Biological samples are often difficult to image due to their thickness, low contrast, and native hydrated state. We will discuss two different techniques available for analyzing these types of samples in Penn State's Material Characterization Lab, including scanning transmission electron microscopy (STEM) with energy dispersive spectroscopy (EDS), and liquid atomic force microscopy (AFM). Using a TEM with STEM-EDS capabilities, we can quickly acquire elemental maps at resolutions of less than 1 nm and sensitivities of less than one atomic percent. This provides many opportunities to answer important scientific questions related to the presence of metal atoms or other biologically relevant elements such as S, P, Ca, etc. in cells and biological structures in general. The other benefit of STEM imaging is the ability to image thicker samples with enhanced mass-thickness contrast as compared to TEM. This also makes the technique ideal for thick biological samples and removes some of the need for heavy metal staining in fixed samples. STEM imaging under cryo conditions or in liquids is also possible but poses significant challenges at high resolutions. However, we can use an AFM in liquid mode to capture the surface topography of biological samples with sub-nanometer-scale resolution in their native hydrated state. Since biological samples typically contain ~80 % water, removing water from or freezing a material can significantly alter its chemistry and structure and affect any analysis performed on that material. The capability of liquid AFM includes high-resolution imaging in fluid/hydrated samples, nanomechanical mapping, nanoindentation, high-speed AFM to molecular movements, and functionalized tip for molecular interaction.
Date and Time
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Location
3rd Floor Café Commons of the Millennium Science Complex
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Presenters
Sarah Kiemle
Organizers