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Endotoxin tests currently rely on the blood of horseshoe crabs, which is blue in appearance.
A recent discovery involving liquid crystals could lead to a replacement test for the presence of endotoxins. Current tests involve the use of horseshoe crab blood, which is blue due to a protein called hemocyanin, the oxygen-carrying pigment the blood contains. This image shows a horseshoe crab in sand at Monomoy National Wildlife Refuge, Mass.
Credit: Bill Perry, U.S. Fish and Wildlife Service
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Related story: Replacing the Blue Bloods