Thousands of years ago, a bright blue pigment colored the walls of tombs, ceramic figurines, and the crown of the Bust of Nefertiti. This colorful chemical, calcium copper silicate, was invented in ancient Egypt and still fascinates researchers today.
A new study published last month in Nature Communications details how nanoscale sheets of the pigment, also called Egyptian blue, can be used in biology research. Through a series of steps, powdered Egyptian blue pigment can be flaked apart into mineral sheets 100,000 times thinner than a human hair, according to a statement. Then, when inserted into biological samples, it can illuminate the molecular mechanisms of life.
“I am sure it will be of growing interest for material scientists as well as biomedical research,” chemist and lead author of the study Sebastian Kruss of Georg August University Göttingen tells artnet News’ Naomi Rea.
Egyptian blue got its start as an artificial replacement for dye made of lapis lazuli, a semiprecious stone mined in a region that is now Afghanistan. The natural resource was relatively rare, so by about 2,500 B.C., the Egyptians found a way to make more of the same hue at home. The recipe involved simply mixing limestone, sand, and copper in high heat, and factories were built to produce the sought-after substance.
Over time, the Egyptians shared their process with neighboring civilizations. Signs of Egyptian blue have been found in relics of ancient Mesopotamia, Greece, and Rome, per History. Production of the pigment seems to have stopped around 1,000 A.D., and its recipe wasn’t rediscovered until 19th century research was prompted by brilliant blue paintings found on the walls of Pompeii.
The archaeological finds point to the pigment’s stability—a key characteristic that could make it useful in biomedical imaging. Another important aspect is the way that the molecule fluoresces under infrared light. In the new study, the researchers focused on how Egyptian blue could be used for near-infrared imaging.
The new study builds on previous research that suggested Egyptian blue pigment could be repurposed for scientific research. In 2009 and 2013, researchers showed the pigment’s fluorescence in near-infrared light, and that it dissolves into flakes when stirred in hot water for a few days. Now, it’s clear that the pigment can be taken up in study samples and that it is stable over time.
Using near-infrared light, which has wavelengths just beyond the longest that humans can see, researchers can look into biological samples. Some fluorescing molecules emit light when they’re hit by infrared waves. But the Egyptian blue nanoparticles in the new study happen to be significantly brighter than other options currently available for near-infrared imaging studies. It also doesn’t bleach over time the way that other molecules do, making it better for studying processes that may take hours.
To show that the bright blue nanoscale sheets could be used in biomedical research, the scientists conducted two imaging experiments. In the first, they put their Egyptian blue particles into a fruit fly embryo and watched under a microscope to see how the fluorescent spots moved as the fly developed. In the second, they put the particles into a plant’s leaves, and compared it with another molecule commonly used to study in near-infrared imaging. Leaves are tricky because they fluoresce slightly on their own. But the researchers showed that the Egyptian blue-containing leaf lit up bright, visible without a microscope, while the other molecule's light was hidden in the leaf’s own fluorescence.
“These tiny [Egyptian Blue] particles are then very useful glowing labels in biomedical research,” Kruss tells artnet News. He calls it a “very powerful fluorophore,” that could be used “to understand how an embryo develops or cells divide,” as well as in “image guided surgery, or labelling of cancer tissue.”