Microscopes: An Overview

  • Microscopes are instruments that magnify small objects, allowing us to see and study them in detail.
  • These are critical tools in microbiology as they enable scientists to observe microorganisms such as bacteria, viruses, and fungi.
  • Using a microscope, microbiologists can study the structures, functions, and behaviours of microorganisms, aiding in diagnostics and research.

Types of Microscopes

Light Microscopes

  • Light microscopes, or optical microscopes, use light and a series of lenses to magnify specimens.
  • They can magnify objects up to 2000 times their actual size, but their resolution is limited by the wavelength of light.
  • Light microscopes are commonly used in schools, hospitals, and research institutions.
  • There are special types of light microscopes, such as phase-contrast microscopes and fluorescence microscopes, which are used to observe specific types of samples or particular aspects of samples.

Electron Microscopes

  • Electron microscopes use a beam of electrons instead of light to create an image of the specimen.
  • They can achieve much higher magnifications and greater resolution than light microscopes, allowing microscopic details to be seen at the nanometer level.
  • There are two main types of electron microscopes: Scanning Electron Microscopes (SEMs), which can create detailed 3D images of the sample surface, and Transmission Electron Microscopes (TEMs), which can show internal structures of the sample at very high magnification.

Using a Microscope

  • The basics of using a microscope include placing the slide on the stage, selecting the appropriate objective lens, and focusing the image using the coarse and fine focus knobs.
  • Always start observing the specimen with the lowest magnification objective lens and gradually increase the magnification if needed.
  • When viewing specimens under a microscope, adjustments for brightness and contrast often need to be made for clearer observation. This is usually done using the condenser and diaphragm.

Importance of Sample Preparation

  • Proper sample preparation is key in microscopy, as it can significantly affect the quality and accuracy of observations.
  • Samples may need to be fixed (preserved), embedded into a substrate, sectioned (cut into thin slices), stained, or mounted before being observed under a microscope.
  • Staining is often used to highlight specific structures within a sample. Different staining methods, such as Gram stain, are used for different purposes.

Microscope Limitations

  • While microscopes are powerful tools, they also have limitations. The most significant is the resolution limit, which is the smallest distance between two points that a microscope can still distinguish as two separate points.
  • Additional limitations are associated with preparation methods. For instance, the use of heavy metal stains in electron microscopy can distort the sample, and some structures can only be seen with specific stains.
  • Finally, most microscopes can only view dead, fixed material, making it impossible to observe dynamic processes in live cells.