The present invention relates to systems that utilize a combination of immunoassay and magnetic immunoassay techniques to detect an analyte within an extended range of specified concentrations. In particular, a device is provided for detecting an analyte in a biological sample. The device includes a first electrochemical sensor positioned on a substrate. The first electrochemical sensor includes an immobilized layer of antibody configured to bind to the analyte. The device further includes a second electrochemical sensor positioned adjacent to the first electrochemical sensor on the substrate, and a magnetic material that generates a magnetic field aligned with respect to the second electrochemical sensor. The magnetic field captures magnetic beads that have an immobilized layer of antibody configured to bind to the analyte, and concentrates the magnetic beads on or near a surface of the second electrochemical sensor.