Rapid synthesis of three-dimensional sulfur-doped porous graphene via solid-state microwave irradiation for protein removal in plasma sample pretreatment

In this work, we prepared three-dimensional sulfur-doped porous graphene (3D-SPG) via solid-state microwave method and first introduced it to plasma sample pretreatment as adsorbent for the removal of proteins. The efficient heating effect of solid-state microwave irradiation endowed the as-prepared 3D-SPG with large specific surface area, porous structures and sulfur-doped conjugated pi electron surface, thus producing an outstanding adsorbent for proteins adsorption. The adsorption behavior of 3D-SPG towards proteins was explored using bovine serum albumin (BSA) as the model protein and several kinetic models and isotherm models were employed to describe the adsorption process. The results indicated that BSA was adsorbed onto 3D-SPG in a monolayer manner with high adsorption capacity, and chemisorption and intraparticle diffusion was the rate controlling step in proteins adsorption process. By applying 3D-SPG as adsorbent to remove proteins in real rat plasma, we found that 3D-SPG solid phase extraction (SPE) gained exceedingly high protein removal efficiency compared with other plasma pretreatment methods, suggesting that 3D-SPG SPE could effectively prevent the deterioration of column performance and decrease the interference caused by matrix effect in the follow-up analysis. Furthermore, in comparison with the tandem mass spectra results between 3D-SPG SPE and methanol precipitation, 3D-SPG SPE demonstrated the ability to extract the protein-binding metabolites which usually could not be extracted by methanol precipitation. This ability made 3D-SPG SPE of great value in untargeted metabolomics profiling, because 3D-SPG SPE could be a complementary method to methanol precipitation to improve the coverage of metabolites.