Scanning electrochemical microscopy with enzyme immunoassay of the cancer-related antigen CA15-3

Scanning electrochemical microscopy (SECM) with enzyme immunoassay was applied to detect the cancer related antigen CA15-3 (Ag). In this method, CA15-3 was concentrated and immobilized on a plane substrate via a sandwich method employing two corresponding antibody (Ab captured on a streptavidin-coated substrate and Ab * labeled with horseradish peroxidase (HRP)). In the presence of hydroquinone (H 2Q) and H 2O 2, HRP on the complex of CA15-3 with Ab and Ab *, Ab–Ag–Ab *, converted H 2Q to the electroactive product benzoquinone (BQ) through the HRP-catalyzed reaction. The reduction current of BQ generated by the HRP-catalyzed reaction corresponding to the amount of CA15-3 was monitored and imaged by SECM. With a view of improving the sensitivity of SECM-enzyme immunoassay to meet our objective, Ab–Ag–Ab * was concentrated on the substrate via a microcell. The detection limit of this method was 2.5 U/mL for CA15-3.