Redox-labelled detection probe enabled immunoassay for simultaneous detection of multiple cancer biomarkers

Some of the cancer biomarkers often lack specificity and sensitivity; thus, simultaneous detection of multiple biomarkers can make the diagnosis more accurate. Also, simple sensing system without utilization of extra reagents like mediator or substrate during detection event is desirable for point-of-care testing. To address this, mediator and substrate-free amperometric biosensor for simultaneous detection of cancer biomarkers carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) have been demonstrated by designing two different redox-labelled detection probes. Colloidal nanoparticles of polyaniline-pectin conjugated with AFP antibody along with ferrocene and silver nanoparticles conjugated with CEA antibody along with anthraquinone were used as redox probes to bind with AFP and CEA during the detection event. Sensor constructed using carboxylic acid tethered polyaniline as immobilization matrix displayed 5 times wider linear range than conventional polyaniline for AFP and CEA detection by sandwich electrochemical assay. The detection limit was 30 pg mL^-1 for AFP and 80 pg mL^-1 for CEA. The biosensor displayed appropriate sensitivity, good specificity, and negligible cross-reactivity between the two targets. The proposed sensor was used to determine APF and CEA in human blood serum. The strategy demonstrated can be further extended for detection of panel of cancer biomarkers by designing appropriate redox probes.