The study addresses the challenge of detecting cancer-related glycoproteins by targeting abnormal glycosylation patterns. A DNA aptamer (PSA-1), originally selected for the glycan moiety of prostate-specific antigen, is used as a lectin-mimicking receptor. This aptamer was incorporated into an electrochemical sandwich biosensor for detecting serum amyloid P (SAP), a glycoprotein with increased sialylation associated with pancreatic cancer. The biosensor combines an anti-SAP antibody for capture and the PSA-1 aptamer for detection. Two antibody immobilization strategies were compared: protein A-based and boronic ester-based, with the latter reducing nonspecific interactions and improving performance. The optimized platform achieved a detection limit of 6.4 ng/mL in human serum, demonstrated high selectivity against other glycoproteins, and showed potential for generalization to other sialylated biomarkers.