Provided herein is a magnetic apparatus for collecting superparamagnetic particles from a subject. The superparamagnetic particles are previously injected into the subject and have ligands bound thereto that are specific for one or more non-cell biomarkers. In one embodiment, the superparamagnetic particles are injected into and retrieved from a cavity such as a joint cavity. These compositions and methods allow for the sequestration and removal of inflammatory mediators, as both a diagnostic of the local immune response and a therapeutic that can reduce inflammation in the local disease environment.