Dual-functionalized magnetic bimetallic metal-organic framework composite for highly specific enrichments of...

In this work, a dual-functionalized magnetic bimetallic metal-organic framework composite denoted as Fe₃O₄@SiO₂@(Zr-Ti-MOF)₁₀-NH₂ was ingeniously designed and fabricated by a facial layer-by-layer assembly technique. The composite not only exhibited strong affinity for phosphopeptide due to the coexistence of Zr-O clusters and Ti-O clusters, but also owned great hydrophilicity for glycopeptides relying on abundant hydrophilic NH₂ groups, meeting the demand for simultaneously enrichment and sequential elution of phosphopeptides and glycopeptides. As expected, the synthesized composite showed great selectivity (1:2000 M ratio of β-casein:BSA; 1:50 M ratio of IgG:BSA), good sensitivity (1 fmol μL^-1 for both α-casein and IgG), and good capacity (80 mg g^-1 for α-casein and 200 mg g^-1 for IgG). By using sequential elution strategy, 29 phosphopeptides and 24 glycopeptides from α-casein and IgG digests mixture could be simultaneously enriched and respectively detected through a single-step enrichment and sequential elution method. Furthermore, the composite was successfully applied to the analysis of intricate biological samples. 4 endogenous phosphopeptides and 20 phosphopeptides were trapped from human serum and non-fat milk tryptic digest respectively. From 0.5 mg of tryptic digest of rat brain, 141 N-linked glycopeptides corresponding to 127 glycoproteins and 918 phosphopeptides corresponding to 397 phosphoproteins were enriched simultaneously and identified respectively, proving the Fe₃O₄@SiO₂@(Zr-Ti-MOF)₁₀-NH₂ to be a dependable candidate for the simultaneously enrichment of trace phosphopeptides and glycopeptides in intricate biological samples.