Ch. 2.3: More Microscopy
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How do electron microscopes work generally?
A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen.
Why are electron microscopes better ( generally ) than light microscopes?
More detail of cell ultra structure can be seen because electrons have a much smaller wavelength than light waves.
How do transmission electron microscopes work? Resolution?
A beam of electrons is transmitted through a specimen and focused to produce an image. This has the best resolution with a resolving power of 0.5 nm
How do scanning electron microscopes work? Resolution ?
A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected. The resolving power is from 3-10nm, so it’s not as good as a TEM but three dimensional images of surfaces are produced which is valuable.
What are the advantages of light microscopes?
• inexpensive to buy and operate • small and portable • simple sample preparation • sample preparation does not usually lead to distortion • vacuum is not required • natural colour of sample is seen ( or stains are used) • specimens can be living or dead • image can be viewed directly
What are the disadvantages of light microscopes?
• relatively low magnification ( up to x2000) - relatively low resolution ( 200nm)
What are the advantages of transmission electron microscopes?
• high magnification and resolution produces detailed images of cells and organelles • allows internal structures of cells/ organelles to be seen
What are the advantages of scanning electron microscopes?
• produces 3D images - reveals details of contours and cell / tissue arrangements
What are the disadvantages of electron microscopes generally?
• Expensive to buy and operate • large and needs to be installed • complex sample preparation • sample preparation often distorts material • vacuum is required • black and white images produced • specimens have to be dead
What are the advantages of electron microscopes generally ?
• over x500 000 magnification - resolving power is high : TEM - 0.5 nm SEM - 3–10 nm
What are the limitations of scanning electron microscopes?
• requires expensive and difficult staining • only reveals the surface detail from a specimen • images can’t be viewed directly
What are the limitations of transmission electron microscopes ?
• produces 2D images of thin cross sections of a specimen - images can’t be viewed directly
How does a laser scanning confocal microscope work?
• it moves a single spot of focused light across a specimen ( point illumination ) • this causes fluorescence from the components lab elder with a dye • the emitted light from a specimen is filtered through a pinhole aperture. Only light radiated from very close to the focal plane is detected • unwanted light emitted from other parts does not pass through the pinhole and is not detected. • therefore it has a very high resolution
What are the advantages of laser scanning confocal microscopy?
• non evasive eg see back of the eye in optometry - high resolution as there is limited blurring as they only see one layer of the specimen