Magnetically promoted rapid immunoreactions using functionalized fluorescent magnetic beads: A proof of principle

BACKGROUND: Accurate detection and monitoring of disease-related biomarkers is important in understanding pathophysiology. We devised a rapid immunoreaction system that uses submicrometer polymercoated fluorescent ferrite (FF) beads containing both ferrites (magnetic iron oxide) and fluorescent europium complexes. METHODS: FF beads were prepared by encapsulation of hydrophobic europium complexes into the polymer layers of affinity magnetic beads using organic solvent. A sandwich immunoassay using magnetic collection of antibody-coated FF beads to a specific place was performed. Brain natriuretic peptide and prostate-specific antigen were selected as target detection antigens to demonstrate the feasibility of this approach. An immunohistochemical staining using magnetic collection of antibody-coated FF beads onto carcinoma cell samples was also performed. RESULTS: The sandwich immunoassays, taking advantage of the magnetic collection of antibody-coated FF beads, detected target antigens within 5 min of sample addition. Without magnetic collection, the sandwich immunoassay using antibody-coated FF beads required long times, similar to conventional immunoassays. Using the magnetic collection of antibody-coated FF beads, immunohistochemical staining enabled discrimination of carcinoma cells within 20 min. CONCLUSIONS: This proof of principle system demonstrates that immunoreactions involving the magnetic collection of antibody-coated FF beads allow acceleration of the antigen-antibody reaction. The simple magnetic collection of antibody-coated FF beads to a specific space enables rapid detection of disease-related biomarkers and identification of carcinoma cells.