Quantitative improvement of magnetic immunoassays in thin channels using magnetofluorescent nanocomposites

This paper presents the characterization and application of prepared magnetofluorescent nanocomposites for quantitatively improving magnetic immunoassays in a thin channel. Magnetofluorescent nanocomposites [(iron oxide@polystyrene,QDg@mSiO2)@SiO2] were characterized for optimizing magnetic and fluorescence properties for multifunctional applications. The prepared magnetofluorescent nanocomposites have several times higher magnetism than those of literature and exhibit strong fluorescence. The number of magnetofluorescent nanocomposites with primary antibody can be reliably estimated through fluorescence measurement and used for a sandwich immunoassay. We used a model biomarker, tumor necrosis factor-α (TNF-α), to demonstrate the feasibility of method. The detection limit of TNF-α was 1.0 pg/ml and the linear range was 1.7 pg/ml to 17 ng/ml. This detection limit was substantially lower and the linear range was considerably wider than those of an enzyme-linked immunosorbent assay (ELISA) and other methods in sandwich immunoassays. The differences between our method and an ELISA for TNF-α measurements of serum samples were less than 11%. The results show that magnetofluorescent nanocomposites are useful to provide higher quantitative accuracy and wider linear range than those of previous methods with 50% of the biofunctional nanocomposites, enabling the simple, rapid, and sensitive detection of biomarkers.