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Nuts for Nanotechnology
Cashew to play role in nanotechnology
Hindustan Times
KS Jayaraman

The delightful cashew nut loved by everybody will soon have a bigger role to play – in nanotechnology.

When Kyathanahalli Nagabhushana submitted his doctoral thesis on cashew (Anacardium Occidentale) in 1998, little did he anticipate the excitement his research would create among materials scientists seven years later.

Not only scientists but cashew growers too will have to thank the Bangalore-born Nagabhushana, whose research has led to a new commercial use for cashew nut shell liquid (CNSL) — the fluid inside the shell casing of the cashew.

CNSL contains anacardic acids, chemicals that Nagabhushana studied for his thesis. Recent findings have shown that anacardic acids are useful in preparing magnetic “nanofluid”, according to Nagabhushana, a participant at the just ended international conference Nano2006 at the Indian Institute of Science here.

India is the largest exporter of cashew nuts and, together with Brazil, accounts for over 80 per cent of the world supply of around 100,000 tonnes.

Less than 20 per cent of CNSL, a byproduct of the cashew industry, is utilized for making paints and lubricants. Its potential application in nanotechnology has opened a new window of opportunity for cashew producers.

Nanoparticles, so called because of their extremely small size, are the basis of a new technology revolution that is in the making. Magnetic nanofluid – a colloidal solution containing magnetic nanoparticles – has medical applications such as targeted drug delivery, Nagabhushana said.

Nagabhushana, currently at the German Institute for Technical Chemistry, is working with Professor H Bönnemann of Max Plank Institute, one of the pioneers in the colloidal nanoparticle chemistry.

“We were looking for a suitable magnetic fluid preparation for medical application and my research experience on cashew in Mysore University led us to use anacardic acid and CNSL in general for this purpose,” Nagabhushana said.

Combined with certain metals, anacardic acids form metal complexes soluble in organic solvents like pentane and toluene. On decomposition, the metal complexes generate colloidal nanoparticles of around one nanometre, Nagabhushana said. (The width of human hair is about 100,000 nanometres).

“Obviously, the size can be altered by changing the ratio of anacardic acid to metal,” Nagabhushana said. “And by mixing different metal complexes in solution, literally any alloy composition (in colloidal form) can be generated which is unprecedented.”

He said this approach has opened new avenues for generating various single and multiple metallic alloy metal nanoparticles of copper, iron, cobalt and nickel “having different properties”.

Production of nanofluids (from nanoparticles) faces major challenges since nanoparticles in solution can clump together and rapidly settle down. CNSL was found to prevent this by acting as a “colloidal stabiliser”, Nagabhushana said.

Nagabhushana told the conference that he was reporting for the first time “the exploitation of natural anacardic acid (from CNSL) as a nanochemical precursor and as a colloidal stabilizer for metal nanoparticles”.

Massachusetts-based US firm Strem Chemicals Inc, which collaborates with Max Plank Institute, is already producing CNSL-stabilized magnetic fluid of iron and cobalt nanoparticles in toluene, Nagabhushana said.

He said his future work would be focused on preparing nanofluids of metallic particles in solvents like alcohol or water in high concentrations for drug delivery.

Targeted drug delivery systems are under development by several research groups. In the “tag and drag” approach, drug molecules attached to the surface of magnetic nanoparticles are directed to a specific target tissue using magnets outside the body and the drug is released by applying a radio frequency pulse.

In hypothermal treatment, magnetic nanoparticles are directed to diseased tissue containing heat sensitive tumours. An alternating current magnetic field is applied such that the nanoparticles become heated, causing destruction of the cancerous cells while sparing normal tissue.

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