Electrochemical immunoassay for the tumor marker CD25 by coupling magnetic sphere-based enrichment and DNA based signal amplification

Interleukin-2 receptor alpha chain (also called CD25) is a tumor biomarker that is frequently expressed on the surface of hematological tumor cells. The authors describe an electrochemical immunoassay for CD25 that involves (a) enrichment of CD25 from samples by using magnetic nanospheres, and (b) utilization of DNA modulated current as the detection signal. Primary anti-CD25 antibody was immobilized onto F3O4 magnetic nanospheres to capture CD25 from samples. A polycytosine DNA sequence (dC20) was conjugated to the secondary antibody through glutaric dialdehyde via the amino groups on both antibody and the end of the DNA sequence. This leads to the formation of a sandwich structure on the magnetic spheres. dC20 is then reacted with molybdate to form redox molybdophosphate and generate electrochemical current (best measured at 0.2 V vs. Ag/AgCl) that is proportional to the concentration of CD25. The method is sensitive, selective, and has a wide linear response that extends from 1 pg.mL−1 to 1 ng.mL−1. The immunoassay was applied in a recovery test for CD25 in spiked serum samples.