Pollen photos using a Scanning Electron Microscope
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Transcript of Pollen photos using a Scanning Electron Microscope
Scanning Electron MicroscopePollen
Chris Cardew 28th February 2016
Light Microscope
• A modern light microscope - 1000x .• The resolving power of the microscope limited
by the wavelength of the light used for illumination.
• Using light with a shorter wavelength--a small improvement.
• Using oil --- small improvement, but all together only brought the resolving power of the microscope to just under 100 nm.
Dr Ganga H
Dr Ganga H
Resolution of a microscope
• Wavelength of the illumination source ( λ )
• The numerical aperture of the lens (N.A.)
Limit of resolution = 0.61 λ/N.A.
• The maximum value of N.A. for a light microscope is approx. 1.4. therefore even the short blue light ( λ = 436 nm) of the visible spectrum will yield a resolution of only 190 nm.
• The wavelength of an electron beam is about 100,000 times less than that of visible light and hence the resolution of an electron microscope is far superior to that of the light microscope.
• NA is the light gathering ability and resolution of the acceptance cone of an objective
Dr Ganga H
Dr Ganga H
THE LIGHT MICROSCOPE v THE ELECTRON MICROSCOPE
VacuumAir-filledInteriorMagnetsGlassLenses
High voltage (50kV) tungsten filament
Tungsten or quartz halogen lamp
Radiation source
X 500,000x1000 – x1500Maximum magnification
0.14nmFine detail
app. 200nm or 0.2micron
Maximum resolving power
Electronsapp. 4nm
Visible light390nm (red) – 760nm
Electromagnetic spectrum used
ELECTRON MICROSCOPELIGHT MICROSCOPEFEATURE
© 2007 Paul Billiet ODWS
Focus Lens is movable Rigidly fixed, adjust lens currents
THE LIGHT MICROSCOPE v THE ELECTRON MICROSCOPE
Copper gridGlass slideSupport
Heavy metalsWater soluble dyesStains
Ultramicrotome Slices - 50nm
Parts of cells visible
Microtomeslices - 20 000nm
Whole cells visible
SectioningResinWaxEmbedding
Glutaraldehyde,OsO4 formaldehydeFixation
ELECTRON MICROSCOPELIGHT MICROSCOPEFEATURE
© 2007 Paul Billiet ODWS
Focussing screen Human eye (retina), photographic film
Fluorescent screen,photographic film
Scanning Electron Microscope
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons
‘The German scientists Max Knoll and Ernst Ruska realized that, since the wavelength (the distance between successive peaks or troughs of any wave) associated with electrons was much shorter than the wavelength of visible light, a microscope based on electron imaging should be able to pick out much finer detail than an optical microscope. This is because any tiny object or detail that has dimensions smaller than the wave falling on it will not influence or affect the wave’
Patricia HodgesPollen Drawings
Rex SawyerHoney Identification
Field Thistle pollen x400 using a light microscope
Field Thistle 2500 times
Intine
Field Thistle 2500 x 42.4um
Field Thistle x 2000
Intine
Field Thistle x 2000
Field Thistle 6000 x
Field Thistle x 8000
Field Thistle x 2500
Field Thistle x 2500
Field Thistle x 3000
Field Thistle x 3000
Field Thistle x 2500
Field Thistle x 2500
Field Thistle x 2000
Field Thistle x 2000
Field Thistle x 3000
Field Thistle x 2000
Field Thistle x 3000
Meadowsweet 4000 x enlargement
Meadowsweet 4000 x enlargement
Meadowsweet 6000 x enlargement.17.2um long
Meadowsweet x 4000
Corn Flower 3000x
Corn Flower 3000x
Corn Flower 5000x
Hogweed x 4000
Hogweed x 4000