A system for modulating a response signal includes aptamer conjugates, e.g., aptamer-particle conjugates, configured to bind 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 binding interaction of the target analytes with the aptamer-particle conjugates. 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.
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