An immunosensor based on an electrochemical-chemical-chemical advanced redox cycle amplification strategy for the ultrasensitive determination of CEA

Highlights: • Redox cycle amplification (RCA) can realize the regeneration of the FcA, thereby amplifying the electrical signal. • CeO₂/Au NPs@SiO₂ as a signal label has good biocompatibility and provides more active sites for RCA reaction. • The detection range of the sensor is 0.01 pg/mL-80 ng/mL, the detection limit is as low as 0.0037 pg/mL. Signal amplification is very important for electrochemical immunoassays. We report an enzyme-free electrochemical immunosensor based on an electrochemical-chemical-chemical (ECC) redox cycle advanced (RCA) signal amplification strategy for the ultrasensitive detection of Carcinoembryonic antigen (CEA). In this scheme, CeO₂/Au NPs@SiO₂ is connected with ferrocene as the redox indicator, and the detection buffer is composed of the reducing agent hydroquinone (HQ) and tris(2-carboxyethyl) phosphine (TCEP). First, ferrocenecarboxylic acid (FcA) is oxidized to FcA⁺ on the electrode. Then, HQ reduces FcA⁺ to FcA to trigger the cyclic reaction of the inner ring. Second, the oxidation product of HQ is catalyzed by TCEP. The product is reduced to HQ again to complete the cyclic reaction of the outer ring, so the entire cyclic reaction forms a closed loop. The system realizes the high-efficiency regeneration of the electroactive material Fc, thereby ensuring the full amplification of the electrical signal. The results show that the immunosensor exhibits good analytical performance, the detection range is 0.01 pg/mL-80 ng/mL, the detection limit is 0.0037 pg/mL, and the immunosensor has excellent selectivity and stability and performs well in the detection of actual samples. This strategy provides a new method for the early screening of CEA.