Enhanced enrichment performance of nickel oxide nanoparticles via fabrication of a nanocomposite with a graphene template

Metal oxide based nanocomposites are applied in phosphoproteomics for enrichment through the surface hydroxyl groups of metal oxides, though the role of the metal is rarely described. Using graphene as a template after modification with nickel oxide, a nanocomposite with an increased surface area is fabricated and applied to phosphopeptides. Characterisation shows a narrow size distribution of 15-20 nm, BET surface area of 179.70 m(2) g(-1) and a pore volume of 0.44 cm(3) g(-1). The graphene possesses well distributed NiO nanoparticles showing selectivity up to 1000 folds of complexity with a sensitivity as low as 1 femtomole. The G-NiO nanocomposite shows a higher selectivity towards phosphopeptides compared to TiO2, ZrO2 and NiO nanoparticles. The enrichment with the G-NiO nanocomposite is tested for biological samples like egg yolk, non-fat milk and human serum. Phosphopeptides having phosphorylations of up to 6 phosphate groups, derived from phosvitin and lipovitellin, are enriched in the egg yolk digest. Phosphopeptides characteristic of casein variants are enriched in the non-fat milk digest with a recovery of alpha S1 21.9%, alpha S2 30% and beta-casein 20%. Phosphorylated proteins are identified in human serum through the enrichment of phosphopeptides.