Using microscopes to view beneath the surface of opaque structures like tumors and bone tissue has been a long sought goal of scientists. At the University of Utah, a technique has been developed that uses a tiny mirror made of silver nanoparticles and an infrared source to peer through the scales of the “photonic beetle“.
From the University of Utah:
“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.
“We found that we can put silver nanoparticles – a fancy word for a silver mirror – beneath the beetle,” he adds. “When illuminated with very intense infrared light, the silver starts to emit white light, but only at very discrete positions on the mirror.”
Those “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” or faces and the existence of vertical stacks of crystals invisible to other microscope methods.
To the untrained eye, an image created using silver nanoparticle beacons – say, the image of the photonic beetle’s scale – looks like a blotchy bunch of spots.
But Lupton says that each of those spots contains a spectrum of colors that reveal information about the scale’s internal structure because the light has interacted with that structure.
“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.” Amorphous materials are those without a crystal structure.
Lupton says the structure within the beetle’s scales scatters light very strongly, like driving through a snowstorm: “Once your windshield gets wet, headlights appear all fuzzy, and different features get mixed up.”
Using the tiny silver nanoparticles as light sources to see crystal structure within the beetle’s scale is like “peering through your smudged windshield at a tiny white spot,” Lupton adds. “It would not appear smeared out.”
Press release: Beaming New Light on Life
Images: Side: 1) In this image, a tiny portion of a scale from a “photonic beetle” is viewed using a conventional fluorescence microscope. When blue or ultraviolet laser light is aimed at the scale, most of the light is absorbed, but some is re-emitted as fluorescence. Thus, the microscope sees only the surface contour of the scale. The brightest area in the upper right is the thickest part of the shell and emits the most light. 2) This image shows the same portion of a beetle scale as the previous image. However, this image was made by a fluorescence microscope using a new method. A mirror-like plate containing silver nanoparticles was placed beneath the scale, and an infrared laser excited the silver nanoparticles so they act as beacons of white light. The spots in the image are places where the light passed through the scale, providing researchers with information about the scale’s internal structure. Almost no light from the beacons passes through the thickest part of the shell (black shadow in upper right) that was the brightest area using a conventional fluorescence microscope.