Investigation Of Self-assembly Of Biological Nanomaterials And The Interaction Between Them With Atomic Force Microscopy

Producing new nanomaterials by self-assembly has aroused people's attention in recent years. Self-assembly is defined as the process that the molecules change their states from chaotic to well-ordered without help. Because of the “automate” features, nanomaterials made by self-assembly don't need manual intervention and the product has the best-combined structures. Self-assembly technique is one of a few feasible ways to make nanomaterials. Some scientific and industrial fields such as manufacturing, microelectronics etc. benefit a lot from self-assembly technique. In addition, many nanostructures in nature come from self-assembly, such as the double-stranded structure of DNA, the tertiary and quaternary structure of protein etc. All of these fine structures come from the self-assembly of small units. So the research on self-assembly not only benefits our understanding of life phenomena, but also makes it possible for us to design new self-assembled nanomaterials by mimicking the self-assembly process in life system. So self-assembly technique has great potential value in biological medicine fields such as anti-bacterial agent and gene or drug delivery.Atomic force microscopy(AFM) is a widely used versatile tool in the biological field. It can detect the fine structures of the sample surface by taking the advantage of the Van de Waals' force between an AFM tip and the sample surface. AFM has become a very important tool in biological field because the requirements for AFM characterization samples are very low. Moreover, AFM measurement can be performed both in air and in liquid conditions. In this thesis, we studied the self-assembly of several biological nanomaterials which have great potential applications in biological medicine field, especially in the field of tissue engineering, gene and drug delivery. The biological materials studied in this thesis mainly include three kinds of cationic polypeptides(poly-l-lysine, poly-l-histidine, and poly-l-arginine) and three kinds of polysaccharides(chitosan, xanthan and gellan.) We not only explored some influencing factors to the self-assembly nanostructures of above materials but also studied the interaction between theses biological materials. The main works of this theis are as followings.1?We have explored the phenomena of xanthan to be unzipped on mica surface. Firstly, we prepared uniform nanostructure of xanthan and gellan by controlling the density, salinity and some other conditions of their solutions and then the solution of certain cationic biological materials like chitosan, poly-l-lysine were dropped on xanthan which has formed network or rod-like structure on mica surface, it is found that numerous thin fibrils appeared. Later data analysis of these results shows that the double strands of xanthan was unzipped. This work is meaningful for the understanding of some disease due to the self-assembly of amyloid protein such as Alzheimer's disease.2?Adjusting the nanostructures of the three kinds of cationic polypeptides named poly-l-lysine, poly-l-histidine and poly-l-arginine. These three kinds of cationic polypeptides are widely used in the fields of anti-bacteria agents, gene and drug delivery and biomineralization because of the cationic groups on their side chains. It was found that these three kinds of polypeptides formed four different types of nanostructures during the culturing process. So we can get these samples with different nanostructures by controlling their culture time. This work provides the basic knowledge for better usage of these three kinds of cationic poly-peptides as anti-bacteria agents and drug delivery agent.3?The nanostructure xanthan formed by self-assembly on the surface of false teeth through different methods was studied. This part of work serves as a steppingstone for the research on the xanthan's protection mechanism for human's teeth.