Designing versatile sandwich-like magnetic Nb₂O₅ nanocomposites derived from Nb₂C MXene for phosphopeptide enrichment

The enrichment of phosphopeptides prior to their detection is essential for the identification of protein phosphorylation followed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry because of their low concentration, low deionization efficiency and suppression from the interference derived from high-abundance counterparts. Niobium-based affinity materials have great potential in the enrichment of phosphopeptide enrichment, yet have not been extensively studied. To date, there are no reports on the application of Nb₂CT_x-based materials in separation science, especially in the application in phosphopeptide enrichment.

In this work, Nb₂C MXene derived sandwich-like magnetic Nb₂O₅ nanocomposites (denoted as m-Nb₂O₅-Fe₂O₃) were designed and synthesized for the first time by HF-etching of Nb₂AlC MAX phase, in situ growth of Fe₃O₄ nanoparticles and calcination in air. The nanocomposites were then applied as magnetic solid-phase extraction (MSPE) adsorbents in the enrichment of phosphopeptides through the synergistic metal oxide affinity chromatography mechanism by Nb-O and Fe-O. The MSPE method exhibited extremely low detection limit (0.1 nmol L^-1 of β-casein), great anti-interference ability (1:2000 of the molar ratio of β-casein to bovine serum albumin), good reusability (3 cycles) and satisfactory recovery (87.6%). The universality of m-Nb₂O₅-Fe₂O₃ was further verified by the successful application in non-fat milk, human saliva and a traditional Chinese medicine injection.

The m-Nb₂O₅-Fe₂O₃ nanocomposites are able to enrich phosphopeptides with high efficiency from diverse samples, thanks to the layered structure which provides abundant specific binding sites of Nb-O and Fe-O towards phosphate groups in phosphopeptides. The composites show great potential as a promising material for phosphopeptide enrichment from complex biological and biomedical samples.