Transmission electron microscopy (TEM) is an imaging technique to observe thin specimen. An electron beam interacts with the specimen while passing and is detected by a sensor, in this case a CCD camera.
DNA consists of atoms with small atomic numbers. This leads to only weak contrast. For fixation on the samples to enhance the contrast, uranyl formiate is applied as negative stain.
As DNA is light material, the samples were stained with uranyl acetate to enhance contrast. Electrons can pass through the origami-structure and are absorbed or scattered by the stain. Read more about preparing samples for transmission electron microscope.
The images taken for this project were made at the BioNano TEM facility (CM 100, Philips, Amsterdam, NL) at a high voltage of 100.0 kV and a nominal magnification of 28500. Images were 4x averaged and integrated to reduce noise.
Besides confirming the proper folding of our structure, the main purpose of the TEM measurements was to provide data on twists and lengths of the structures, dependent on concentrations of the DNA binders. These angle and length measurements were accomplished with the the free tool imagej.