Magnetic γ-Fe2O3@REVO4 (RE = Sm, Dy, Ho) affinity microspheres for selective capture, fast separation and easy identification of phosphopeptides

The multifunctional microspheres consisting of the magnetic γ-Fe2O3 core and the affinity REVO4 (RE = Sm, Dy, Ho) shell have been synthesized via the homogenous precipitation–calcination–ion exchange three-step synthetic route. Their morphologies, structures, surface properties, and magnetisms were characterized, respectively. SEM and TEM images indicate that they all have an average size of about 400 nm and very rough surfaces. The TEM images further reveal that the γ-Fe2O3@REVO4 microspheres are all core–shell structures and the REVO4 shells are about 55–60 nm in thickness. The XRD pattern analyses show that the magnetic γ-Fe2O3 cores belong to cubic structure and the REVO4 (RE = Sm, Dy, Ho) shells are composed of their corresponding tetragonal major phases. HRTEM images, FTIR spectra and EDS further demonstrate the formations of tetragonal REVO4 shells based on checkup of the corresponding lattice fringes, characteristic IR absorption peaks and element signals. Their potentials for selective capture, rapid separation, and convenient mass spectra (MS) labeling of the phosphopeptides from complex proteolytic digests are explored and evaluated for the first time. The experimental results show that the magnetic γ-Fe2O3@REVO4 core–shell structured microspheres have high selective affinity for the phosphopeptides. The trapped phosphopeptides can be rapidly isolated by an external magnetic field, and can be easily identified by characteristic MS signals from 80 Da mass losses in the mass spectra (MS). Additionally, the γ-Fe2O3@REVO4 affinity materials can be reused after recovery.