Considerable effort has been focused on improving the control of size, shape, and surface modifications to detect proteins. The purpose of this study was to compare the efficiencies of aminosilane-coated magnetite (As-M) nanoparticles (NPs), dextran-coated magnetite nanoparticles (Dx-M), and bare nanoparticles for conjugating single-chain variable fragment antibodies (scFvs) with the aim of detecting the human epidermal growth factor receptor 2 (HER2) protein. Dx-M and As-M NPs were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. Dx-M and As-M were conjugated with a monoclonal scFv for active targeting of the HER2 antigen. Aminosilane surface coating enhanced the scFv conjugation efficiency over twofold compared to that of the dextran-coated magnetite NPs for the detection of HER2 proteins.