Paper-based colorimetric immunosensor for visual detection of carcinoembryonic antigen based on the high peroxidase-like catalytic performance of ZnFe_2O_4-multiwalled carbon nanotubes

摘要

A new paper-based colorimetric immunosensor for the detection of carcinoembryonic antigen (CEA) was developed based on the intrinsic peroxidase activity of ZnFe_2O_4-multiwalled carbon nanotubes (ZnFe_2O_4@MWNTs). The immunosensor platform was prepared by depositing chitosan and porous gold onto filter paper and entrapping the primary antibodies (Ab_1) onto the layers. Secondary antibodies (Ab_2) were assembled on the surface of the functionalized ZnFe_2O_4@MWNTs. The immunosensor response was quantified as a color change resulting from ZnFe_2O_4@MWNTs catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of H_2O_2. The catalytic performance of ZnFe_2O_4@MWNTs was higher than ZnFe_2O_4 due to the high electrical conductance of MWNTs, moreover, the electron communications between ZnFe_2O_4@MWNTs and substrates are electrically "wired". Detection was achieved by measuring the color change when the concentrations of CEA were different. The color change can be quantified with the naked eye but a digitalized picture can also be used to provide more sensitive comparison to a calibrated color scheme. This method was simple for CEA detection with a linear range from 0.005 to 30 ng mL~(-1) and a detection limit of 2.6 pg mL~(-1). Such an equipment-free immunoassay has great potential in resource-limited environments.