UCLA

Atomic force microscopy (AFM) is a class of high-resolution scanning probe microscopy (SPM) for non-conducting materials. Of these non-conducting materials, biomolecules such as cells, organelles, proteins, and nucleic acids are of interest as we seek to describe laws of nature and life. However, it is not trivial to resolve structures or mechanics of biomolecules due to their small sizes and soft constructions. AFM enables one to obtain high-resolution images of biological structures in their native state both in air and in fluids as AFM is considered as a non-destructive technique. In addition to these advantages, AFM is providing the mechanical information of the sample surface. For these reasons, since the development of AFM, an expansion and re-assessment has led to significant discoveries and scientific enlightenment in biology. In this dissertation, I focus on the application of AFM to biological systems, which will add new scores in the field of both microscopy as well as a higher understanding of specific biological systems. I have explored the mechanical properties of mammalian cells and bacterial cells. I have examined mammalian cell stiffness in relation to cancer metastasis and the changes in extracellular biofilm adhesions from bacterial cells. I have resolved the high-resolution structure of exosomes which are 50-120 nm sized vesicles secreted from mammalian cells. With an accurate adjustment of the force applied to the sample, I have been able to observe and verify nanofilaments attached to exosomes. I also have discovered that the surface and the size distributions of exosomes are different depending on their purification methods. Lastly, I have obtained high-resolution images of an actin binding protein, INF2, which showed nanostructured self-assemblies with or without f-actin.