A novel label-free microfluidic paper-based immunosensor for highly sensitive electrochemical detection of carcinoembryonic antigen

• A novel paper immunosensor which was made up of a sample tab and an auxiliary tab was fabricated. The microfluidic channel was built through wax printing while the electrodes were through screen-printing.
• A new label-free electrochemical method was used during measurement, which avoids labeling either antigens or antibodies, to make the detection of CEA faster, simpler and cheaper. Combining the method with paper- based device, a fully functional μPAD was made, which truly realized the target of point-of-care testing.
• NH2-G/Thi/AuNPs nanocomposites was successfully synthesized and used to modify the working electrode. After modification, the working electrode possessed high bioactivity and could be used to detect CEA.

In this work, a highly sensitive label-free paper-based electrochemical immunosensor employing screen-printed working electrode (SPWE) for detection of carcinoembryonic antigen (CEA) was fabricated. In order to raise the detection sensitivity and immobilize anti-CEA, amino functional graphene (NH2-G)/thionine (Thi)/gold nanoparticles (AuNPs) nanocomposites were synthesized and coated on SPWE. The principle of the immunosensor determination was based on the fact that the decreased response currents of Thi were proportional to the concentrations of corresponding antigens due to the formation of antibody–antigen immunocomplex. Experimental results revealed that the immunoassay enabled the determination of standard CEA solutions with linear working ranges of 50 pg mL−1 to 500 ng mL−1, the limit of detections for CEA is 10 pg mL−1 (S/N=3) and its corresponding correlation coefficients were 0.996. Furthermore, the proposed immunosensor could be used for the determination of clinical serum samples. A large number of clinical serum samples were detected and the relative errors between measured values and reference concentrations were calculated. Results showed that this novel paper-based electrochemical immunosensor could provide a new platform for low cost, sensitive, specific, and point-of-care diagnosis in cancer detection.