Princeton engineers have developed a sensor that may revolutionize how drugs and medical devices are tested for contamination, and in the process also help ensure the survival of two species of threatened animals. In the wild, the African clawed frog produces antibacterial peptides - small chains of amino acids - on its skin to protect it from infection. Princeton researchers have found a way to attach these peptides, which can be synthesized in the laboratory, to a small electronic chip that emits an electrical signal when exposed to harmful bacteria, including pathogenic E. coli and salmonella. "It's a robust, simple platform," said Michael McAlpine, an assistant professor of mechanical and aerospace engineering. "We think these chips could replace the current method of testing medical devices and drugs."
The current testing method relies on the blood of the horseshoe crab, a species that is roughly 450 million years old. Both the crab and the red knot, a species of shore bird that relies on the crab for food, have declining populations. The crab became desirable for testing because its immune system has evolved to cope with the constant threat of invasion from its bacteria-rich environment. Its blood contains antimicrobial cells, known as amebocytes, that defend the crab against bacteria. For almost 40 years, an aqueous extract made from horseshoe crab blood cells, called Limulus amebocyte lysate (LAL), has been used for testing drugs and medical devices for contamination. When a sample from a drug or device is added to LAL and the solution hardens into a gel, it indicates the sample is contaminated and not safe for human use. To produce LAL, the crabs are captured and roughly 30 percent of their blood drained before they are returned to the ocean with an estimated 30 percent mortality rate.