Low-vacuum scanning electron microscopy for informative three-dimensional imaging of cell/tissue architectures and biomedical target localization

This review focus on the recent advances of practical application of low-vacuum scanning electron microscopy to informative three-dimensional imaging of cell/tissue architectures and biomedical target localization on microscope slides for biomedical sciences and clinical diagnoses. Scanning electron microscopy under low-vacuum conditions allows high-resolution imaging of complex cell/tissue architectures in nonconductive specimens because the negative charge that accumulates on the nonconductive materials can be neutralized by the positive ions in the residual gas molecules. However, the conventional methods for metal staining of biological specimens require harmful uranium compounds, which hampers the applications of electron microscopy. The development of uranium-free KMnO4/Pb metal staining allows multiscale imaging of extensive cell/tissue architectures to intensive subcellular ultrastructure. The obtained image contrast was equivalent to that of Ur/Pb staining and sufficient for ultrastructural observation. Observation of the 20 µm-thick section facilitates distinctive perception of the face-side images of the epithelium, which are seldom seen within 5 µm-thin sections. Visualization of the exact location of targeting molecules by in situ strategy provides unique insight into nanogold development via nanogold nucleation and secondary growth under hot-humid air conditions. These user-friendly techniques are highly anticipated to fill the gap between light and electron microscopy to correlate cell/tissue structure and function. Importantly, paraffin and cryostat blocks of cell or tissue samples are semipermanent, making them valuable for retrospective studies through the re-evaluation of archived specimens.