"We took a gene from a single-celled organism, Sulfolobus shibatae, which lives in near-boiling acid mud, and changed the gene to add instructions that describe how to make a protein that sticks to gold or semiconductors," said Andrew McMillan of NASA Ames. "What is novel in our work is that we designed this protein so that when it self-assembles into a two-dimensional lattice or template, it is also able to capture metal and semiconductor particles at specific locations on the template surface."
The scientists altered the protein chaperonin from the Sulfolobus shibatae microbe, cloning the modified gene segment into a form of E. coli bacteria. Then they grew the rapidly multiplying modified E. coli bacteria in vats. Because Sulfolobus shibatae can handle hot temperatures, the team was able to purify the modified protein by heating the cloned bacteria to destroy natural E.coli proteins.
"The cage-like chaperonin provides an ideal structure that we envisioned as being a vessel or container to use to organize nanophase materials," McMillan told nanotechweb.org. "The higher-order crystalline structures that these protein-cages can be induced to form closely resemble similar patterns that the electronics industry uses, namely in the formation of precise, regular arrays of materials on substrates."
The researchers applied the proteins to a substrate, such as a silicon wafer, where they self-assembled into an organized lattice consisting of rings of about 20 nm across. Adding a gold or semiconductor slurry caused particles of gold or cadmium selenide-zinc sulphide of about 1 to 10 nm across to stick to the lattice.
The scientists say that the arrays of nanoparticles could have applications in computer memories, sensors or logic devices. "There are two approaches that we are now taking to move this research forward," added McMillan. "One is the incorporation of different functionality into the chaperonins so that, when crystallized into templates, they will have specificity for materials other than gold and zinc-containing nanoparticles."
The other approach is to fine-tune the properties of the arrays by controlling the nanoparticle sizing, spacing and composition, as well as the interaction of the nanoparticles with one another. "We also anticipate investigations on the use of molecular-scale conductors to wire the arrays together into functional devices," said McMillan.
The scientists published their work in Nature Materials.