MadSci Network: Microbiology

Re: is there any other way to view a virus other than the electron microscope.

Date: Thu Jul 8 19:20:30 1999
Posted By: Mark Sullivan, Staff, Molecular and Microbilogy, Fred Hutchinson Cancer Res. Center
Area of science: Microbiology
ID: 931209863.Mi

   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

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