Probing biological systems with optical and atomic force microscopy

Contact mode atomic force microscopy and optical microscopy were used to investigate the morphology and physical characteristics of biological samples. Single, live yeast cells were investigated with atomic force microscopy, as well as, with Differential Interference Contrast microscopy. While Differential interference Contrast microscopy was suitable for general cell characterization, detailed surface structures were only visible using atomic force microscopy. Nanometer resolution images of actin filaments were also obtained with atomic force microscopy. Filaments, which were never dried down on the surface, were imaged with an atomic force microscope. Nanometer resolution images were obtained on these samples; both the filament height (7–8 nm) and the helical repeat (37 nm) were measured using contact mode atomic force microscopy.; The formation of actin rings was also investigated in this work. Using fluorescence microscopy to visualize the actin rings, the persistence length of both muscle and yeast actin was measured. The measured persistence length did not significantly differ for the two types of actin studied. Also, it was shown that ring formation was not due to lateral association.; The atomic force microscope was also used to investigate the hydrogen bond strength and the hydrophobic interaction strength. How the strength of the interaction differed in heavy water compared to light water was studied. Both the hydrogen bond strength and hydrophobic interaction strength was found to be greater in heavy water. A method denoted “variance analysis” was utilized to analyze the data. This method is independent of the contact area of the interaction and is easily performed. Spectral approximation analysis was also performed on the force measurement data. Results from this method of analysis were used to substantiate the findings of the variance analysis.