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Invisible weave

Nanoparticles of silver obtained using vegetable fungus form the basis of new tissues and medicines

HÉLIO ALMEIDAA fungus found in vegetables and a bacterium from the Amazon form the basis of nanobiotechnological systems with the potential for use in the transportation and delivery of medicines within the human organism and even in the production of tissues with bacteriological properties. From the fungus Fusarium oxysporum, which brings about the death of plants after infecting their roots and that causes significant losses to Brazilian agriculture such as those to the silver and gold banana varieties, researchers at the State University of Campinas (Unicamp) have managed, by way of the action of two components present in the phytopathogen, the nitrate enzyme reducing agent and the organic compound quinone, to transform silver ions (Ag+) into nanoparticles of metallic silver, which demonstrate strong bacteriological action.

The use of these nanoparticles in tissues that help to heal lesions is one of the possible applications of the material observed only by way of a transmission or sweep electronic microscope. “We’re evaluating the application of these nanoparticles in bandages made from gauze, or similar tissue, impregnated with silver that could be indicated for diabetic patients, with frequent ulcerations on their feet”, explains professor Oswaldo Luiz Alves, the coordinator of the Solid State Chemistry Laboratory, who developed the research in partnership with professor Nelson Duran, the coordinator of the Biological Chemistry Laboratory. “As the particles are highly active, they end up destroying the undesirable substances.”

Another application in the line of nanobiotextiles forecasts the production of anti-smell tissues, indicated for socks, for example. “In the United States there is on the market bacteriological socks impregnated with nanoparticles of silver, but the process of obtaining them is completely different from ours”, says the researcher.

Associated compounds
The proposal of the mechanism through which the nanoparticles of silver are formed starting from the fungus F. oxysporum has resulted in a patent, as well as the application of the process for impregnating tissues with these silver particles, both registered by Unicamp’s Innovation Agency (Inova). “The research has permitted the definition of a platform for the application of these particles with other systems involving various families of the compounds, such as antibiotics and anti-malarials, associated with metallic nanoparticles”, says Alves.

The mechanism used to attain the extremely small particles of silver had as its basis a chemical process known as oxidation-reduction, which basically promotes the transfer of electrons between molecules, ions and neutral atoms. The researchers used a solution containing silver nitrate mixed in with selected sepsis of the fungus, a selection necessary because not all of the lineages possess the nitrate reducing enzyme, essential for the occurrence of the oxidation-reduction reaction.

The quinones, organic compounds present in plants such as the pau d’arco (Tabebuia avellanedae), for example, are also important in this process, because they have a large facility for the transfer of electrons. In the measure in which the metallic silver is formed, the solution changes color from clear yellow to nut-brown. The absorption band coming from the reduction of the silver ions to metallic silver is observed through the technique of ultraviolet-visible absorption spectroscopy, which allows for the association of the optical spectra of the chemical species present.

The research was published in a well known magazine in the area of nanobiotechnology, the Journal of Nanobiotechnology, where the article figured among the ten most accessed during last year. The project was also able to count upon the participation of Priscyla Marcato, also from Unicamp, and Gabriel de Souza and Elisa Esposito, both from the Biological Chemistry Laboratory of the University of Mogi das Cruzes.

The perspective of the researchers in the current phase is to work with other fungi, bacteria, microorganisms and vegetal systems that have the capacity to transform silver ions into nanoparticles of metallic silver. Preliminary results of the recently performed research point to the possibility of obtaining this material from from the extracts of some flowers well known in the region of Campinas. “This is leading us to an understanding that we could execute the same type of metal reduction process whenever we have the presence of the enzyme and of reducing substances”, says Alves.

The other line of research, also developed in a partnership between the two Unicamp laboratories, deals with the development of a nanobiotechnological system for combating cancerous cells that involves nanoparticles of gold and violacein, the main active ingredient of Chromobacterium violaceum, a bacterium found in large quantities in the river Negro, in the Amazon, and known for its capacity to combat illnesses such as Chagas’ disease and Leishmaniosis.

In order to transport the violacein, a violet colored pigment, which is insoluble in water, was chosen with cyclodextrin, a ring of glucose molecules that takes the form of a bucket, capable of storing various substances. However, the tests done in vitro show that the association between the violacein and the cyclodextrin does not act in a selective manner, or that is, as well as the cancerous cells they had also killed the normal cells.

Selective pigment
The solution found to lead the molecules of the medicine to the tumor cells was to add in nanoparticles of gold to the compound. In this case the nanoparticles are formed via a different mechanism to that proposed for the fungi. The process of obtaining them involves a substance that contains gold, such as tetrachloroauric acid, the cyclodextrin and a reducing agent, such as anhydrous sodium borate. The nanobiotechnological system proposal, as well as resolving the problem of insolubility of the violacein, also confers selectivity to the pigment, which means that it kills only the cancerous cells, a capacity that the majority of the chemotherapeutic substances currently used have not shown.

The researchers are now attempting to understand the mechanism that makes the nanoparticles attractive to the cancerous cells, such as leukemias tested in vitro. The first trials with animals, within the protocol of new medicine tests, are forecast to be started in the second semester and could contemplate other cancerous cells as well as those of leukemias. The project also has the participation of the researchers Iara Gimenez, Maristella Anazetti, Patrícia Melo, Marcela Haun and Marcelo Mantovani de Azevedo. The development was published in the magazine Journal of Biomedical Nanotechnology, at the end of 2005.

The pathway to arrive at these new biotechnological systems, which use nanoparticles of gold and silver as a means of transportation, began back in 1989, when professor Alves and his team began to work with semiconductor nanoparticles called quantum dots, established within the different families of glasses.

The development of these nanocompounds based on glass and nanoparticles had basically been destined towards the area of telecommunications, or that is, to optical amplifiers and material for non-linear and photonic optics. The privatization of Telebras, the government organ that was responsible for the Brazilian telecommunications system, and the consequent interruption in the development of new materials, led the researchers to look for other pathways for the application of the experience accumulated in the study of quantum dots, such as research with metallic nanoparticles.