Lectin-Mediated Labeling of Alkaline Phosphatase for Enzymatic Silver Deposition-Based Electrochemical Detection of Glycoprotein Tumor Markers

The screening of glycoprotein markers has become an integral part of the in vitro diagnosis of malignant tumors. Herein, an electrochemical method based on alkaline phosphatase (ALP)-mediated enzymatic silver deposition is reported for the highly sensitive detection of glycoprotein tumor markers, in which ALP enzymes are decorated to the glycan moieties of targets via the lectin-carbohydrate interactions. As glycoproteins are conjugated with multiple glycan chains, lectin-mediated labeling can result in the decoration of each target with multiple ALP enzymes. Moreover, the enzymatic hydrolysis of ascorbic acid 2-phosphate into ascorbic acid can result in the deposition of a high density of silver particles, which can then be sensitively assayed via the robust Ag/AgCl solid-state voltammetric process. As a result, the enzymatic silver deposition-based electrochemical method exhibits high sensitivity. Using the aptamer-based electrochemical detection of the breast cancer-associated glycoprotein CA15-3 as a proof of concept, a detection limit of 0.32 mU/mL has been demonstrated. Results show that the synergism of the aptamer-based capture and the glycoform-specific discrimination capability of the lectin-carbohydrate interactions can endow this method with high selectivity, and its practical use in the assay of CA15-3 levels in serum samples has been illustrated. With benefits from the high efficiency, mild reaction conditions, and user-friendly operation, the lectin-mediated labeling of ALP enzymes for enzymatic silver deposition is highly applicable to the electrochemical detection of low-abundance glycoprotein tumor markers.