Fe₃O₄/Au Core/Shell Nanoparticles Modified with Ni²⁺−Nitrilotriacetic Acid Specific to Histidine-Tagged Proteins

Well-defined Fe 3 O 4 /Au core/shell nanoparticles were successfully prepared with polyethyleneimine (PEI) as a linker, which are of good monodispersity and strong magnetism. The intact gold shell made these nanoparticles easily modified and biofunctionalized for different biodetection and biosensing purposes. Hereby, they were surface modified with mercaptopropionic acid, followed by conjugating nitrilotriacetic acid (NTA) and subsequently chelating Ni 2+ . The resulting biofunctionalized Fe 3 O 4 /Au−NTA−Ni 2+ composite nanoparticles were used to enrich and separate the histidine-tagged (His-Tag) maltose-binding protein (MBP) directly from the mixture of lysed cells. It has been found that Fe 3 O 4 /Au−NTA−Ni 2+ can be used for rapid, efficient, and specific enrichment and separation of His-Tag fusion proteins. The enrichment efficiency of the Fe 3 O 4 /Au−NTA−Ni 2+ nanoparticles is significantly higher than that of metal−chelate affinity chromatography (MCAC). The detection limit of the current method coupled with facile SDS-PAGE can be lower than 5.5 × 10 −8 M. Due to the ease of operation and good efficiency of separation, diverse bifunctional and even multifunctional nanomaterials can be further developed for biological applications.