Characterization Of Nucleic Acid And Investigation Of Interaction Between Angiogenin And Its Aptamer Based On Atomic Force Microscopy

Atomic force microscope (AFM) is developed on the basis of scanning tunneling microscope (STM). This technique can not only obtain surface topography at atomic level, but also measure intermolecular forces as low as 10^-12N (pN) grade. Because of its ability of imaging samples both in air and solution at nanometer resolution as well as detecting and manipulating single molecule, AFM has been evolved into a powerful tool in biological, chemical, physical and macromolecular systems studies. In this thesis, DNA strands with different sequence modified on silicon substrate were characterized using AFM imaging and gold nanoparticle labeling. And the interaction between aptamers and proteins was investigated using AFM force detection. The thesis is composed of the following parts:1. DNA strands with different sequence modified on silicon substrate were characterized using AFM imaging and gold nanoparticle labeling. Two sequences of single-strand DNA, as a model, were immobilized on silicon substrate and hybridized with their sequence-complementary DNA modified with two various sizes of gold nanoparticles, respectively. Size and coverage of gold nanoparticles on the surface of silicon substrate before and after hybridization, were characterized through AFM imaging. Density and distribution of two sequences of DNA on silicon substrate were investigated. This simple method with cheap labeling has potential to characterize DNA on the multi-functional microarray at nanometer scale.2. The specific interaction between angiogenin and its aptamer was studied by AFM. The pull-off force between the aptamer and RNase A, a homologue of angiogenin, was measured and compared to the force between angiogenin and the aptamer. The results showed that the specific interaction force between angiogenin and its aptamer was much higher than that between the aptamer and RNase A. The single molecular pull-off force between angiogenin and its aptamer was determined using the Poisson statistical method. The results are helpful in explaining the inhibition of the angiogenic activity and ribonucleolytic activity of angiogenin after binding angiogenin with its aptamer.3. The influence of aptamer on the interaction between angiogenin and angiogenin binding element (ABE) was investigated by AFM. The results showed that there was no obvious difference between angiogenin/ABE and angiogenin-aptamer complex/ABE, which indicated that aptamer did not affect the binding...