Coloured lights can sculpt nanoparticles

LONDON - In a new research, scientists have shown that choosing the color of an LED light bulb can select the shape of nanoparticles growing out of a solution of silver.

According to a report in New Scientist, the research was done by Kevin Stamplecoskie and Juan Scaiano at the University of Ottawa in Ontario, Canada.

They 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.

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 said.

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.

The conventional way to shape silver nanoparticles is to grow them at a specific temperature, according to 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. (ANI)