Nanosilver-enabled microscopy method reveals structure, composition

SALT LAKE CITY, UT, USA--A new microscopy method, devised by scientists at the University of Utah, uses a mirror of silver nanoparticles to reveal the internal structure of nearly opaque biological materials like bone and tumor cells.

SALT LAKE CITY, UT, USA--A new microscopy method, devised by scientists at the University of Utah, uses a mirror of silver nanoparticles to reveal the internal structure of nearly opaque biological materials like bone and tumor cells.

The approach, developed by John Lupton, an associate professor of physics, and several colleagues, is a variation of fluorescence microscopy. It involves using an infrared laser to excite clusters of silver nanoparticles placed below the sample being studied. The particles form "plasmonic hotspots," which act as beacons, shooting intensely focused white light upward through the overlying sample. The spectrum of transmitted light reveal information about the composition and structure of the specimen.

Lupton conducted the study with Michael Bartl, an assistant professor of chemistry; Debansu Chaudhuri, a postdoctoral researcher in physics; and graduate students Jeremy Galusha in chemistry and Manfred Walter and Nicholas Borys in physics. Available online now, it will be published in the March 2009 issue of Nano Letters.

Development of the new method began after Bartl, Galusha and others published a study last May revealing that a beetle from Brazil--a weevil named Lamprocyphus augustus--has shimmering green scales with an "ideal" photonic crystal structure. They wanted to know more about these naturally occurring crystals.
"A normal light microscope generally won't do the trick," Lupton says, because visible light is easily scattered by the scales, thwarting efforts to view their internal structure. The researchers found that if they placed a mirror made of silver nanoparticles beneath the beetle, and illuminated the specimen with "very intense infrared light, the silver starts to emit white light, but only at very discrete positions on the mirror."

The beacons of intense light were transmitted upward through the beetle scale, allowing scientists to view the scale's internal structure, including tiny differences in the angles of crystal facets and the existence of vertical stacks of crystals invisible to other microscope methods.
"There really does not appear to be any other useful technique to look at these natural photonic crystals microscopically," Lupton says. "The silver nanoparticle approach to microscopy potentially could be very versatile, allowing us to view other highly scattering samples such as tumor cells, bone samples or amorphous materials in general."

The researchers are seeking a patent on the new method.

More information:
See the paper, Toward Subdiffraction Transmission Microscopy of Diffuse Materials with Silver Nanoparticle White-Light Beacons, published by Nano Letters.

Posted by Barbara G. Goode, barbarag@pennwell.com.

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