DESCRIPTION OF INTERACTIVE

Imaging Technologies

1. Eye: The eye is the easiest tool for viewing biological samples. The ability to be able to tell two separate objects apart is called resolution. For the trained naked eye, our resolution is about 75 μm; 
2. Light Microscopy: Improvements to optical microscopy over the past 300 years have increased magnification up to 1,500x and allowed optical microscopes to resolve objects as small as 200 nm. This resolution is a physical limit dictated by the wavelength of light; 
3. Electron Microscope: Electron microscopes (EM) use accelerated electrons and magnetic coils to make an image instead of light and glass lenses. Electrons have a wavelength (size) that is 104 to 105 times smaller than the wavelength of light. EMs can resolve objects that are 103 times smaller than the smallest resolvable object in a light microscope. The high-resolution transmission EM can magnify a sample up to 50,000x and provide a resolution of 0.1 nm. In cryo-EM, specimens are frozen rapidly to eliminate ice crystals from forming that can distort the specimen’s structure. Samples are then viewed at temperatures as low as –185ºC. Two- and three-dimensional models of the sample can be reconstructed using a computer program that averages many electron micrographs taken from different angles. Electron microscopy requires a sample thin enough to allow electrons to pass through. Samples smaller than 1/500th the diameter of a human hair are used; 
4. X-ray Crystallography: X-rays, with wavelengths approximately the same size as the spacing between atoms, are directed through a crystal of the substance under study. The X-rays are bent by the electrons surrounding the atoms in the crystal. The scattered X-rays produce a pattern as they exit the crystal. Sophisticated computer programs use measurements of the angles of the scattered X-rays and their intensities to calculate the three-dimensional positions of the atoms in the crystal. By rotating the crystal and making many two-dimensional images, it is possible to combine results to produce a three-dimensional picture of the molecule; 
5. Cell Tagging: In many cases, it can be difficult to pick out a cellular structure in a light microscope or electron microscope image. Cell tagging takes advantage of being able to follow individual molecules that make up a part of the cell. There are different methods of tagging biomolecules. For example, radioactive isotopes of atoms can be introduced to cells. Isotopes are used the exact same way as regular atoms except that their radioactive emissions can be detected with X-ray film. As cells consume the isotopes, they incorporate them into their cell structures. Another method involves adding a coloured or fluorescent chemical that binds to specific functional groups. In all cases, the final result is that the cell structure is highlighted compared to the rest of the cell.