Design of magnetic polyethyleneimine-fluorescein isothiocyanate composites toward efficient enrichment of phosphopeptides

Phosphoproteins maintain the normal metabolic activity of the organisms. Direct phosphopeptides detection is difficult to be realized by mass spectroscopy (MS) due to the low ionization efficiency, low abundance of phosphopeptides and interferences of complicated biological fluids. In the present work, a magnetic composite material was prepared by combining polyethyleneimine (PEI) and fluorescein isothiocyanate (FITC) focusing on phosphopeptides enrichment. Fourier-transform infrared spectroscopy, thermogravimetry analysis, X-ray photoemission spectroscopy, X-ray diffraction and UV–vis spectrometry measurement results confirmed the successful synthesis of Fe₃O₄@PEI@FITC material. FITC was facilely connected with PEI, and the two motifs endowed the efficient enrichment capacity of phosphopeptides by simple regulation of pH. The Fe₃O₄@PEI@FITC material was applied to the detection of phosphopeptides from real samples, implying that it can serve as an applicable platform for phosphoproteomics analysis.