One-Pot Two-Nanoprobe Assay Uncovers Targeted Glycoprotein Biosignature

We report a one-pot two-nanoprobe approach coupled to mass spectrometry for simultaneous quantification and post-translational modification (PTM) profiling of targeted protein in biofluid. Using N-glycoprotein as model, the assay employs two nanoprobes, antibody-conjugated SiO₂ nanoparticles and lectin-conjugated magnetic Fe₃O₄ nanoparticles, to achieve target glycoprotein isolation from biofluid and subsequent glycopeptide enrichment in a single tube. As demonstrated on α-fetoprotein (AFP), a serum biomarker for hepatocellular carcinoma (HCC), the assay has high purification specificity (20 glycopeptides) with 2-fold and 10-fold superior total glycopeptide intensity compared to non-one-pot method (9 glycopeptides) or without enrichment (6 glycopeptides), respectively. By multiple reaction monitoring mass spectrometry (MRM-MS) analysis of the nonglycopeptides, the assay can quantify low abundant AFP expression (0.5 ng) with good correlation with conventional ELISA method (Pearson's r = 0.987). Furthermore, we present the first study revealing AFP glycopeptide signatures of individual HCC patients, comprised of 23 heterogeneous glycoforms of bi- and triantennary, core and terminal fucosylation, and mono- to trisialylation. In addition to 12 novel AFP glycoforms, our quantification result uncovers five abundant glycoforms in HCC, including 3 core-fucosylated (CF) forms. These identified CF forms may be evaluated in future studies as potential targets in a glycopeptide biomarker panel to further improve accuracy of conventional AFP-L3 tests. Through this one-pot assay, a comprehensive target protein profile comprised of protein expression and glycosylation pattern was achieved in simple protocol with high sensitivity, reduced analysis time, and minute starting material. This assay can be extended to other PTM biosignatures by conjugation of other affinity ligands on the nanoprobe.