Microscopes Flashcards
What is an artefact?
Structures present in an image due to preparation process
What are the 3 types of microscope?
Light / optical microscope
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
How does a light / optical microscope work?
Use light waves to produce an image
Wavelength of visible light = 500-650 nanometres
Max resolution: 0.2 micrometers
Max magnification: x1500
How does a TEM work?
- Use electromagnets to focus a beam of electrons
- This beam of electrons is transmitted through the specimen
- Denser parts of the specimen absorb more electrons so are darker on the final image
Max resolution: 0.2 nanometers
Max magnification: x1,500,000
How does an SEM work?
- SEM scan a beam of electrons across the specimen
- The beam bounces off the surface of the specimen and the electrons and detected, forming an image
- Can produce a 3D image that show the surface of specimens
What are the advantages and disadvantages of an optical / light microscope?
STRENGTHS:
- affordable and accessible
- can view living and transparent specimens
- easy to use as no complex sample preparation is required
WEAKNESSES:
- limited resolution
- limited ability to observe fine details
- inability to observe structure smaller than wavelength of light can pick up
What are the advantages and disadvantages of an SEM?
STRENGTHS:
- high resolution image with great depth of field
- ability to observe surface feature and 3D structures
- high magnification
WEAKNESSES:
- expensive and requires a dedicated facility
- samples must be conductive or coated in conducting material
- time consuming sample preparation
- can’t observe living specimens
What are the advantages and disadvantages of a TEM?
STRENGTHS:
- highest resolution
- detailed examination for cellular structures
- high mangification
WEAKNESSES:
- limited sample penetration
- sample must be extremely thin
- complex preparation
