Function: Lets users look at the surface of objects that contain liquid (avoids sample preparation steps for conventional SEM).
Maximum magnification: Approximately 500,000x.
Best for:
Looking at biological samples in a lifelike state.
Looking at biological samples too delicate to survive preparation for conventional SEM.
Looking at hydrated or wet surfaces of biological samples.
Disadvantages:
Resolution often not as high as the transmission electron microscope.
Can’t be used to look at living things (sample needs to be frozen before visualising).
Frozen water may hide important information.
Costly to run.
Video: University of Otago experts Liz Girvan and Dr Bronwyn Lowe tell us why cryoSEM is best when looking at things that contain moisture, such as plants or food.
Transcript
Liz Girvan
CryoSEM is quite different from conventional SEM. So in cryoSEM, we take the sample as it is from nature or from industry, and we simply freeze it and then view it frozen. So we don’t do any of the fixation steps, we don’t need to dry it – we just freeze it and look at it.
Dr Bronwyn Lowe
Why would you use cryoSEM looking at plant materials? In order to prepare a sample to put in an SEM, you have to treat it, you have to dry it, you have to chemically set it, and when you do that, you can introduce a lot of changes into your sample that are then artefacts of your preparation steps rather than what the plant really looks like. And because I really wanted to know what does the plant look like immediately it comes off the bush, all of those preparation techniques were not possible.
So cryoSEM gets around those problems because you take your sample and it gets dunked into liquid nitrogen so it’s snap frozen, and so you capture all the cells, all the arrangement of the cells, everything is just frozen instantly. And so that means that you don’t alter the sample much in putting it in the microscope.
Acknowledgements
Liz Girvan, University of Otago
Dr Bronwyn Lowe, University of Otago
Allan Mitchell, University of Otago
