Microscopic Observation

Resolution

The ability to distinguish small objects close together

Magnification

An enlarged image of an object

Contrast

The difference in color intensity between an object and its background

What lab technique can increase a microbial sample’s contrast?

Staining

Light microscope

Microscope that relies on light to create and capture an image

Light (and compound) microscope examples

Bright-field

Dark-field

Phase-contrast

Fluorescence

Compound microscope

Microscope that relies on two or more lenses to form an image

Downsides of bright-field microscopy

• Resolution limit (~0.2 um)

• Requires staining (kills cells)

• Refraction of light (decreases resolution)

Advantages of dark-field microscopy

• Helpful for objects that are very thin

• No staining needed

• High contrast image

Disadvantages of dark-field microscopy

• Resolution limit (~0.2 um)

• High sensitivity (dust particles can contaminate sample)

Phase-contrast microscopy advantages

• Able to visualize cell components

Phase-contrast microscopy disadvantages

• Expensive

Fluorescence microscopy advantages

• Able to tag molecules

• High-contrast imagery

Fluorescence microscopy disadvantages

Fluorophores

Chemical compounds that absorb/emit light of specific wavelengths. Can be a dye or protein.

Electron microscopy advantages

• Very high resolution (~0.5 nm)

Electron microscopy disadvantages

• Images are not in color