A porous graphene sorbent coated with titanium(IV)-functionalized polydopamine for selective lab-in-syringe extraction of phosphoproteins and phosphopeptides.

A novel polydopamine coated three-dimensional porous graphene aerogel sorbent carrying immobilized titanium(IV) ions (denoted as Ti4+@PDA@GA) was fabricated without using an organic solvent. The material is shown to be a viable carbon foam type of monolithic sorbent for selective lab-in-syringe enrichment of phosphoproteins and phosphopeptides. The phosphoproteins can be separated from a sample by aspiration and then bind to the sorbent. The analytes then can be dispensed within 5 min. The weight percent of titanium in the monolith typically is 14%, and the absorption capacities for the model proteins β-casein and κ-casein are 1300 and 1345 mg g-1, respectively. The absorption capacities for nonphosphoproteins are much smaller, typically 160 mg g-1 for β-lactoglobulin, 125 mg g-1 for bovine serum, and 4.8 mg g-1 for lysozyme. The results demonstrate that the selectivity for phosphoproteins was excellent on multiple biological samples including standard protein mixtures, spiked human blood serum, and drinking milk. The selective enrichment of phosphopeptides also makes the method a promising tool in phosphoproteomics. Graphical abstract Schematic of a polydopamine coated three-dimensional porous graphene aerogel for immobilization of titanium(IV) ions. The material served as a monolithic sorbent for selective enrichment of phosphopeptides and phosphoproteins from biological samples. The enrichment process can be carried out conveniently using a lab-in-syringe way.