Synthesis of a new type of echinus-like Fe3O4@TiO2 core–shell-structured microspheres and their applications in selectively enriching phosphopeptides and removing phospholipids

Some compounds of low abundance in biological samples play important roles in bioprocesses. However, the detection of these compounds at inherently trace concentrations with interference from a complex matrix is difficult. New materials for sample pretreatment are essential for the removal of interferences and for selective enrichment. In this study, echinus-like Fe3O4@TiO2 core–shell-structured microspheres (echinus-like microspheres) have been synthesized for the first time. Rutile phase TiO2 nanorods with a length of approximately 300 nm and width of approximately 60 nm are arranged regularly on the surface of the microspheres. This novel type of material exhibited good selectivity and adsorption capacity toward phosphate-containing compounds. In proteomics research, the echinus-like microspheres were used to selectively enrich phosphopeptides from complex peptide mixtures. Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS) analysis showed that fourteen phosphopeptides were detected from α-casein tryptic digests after enrichment. Even in peptide mixtures that contained highly abundant nonphosphorylated peptides with interference from bovine serum albumin, these phospopeptides could still be selectively trapped with little nonspecific adsorption. In metabolomics studies, the echinus-like microspheres were further used to selectively remove phosphocholines (PCs) and lysophosphocholines (LPCs), which are the main matrix interferences for the detection of metabolites of low abundance in plasma. Liquid chromatography–quadrupole time-of-flight mass spectrometry was used to perform the metabolic profiling of plasma. The high concentrations of PCs and LPCs were effectively eliminated, and many endogenous metabolites of low abundance were enhanced or even observed for the first time. All of the results suggest that echinus-like microspheres have potential applications in proteomics and metabolomics to improve the detection sensitivity of important compounds.

► Echinus-like Fe3O4@TiO2 core–shell microspheres were firstly synthesized. ► This material exhibits high selectivity toward phosphate-containing compounds. ► Phosphopeptides were selectively enriched from complex peptides mixtures. ► Phospholipids were effectively eliminated from plasma. ► Many metabolites of low abundance were enhanced or even newly observed.