A system for modulating a response signal includes functionalized particles configured to interact with target analytes, a detector configured to detect an analyte response signal transmitted from the body, a modulation source configured to modulate the analyte response signal, and a processor configured to non-invasively detect the one or more target analytes by differentiating the analyte response signal from a background signal, at least in part, based on the modulation. The analyte response signal is related to the interaction of the target analytes with the functionalized particles. In some examples, the system may also include magnetic particles and a magnetic field source sufficient to distribute the magnetic particles into a spatial arrangement in the body. The analyte response signal may be differentiated from the background signal, at least in part, based on modulation of the signals due, at least in part, to the spatial arrangement of the magnetic particles.