Displacement-type amperometric immunosensing platform for sensitive determination of tumour markers

• The displacement-type of glucose-phenylboronic acid-Alizarin Red S was successfully utilized in amperometric immunosensors.
• Alizarin Red S could drop out form the surface of electrode, which led to the huge change of SWV current response.
• The sensitivity of electrochemical immunosensor was enhanced by this displacement assay.

The sensitive determination of carcino embryonie antigen (CEA)-a set of highly related glycoproteins involved in cell adhesion-is beneficial to the early diagnosis of colorectal cancer. In this study, a novel displacement-type amperometric immunosensing platform, based on the fact that glucose and Alizarin Red S (ARS) compete for phenylboronic acid bindng sites, was projected for sensitive detection of tumour marker (CEA, used as a model) on a PAMAM dendrimer-encapsulated nanogold (PAMAM-Au)-functionlized sensing interface. Firstly, 4−mercaptophenylboronic acid (S-PBA) was assembled onto the PAMAM-Au via the S-Au interaction, and then ARS was immobilized by S-PBA binding of cis-diol moieties, which was dropped on the surface of glassy carbon electrode as sensing platform to combine antibody. Meanwhile, amylase modified gold nanoparticles were employed as labels. Accompanying the sandwich immunoassay, the carried amylase could hydrolyze amylose into glucose, and the displacement-type format was triggered due to the stronger adhesion between glucose and PBA, which resulted in the change of electrochemical signals due to the decrease of ARS (as an electron mediator). Under optimal conditions, the SWV signals were related to the concentration of CEA, indicating a certain proportional relation in a range of 0.01~50 ng mL−1 with a detection limit (LOD) of 0.003 ng mL−1. Intra- and inter-assay coefficients of variation were below 10%, respectively. In addition, the methodology showed good accordance with a commercialized enzyme-linked immunosorbent assay (ELISA) method.