A recent article in the New York Times (http://nyti.ms/93t30y) gives a recipe for making edible nanostructures. It requires sugar (gamma-cyclodextrin), a salt (potassium benzoate), 190 proof ethyl alcohol, and water. The recipe involves mixing the sugar, salt, and water in a small glass or plastic cup, placing the cup into a larger glass, cup, or bowl, adding the alcohol to the larger container, and then enclosing everything air-tight in a plastic bag or container. After standing for a week, cubic crystals several millimeters on a side grow inside the cup. These crystals are built from metal-organic frameworks (MOFs) with many tiny pores. On the atomic scale the crystals consist of rigid structures with lots of empty space inside lots of tiny compartments. As a result the structures have lots of surface area on which other molecules can adsorb and where reactions might be catalyzed. The surface area is more than 1300 square meters per gram of crystal.

The abstract of a paper describing these nanostructures written by scientists at Northwestern University reads: “Take a spoonful of sugar (gamma-cyclodextrin to be precise), a pinch of salt (most alkali metal salts will suffice), and a swig of alcohol (Everclear fits the bill), and you have a robust, renewable, nanoporous (Langmuir surface area 1320 square meters per gram) metal-organic framework for breakfast.” (Everclear 190-proof alcohol is available in some states in the U.S. and some Canadian provinces, but not others; see http://bit.ly/aJPCPS. Clearly such concentrated alcohol needs to be handled with care.) The paper is slated for publication in the journal Angewandte Chemie in November.

In addition to revealing that scientists have a sense of humor, the edible nanostructures seem to me to provide many opportunities for students to experiment–as a science fair project or even an in-class project. Close supervision would be required because alcohol is involved, but otherwise all of the ingredients are safe and edible. It appears that a broad range of salts could be tried (NaCl and KCl certainly) to see whether the crystals form. Once the nanostructures have been synthesized, students could experiment with adsorption of other substances. The article quotes chef Wylie Dufresne regarding various ideas for using the nanostructures to encapsulate other foodsutffs. For example, they might provide a way to make crunchy soy sauce!

What ideas do you have for using edible nanostructures as a pedagogical tool?

Size Matters: Introduction to Nanoscience