A sensitive platform for in vitro immunoassay based on biofunctionalized magnetic nanoparticles and magneto-optical Faraday effect

Abstract The magneto-optical Faraday effect is a powerful tool to study the interaction between magnetism and light. In this study, a highly sensitive in vitro immunoassay platform based on the magneto-optical Faraday effect and biofunctionalized magnetic nanoparticles (BMNs) has been demonstrated for the detection of C-reactive protein (CRP). The BMNs employed in this study were magnetic nanoparticles (MNPs) coated with CRP antibody (anti-CRP). The Faraday effect was used to observe the conjugation of the BMNs with CRP in a liquid under ac magnetic fields. When anti-CRP conjugates with CRP, BMNs aggregate to form larger magnetic clusters. We observed that the Faraday rotation angle changes during the clustering of BMNs and gradually reaches an equilibrium when the association of anti-CRP and CRP is complete. By monitoring the variations of the Faraday rotation angle, the CRP concentration can be calculated. We achieved a detection limit of 0.53 ng/mL for CRP via the collaboration of the Faraday effect technique and BMNs. In summary, we have developed a novel high-sensitivity magneto-optical platform for in vitro immunoassay.