Detection of Tumor Marker Using ZnO@Reduced Graphene Oxide Decorated with Alkaline Phosphatase-Labeled Magnetic Beads

The magnetic-bead-based electrochemical enzyme-linked immunoassay (MB-eElisa) represents an attractive approach to develop cost-effective systems that are suitable for sensing complex biological samples. Its sensitivity essentially depends on the transduction efficiency of enzyme catalytic reactions into electrochemical responses. Here, an ultrahigh signal-to-noise alkaline phosphatase (ALP)-based MB-eElisa system is developed with a renewable zinc oxide-reduced graphene oxide composite modified carbon paste electrode (ZnO@rGO/CPE). This biosensing system employs one antibody decorated MB (MB-Ab1) to capture a model tumor marker—carcinoembryonic antigen (CEA)—from samples, while other antibody coated gold nanoparticles-ALP bioconjugates (Ab2-AuNPs-ALP) convert 1-naphthyl phosphate (1-NPP) into electroactive 1-naphthol (1-NP). Benefitting from the unique electrochemical properties of a ZnO@rGO/CPE, including nearly zero background and significantly enhanced responses toward the hydrolyzed 1-NP in the presence of trace surfactants, the MB-eElisa system detects selectively CEA in a calibration range of 0.01–6.0 ng mL–1 and with a detection limit of 4.0 pg mL–1 (S/N = 3). Such a system was further applied to the detection of CEA in serum samples of cancer patients. The combination of MB-based ALP-linked immunoassay with a ZnO@rGO/CPE thus establishes a reusable and inexpensive electrochemical sensing platform for the rapid and sensitive detection of ultratrace biomarkers in complex biological samples.