Samples from living things need to be prepared carefully before they can be viewed using transmission electron microscopy. Allan Mitchell (University of Otago) describes the key steps in this process, which are designed to protect the sample from the hostile environment within the microscope. Allan also points out that the sample must remain as close to the living state as possible throughout the preparation process.
The environment inside an electron microscope is incredibly hostile to the living cell, so it needs to go through quite an elaborate process to enable it to survive that hostile environment. Firstly, we have a very high vacuum, and if you stick biological samples into a vacuum, they’ll just escape very quickly and be destroyed. We have a very high-energy electron beam, which is required to be able to penetrate the sample.
When the electron beam strikes the sample, it gets very, very hot – it can get up to 150 degrees Celsius where the electron beam actually hits the sample – so it needs to be able to survive that very high temperature. And lastly, we need to be able to cut a very, very thin slice of the sample to allow the electron beam to pass through. And if we have a biological sample that’s still full of cell water, then we aren’t able to cut that very thin slice – it’s a wee bit like trying to cut a thin slice of a tomato, you just can’t do it.
So specimen preparation is really important to meet all those criteria. One of the very important things about specimen preparation of course is that, after all that preparation, the sample still must be as close to the living state as possible.