| MadSci Network: Microbiology |
Even the best light microscopes can only resolve objects to a size
around 200nm= 2/10,000,000 of a meter. This is about the size of
mitochondria, or small bacteria. The electron microscope, however, is able
to resolve objects to about 200pm= .2nm= 2/10,000,000,000 of a meter. That
is only a 1000 fold improvement on the light microscope, but enough to make
a big difference. Electron microscopy is really the only existing method
of viewing objects as small as viruses. Bacterial viruses average about
10-50nm in diameter, while animal and plant viruses average about 50-300nm.
You'll notice that the upper size of animal and plant viruses are at about
the absolute resolving ability of the regular light microscope.
The resolving power of a microscope is inversely proportional to the
wavelength of the radiation source used to view the object(remember that
light is a part of the elctromagnetic radiation spectrum. The visible
spectrum of light ranges in wavelength from about 380nm(violet light) to
750nm(red). So if we use a radiation source that has very large
wavelengths, such as visible light, our absolute resolving power isn't that
great compared to a source with much smaller wavelengths, such as
electrons(about 2pm= .002nm). With a microscope of either type, when you
magnify the object more and more, you lose resolution. So even though the
light microscope can resolve down to 200nm, it isn't really that clear. So
we have to turn to the electron microscope. As for building your own
devise that would allow you to view a virus better than an electron
microscope, it will be pretty tough. You'll have to find a radiation
source that has a very small wavelength, and doesn't destroy your sample.
The smaller you get in wavelength, there is higher energy, and that creates
damage. Gamma rays have a very small wavelength, but create a lot of
damage to biological molecules, especially DNA. But if you find a way pull
it off, you'll be famous! Good luck.
Mark Sullivan
Try the links in the MadSci Library for more information on Microbiology.