Facile synthesis of magnetic iron oxide nanoparticles for nattokinase isolation

Nattokinase, derived from a traditional Japanese food, has been considered a promising supplement for use in thrombosis prevention. The development of nano-technologies has resulted in new approaches for its bioseparation. A facile synthesis of the magnetic nanoparticles (MNPs) for nattokinase isolation has been developed in this study. The arginine-modified MNPs showed four-fold increase of nattokinase adsorption compared with the carboxylated MNPs. The content of arginine on the modified MNPs was 9.6–30 μmol/mg by using the ninhydrin assay. A dose-dependent relationship between the nattokinase adsorption and the amount of arginine conjugated on MNPs was observed. The Langmuir isotherm model further confirmed the monolayer adsorption of nattokinase onto the surfaces of nanoparticles. The bare and arginine-modified MNPs were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The arginine-modified nanoparticles could efficiently separate nattokinase from natto solution. Purified nattokinase will make further contributions in various biological and clinical fields. The conjugation process developed in the present study can be applied to modification of nanoparticle surfaces.