Final answer:
To prepare ethanol-preserved insects for SEM imaging, specimens must be critically point dried with CO2, and then sputter-coated with a metal such as palladium to prevent electron beam charging during imaging.
Step-by-step explanation:
To prepare ethanol-preserved insects for imaging using Scanning Electron Microscopy (SEM), the specimens undergo a rigorous dehydration process before imaging. After being preserved in ethanol, which serves to displace the water content within the specimen, a more thorough drying process is necessary for SEM analysis compared to Transmission Electron Microscopy (TEM).
The key technique to completely dry out the specimens without causing artifacts such as shriveling is critical point drying with inert liquid carbon dioxide under pressure to fully displace any remaining water.
Once the specimens are suitably dried, they are made conductive to prevent charging from the electron beam in the SEM. This is achieved through sputter-coating the specimen with a metal layer, often palladium. Sputter-coating involves knocking atoms off of a target— in this case, palladium—using energetic particles to create a fine conductive coat over the specimen.
Only after these meticulous preparation steps can the ethanol-preserved insects be imaged with the high-resolution detail that SEM provides, revealing textures and structures of the specimen's surface.