A novel sandwich electrochemical immunosensor utilizing customized template and phosphotungstate catalytic amplification for CD44 detection

A sandwich-type electrochemical immunosensor was proposed for the ultra-sensitive detection of CD44, a potential biomarker for breast cancer. In this design, a customized template-based ionic liquid (1-butyl-2,3-dimethylimidazolium tetrafluoroborate) carbon paste electrode (CILE) served as the sensing platform, and thionine/Au nanoparticles/covalent-organic frameworks (THI/Au/COF) were used as the signal label. Moreover, an enzyme-free signal amplification strategy was introduced by involving H₂O₂ and phosphotungstate (PW₁₂) with peroxidase-like activity. Under optimized conditions, the linear range is as wide as six orders of magnitude, and the detection limit is as low as 0.71 pg mL⁻¹ (estimated based on S/N = 3). Average recoveries range from 98.16 %-100.1 %, with a relative standard deviation (RSD) of 1.42–8.27 % in mouse serum, and from 98.44 %-99.06 %, with an RSD of 1.14–4.84 % (n = 3) in artificial saliva. Furthermore, the immunosensor exhibits excellent specificity toward CD44, good stability, and low cost, indicating great potential for application in clinical trials.