Joester and Gordon imaged teeth of the chiton, a tiny marine mollusk, because much is known about the biomineralization process. The chiton lives in the sea and feeds on algae found on rocks. It continually makes new rows of teeth -- one a day -- to replace mature but worn teeth; in conveyor-belt fashion, the older teeth move down the creature's tongue-like radula toward the mouth where it feeds.
Chiton teeth resemble human teeth in that they have a hard and tough outer layer -- equivalent to our enamel -- and a softer core. Instead of enamel, the rock-chewing chitons use magnetite, a very hard iron oxide, which gives their teeth a black luster.
The researchers extracted micron-sized samples from the leading edge of the tooth. Using a focused ion beam tool at the Northwestern University Atomic and Nanoscale Characterization Experimental Center core facility, these samples were fashioned into very sharp tips (less than 20 nanometers across). The process is reminiscent of sharpening a pencil, albeit with a supercharged stream of gallium ions.
The APT technique applies an extremely high electric field to the sample; atoms on the surface ionize, fly off and hit an imaging detector (similar to those found in night-vision equipment). The atoms are stripped off atom-by-atom and layer-by-layer, like peeling an onion. Computer methods then are used to calculate the original location of the atoms, producing a 3-D map or tomogram of millions of atoms within the sample.
Joester and Gordon now are studying the tooth enamel of a vertebrate and plan to apply APT to bone, which is also made of organic and inorganic parts, to learn more about its nanoscale structure.
|Contact: Megan Fellman|