The Lycurgus Cup is a Roman goblet, recently found to make use of nanotechnology to change color. Know what else changes color? A pregnancy test! Amazingly, both of these objects use similar nanotechnology.

The Lycurgus Cup

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Romans are known for two things: fighting and having a good time. The Lycurgus Cup celebrates the triumph of the latter over the former. In Greek legend, Lycurgus was a war-like king, who didn't suffer fools gladly. When faced with the antics of the wine god Dionysus and his faithful maenad Ambrosia, Lycurgus attacked Ambrosia. Ambrosia called out to her Mother Earth to help her, and Earth sent a vine twisting around Lycurgus, imprisoning him while the maenads and Dionysus taunted him.

The scene is picked out in bas relief on a green glass goblet. But when light shines through the Lycurgus cup, it shines a dazzling red, the figures appearing dark against the background.

The Lycurgus Cup puzzled archaeologists for some time, as it was discovered back in the 1840s. In the 1960s, scientists analyzed a small fragment which had broken off from the main cup, and found that the glass itself was pretty much like modern-day window glass. They also found that about 1% of the glass was made up of tiny particles of gold and silver. These particles were ground down to a precise size, from 50 to 100 nanometers, and were added in a deliberate concentration. The Romans were using basic nanotechnology.

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Gold! Gold!

Gold, it seems, is one of the materials used in the oldest forms of nanotechnology. This makes sense. For the last thousand years, people have been fascinated with it. Study anything long enough and useful functions will eventually be found for it.

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The primary use for gold was exactly what the Lycurgus cup demonstrates. When light shines through it, it makes a deep, vibrant red color. They Lycurgus cup is a colloid – a suspension of gold and silver particles in the glass. Gold scatters green light, sending it flying off in every direction. When people look at the cup in ordinary light, it appears green for the same reason the sky appears blue. All anyone sees is the light that's scattered toward the eye.

When the light shines directly through the cup, the situation changes. Suddenly people see a focused beam of light with the green light scattered away. Because the green light is filtered out, the beam of light is a brilliant red. During the Middle Ages in Europe, artists took advantage of this same phenomenon. Many of the red stained-glass windows in churches are bright red because they are embedded with nanoparticles of gold.

The Lycurgus Cup, scientists speculate, might take it one step further. Different liquids in the cup might cause the electrons in the gold to vibrate in a slightly different matter. So the cup would appear one color with lit by incident light, one color when lit by direct light, and yet another color when full of wine.

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Liquid Gold

And speaking of getting gold wet, modern humans do it every time they take a pregnancy test. That's right, the little kits sold in stores use gold particles and nanotechnology to confirm that someone is up the spout. And the confirmation also comes with a change in color.

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Among the rush of hormones that come in early pregnancy is human chorionic gonadotropin, or hCG. This hormone is present in urine, and has two components. One component is included in the test, affixed to the infamous "strip that turns pink." The other component is provided (or not) by the woman. In the section of the strip that the woman pees on, a bunch of gold nanoparticles are tagged with a certain antibody that will attach itself to the other component of hCG. Urine with hCG hits the test, the antibodies grab the second component, and they slowly seep towards the "strip."

When they get to the strip, the two components of hCG bind together, bringing along the gold. The gold-hCG combination is colored red. Enough hCG in the urine, and this pigmentation becomes clearly visible, the strip turns pink, and the test confirms a pregnancy. The gold nanotechnology tradition remains.

Anyone want to speculate on whether people peed in the Lycurgus Cup? I think they definitely did.

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[Via Smithsonian Magazine, The Lycurgus Cup: A Roman Nanotechnology, The Lycurgus Cup, Nanoscale Gold]