State Key Laboratory of Analytical Chemistry for Life Science, Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry & Chemical Engineering and Center of Materials Analysis, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, China. Electronic address: [Email]
The iron oxide nanoparticles (Fe3O4) were prepared by organic molecule-assisted method in aqueous solution. The facile synthetic process of Fe3O4 nanoparticles was conducted only by mixing FeCl2 and 2-methylimidazole (2-MIM) without any additives. A possible growth mechanism of the Fe3O4 nanocrystals was proposed for this mild reaction. Then, the Fe3O4 nanoparticles were anchored onto graphene oxide (GO) sheets in water by ultrasound-assisted method, forming an affinity probe with strong biocompatibility. Due to the hydroxy and carboxylic groups of GO sheets, Fe3O4/GO probe exhibits excellent performance for enriching low-abundance hydrophilic peptides, while the Fe3O4 nanoparticles endure the probe with specific affinity to phosphopeptides. The analytical protocol was developed for sequential enrichment of low-abundance peptides and phosphopeptides by the affinity probe. It exhibited the sequence coverage of 26% for capture of 17 low-abundance peptides from bovine serum albumin (BSA), as well as the selectivity of 1:1:100 for phosphopeptides from α-/β-casein/BSA, and low detectable concentration of 2.5 fmol and probe reusability of 5 times for capture of phosphopeptides from α-/β-casein. Consequently, the prepared Fe3O4/GO material possesses excellent feature as multifunctional affinity probe for low-abundance peptides including phosphopeptides from complex biological matrices detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.