Delphinidin

Scientists use the scanning electron microscope (SEM) to study the details of many different types of surfaces. Unlike the light microscope or even a transmission electron microscope, which form images by passing either a beam of light or electrons through a thin slice of fixed tissue, the SEM’s great advantage is its ability to allow us to look at surfaces of specimens and observe topographical detail not possible with other types of microscopy.

The basic concept of a scanning electron microscope is that a finely focused beam of electrons is scanned across the surface of the specimen. The high-velocity electrons from the beam create an energetic interaction with the surface layers. These electron-specimen interactions generate particles that are emitted from the specimen and can be collected with a detector and sent to a TV screen (cathode ray tube).

Particles that form the typical scanning electron image are called secondary electrons because
they come from the electrons in the specimen itself. The more electrons a particular region emits, the brighter the image will be on the TV screen. The end result, therefore, is brightness associated with surface characteristics and an image that looks very much like a normally illuminated subject. SEM images typically contain a good deal of topographical detail because the electrons that are emitted and produced on the TV screen represent a onefor-one correspondence with the contours of the specimen.

All scanning electron images have one very distinctive characteristic because of this feature of electron emission and display—the images are three dimensional rather than the flat, two-dimensional images obtained from other types of microscopes. The images can be understood even by the lay person because the eye is accustomed to interpreting objects that are in three dimensions.

Take, for instance, a leaf surface, which looks smooth with an ordinary light microscope. But with a scanning electron microscope, the leaf surface is a rich composition of undulating cell walls, cells joined together like pieces of a jigsaw puzzle, squiggly ridges of waxes that look like frosting decorations on a cake, and lens-shaped stomata. The stomata even provide a window into the interior of the leaf where deeper cellular layers are visible. That remind us of some sinister sea creature. No stinging tentacles here, but rather the surface of a small flower of a common weed called mouse-ear cress (Arabidopsis thaliana).

The “tentacles” are actually stigmatic papillae that serve to trap pollen grains, which are released from the pollen sacs of the flower. While biologists utilize the SEM extensively, other types
of scientists put it to work in diverse ways as well, whether looking at “moon rocks” brought to earth by the Apollo astronauts or studying the impact craters created by micrometeorite projectiles striking the space shuttle’s heat-resistant tiles.

Recently, a textile technologist in England examined a piece of the frayed linen tunic of King Tut, the ancient Egyptian boy-Pharaoh whose tomb was discovered in 1922. Apparently, the tunic had either been washed about 40 times in water or had been washed less frequently in a solution of sodium carbonate, a chemical used to whiten as it cleans. Additionally, unlike the clothing of ordinary people, King Tut’s tunic had few mends in it—not surprising considering the wealth of the deceased.

The tomb was filled with golden treasures as well as wooden chests containing his clothes and footwear. Whether used by biologists or material scientists, the scanning electron microscope provides a stunning view of the previously unseen, but nevertheless real, world. As the beauty of nature becomes seen for the first time in startling detail, micrographs do indeed become “microscapes.”