Principles and application of Laboratory instruments

Microscope

Principle

  • This instrument produces enlarged and clear images of minute objects, which can not be differentiated with naked human eyes.
  • Objects are magnified with the help of a series of lenses.
  • The image seen through the microscope is virtual.
  • The size of the enlarge image depends upon the 'magnification' and 'resolution power'.
  • For light microscopes, magnification depends upon the product of the power of each lens. It is denoted by 'X' next to a numeric value.
  • The resolution power is the smallest distance between the two close points, which can be differentiated. For a light microscope minimum resolution power is ∼0.2 μm. (for human eyes it is 0.1 mm).
  • It has following parts:
    1. Eyepiece: Also known as ocular. It is the topmost part. Magnification of the ocular is usually 10X.
    2. Eyepiece tube: Holds the eyepiece.
    3. Parts of light microscope
      Parts of compound light microscope
      Objective lenses: Usually 4 in number ranging from 4 to 100X magnification.
    4. Nose piece: Also known as revolving turret. It holds the objective lenses and is used to align the lens of required magnification.
    5. Adjustment knob: Use to focus the object. Two in number; coarse and fine adjustment knob.
    6. Stage: is the platform on which an object on a glass slide is placed.
    7. Aperture: is the hole in the center of stage to allow the light to pass through the object.
    8. Condenser: It is fitted below the stage and condenses the light coming from the source to make the image sharp.
    9. Diaphragm: also known as iris control the amount of light beam.
    10. Light source: A glass mirror or tungsten bulb to produce light that passed through the object to make an image.
    11. Head: also known as 'body' holds optical parts in the upper part.
    12. Arm: connects head to base.
    13. Base: is the main support of microscopes and holds illuminator parts.


Application

Microscope is used to observe the larger and clear image of the small sized-objects. It is used to clearly see the internal details of the microbes, which can be photographed or drawn on a piece of paper.


Autoclave

Principle

  • Parts of vertical autoclave
    Autoclave is a typical instrument required in all microbiological laboratories for the purpose of wet-sterilization.
  • To all intents and purposes, it is a large-scale pressure cooker.
  • Autoclave works on "steam under-pressure" and maintain the temperature of steam 121 °C at 15 lbs pressure. That is enough to kill all the microbes.
  • Autoclave runs on electricity.
  • It has following parts:
    1. Metallic body: Autoclave is made up of a thick metallic body.
    2. Heating element: Dipped in water, it raises the temperature of water at the bottom.
    3. Perforated Basket: Rest inside the autoclave over stage on water.
    4. Lid: Fitted with rubber gasket and tightened with wing-nut to close the autoclave.
    5. Pressure gauge: Monitor the pressure of steam inside the vessel.
    6. Pressure control valve: Fitted with whistle, used to adjust the pressure.
    7. Safety valve: Broken at over-pressure.

Application

Autoclave is used for sterilization of thermolabile (heat-sensitive) materials, such as: culture media, cotton, bandages, etc.


Laminar Air Flow (LAF)

Principle

  • LAF hood provides a sterilized chamber to perform microbiological operations.
  • Instrument blows the sterilized air that passes through High Efficiency Particulate Air (HEPA) filter.
  • The pores of HEPA filter are so small to retain all forms of microbes.
  • LAF runs on electricity.
  • It has following parts:
    1. Hood: Provide the space to perform experiments.
    2. HEPA filter: Filter the air to sterilize it.
    3. Blower fan: Blow the air unidirectional through HEPA filter.
    4. UV lamp: For sterilization of the inner side of the hood.

Application

LAF is used to perform microbiological experiments such as: handling of sterilized culture media, isolation, inoculation and pure culture of bacteria as well fungi.

Biological Oxygen Demand (BOD) incubator

Principle

  • BOD incubator maintains the specific temperature for optimum growth of bacteria (37 ± 1 °C) or fungi (26 ± 2 °C).
  • The instrument maintains the required humidity and circulates the air inside.
  • BOD incubator runs on electricity.
  • It has following parts:
    1. Metallic body: Outer body is just like a vertical refrigerator with a door and PID controller.
    2. Rack/shelves: Culture plates/slants to be incubated are kept over the different racks inside.
    3. Freezer: Compressor provides cooling.
    4. Heater: Heating element heats the air.
    5. Circulating fans: Circulate the air.

Application

In order to culture the bacteria and fungi, a BOD incubator is used.

Content first created on 17-09-2022
last updated on 24-11-2022