Every year, thousands of heart attack victims are sent home without treatment by emergency-room doctors because tests don't show clear signs of a problem, such as elevated levels of proteins released into the blood by dying heart cells. But an ultrasensitive detector, expected to be widely available for clinical evaluation later this year, could save lives by recognizing those proteins at a thousandth the concentration that current methods can detect -- or even less. The device, built by Nanosphere of Northbrook, IL, is based on research by Northwestern University chemist Chad Mirkin, who developed a way to coat gold nanoparticles with selectively "sticky" substances, such as DNA strands constructed to bind with complementary target DNA in a sample. When the nano-particles, stuck to their targets, attach to a microarray that also bears complementary DNA, a digital camera can scan them to find the sample's DNA concentration. A similar method, using antibodies as the glue, can measure protein concentrations.

Clinical trials are now testing techniques that could be used to diagnose previously undetected heart disease and Alzheimer's disease. Nanosphere's CEO, Bill Moffitt, says the device could reveal levels of telltale Alzheimer's proteins in the blood at concentrations "undetectable by any other technology."