Polydopamine-coated eppendorf tubes for Ti⁴⁺ immobilization for selective enrichment of phosphopeptides

Mass spectrometric technique has emerged as a preferred technique in the analysis of protein phosphorylation. Owing to the low stoichiometry of phosphopeptides and the signal suppression effect by non-phosphopeptides, there is a demand for efficient enrichment of phosphopeptides. The selective enrichment of phosphopeptides in modified eppendorf tubes prior to mass spectrometry analysis, which can minimize sample loss as well as nonspecific interferences effectively, has become a hot topic in current proteomics field. In our work, an easy-to-use phosphopeptide-selective eppendorf tube was initially prepared, with its inner surface being modified with a Ti(4+)-immobilized polydopamine (PDA) layer. The unique Ti(4+)-immobilized PDA-modified eppendorf tubes (EP tube@PDA-Ti(4+)) are investigated for its application in selective enrichment of phosphopeptides from complex biological samples. Due to the high Ti(4+) loading amount on the surface of PDA, the EP tube@PDA-Ti(4+) exhibits remarkable phosphopeptide enrichment ability in protein digests and human serum, which presents a powerful evidence for its high selectivity in detecting the low-abundance phosphopeptides from complex biological samples.