Turning silver into gold - at least on the nanoscale

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Turning silver into gold - at least on the nanoscale
by Michael Berger

The color of metal colloids is highly dependent on their size and therefore being able to control the size is very important to tune the metal colors systematically.

By controlling the wavelength of optical resonance of metal nanoparticles and their composition, researchers in South Korea have found a way to fabricate various colored metal colloids both easily and reproducibly. These findings could be very useful for biological assays.

The deposition of metal nanoparticles on the surface of nanospheres gives rise to significant changes in the optical properties. Compared with originally colorless polymers, metal-coated polymers turn to yellow or red, depending on the components of the deposited metals. This then makes them useful in biological sensing applications such as contrast agents, blood flow cytometry or surface-enhanced Raman scattering.

To control the color of metal colloids, numerous researchers have tried to fabricate different sized and shaped nanoparticles using various metals. They succeeded in synthesizing various colored metal colloids by controlling the size, shapes (spherical, cube, rod, triangle, prism, etc) and geometry (core/shell, hollow, etc) ot the particles. However, they need different chemical reaction conditions to synthesize different colored metal colloids.
One of the disadvantages of current approaches is the fact that it is very difficult to synthesize monodispersed metal colloids on a large scale. The production yields are also very low.

In contrast to the previous approaches, researchers at the Korea Research Institute of Bioscience and Biotechnology (KRIBB) suggest a method that is very easy and reproducible.

"We can control the color of metal colloids systematically by just using the wavelength and intensity multiplexing of three different colored metal nanoparticles" Dr. Bong Hyun Chung, Director of the BioNanotechnology Research Center at KRIBB, explains to Nanowerk. "We just need three colored metal colloids (blue, yellow, red) that can be easily fabricated by simple water-based chemistry. By controlling the wavelength of optical resonance of metal nanoparticles and their composition, we can fabricate various colored metal colloids both easily and reproducibly."

In a recent paper, titled "Multicolor nanospheres fabricated by in situ transformation of metal nanostructures on the surface of polymer spheres" Chung and his colleagues describe how the optical properties of polymer nanospheres were tuned by in situ transformation of metal structures on their surfaces. The paper was published in the June 27, 2006 issue of Nanotechnology.


Source and more information:

http://www.nanowerk.com/spotlight/spotid=634.php


This story was first posted on 10th July 2006