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Nano Particles

New magnetic materials on a molecular scale will be useful in electronics and in medicine

At first sight, the raw materials used by a group of researchers from the Federal University of Minas Gerais (UFMG) could not be more prosaic. They are ferrites, basically the same kind of metal compound present in magnets and used for thousands of years by humanity. There is, however, a fundamental difference. Researcher Nelcy Della Santina Mohallem and her colleagues from the Chemistry Department are using these old acquaintances, but on a nanometric scale, a measure equivalent to 1 millimeter divided 1 million times. At this size, the ferrites can generate innovative materials and devices in fields as diverse as electronics, industrial chemicals and medicine.

Nelcy explains that the researchers’ main interest in manipulating the ferrites – iron oxides that may also include other metals, such as zinc, nickel and cobalt in their composition – is due to the rapidity of the response from its magnetic properties. That is why, for several decades, magnets have been much used in motors and in radar and telecommunication systems. “In the course of time, the size of the devices has been decreasing”, the researcher says. However, below a certain limit, the use of ferrites begins to face problems, due to their electrical resistance, which limits a greater miniaturization of electronic equipment. That is where nanotechnology comes in.

Nelcy and colleagues like Juliana Batista da Silva, from the Nuclear Technology Development Center (CDTN), of Belo Horizonte, and Miguel Novak, from the Federal University of Rio de Janeiro (UFRJ), with support from the National Synchrotron Light Laboratory (LNLS), in Campinas, are developing nanocompounds that are hybrid materials, with a size varying between 5 and 100 nanometers. They combine a core of ferrite with an inert matrix, which can be made up of silicon or aluminum oxide, for example. The matrix, called dense by the researchers, creates several separate nanomagnets. “This makes it possible to eliminate the interference and the losses, and to increase the electrical resistance, besides producing a coupling up of the neighboring nanoparticles, creating better magnetic properties”, the researcher explains.

Turbocharged memory
One of the promising applications of this kind of nanoparticles is the computer’s hard disk: using nanometric units to store information in magnetic form increases the potential for miniaturizing computers, and the material could also turbocharge the speed with which the memory is accessed. In this case, the nanocompound would be arranged in the form of a film. “We are also capable of molding the microstructure of these compounds in parts of a few millimeters, according to the needs of each apparatus”, Nelcy says.  This is an advantage, when one considers that the majority of these compounds today only exists in powder form.

Alterations in the structure of the matrix make it possible for the nanocompounds to be used for a completely different end: to facilitate chemical reactions. This is the role of the so-called catalysts, and the nanometric scale, once again, are helping to make this work more efficient. For the purposes of catalysis, the team from UFMG set up the ferrite nanoparticles inside an extremely porous matrix, and not a dense one, as in the case of the computer hard disks. “We could say that 95% of the matrix is air”, says Nelcy. This means that the particles acquire a proportionally very large volume. The contact surface that this expanded volume affords makes them cause chemical reactions with greater efficiency. “Using much less material than would normally be used, it is possible to maintain and even to increase the speed of the chemical reactions catalyzed by the nanocompound”, the researcher explains.

Against cancer
Another of the group’s ideas involves an even more delicate environment than the inside of a computer or the chemical industry: the human body. Just as other researchers in Brazil and abroad, Nelcy and her colleagues are exploring the possibility that the nanomagnets may attack diseases like cancer and infections. It would work like this: magnetic particles in fluid form, wrapped in a biocompatible material, would be injected into the patient’s bloodstream.

In the case of a tumor, for example, there could be two ways of taking the nanoscopic magnets to their destination. A magnetic field could conduct them manually to the tissue affected by the cancer, or, coupled to them, there would be antibodies specific for the kind of tumor that one wanted to attack, so that the nanomagnets would stick to the diseased tissue. Having finished this stage of the process, the idea is to apply, quickly and alternately, the outer magnetic field. The movement of the particles would generate sufficient heat to kill the cancerous cells. Other works by the group suggest that a system like this would be particularly useful for treating tumors at an early stage, while still small.

The cover of the nanomagnets to make them biocompatible is made of a kind of sugar called cyclodextrin. This composition was developed jointly with Professor Rubén Sinisterra, from the same Chemistry Department at UFMG, giving rise to a patent. “We have the material very well characterized in chemical terms”, Nelcy says. The intention now is to enter into partnerships that make it possible, in the scientific ambit, to test the product on human beings.

According to Nelcy, there is a great race in the world to transform materials like these nanocompounds into components for equipment of daily use. Governments like the United States recognize that their potential is strategic. “Our proposals are every bit as good as what is done outside Brazil. When we present them at scientific congresses, it is common for people to be impressed”, says the researcher from UFMG. “But with the problems we face with funding, we often end up not being the first to publish in scientific magazines.” He mentions the interest of Brazilian companies, still rather incipient, in incorporating some nanotechnological component in their products, and suggests that they could be more daring. “They are interested in things we were doing ten years ago, and not in cutting edge nanotechnology”, she reports.