Organic molecule-assisted synthesis of Fe3O4/graphene oxide nanocomposites for selective capture of low-abundance peptides and phosphopeptides

The iron oxide nanoparticles (Fe 3 O 4 ) were prepared by organic molecule-assisted method in aqueous solution. The facile synthetic process of Fe 3 O 4 nanoparticles was conducted only by mixing FeCl 2 and 2-methylimidazole (2-MIM) without any additives. A possible growth mechanism of the Fe 3 O 4 nanocrystals was proposed for this mild reaction. Then, the Fe 3 O 4 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, Fe 3 O 4 /GO probe exhibits excellent performance for enriching low-abundance hydrophilic peptides, while the Fe 3 O 4 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 Fe 3 O 4 /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.