Simplified Fabrication of Magnetic Nanoparticles With Directly Adsorbed Antibodies for Bacteria Detection

Antigen–antibody reactions with conjugated magnetic nanoparticles (MNPs) are widely used for detecting viruses, bacteria, and proteins. In this study, we proposed a novel method for adsorbing antibodies directly on the surface of MNPs without coating any proteins. MNPs (Fe
₃
O
₄
; average size 4 nm) were synthesized by a thermal decomposition method using oleyl amine as a surfactant, the fabricated MNPs exhibit superparamagnetic characteristics, and the antibodies (anti-
Bifidobacterium longum
) were adsorbed. We found that 15
$\mu \text{g}$
/mg of antibody adsorbed to MNPs and were able to detect the bacteria bound to the produced antibody-MNPs based on the antigen–antibody reaction, offering potential for highly sensitive bacteria detection.