Scientists are developing blood-cleansing technology. The device will be used to treat bloodstream infections that are the leading cause of death in critically ill patients and soldiers injured in combat. To rapidly cleanse the blood of pathogens, the patient's blood is mixed with magnetic nanobeads coated with a genetically engineered version of a human blood 'opsonin' protein that binds to a wide variety of bacteria, fungi, viruses, parasites, and toxins.