Comprehensive Comparison Between STEM-HAADF and TEM Bright-field Mode for Imaging Resin Embedded Biological Samples

Most investigations of resin embedded biological samples by transmission electron microscopy (TEM) have been performed in TEM bright-field mode where the electron beam transmits through the sample. Modern TEMs can also be used in scanning TEM mode (STEM) where the beam scans across the sample. The preferred detector for STEM mode is the high-angle annular dark-field (HAADF) detector. The aim of this study was to compare image quality of resin embedded biological samples such as yeast (Saccharomyces), algae (Chlorella, Haematococcus), plant leaves (Nicotiana), human cells (MCF7), and animal tissue (mouse liver and brain) between TEM bright-field and STEM-HAADF mode. Generally, images taken in STEM-HAADF mode showed better image quality in terms of contrast, brightness, and signal-to-noise ratio. Samples of sections that did not receive postcontrasting with uranyl acetate or lead citrate appeared significantly less grainy. Specifically, STEM-HAADF mode resulted in significantly better image quality of algae cells, MCF7, and liver cells that did not receive postcontrasting. Artifacts visible in TEM mode were absent in STEM-HAADF mode. Thus, we can conclude that STEM-HAADF mode has significant advantages when investigating resin embedded biological samples that have little contrast or sections that did not receive postcontrasting rendering postcontrasting of sections unnecessary.