"Rapidly identifying the pathogen responsible for an infection and testing for the presence of resistance are critical not only for diagnosis but also for deciding which antibiotics to give a patient," says Ralph Weissleder, MD, PhD, director of the MGH Center for Systems Biology (CSB) and co-senior author of both papers. "These described methods allow us to do this in two to three hours, a vast improvement over standard culturing practice, which can take as much as two weeks to provide a diagnosis." Investigators at the MGH CSB previously developed portable devices capable of detecting cancer biomarkers in the blood or in very small tissue samples. Target cells or molecules are first labeled with magnetic nanoparticles, and the sample is then passed through a micro NMR system capable of detecting and quantifying levels of the target. But initial efforts to adapt the system to bacterial diagnosis had trouble finding antibodies — the detection method used in the earlier studies — that would accurately detect the specific bacteria…