Ultralight Gold Aerogels

The new gold form is almost impossible to differentiate from conventional gold with the naked eye - the aerogel even has a metallic shine. But in contrast to its conventional form, it is soft and malleable by hand. It consists of 98 parts air and only two parts of solid material. Of this solid material, more than four-fifths are gold and less than one-fifth is milk protein fibrils.

The porous material was created by first heating milk proteins to produce nanometre-fine protein fibres, called amyloid fibrils, which were then placed in a solution of gold salt. The protein fibres then directed the nucleation of gold crystals that were stabilized in an amyloid fibril network.

One of the big challenges to solve in this project was to dry this fine network structure without destroying it. As a first step a gentle protocol to stabilize the liquid material in a gel phase using salt was developed and as air drying causes too much capillary stresses on the structure dyring using supercritical carbon dioxide was used. Since the optical properties of the gold aerogels on the size and shape of the gold particles we showed that if we change the reaction conditions in order that the gold doesn't crystallise into microparticles but rather smaller nanoparticles, it results in a dark-red gold. By this means we can change both the color and the physical (e.g. conductive or catalytic) properties of the material. This means that the material can be used directly as a gold material but also further applications as pressure sensing and catalysis membrane was also demonstrated.

The original work was published in the journal Advanced Materials and widely reported in the press including Daily Mail, Scientific American and USA Today.