GMR detection of magnetic beads with different sizes

•The detection process adopts the method of separate detection, which significantly simplifies the detection process.•Fe3O4 magnetic beads with particle sizes of 100, 200, 300, 600, 800, and 1000 nm are selected for analysis.•A high-resistance GMR sensor with a resistance value of 298 kΩ was prepared using MEMS technology. In recent years, there has been a growing body of research concerning the detection of biomolecules using giant magnetoresistance (GMR) sensors in conjunction with magnetic beads. Researchers have primarily focused on enhancing detection accuracy through various means, including increasing the sensitivity of the sensor itself and refining the signal detection scheme. In this paper, we investigated the impact of magnetic bead particle size on the GMR sensor signal. We selected Fe3O4 magnetic beads with varying particle sizes for analysis. We discuss their internal composition, grain structure, and magnetic properties. Employing microelectromechanical system (MEMS) technology, we fabricated a high-resistance GMR sensor with a resistance value of 298 kilohms. We then conducted magnetic bead signal detection on a custom-built platform. We also explored the optimal operating point for magnetic bead detection based on the magnetic response of the GMR sensor. Our findings demonstrate that enhancing the magnetic properties of the beads is crucial for improving detection, as larger bead sizes result in higher saturation magnetization and larger signal outputs from the GMR sensor.