What is a Microscope?
A microscope is an instrument used to view objects or specimens that are
too small to be seen with the naked eye. It uses lenses or a series of lenses
to magnify the image of the object, allowing us to see details that would
otherwise be invisible.
Microscopes come in many types and sizes, from simple handheld magnifying glasses to complex electron microscopes used to see the ultrastructure of the cell.
In this post let us discuss ten microscopes used in biological science.
Types of Microscope used in Biology
1. Simple Microscope
- uses a single convex lens to magnify an object.
- It includes magnifying glasses and dissection microscope used to study the morphology of plants and animals
Limitations:
- Low magnification Only
- used to see morphology because of low magnification.
2. Compound Microscope
A compound microscope is an optical instrument that uses two or more
lenses to magnify small objects.
How Compound Microscope works?
It consists of an objective lens and an eyepiece lens that work together
to produce a magnified image of the specimen. The objective lens is located
close to the specimen and produces a real, inverted image, which is then
magnified by the eyepiece lens. The magnification of a compound microscope is
the product of the magnifications of the objective and eyepiece lenses.
- Maximum magnification is 1000 X. Compound microscopes are commonly used in biology to observe cells, bacteria etc.
Limitations:
- Thin stained section required
- Low resolution and image contrast
- Cannot observe live specimens
- Maximum Magnification 1000X
3. Dark field microscope
- A dark field microscope produces a bright image of the specimen against a dark background.
- used for observing live, unstained biological specimens.
The dark field technique works by illuminating the specimen with a cone
of light that is directed at an angle, causing light to scatter off the
specimen and enter the objective lens at an oblique angle. This scattered light
is then magnified to produce a bright image against a dark background.
- Dark field microscopy is commonly used in microbiology to visualize bacteria, parasites, and other transparent microorganisms.
Limitations
- Limited to viewing transparent specimen
- Cannot view stained specimen
- Cannot view thick specimen
4. Phase contrast microscope
- A phase contrast microscope is a type of microscope that enhances the contrast of transparent and colorless samples.
- view live specimens with low contrast by amplifying differences in refractive index.
2 specific microscope components are condenser annulus and objective phase plate to create a phase shift of light that results in an image with greater contrast. The phase plate converts the phase shift into an intensity shift, which is then detected by the microscope's objective lens and converted into contrast that enhances the visibility of the specimen's features.
It was invented by Dutch physicist Frits Zernike in the 1930s
Limitations
- Low resolution
- Causes halo effect
5. Differential Interference Contrast Microscope
- also called as Nomarski microscopy
- used to observe high contrast images of live transparent samples
How DIC Microscope works?
It works by transforming
differences in the refractive index of the specimen into contrast variations.
It works by splitting a polarized light beam into two beams that pass through
the sample at slightly different angles, creating interference patterns
resulting in a 3D-like image with high resolution and clarity.
Limitations
- 3D image may not be accurate
- More expensive
6. Fluorescence Microscope
- Used to view fluorescently-labeled live specimens in high contrast.
How Fluorescence Microscope Works?
It uses fluorescence to produce an image. It works by exciting fluorescent
molecules in a sample with a specific wavelength of light, causing them to emit
light of a different wavelength. The emitted light is then detected by the
microscope and used to generate an image with high spatial resolution.
- Widely used to see specific cell structures or proteins
Limitations
- Need for fluorescent tagging of specimens
- expensive
7. Confocal Microscope
A specific fluorescent microscope that allows obtaining 3D images of the
live sample in real time with good resolution.
How Confocal Microscope Works?
It uses a laser to illuminate the specimen and a pinhole to eliminate
out-of-focus light. This creates a sharper, clearer image with greater depth
resolution than traditional fluorescence microscopes.
Limitations
- limited number of excitation wavelengths available with common lasers
- Expensive
- need for fluorescent tagging of specimens.
8. Scanning Electron Microscopes
- Scanning electron microscopes (SEMs) are powerful tools used to obtain high-resolution images of the surfaces of solid objects.
They work by scanning a beam of electrons over the surface of the
sample, which interacts with the atoms and produces signals that are used to
generate an image. In SEM, scattered secondary electrons are used to generate an
image.
- View and analyze surfaces at high magnification by scanning a focused beam of electrons over the surface of a sample.
- magnifying samples up to 2 million times with high depth of focus
- Less expensive than TEM
Limitations
- cannot view living specimens
- Low resolution
- Skilled operators
- Expensive
9. Transmission Electron microscopes
Transmission electron microscopes (TEMs) are powerful tools used to
observe the ultrastructure of cells and tissues at high magnifications and
resolutions.
How TEM works?
TEMs use a beam of electrons to illuminate a thin sample, the
transmitted primary electrons is used to generate an image of high
magnification and resolution.
- Subcellular components such as organelles, viruses, and macromolecules.
- 10-50 million times magnification
Limitations
- Require extremely thin samples
- Cannot view living specimens (less than 150nm)
- Skilled operators, Expensive
- A scanning transmission electron microscope (STEM) is a type of electron microscope that is a combination of SEM and TEM.
- The STEM works by passing a beam of electrons through a thin sample, which then scatters the electrons and produces an image.
- TEM is updated to STEM by an addition of a system that scans a focused beam across the specimen to form the image.
- produce high-resolution images of thin samples
Limitations
- Require thin samples
- Sensitivity to contamination
- Skilled operators
- Expensive
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