This invention relates generally to NMR systems for in vivo detection of analytes. More particularly, in certain embodiments, the invention relates to systems in which superparamagnetic nanoparticles are exposed to a magnetic field and radio frequency (RF) excitation at or near the Larmor frequency, such that the aggregation and/or disaggregation of the nanoparticles caused by the presence and/or concentration of a given analyte in a biological fluid is detected in vivo from a monitored RF echo response.
