Transduction of Glycan–Lectin Binding via an Impedimetric Sensor for Glycoprotein Detection

Glycoproteins are produced by glycosylation modification of proteins, and a number of glycoproteins have served as important tumor biomarkers in clinical application. Alpha-fetoprotein (AFP) is one of the representative glycoproteins that has been employed as a useful predictive and prognostic biomarker for hepatocellular carcinoma. Human AFP has an N-glycan portion at the asparagine residue, which includes four N-acetyl-glucosamine and three mannoses. In this work, building upon lectin–glycan interactions, one type of facile and capable impedimetric biosensor was fabricated utilizing microwave-prepared NH₂-MIL-101(Fe) to decorate lectins as a recognition element. Two different lectins of wheat-germ agglutinin (WGA) and concanavalin A (Con A) were employed to target the N-acetyl-glucosamine and mannose of N-glycan in AFP, respectively. This work has not only accomplished the sensitive impedimetric biosensing of the AFP tumor marker (with the limit of detection down to 0.5 pg/mL and linear concentration spanning 5 orders of magnitude from 10^–2 to 10³ ng/mL) but also replied on two kinds of lectins to “read” the sugar chain, transducing the minor difference of this process to impedimetric signals for display. The impedimetric data shed some light on the local microenvironment of the lectin–glycan binding event, providing some electrochemical experimental support for the biantennary structure of N-glycan in AFP. The mannoses were “buried” in the interior core of the whole N-glycan, increasing steric hindrance for Con A to approach and thus rendering the WGA@MIL-101(Fe)-based biosensor more superior sensing responses.