Full-length antibodies versus single-chain antibody fragments for a selective impedimetric lectin-based glycoprofiling of prostate specific antigen

The main aim of the research was to design a functional impedimetric biosensor able to glycoprofile prostate specific antigen (PSA), a biomarker for prostate cancer (PCa), with high specificity using lectins as glycan recognising proteins. Traditionally, full-length antibody is immobilised on the biosensor interface for specific capture of PSA with subsequent glycoprofiling of PSA by addition of lectins. Since full-length antibodies contain glycans in the Fc domain, particular attention has to be paid to suppress direct binding of lectins to immobilised full-length antibodies, which would compromise accurate glycoprofiling. This issue is addressed here using a recombinant single-chain antibody fragments (scAb), which do not contain any carbohydrate moiety. Surface plasmon resonance was applied to prove negligible interaction of lectins with immobilised scAb fragments, while substantial binding of lectins to full length antibodies was observed. Eight different biosensor designs were tested for their ability to detect PSA. The biosensor device based on scAb fragments covalently immobilised on the gold electrode surface, patterned by a mixed SAM using standard amine coupling chemistry, proved to be the most sensitive. The scAb fragment-based biosensor exhibited sensitivity of 15.9 ± 0.8% decade−1 (R2 = 0.991 with an average RSD of 4.9%), while the full antibody-based biosensor offered sensitivity towards PSA of 4.2 ± 0.1% decade−1 (R2 = 0.999 with an average RSD of 4.8%). Moreover, the selectivity of the scAb-based biosensor was tested using a kallikrein 2 protein, a protein structurally similar to PSA, and the results indicated high selectivity for PSA detection.