An "on-off" electrochemical immunosensor for the detection of the glycan antigen CA125 by amplification signals using electropositive COFs.

Cancer Antigen 125 (CA125), is a high molecular weight mucinous glycoprotein found on the surface of ovarian cancer cells. Generally, 90 % of women may appear a high concentration of CA125 when they got the cancer; thus, CA125 can act as a marker for ovarian cancer diagnosis and therapeutic evaluation. COFs have been widely used for disease detection due to their structural stability, high loading capacity and biocompatibility. However, the limited variety of electroactive COFs used as signal probes, fewer enriched signaling molecules, weaker electrical signals generated, and higher oxidation or reduction potentials of electroactive substances, a series of side reactions are easily triggered causing serious interference. To solve the above problems, [Fe(CN)6]^3/4- as a signal probe and COFs for signal amplification were selected to creating a highly sensitive electrochemical immunosensor for glycan antigen CA125. Firstly, two-dimensional (2D) EP-TD-COF with ultra-high specific surface area was modified on bare GCE, which could covalently bound numerous Ab1 molecules due to the epoxy-rich functional groups. Then, the electropositive AuNPs@2DCOFBTT-DGMH was prepared by the in situ growth of AuNPs, proved an effective platform for loading Ab2 molecules via Au-S bonds. Based on the positively charged AuNPs@COFBTT-DGMH/Ab2 and negatively charged [Fe(CN)6]^3/4- of electrostatic interactions, which could significantly enchaned signal for quantitative and sensitive detection of CA125. The constructed immunosensor exhibits excellent stability performance and high sensitivity, enabling ultrasensitive detection of trace glycan antigens. This study provided a new idea for the use of non-electroactive substances for the construction of electrochemical immunosensors and provided an effective signal amplification strategy.