meet the microscopes
These machines use different techniques to let us see some of the smallest objects in our universe
optical microscopes
Optical microscopes use light and a series of magnifying lenses to view specimens such as blood or tissue cells. They’re probably the sort of microscope you used during science class at school. While they are the oldest microscope design, they remain vital in biological research and medical diagnostics.
advantages
• Researchers can see the natural colour of the sample. • Samples can be living or dead. • Optical microscopes are not affected by magnetic fields.
disadvantages
• The preparation to make a sample may distort specimen. • Magnification is limited to 1500x. • The resolving power (the distance needed to distinguish two points) for biological specimens is only around 1nm.
scanning electron microscopes
Scanning electron microscopes use a beam of electrons that are scanned over the surface of a sample, which causes the production of secondary electrons, backscattered electrons and characteristic X-rays. These microscopes are held in vacuum chambers to prevent the electrons from hitting air molecules, and modern full-sized SEMS can provide a resolution between 1–20nm.
advantages
• Minimal preparation of samples is required. • Can provide detailed, three-dimensional and topographical imaging. • Works fast and provides images within minutes.
disadvantages
• Samples must be solid and able to tolerate vacuum pressure (not suitable for biological samples). • Risk of radiation exposure due to the scatter of electrons from beneath the sample. • Complicated and expensive, they are large and sensitive to electrical, magnetic and vibrational interference.
transmission electron microscope
Transmission electron microscopes are the most powerful microscopes we have today. The electrons pass through the sample and are focused to form an image on a screen or onto a photographic plate. The faster the electrons hurtle down the microscope, the smaller the wavelength and the more detailed the image.
advantages
• The most powerful microscopes, they can magnify by over 1 million times. • Provide information on the element and compound structure of samples. • Can determine shape and size as well as structure and surface features.
disadvantages
• Samples must be ‘electron transparent’ (a thickness less than 100nm). • Images are composed in black and white. • Preparation of specimen is difficult and complex.