Click Synthesis of Hydrophilic Maltose-Functionalized Iron Oxide Magnetic Nanoparticles Based on Dopamine Anchors for Highly Selective Enrichment of Glycopeptides

The development of methods to isolate and enrich low-abundance glycopeptides from biological samples is crucial to glycoproteomics. Herein, we present an easy and one-step surface modification strategy to prepare hydrophilic maltose functionalized Fe₃O₄ nanoparticles (NPs). First, based on the chelation of the catechol ligand with iron atoms, azido-terminated dopamine (DA) derivative was assembled on the surface of magnetic Fe₃O₄ nanoparticles by sonication. Second, the hydrophilic maltose-functionalized Fe₃O₄ (Fe₃O₄-DA-Maltose) NPs were obtained via copper­(I)-catalyzed azide–alkyne cycloaddition (click chemistry). The morphology, structure, and composition of Fe₃O₄-DA-Maltose NPs were investigated by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM). Meanwhile, hydrophilicity of the obtained NPs was evaluated by water contact angle measurement. The hydrophilic Fe₃O₄-DA-Maltose NPs were applied in isolation and enrichment of glycopeptides from horseradish peroxidase (HRP), immunoglobulin (IgG) digests. The MALDI-TOF mass spectrometric analysis indicated that the novel NPs exhibited high detection sensitivity in enrichment from HRP digests at concentration as low as 0.05 ng μL^–1, a large binding capacity up to 43 mg g^–1, and good recovery for glycopeptides enrichment (85–110%). Moreover, the Fe₃O₄-DA-Maltose NPs were applied to enrich glycopeptides from human renal mesangial cells (HRMC) for identification of N-glycosylation sites. Finally, we identified 115 different N-linked glycopeptides, representing 93 gene products and 124 glycosylation sites in HRMC.