The Adsorption And Imaging Of DNA Molecular On HOPG Surface Studied By Atomic Force Microscope

In recent years, researchers have been exploring the use of new carbon materials such as carbon nanotubes and graphene as anticancer drug carrier and have obtained good results in vitro and in vivo experiments. When these novel carbon carrier were in the body, they may interacter with in vivo biological macromolecules such as DNA and various proteins, and thus affect the drug release process. Therefore, it was very important to deeply study the interactions between the biological molecule DNA and carbon materials for exploring new carbon nanometer carrier. New researches were reported that DNA molecules could indeed be adsorbed on the surface of carbon materials and the system could be used as various biomolecules sensor by showing adsorption and desorption process of DNA molecular. There are many imaging researches about DNA molecule on HOPG surface by adding ions, modifying HOPG surface, electrochemistry and other methods. However, there are few free adsorption research of low concentration DNA molecule on HOPG. According to this literature retrieval, there have not been a high resolution and systematic observation and study of the adsorption structure and morphology of all kinds of DNA molecules on carbon materials.The highly oriented pyrolytic graphite (HOPG) and other carbon materials such as carbon nanotubes and graphene have very similar surface structure and properties, and it also has a larger atomic level flat area. Therefore, it can be studing the adsorption process and morphology of DNA molecules on carbon materials by the atomic force microscopy(AFM) results on HOPG surface. This thesis focused on the use of AFM in the adsorption and imaging study of a variety of DNA molecules, including linear DNA, plasmid DNA, ssDNA, dsDNA and the oligonucleotide chain on HOPG surface as well as other influencing factors such as the addition of metal ions, temperature and PH conditions. Specific research summary was as follows:1. Free adsorption and imaging of DNA molecule on HOPG surfaceIn this research, we studied the free adsorption of pBR322DNA and A,-DNA of low concentration on HOPG The AFM results revealed that both circular and linear DNA tends to form hexagonal pattern on bare HOPG surface. Some unusual DNA structures including nodes, protrusions, cruciform structures and paralleled single stranded DNA have been identified and discussed. Furthermore, paralleled ssDNA arrays and their crossover structures have been obtained under our preparation condition. In addition, The present results is very similar to those on the alkylamines modified HOPG, and implied that bare HOPG themselves have a good aligning ability for biomolucules. The present study is very helpful for understanding the diversities of DNA structures and the adsorption and aligning ability of carbonaceous surfaces. 2. The influence of Mg2+, Ni2+and Cu2+to the adsorption and imaging of pBR322DNA on HOPG surfaceAdsorption of circular DNA onto bare highly oriented pyrolytic graphite (HOPG) surfaces by addition of Mg2+, Ni2+and Cu2+has been investigated by atomic force microscopy (AFM). AFM results revealed that the topography and height of DNA on HOPG surface by addition of different metal ions are quite different. After addition of Mg2+for incubation, DNA molecules tend to form many loops on HOPG surfaces, which are derived from the crossover of intramolecular and intermolecular chains. After addition of Ni2+, DNA molecules can form networks on HOPG surfaces, and the density of DNA network was significantly increased with increasing DNA concentration. This result implied that dense DNA network can be obtained with relative low concentration of DNA and Ni2+. As for addition of Cu2+, angular DNA loops composed of flat chains were observed. The observed flat DNA chains with lower average height can be ascribed to Cu2+insert into the site between bases and phosphate group of DNA inducing denaturation of DNA molecules. The present study is very helpful for understanding the interactions of metal ions and DNA molecules, and for constructing various DNA structures on the carbonaceous surfaces.3. Assembly of single stranded DNA onto HOPG surface at different temperatureAssembly of long single stranded DNA (ssDNA) and short oligodeoxynucleotides onto bare highly oriented pyrolytic graphite (HOPG) at different temperature has been studied. It is revealed that ssDNA can sequentially form network, straight chains and layer structures when the adsorption temperature was increased from room temperature to55℃. Further AFM observation of the layer structures revealed that they are composed of parallel ssDNA chains with relatively higher height and tend to form patterns with three fold symmetry. The present assembly method is expected to be used for biosensing and constructing DNA-based nanodevices...