The Interactions Between CdSe Quantum Dots And Biosystem Measured By Atomic Force Microscopy

Since1990s, the rapid development of nanotechnology has brought renovation in materials, electronics technology, biomedicine and so on. In biomedicine field, the nanomaterials can be utilized for the early diagnosis of disease, in long vivo tracking and even as new drug carrier. In these processes, with the increasing opportunity of nanomaterials exposing to human, the resulting effects attract wide attention. Due to the unique property of nanomaterials and their ’active’ behavior to complex biosystem, the interaction between nanomaterials and biosystm should be explored in depth for better understanding those effects or even taking advantage of them.As is well known, these interactions are not only affected by the size, surface functional groups or charges of nanomaterials, but also relevant to the type, conformation and growth condition of the biomaterials. Previous researches mainly focused on the thermodynamic properties of interaction, such as the dissociation constant, binding stoichiometry and the changes of entropy. However, the complexity of the interaction is pressing for new methods for further understanding. As atomic force microscope was invented based on high sensitive force measurement, based on analyzing the force-distance curves, interactions could be measured directly. Since its birth, it has been widely used to investigate layer-layer interactions of proteins.Based on these, this thesis has tried to utilize atomic force microscopy for better understanding interaction between nanomaterials and biosystem as the following:(1) Providing methods of the investigation including probe selection, surface modification, immobilization, experimental setup and data processing;(2) The interaction between CdSe/ZnS QDs and three kinds of proteins (BSA, IgG and WGA) were investigated with the combination of atomic force microscopy and colloid probe technique. Results showed that van der Waals forces played the major role in the interaction between QDs and proteins, while the electrostatic forces also strongly affected the interaction. This method not only applied to the investigation of interactions between nanomaterials and biomaterials, but also offered hints to adjust the nonspecific interaction on different demands. (3) Based on efficient immobilization with poly-L-lysine, the mechanical strength of yeast cells in the CdSe QD biosynthesis process was measured by atomic force microscopy. Results showed that with the increasing incubation time, both the cell wall thickness and the mechanical strength of the cell increased. The generation of QDs affected the expression of key genes that were related to glucan. In this case, the cell wall thickness increased and the mechanical property of yeast cell was strengthened as a result.(4) Utilizing the specific reaction between amino and succinamide to quantify the amount of amino group on QDs surfaces. Using isothermal titration calorimetry to monitor the thermal variation in the SA-QDs coupling process for the SA quantitation.