Label-free impedimetric detection of glycan-lectin interactions.

A compact biosensor for a label-free, rapid (<80 s) detection of glycan-lectin interactions using ac impedance measurements was developed for the first time. A galactose-binding peanut agglutinin (PNA) and sialic acid-binding Sambucus nigra agglutinin (SNA) were covalently surface-immobilized on the layered Cu/Ni/Au printed circuit board (PCB) electrodes. Samples of artificial and natural glycoconjugates consisting of (1) gold glyconanoparticles encapsulated with approximately 90-100 copies of TF-antigen disaccharide Galalpha1-3GalNAc (TF-AuNP), (2) asialofetuin (ASF) containing both LacNAc (Galbeta1-4GlcNAc) and TF-antigen, and (3) fetuin (FET), the sialylated glycoform of ASF. The samples were run separately on PNA- and SNA-immobilized PCB electrodes. Our results indicate that TF-AuNP could be rapidly and reliably detected up to 1 pg/mL (13 fM) concentration on PNA electrode but, as expected, yielded no response on the SNA electrode. ASF and FET glycocoproteins were unambiguously detectable up to 10 pg/mL (150 fM) on PNA and SNA electrodes, respectively. Moreover, the technique allowed us to observe glyco-microheterogeneity of FET as well as establish the presence of two isoforms of SNA lectin, SNA-I and SNA-II, in one of the vendor's formulations. Further elaboration of the described technology into novel electrochemically driven lectin arrays may find applications in diagnosis of cancer and other diseases with multiple glycobiomarkers or as a rapid low-cost bioanalytical tool for glycoproteome analyses.