs to explore and control intracellular processes. In this thesis, based on the electron ransfer or fluorescence resonance energy transfer mechanism, we assembled new nanoprobes for determination of biological active substances in order to develop the related techniques of potentially biomedical significance. Three chapters are included.In the first chapter, the recent application and progress of QDs in biological biosensing, bioimaging, as well as biolabeling are also briefly summarized.In the second chapter, based on electron transfer, a novel fluorescent nanoprobe, 4-amino-2,2,6,6-tetramethylpiperidine oxide (AT)-functionalized CdTe quantum dots (QDs), was synthesized and used to detect nonprotein thiols. In the presence of nonprotein thiols, the nitroxide abstracts a hydrogen atom from mercapto-group to produce diamagnetic hydroxylamine, resulting in the fluorescence recovery of the QDs, which was further confirmed by fluorescence spectra and capillary electrophoresis. On the contrary, the nanoprobe shows no fluorescence response to protein thiols because it may be difficult for the nanoprobe to touch mercapto-group of protein thiols due to steric hindance. With the optimum conditions described, the system exhibits a dynamic response range for GSH from 5×10-7 to 1×10-5 M with a detection limit of 7.1×10-8 M. The fluorescence changes of the system are extremely specific for nonprotein thiols even in the presence of several kinds of potential interfering substances such as metal ion, bio-amines, biilogical antioxidants and reactive oxygen species (ROS). Furthermore, the proposed method was successfully used to probe the differences in the concentration of nonprotein thiols in HL-7702 cells and HepG2 cells extracts. Because concentration of intracellular GSH is much higher than that of others nonprotein thiol, the method can be considered as a good way for selectively detecting intracellular GSH. Such a fluorescent nanoprobe will have great potential in detecting and imaging intracellular GSH, and in investigating the mechanisms of redox state changes and diseases in a biological context.In the third chapter, a new nanoprobe QDs-DNA/Aptamer-Dye was assembled and used to detect potassium ion based on the the switching on of fluorescence resonance energy transfer (FRET) between CdTe QDs and dye. In the presence of potassium ion, the aptemer will fall off because of the high specific recognition of aptamer to potassium ion, and QDs-DNA-Dye forms a beacon. Thus, QDs are close to dye, resulting into the switching on of FRET between QDs and dye.