Studies On Interaction Of CdTe Quantum Dots With Protein

In this thesis, the mixture of MPA capped CdTe quantum dots (QDs) synthesized in aqueous and Bovine Serum Albumin (BSA) was employed as the model to study the interaction of QDs with protein. Moreover, the denatured BSA was used to modify the surface of MPA capped CdTe QDs to enhance the quantum yield and stability.Compared to organic fluorophores, QDs possess the unique optical properties including photostability, brightness, narrow but tunable emission spectra, and a broad spectral excitation cross section.Currently, QDs received tremendous applications in biological and medicinal realm. In spite of numerous applications, the knowledge of interaction between QDs and biomolecule are correspondingly little. A deep understanding of biological and their potential toxic effects will require a detailed description of the binding of proteins to QDs in terms of affinities, stoichiometries, entropy, enthalpy, coverage, and the underlying driving forces. Each of these parameters is likely to be strongly dependent on both the particle and protein identity, as well as on the solution conditions. In order to distinguish between different effects and to pinpoint their molecular origins, there is a need for accurate and reproducible methods and simplified in vitro model systems that can qualitatively and quantitatively define QDs-protein interactions and characterize the QDs-protein complex.Bioconjugation is a critical step in QDs biological application. At present, CdTe QDs have the best optical properties in aqueous synthesized QDs. However, the chemically stable protein-conjugated CdTe QDs are difficult to obtain, and agglomeration of QDs is often observed, resulting in a loss of brightness. The occurrence of agglomeration during the condensation reaction makes direct bioconjugation of CdTe QDs with biomolecules difficult, consequently affecting their potential for use as biological labeling agents. Therefore, to establish a methodology to enhance the stability of QDs and their bioconjugation and maintain the QY of QDs is essential, and of practical interest.This work can be separated into two parts based on the issues mentioned above:1. BSA and CdTe QDs were used to study the interaction of protein with QDs as model samples. Ultra-filtration, capillary electrophoresis and fluorescence correlation spectroscopy were used to investigate the stoichiometry and thermodynamic parameters of interaction. A facile and reproducible methodology in vitro was established to study on the interaction of QDs with biomolecule. Moreover, based on the evaluation of association constant of various the ionic strength and pH value, we speculated that the interaction of CdTe QDs with BSA was mainly due to electrostatic attraction.2. The chemical reduced BSA here was used to modify the surface of MPA capped CdTe QDs in aqueous. The luminescent properties, hydrodynamic radii and stability of denatured BSA capped CdTe were characterized and evaluated by ensemble and single molecular technique. Compared to MPA capped CdTe, denatured BSA capped CdTe possess better QY and chemical stability.