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  • 'Nano-Camo' Clothing Coming

Photonics.com
Apr 2009
ALBUQUERQUE, N.M., April 7, 2009 — Just as certain fish species blend with their environment by changing color, researchers have theorized that they could cause synthetic materials to change color by manipulating motor proteins through the use of nanoscopic, light-emitting dots of cadmium selenide.

“Camouflage outfits that blend with a variety of environments without need of an outside power source – say, blue when at sea and then brown in a desert environment – is where this work could eventually lead,” said principal investigator George Bachand of Sandia National Laboratories. “Or the same effect could be used in fabricating chic civilian clothing that automatically changes color to fit different visual settings.”

Such clothing could be a reality in five to 10 years, he said.
NanoCamo.jpg
Sandia researcher George Bachand examines an enlargement of actual images of light-emitting quantum dots. These ride microtubules that have spontaneously formed stable circles of about 5-µm diameter. The picture superimposes two separate images – one of green rings and one of red – for visual effect. The images were processed to remove noise and maximize contrast. (Photo: Randy Montoya)
The power source for both the biological and the lab method relies on the basic cellular fuel, called ATP, which releases energy as it breaks down. About 50 percent is absorbed by the motor proteins – tiny molecular motors able to move along surfaces.

When fish change colors, motor proteins aggregate and disperse skin pigment crystals carried in their “tails” as they walk with their “feet” along the microtubule skeleton of the cell. By this means, they rearrange the color display.

To put motor proteins in motion or switch them off, nature uses complex signaling networks. The Bachand group’s method is simpler. It involves the simple genetic insertion of a kind of docking port in the motor protein’s structure. What docks are zinc ions. Bound zinc ions turn the protein’s action to “off.” Stripping zinc ions out with chemical agents allows the motor protein to work again. The effect is controllable – even reversible.

“We essentially re-engineered the protein structure to introduce a switch into the motor,” Bachand said. “So we can now turn our nanofluidic devices on and off.”

Previous efforts at regulating motor activity have used fuel intake as a control mechanism: The less the fuel, the slower the process. The Bachand group’s switch, operated independently of fuel changes, resembles the improvement in early automobile technologies when a simple ignition switch took over for more complicated rheostats. The paper describing this work was a spotlighted article in the journal Biotechnology and Bioengineering.

But what is it that the switch operates?

In a Dec. 2, 2008, cover article in the journal Advanced Materials, the Sandia team describes a kind of inverted cellular world, where motor proteins do not run about but instead are upended so that their tails are embedded in a protein-modified layer on a glass slide. Free-ranging microtubules – cylindrical protein filaments– instead of forming the cellular skeleton of cells, are passed along by the waving feet of the motor proteins like crowd surfers at a rock concert, or like buckets passed hand to hand along a line of firefighters.

The traveling microtubules are coated with quantum dots – nanoscopic groups of atoms that emit light, their frequency dependent on dot size.

The dots emit a different frequency of light from what they adsorb, while the biological system merely reflects incoming wavelengths. But they perform similar coloring functions.
NanoCamo2.jpg
Shown is a scanning electron microscope image (tinted) of forming rings. (Photo: Bonnie McKenzie and Erik Spoerke, Sandia National Laboratories)
When motor-transported microtubules collide, the microtubules stick together and twist until they resemble a desk phone cord. The twisting process ultimately forces the formation of stable rings ~5 µm in diameter. Their docked quantum dots (cadmium selenide) produce a range of light frequencies.

When mechanical strain in the rings causes them to rupture, the cracked segments are tugged out by the nearby motors until the ring is completely disassembled. The formation and destruction of the two states – free microtubules and rings – can be reversibly controlled.

Thus, the dots can be tightly packed or dispersed – optically, an essential ingredient in the perception of color change.

The process resembles the action of fish color changes, which require one group of motor proteins carrying pigments to be “on” all the time while a second group of motor proteins is turned on by complex biological processes at the right time. This produces a tug-of-war between motor groups that results in pigment dispersion and, ultimately, a color change. When the second motor is switched off, the color returns to the ground aggregate state.

“Our overall process mimics the fish,” Bachand said. “We essentially go from a dispersed particle state to a concentrated one and then back again to dispersed, similar to the fish. Thus, in principle, the mechanism could produce a color change. The underlying science provides a new basis for materials scientists to begin working toward real-world applications.”

The work was supported by the US Department of Energy’s Basic Energy Sciences and by Sandia’s Laboratory Directed Research & Development office.

Key contributors to the Biotechnology & Bioengineering paper were Adrienne Greene and Amanda Trent (now a graduate student at the University of California, Santa Barbara). Advanced Materials paper contributors were Haiqing Liu (now at Los Alamos National Laboratory), Erik Spoerke, Marlene Bachand, Steven J. Koch (a former Sandia employee, now an assistant professor at the University of New Mexico in Albuquerque) and Bruce Bunker.

For more information, visit: www.sandia.gov


GLOSSARY
color
The attribute of visual experience that can be described as having quantitatively specifiable dimensions of hue, saturation, and brightness or lightness. The visual experience, not including aspects of extent (e.g., size, shape, texture, etc.) and duration (e.g., movement, flicker, etc.).
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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