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In this paper, we deal with novel inductive microsensors, realized by using standard CMOS microelectronic technologies, for the detection of small amounts of magnetic beads that are placed in selected regions over the surface of the microsensor. The sensor proposed here represents a step toward the development of integrated inductive biosensors for application in the area of magnetic immunoassay where magnetic markers, carrying specific antibodies that selectively bind to the cells or molecules to be detected, are used; the measurement of the analyte concentration is therefore accomplished by determining the concentration of magnetic particles tied to it. A planar differential transformer structure is proposed here as part of the measurement strategy. The analysis, simulation, and design of the proposed device are reported, and its sensitivity to the quantity of micromagnetic beads deposited over its surface has been also demonstrated through experiments.