Tuesday, May 08, 2012

#MATERIALS: "Graphene + Proteins Enabling Cheap Semiconductors"

Graphene is the next-generation miracle semiconductor material, many believe, but it is hard to work with and harder to mass produce. The Swiss Federal Institute of Technology (ETH) now believes it has the an answer--combine graphene with organic proteins to create a conductive paper from which future electronic devices can be fabricated: R. Colin Johnson

The final hybrid nanocomposite paper made of protein fibrils and graphene after vacuum filtration drying. The schematic route used by the researchers to combine graphene and protein fibrils into the new hybrid nanocomposite paper. (Reproduced from Li et al. Nature Nanotechnology 2012)

Here is what ETH says about their graphene paper: Researchers led by Raffaele Mezzenga, a professor in Food and Soft Materials Science, have created a new nanocomposite made of graphene and protein fibrils: a special paper, which combines the best features of both components.

The circular sheets that Raffaele Mezzenga gently lifts from a petri dish are shiny and black. Looking at this tiny piece of paper, one could hardly imagine that it consists of a novel nanocomposite material, with some unprecedented and unique properties, developed in the laboratory of the ETH professor.

This new "paper" is made of alternating layers of protein and graphene. The two components can be mixed in varying compositions, brought into solution, and dried into thin sheets through a vacuum filter.

Graphene is mechanically strong and electrically conductive, as well as, highly water repellent by nature. On the other hand, the protein fibrils are biologically active and can bind water. This allows the new material to absorb water and to change shape under varying humidity conditions. Furthermore, the "graphene paper" has shape memory features such that it can deform when adsorbing water, and recover the original shape upon drying. This could be used, for example, either in water sensors or humidity actuators.

The material can also be designed to meet other needs. For example, the higher the proportion of graphene, the better it conducts electricity. On the other hand, the more fibrils are present, the more water can be absorbed by this material, with enhanced deformations in response to humidity changes.

Interestingly, this new material can be made with relatively simple means. The protein, in this case, beta-lactoglobulin, a milk protein, is first denatured by high temperatures in an acidic solution. The end-products of this denaturation process are protein fibrils suspended in water; these fibrils then act as stabilizers for the hydrophobic graphene sheets and allow them to be finely dispersed in water and processed into nanocomposites by a simple filtration technology.

In view of the widespread tendency of proteins to form fibrils, under specific conditions, this concept can be extended, in principle to other food proteins, such as those found in eggs, blood serum and soy. The beta-lactoglobulin fibrils are digested specifically by pepsin, an enzyme present in the stomach to enable the digestion of several food components. However, varying the protein types could provide a new method of targeting a much larger class of enzymes.

Inspired by their past research on amyloid fibrils and by the rise of graphene, the ETH researchers have combined these two building blocks to generate a new class of versatile and functional materials.
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