Hydrophilic polydopamine‐coated magnetic graphene nanocomposites for highly efficient tryptic immobilization

In this work, polydopamine‐coated magnetic graphene ( MG @ PDA ) nanocomposites were synthesized by a facile method. Trypsin was then directly immobilized on the surface of the nanocomposites through simple PDA chemistry with no need for introducing any other coupling groups. The as‐made MG @ PDA nanocomposites inherit not only the large surface area of graphene which makes them capable of immobilizing high amount of trypsin (up to 0.175 mg/mg), but also the good hydrophilicity of PDA which greatly improves their biocompatibility. Moreover, the strong magnetic responsibility makes them easy to be separated from the digested peptide solution when applying a magnetic field. The feasibility of the trypsin‐immobilized MG @ PDA ( MG @ PDA ‐trypsin) nanocomposites for protein digestion was investigated and the results indicated their high digestion efficiency in a short digestion time (10 min). In addition, the reusability and stability of the MG @ PDA ‐trypsin nanocomposites were also tested in our work. To further confirm the efficiency of MG @ PDA ‐trypsin nanocomposites for proteome analysis, they were applied to digest proteins extracted from skimmed milk, followed by nano RPLC ‐ ESI ‐ MS / MS analysis, and a total of 321 proteins were identified, much more than those obtained by 16‐h in‐solution digestion (264 proteins), indicating the great potential of MG @ PDA ‐trypsin nanocomposites as the supports for high‐throughput proteome study.