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 includes a first electrochemical sensor positioned within a conduit adjacent to a second electrochemical sensor and spaced apart from one another at a predetermined distance. The first electrochemical sensor includes an immobilized layer of antibodies. The second electrochemical sensor includes a magnetic field disposed locally around the second electrochemical sensor, and the magnetic field is configured to attract magnetic beads onto a surface of the second electrochemical sensor. The device further includes a scavenging electrode positioned between the first electrochemical sensor and the second electrochemical sensor. The scavenging electrode is configured to prevent crosstalk between the first electrochemical immunosensor and the second electrical immunosensor.