A guanidyl-functionalized TiO₂ nanoparticle-anchored graphene nanohybrid for enhanced capture of phosphopeptides

TiO₂-based MOAC (metal oxide affinity chromatography) nanomaterials are regarded as one of the most promising materials for phosphopeptide enrichment. However, the serious non-specific adsorption of acidic peptides and the limited chemisorption performance to phosphopeptides will greatly reduce the enrichment efficiency. To overcome the above problems, a novel TiO₂ hybrid material with guanidyl-functionalized TiO₂ nanoparticles (GF-TiO₂) anchored on the surface of a graphene oxide (GO) platform (denoted as GF-TiO₂-GO) is successfully synthesized and applied as a biofunctional adsorbent for selective enrichment of trace phosphopeptides. Due to the improved selectivity to phosphopeptides and larger loading capacity, the novel GF-TiO₂-GO nanohybrids exhibited higher selectivity toward phosphopeptides and a lower detection limit even when the concentration of β-casein was decreased to only 1 × 10^-11 M. The selective enrichment test toward phosphopeptides from the tryptic digests of nonfat milk and human serum further validated that the GF-TiO₂-GO nanohybrids were capable of selectively capturing global phosphopeptides from complicated biological samples.