Highly selective enrichment of phosphopeptides using Zr⁴⁺-immobilized Titania nanoparticles

It is urgent to selectively enrich trace phosphorylated proteins or peptides from complex biological sample for mass spectrometry (MS)-based phosphoproteomics. In this study, a novel immobilized metal affinity chromatography (IMAC) material with DOTA(1,4,7,10-tetraazacyclododecane N, N', N'', N'''-tetra-acetic acid) coated on the surface of TiO₂ nanomaterials and functionalized with the metal ion Zr⁴⁺(TiO₂@DOTA-Zr) has been synthesized successfully to improve the enrichment specificity and sensitivity for phosphopeptides. TiO₂ nanomaterials were chosen as a support matrix, which will offer a high specific surface area to enhance the amounts of immobilized Zr⁴⁺ ions and will provide an additional selectivity for the special enrichment of phosphopeptides. Also, the introduction of DOTA will endow a stronger binding interaction between the Zr⁴⁺ ion and DOTA to reduce the loss of the metal ion Zr⁴⁺ during sample loading and washing steps. The novel TiO₂@DOTA-Zr nanohybrids exhibited higher sensitivity and selectivity for phosphopeptides from the standard protein digests, the tryptic digests of nonfat milk and human serum, showing a great selective enrichment capability toward the complicated biological samples.