A pH-Dependent Electrochemical Immunosensor Based on Integrated Macroporous Carbon Electrode for Assay of Carcinoembryonic Antigen

A novel pH-dependent immunosensor to detect tumor biomarker, carcinoembryonic antigen (CEA), was developed by using the pH-dependent AuNPs-Ab 2 -glucose oxidase-Concanavalin A as tracing tag and the albumin bovine V-Ab 1 /chitosan-AuNPs/three-dimensional kenaf stem-derived macroporous carbon (3D-KSCs) integrated electrode as signal collector based on a sandwich-type assay mode. The integrated 3D-KSCs electrode provided a large specific surface area to load a large number of Ab 1 effectively and the tracing tag with a lots of pH-dependent surface negative charges repulsed the negatively charged probe of Fe(CN) 6 3− in a pH 9.0 solution. Accordingly, after a sandwich immunoreaction, the quantitative capture of tracing tag on the signal collector greatly hindered the electron transfer of Fe(CN) 6 3−/4− due to the electrostatic repulsion, which improved the sensitivity and selectivity of the immunosensors significantly. It was verified by electrochemical impedance spectroscopy. The resistance to charge transfer of Fe(CN) 6 3−/4− changed proportionally toward CEA concentration from 4   pg   mL −1 to 50   ng   mL −1 with a low detection limit of 1.3   pg   mL −1 ( S / N   =   3) and a high sensitivity of 57.57   Ω   ng −1   mL. Based on human serum experiments, the sensing platform was proved to be suitable to assay CEA in a practical biosystem. This work not only gives a sensitive way to detect CEA but also provides a potential strategy for immunosensors based on 3D-KSC electrode and pH-dependent behavior.