Avi Blizovsky
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Weizmann Institute scientists succeeded, for the first time in the world, in creating nanotubes made of gold, silver and nanoparticles of other metals. The new nanotubes are characterized by unique optical and electrical properties, which vary according to the components that make them up. Thanks to these properties, it will be possible to use them for the development of nanosensors, carriers of various catalysts and chemical and biological systems on a chip.
The creators of the new nanotubes, Prof. Israel Rubinstein, Dr. Alexander Vaskevich, post-doctoral researcher Dr. Michal Lahav and research student Tali Sahaik, from the Department of Materials and Surface Research at the Weizmann Institute of Science, recently published their research findings in the scientific journal Angewandte Chemistry.
Nanotubes are tiny cylindrical structures ("nanometer" is one millionth of a millimeter). The first nanotubes discovered, in 1991, were made of carbon, conducted electricity and heat and excelled in their strength - they were 100 times stronger than steel. In contrast, the new nanotubes recently developed at the Weizmann Institute of Science are not as strong, but their unique structure gives them other advantages, which depend on the identity of the nanoparticles that make them up, and the order in which they are organized. Changes in the relative amounts of the nanoparticles, as well as a change in the structure they create, affect and change the properties of the nanotube they create. In other words, by determining the identity of the nanoparticles that make up the nanotube, the scientists can change and determine the properties of the nanotube, according to their needs. In fact, it is even possible to mix particles of different types in a way that results in the formation of a composite nanotube. (A composite material is built as a kind of mold into which another material is cast. Composite materials are known for their strength and light weight and are used, among other things, in the aviation and space industry, as well as for the production of helmets for cyclists, special tennis rackets, bone implants, tooth replacements, and more). Many additional application possibilities arise when different materials are added to the new nanotubes, such as metals, semiconductors or polymers.
The nanotubes are built in three steps, with the entire process being carried out at room temperature. In the first step, the institute's scientists used an aluminum oxide template in which there are cylindrical nanoholes. Then change the properties of the template so that it easily binds gold or silver particles. At this stage, when a solution of nanoparticles (each of which is 14 nanometers in size) is passed through the holes in the mold, these nanoparticles bind, inside the holes, both to the wall of the mold and to each other. In this way, nanotubes with several layers are formed inside the nanoholes in the mold. In the third step, the aluminum oxide template is dissolved, so that the nanotubes remain free.
"When the nanotubes were revealed to our eyes for the first time, we were really amazed," says Prof. Rubinstein. "In the past, there were no known cases where nanotubes were produced from nanoparticles. We did not intend to produce nanotubes either. All in all, we examined possibilities to bind nanoparticles to the wall of the mold. The amazing thing is that this entire process, including connecting the nanoparticles to each other, It took place at room temperature. In fact, we still do not fully understand how exactly this happens, and we are preparing and hope to find out in our next studies."
In fact, the original goal of the research was to create a template in which there are nanoholes, which will serve as a model for biological membranes such as the membranes of living cells. Using such a template, they hoped that it would be possible to study the transition processes of biological molecules through different membranes.
The new nanotubes are characterized by electrical conductivity, unique optical properties, as well as their relatively large surface area, and the fact that there are many holes in them. These unusual properties can allow the new nanotubes to be used for the design of various chemical sensors and catalysts (both of which require a large surface area). Another possible application is the installation of complete chemical systems on a chip that will contain the new nanotubes. Such "microfluidic" systems may be important tools in the chemical industry and the biotechnology industry.
The Weizmann Institute scientists who used the new method have already created different types of new, composite and metallic nanotubes, including nanotubes made of gold, silver, a combination of gold and palladium and also those made of copper-plated gold. All of these strengthen the possibility of applying the new nanotubes to the development of sensors and catalysts (the metal palladium, for example, is an important component in hydrogen sensors and various catalysts). Adding copper increases the stiffness and conductivity of the nanotube, which opens the door to many more applications.
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