Recebi via Twitter (
@newscientist) esta notícia, achei ótimo compartilhar.
E o que tem a ver o formato de nanopartículas com Micro e Epi?
Dependendo do formato da nanopartícula, a propriedade / ação é alterada. Por exemplo, nanopartículas de prata são utilizadas para criar tecidos antibacterianos, e a nanopartícula triangular truncada é a mais eficiente!
Para alterar o formato, os cientistas incidem feixes de luz de diferentes cores na solução de nitrato de prata, e cada cor promove diferentesformatos nas partículas.
Segue abaixo a notícia publicada pela
NewScientist, em inglês.
* 14:26 12 February 2010 by Colin Barras
* For similar stories, visit the Nanotechnology Topic Guide
How many chemists does it take to change an LED light bulb? Two – and they've shown that choosing its colour selects the shape of nanoparticles growing out of a solution of silver.
Kevin Stamplecoskie and Juan Scaiano at the University of Ottawa in Ontario, Canada, can grow silver particles shaped as hexagons, rods, triangles, spheres or dodecahedrons by shining green, red, orange, violet and blue light on the liquid respectively.
Being able to select the shape of nanoparticles is important because it changes their properties. For example, silver nanoparticles are used to make bacteria-killing clothing – and truncated triangular particles are the deadliest.
Shape shifter
Stamplecoskie and Scaiano use a solution of silver nitrate with two additives. One initiates the formation of the particles, while the other stops them growing too large.
The particles are called into being by a burst of ultraviolet light, which causes tiny silver "seeds", each 3 nanometres across, to precipitate out of the solution. Switching to coloured LEDs of a specific frequency for around 24 hours makes the seeds grow into nanoparticles of a desired shape, each some 50 to 200 nanometres across.
The trick works because the coloured light induces an electromagnetic field around the silver seeds that makes them stick to their nearest neighbours. "The light causes the formation of particles that absorb at [the] wavelength [of the light], and the process continues until all the particles share that absorption," Stamplecoskie says.
The specific colour used induces an electromagnetic field of a specific form, which helps grow nanoparticles of a specific shape: that's because the light energy absorbed turns into heat that fixes the seeds in that shape.
Because the particles absorb light at a certain frequency, the colour of the solution also changes – for instance, the blue light-absorbing dodecahedra turn their mixture orangey-yellow (see image).
Flipping lights
The conventional way to shape silver nanoparticles is to grow them at a specific temperature, says Stamplecoskie. But flipping the temperature of a solution rapidly is difficult, and the process tends to produce a mix of particle shapes. Flipping a coloured light on and off is easier, and can produce more consistent results.
George Schatz's team at Northwestern University in Evanston, Illinois, was the first to show light could be used to trigger silver nanoparticle growth. But he says demonstrating that the method can so easily select from a menu of different shapes is "exciting".
Carefully chosen nanoparticles are of interest in sensing and medical diagnostics, he says.
John Kelly, a photochemist at Trinity College Dublin, Ireland, also works with silver nanoparticles. "As the process is light driven, it can be performed at room temperature or lower if desired," he points out.
Journal reference: Journal of the American Chemical Society, DOI: 10.1021/ja910010b
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