20 carat gold foam lighter than a feather

A gold aerogel, so light it can sit on a feather, or float on the froth on top of a cappuccino, has been developed by researchers at ETH Zurich. The 20 carat gold ‘foam’ is a thousand times lighter than its solid counterpart, and the lightest gold nugget ever to be made.

Raffaele Mezzenga and colleages made the highly porous gold mesh by directly crystallising gold nanoparticles onto a gel network of ß-lactoglobulin protein fibrils which then underwent supercritical carbon dioxide drying to produce an aerogel. The colour can be varied by altering the reaction conditions which influence the size and shape of the gold nanoparticles that form. The aerogel contains just 2% solid material, of which more than 80% is gold (the rest being protein).

The foamy gold’s potential properties extend beyond decorating hot beverages. Its extremely high surface area could be useful for catalysis, or the foam could be used as a pressure sensor, as compressing it brings the gold nanoparticles close enough together to conduct electricity.