Nonlinear polymer brush modified magnetic nanoparticles in phosphopeptides enrichment

Magnetic nanoparticles attached to hydrophilic polymer brushes containing immobilized Fe³⁺ ions were synthesized and used as a new strategy for phosphopeptide enrichment from digested tryptic proteins. To test the performance of nanoparticles in phosphopeptide enrichment, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used. Magnetic nanoparticles with the following features such as high adsorption capacity (about 360 mg/g), easy control and transfer by external magnetic field (high magnetic saturation, about 50 emu/g), excellent phosphopeptide recovery (93.4%) and no shadow effect (due to their non-porous structure), were synthesized. It has been shown that the presence of other proteins in high concentrations does not affect on the performance of nanoparticles. Furthermore, the lowest concentration of digested β-casein phosphopeptides detectable by nanoparticles was determined to be approximately 0.5 fmol µL^− 1. The function of synthesized nanoparticles to enrich phosphopeptides in complex biological samples was also demonstrated by isolating four endogenous phosphopeptides from human serum.

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