One-step polymerization of functionalized ionic liquid as polymer microspheres for highly specific enrichment of phosphopeptides from cell lysate and serum

A Ti4+-functionalized ionic liquid polymer microsphere was proposed and prepared through free radical precipitation polymerization. The polymer microsphere demonstrates excellent performance on phosphopeptide enrichment, with a low detection limit (0.5 fmol) and good selectivity (1:2500). Through the analysis of HepG2 cell lysate using nano LC-MS/MS after material enrichment, a total of 1100 phosphopeptides and 733 phosphoproteins were identified. Additionally, in the serum of liver cancer patients, 69 phosphopeptides, 47 phosphoproteins, and 52 phosphorylation sites were identified, while healthy controls exhibited 55 phosphopeptides, 31 phosphoproteins, and 40 phosphorylation sites. Label-free quantification revealed 10 differentially expressed proteins (DEPs), with five proteins (FN1, SERPIND1, SERPINF2, IGFBP3, and MENT) being up-regulated and five proteins (SELENOP, PLG, SPP2, SERPINC1, and GP1BB) being down-regulated. These findings highlight the potential of the MBA-VImDOPA-Ti4+ polymer microsphere in specifically enriching phosphopeptides from clinical biological samples.