Recent advances in nanoporous materials as sample preparation techniques for peptidome research

As the lower-molecular-weight subset of proteome, the peptidome has attracted increasing attention in recent years due to the simple usability of sample (without digestion) and great potential in acting as diagnostic biomarkers for many diseases. However, the relative low abundance of endogenous peptides and serious interferences from large-size proteins and salts in practical biosamples results in that it is seriously difficult to directly conduct mass spectrometry identification of endogenous peptides. Nanoporous materials such as mesoporous materials and metal organic framework materials are most popularly used for sample pre-treatment in peptidomics research, since their unique porous structures can exert size-exclusion effect that prevents the large-size proteins from entering into the porous channels while adopting the opposite attitude for small-size endogenous peptides. In this review, recent advances in nanoporous materials for sample preparation, including the enrichment of common endogenous peptides, endogenous phosphopeptides and glycopeptides are summarized and discussed comprehensively. Moreover, the concerns regarding the synthesis of nanoporous materials and enrichment biases of different functionalized nanoporous materials towards different targeted endogenous peptides are also discussed.