Concepts explained
The Electron Microscope — How to See What the Eye Cannot
At school you look at onion skin through a microscope. Turn up the magnification and it only goes blurry. The reason is not the lens. In Daejeon there is an institute that keeps the instruments that see past that limit and lends them to researchers across the country.
Looking larger, and telling apart
Everyone has stretched a blurred photograph with two fingers. What comes out? A large blurred photograph. Nothing appears that was not there.
A microscope is the same. How large a thing is made to look and whether two close points are shown as two are different questions. The second is called . Magnifying without it is called empty magnification, and it is worth nothing.
Seeing is catching what bounced back
So what sets the resolution? Step back a moment. To see something is to catch the that struck it and came back.
Light is a wave. Visible light has a wavelength of about a two-thousandth of a millimetre, so anything smaller is simply passed over. That is why cells are visible and the machinery working inside them is not.
What matters is that this is not a fault of grinding. No amount of care with glass gets past it. Seen by light, that is as far as it goes. To go further you change not the lens but the light.
So look with electrons
An is a particle that also behaves like a wave (a ), and its wavelength is some hundred thousand times shorter than visible light. It catches on far smaller things.
So electrons are fired instead of light. Electrons do not pass through glass, so the lens must change too: magnets are used. An electron crossing a magnetic field bends, and gathering that bending does a lens's work.
One more thing. Electrons scatter off air molecules, so the inside of an electron microscope is a . The air has to be pumped out.
A little further in
The hard part is the cutting
You might think that buying the instrument is the end of it. In the mode where electrons pass through the specimen, the specimen must be thinner than a hundred nanometres — about a thousandth of the width of a hair.
Living material adds a second problem. Biological specimens hold water, which boils in a vacuum, and they burn under the beam.
So they are frozen. Freeze slowly and ice crystals grow and tear the inside apart, so it is done in an instant, giving the crystals no time. Looking at frozen specimens this way has recently transformed the study of protein structure.
Second instrument — weigh it and you know it
Seeing is not the only way. To find out what is present there is another route: . Not looking but weighing.
Push a ping-pong ball and a steel ball with the same force and the ping-pong ball flies much further. The push alone tells you which is heavier.
That is what the instrument does. The substance is first made into so that it carries charge. Then electricity flings the ions along and a magnet bends their path: light ones bend far, heavy ones bend little.
Its power lies in catching very small amounts: doping tests, pesticide left on fruit, microplastics in seawater, whether some in the body has risen or fallen. Quantities too small to see or smell are pinned down as numbers.
Third instrument — ask in time
The third is . It neither looks nor weighs. It asks.
Some have a spinning-top quality (). Put them in a very strong magnet and they wobble at a steady rate like a tilted top. Radio waves at exactly that get a response; anything off it gets none.
The use follows. That rate shifts very slightly with whatever sits around the nucleus, so reading the returning signal reveals how the atoms in a molecule are joined — the arrangement, without seeing it.
Hospital MRI works the same way, watching hydrogen nuclei in the water of the body. Its original name was nuclear magnetic resonance; the word nuclear sounded alarming and was dropped. No radiation is involved.
Set the three side by side and they are one thing: reading what the eye cannot see by turning it into another sense. Drawn with electrons, weighed as mass, heard as a returning signal.
Why keep them in one place
These instruments are expensive. But the price is not the largest problem.
- They are sensitive to vibration. A lorry on the road outside blurs the image, so the buildings are built on floors floated free of the ground.
- They are sensitive to magnetic fields and electrical noise. A lift nearby can be enough to interfere.
- Someone has to know how to run them. The people are rarer than the machines.
- And they are not in constant use. Bought by one laboratory, they would sit idle most days.
So they are gathered in one place and booked. Researchers from across the country send specimens or come in person. The Korea Basic Science Institute in Yuseong-gu, Daejeon, is built on that idea.
It is an old habit of science. Large telescopes, accelerators and synchrotrons are used the same way — holding in common an eye no one can own alone.
What you would study to do this
Using the instrument, running it and keeping it alive are three different jobs.
- Someone who decides what to look at — chemistry, life science, materials, geology, each in their own field.
- Someone who prepares the specimen — cutting, freezing, staining. The result turns on these hands.
- Someone who runs the instrument and reads the signal — analytical chemistry and instrumentation.
- Someone who keeps the building steady — vibration, temperature, electromagnetic noise. This is plant engineering.
- Someone who handles the data — hundreds of thousands of images are now stacked by computer into a shape.
Look at the second line. Their names rarely appear on the paper, and without them no result appears at all. It is where the student who was good with their hands in the practical class ends up.
The fourth line is a real job too. The finest microscope in the world takes blurred pictures if the floor shakes.
The question that remainsWhen what cannot be seen is read through another sense — may we still say that we saw it?