Golden technique

To make nanoprisms

Published: Friday 15 April 2005

scientists at the National Chemical Laboratory (ncl) in Pune have found a way to make nanoprisms of gold using an environment-friendly technique that is also more efficient than the methods used earlier (csir News, Vol 55, No 4).

Two ncl teams -- one led by Murali Sastry of Physical & Materials Chemistry Division and the other by Absar Ahmed of the Biochemical Division -- added the extract of lemon grass (Cymbopogon flexuosus) to a solution of gold chloride at room temperature. After about six hours, they found 45 per cent of the nanoparticles formed were triangular gold nanoprisms of 8-18 nanometre (nm, equals a billionth of a metre) thickness with an edge length of 200-500 nm. Repeated centrifugation (rotating the solution at high speed to separate the nanoprisms) enabled almost 95 per cent of nanoparticles to be converted into nanoprisms, they say.

In comparison, the use of other environment-friendly methods using bacteria and fungi yielded a low number of nanoprisms, making such methods economically unfeasible. For instance, the use of chemicals secreted by a type of bacteria, Escherichia coli, induced the growth of gold nanoprisms at a four per cent yield relative to the total nanoparticle formation.

The properties of nanoparticles depend on their shape and size. Nanoprisms have important applications in catalytic reactions (such as conversion of carbon monoxide to carbon dioxide), biosensing (where they are used to label dna fragments) and high-density recording media such as the cd-rom.

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