Controllable synthesis of sandwich-type magnetic beads for procalcitonin detection on a magnetic enzyme-linked immunosorbent assay

Although magnetic beads have been widely utilized as a homogeneous carrier for immunoassays, the effectiveness of the immuno-response is often hindered by the physical and chemical characteristics of these beads, such as the challenge of achieving an optimal equilibrium among magnetic response, suspension performance and colloidal dispersibility. Herein, we present the fabrication of monodisperse polystyrene magnetic beads in a sandwich-like configuration and further explore their immunoassay capabilities as capturing substrates in the detection of procalcitonin (PCT) using the enzyme-linked immunosorbent assay (ELISA). The developed two-step magnetic particles assembly process effectively regulates the magnetic content, while the organic/inorganic double silica layer coating imparts desirable stability and dispersion to the assembly structure. Notably, the prepared magnetic beads exhibit high aqueous dispersity (PDI ∼ 0.2), rapid magnetic separation (25 s) and gradual half-sedimentation time (5 h). Leveraging the magnetic bead-based ELISA, we accomplish not only qualitative screening of PCT at an exceptionally low concentration by naked eye (cut-off value: 0.1 ng/mL) but also highly sensitive quantification of PCT using a microplate reader (limit of detection: 0.031 ng/mL). This investigation offers a solution for striking a harmonious balance among the diverse properties of magnetic beads and demonstrates the perspective of the magnetic capturing substrates in the field of immunoassays.