Tiny implanted sensors detect MI markers and gauge infarct size

In a futuristic project that might one day allow physicians to respond much more quickly to asymptomatic MIs, researchers at MIT have developed a tiny, subcutaneous sensor that can detect elevations of myoglobin, cardiac troponin I, and creatine kinase. Not only can these minute implanted sensors pick up on an MI as muscle damage begins, they can also capture the extent of damage after the fact, even after blood-level markers themselves have vanished.

Dr Yibo Ling (MIT, Boston, MA) and colleagues published a study of their sensors, used in mice, in a research letter published online February 13, 2011 in Nature Biotechnology. The sensors themselves employ a novel biomaterial called "magnetic relaxation switches" (MRSw)—essentially a nanoparticle-based magnetic resonance contrast agent coated with antibodies for specific biomarkers. In the study, two sensors for each marker, for a total of six, were implanted in each mouse. Upon interrogation, the sensors accurately distinguished mice in which infarcts had been induced from control mice or mice that had undergone thoracotomies alone.

In clinical medicine, cardiac biomarkers are currently assayed in blood samples taken at a single time point or as serial samples. "You don't know whether [the protein] is rising or falling or how much has preceded the test," senior author Dr Michael J Cima (MIT). "These sensors integrate all the protein that has been around the device since the heart attack, and because the affinity of these antibodies for the protein is a one-way street, once the protein goes in it agglomerates these particles and they don't come apart when the protein concentration drops. And probably the most surprising thing to me was that we could not only measure that the protein was there, but by the magnitude of the signal, we could see how large the infarction region was, and we could determine that from the measurement of any of the three different sensors."