Preparation of porous graphene oxide-poly(urea-formaldehyde) hybrid monolith for trypsin immobilization and efficient proteolysis

Porous graphene oxide-poly(urea-formaldehyde) (GO-PUF) hybrid monolith was prepared by the in situ polycondensation of the urea-formaldehyde prepolymer solution in the presence of GO sheets and ammonium chloride. The amide groups in the residues of asparagine and glutamine in trypsin was allowed to condense with the residual N-hydroxymethyl groups of PUF in the monolith at low pH to fabricate bioreactors for proteolysis. The morphologies and structures of the prepared materials were investigated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results indicate that both GO-PUF hybrid and trypsin-immobilized GO-PUF hybrid mainly consist of irregular micrometer size flakes and pores that are interconnected to form 3D porous architectures. In addition, the feasibility and performance of the novel capillary bioreactors were demonstrated by the digestion and identification of bovine serum albumin, lysozyme, ovalbumin, and cytochrome c. The digestion time was significantly reduced to less than 10 s. The digests were identified by mass spectrometry with results that were comparable to those obtained by 12-h conventional in-solution tryptic digestion.