Miniature magnetic resonance system for robust and portable diagnostics*

We have recently developed a new diagnostic platform, microNMR($\mu$NMR), specifically designed for clinical applications This new $\mu$NMR system performs rapid, accurate, and robust measurements of cells, proteins and small molecules in point-of-care settings. The system utilizes magnetic nanoparticles (MNPs) to amplify the analytical signals in NMR detection. When molecularly-specific MNPs identify their targets, the particles induce large, amplified changes in the transverse relaxation of water protons by producing local magnetic fields. A major challenge in achieving reliable NMR detection is the fluctuation of NMR frequency ($f$0) with temperature, which originates from the the temperature-dependent drift of the magnetic field. To overcome the challenge, we have implemented a new, automated feedback controller that keeps track of $f$0 and reconfigures measurement settings. The mechanism enables robust $\mu$NMR measurements in realistic clinical environments (4-50 $^{\circ}$C). Moreover, the $\mu$NMR interfaces with mobile devices for its operation, maximizing the portability of $\mu$NMR. The clinical utility of the new $\mu$NMR system is demonstrated by detecting and molecularly profiling cancer cells from patient samples.