A giant magnetoresistance-spin valve (GMR-SV) having highly sensitive magnetic properties was prepared with a multilayer soft ferromagnetic/non-magnetic/pinned ferromagnetic/anti-ferromagnetic iridium manganese (IrMn) top layer (NiFe/CoFe/Cu/CoFe/IrMn) structure. Micron-sized magnetic beads (MBs) with a diameter of 1 μm immersed in a solution containing 50 mg of Co-Si-OH/ml were attached to red blood cells (RBCs) having the very low magnetization of hemoglobin (HEM) to detect a deoxidized RBC combined with MBs (RBC+MBs). The RBC+MB combinations can be captured on a single-turn μ-coil that maintains a magnetic field large enough to detect the MBs attached to the RBC. When the RBC+MBs passes through a PR μ-channel with a width of 10 μm, its stopping and starting are controlled by the electrical AC input signal applied to the single-turn μ-coil. The RBC+MBs combinations captured above the μ-device of the GMR-SV change the output signal and thus, can be used for detection. This observation implies that this device can be used as a biosensor to analyze the coupling force between the HEM and the MBs for RBCs with deformed membranes passing through a narrow capillary.