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Rainbow of Nanoparticle Colors is 'Hot' Development from Xu Research Group

Rainbow of colors for nanoparticles in solution

More sizes. More colors. That's the prescription for success in the marketing of any number of items, ranging from automobiles to blouses. Old Dominion University chemist X. Nancy Xu and her research group are now demonstrating that the same holds true for silver nanoparticles, which shows size- and shape-dependent optical and electronic properties.

Over the past decade, Xu has become an international leader in nanobiotechnology by devising ways to create and use flecks of precious metals no larger than one-millionth of a meter in length. Her exceptionally stable nanoparticles have proven to be reliable probes of living cells and embryos.

In her latest research paper, she and ODU research scientist Tao Huang report that they have developed a simple synthesis method to produce silver nanoparticles in an array of shapes and in a full rainbow of colors.

"These nanoparticles have the potential for use as multicolored optical probes for the real time study of dynamic events in living cells and organisms," Xu said. This could help answer fundamental medical questions, such as how cancers occur and how proteins work.

The article by Xu and Huang, "Synthesis and Characterization of Tunable Rainbow Colored Colloidal Silver Nanoparticles Using Single-Nanoparticle Plasmonic Microscopy and Spectroscopy," has been published online by the Journal of Materials Chemistry, and will be published in the print journal later this fall. It will be featured on the back cover of the print journal.

Xu was informed Oct. 1 that the journal has designated her research paper as a "hot article" and has highlighted it at http://blogs.rsc.org/jm/2010/10/01/hot-articles-rainbow-nanoparticles-atomic-layer-deposition-and-liquid-crystals/.

The Journal of Materials Chemistry is a publication of the Royal Society of Chemistry based in Cambridge, England.

The Xu group has found ways over the last few years to synthesize and purify both silver and gold nanoparticles that will stay stable - their sizes and number unchanged - over an extended period. The researchers have also reported breakthroughs in the way they image and characterize nanoparticles using dark-field optical microscopy and spectroscopy (DFOMS), which allows individual nanoparticles to be imaged and characterized in solution, instead of under vacuum using a transmission electron microscope.

These new findings reported by Xu and Huang hinge on the fact that particles of nanoscale size reflect different colors based on their size and shapes. This means that single nanoparticle probes may look violet under dark-field microscopy, but if a particular dynamic event of interest within a living cell were to cause the change of surface properties of violet nanoparticles, the color could shift to red.

Biomedical and material researchers have many reasons to want an array of shapes, sizes and colors of nanoparticles for use in probes of organisms, or to harvest the energy of sunlight (rainbow colors of visible sunlight).

Such an array of nanoparticles would make possible multiple, simultaneous biological probes, or effectively collect all wavelengths (colors) of the light form the sun. All these potential applications require the sizes and shapes of individual nanoparticles to be characterized in situ, which is difficult to do at the nanoscale.

The ODU researchers write in their latest article that they have found a new, more accurate way of accomplishing characterization. They identified spherical, rod, triangular and cookie-shaped single nanoparticles, and stated that the cookie-shaped versions have not been previously reported.

"New calibration approaches enable the identification of individual silver nanoparticles with given sizes and shapes in solution in real time at nanometer scale using DFOMS, which overcomes the optical diffraction limit of optical microscopes and offer the feasibility of using single silver nanoparticles as multiple colored optical probes for study of dynamic events of interest in situ and in vivo," Xu said.

Research by Xu has shown that these miniscule agents can infiltrate living cells or embryos and literally light them up, allowing scrutiny of life processes. To this end, her group has also studied the biocompatibility and potential toxicity of nanoparticles, aiming to rationally design biocompatible nanoparticle probes that will not harm the cells or living organisms that are under investigation by the nanoprobes. The group's studies also provide new knowledge and tools to identify nanomaterials that might pose an environmental risk if they found their way out into the wild.

In general, Xu's research, which is funded by the National Science Foundation and the National Institutes of Health, explores fundamental questions posed by nanobiotechnology. She has been recognized for her achievements by two of NASA's NANO 50 awards and by the National Cancer Institute in its publication "Mission to the Inside of a Living Cell."

This article was posted on: October 7, 2010

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