Highly sensitive impedimetric immunosensor for determination of interleukin 6 as a cancer biomarker by using conjugated polymer containing epoxy side groups modified disposable ITO electrode

A novel impedimetric immunosensor based on a conjugated polypyrrole polymer containing epoxy active side groups (PPCE) modified indium tin oxide (ITO) electrode was developed for detection of interleukin 6 (IL 6), a prostate cancer biomarker. IL 6 receptor was used as a biorecognition molecule and successfully immobilized by covalent linkage on the modified ITO electrode. Pyrrole monomer containing epoxy active side group was electropolymerized on the disposable ITO electrode for the first time and used as an immobilization matrix for IL 6 receptor. The designed biosensor fabrication stages were analyzed by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. For the quantification of IL 6 biomarker, EIS technique was utilized. In addition, the specific immuno-interaction between IL 6 receptor and IL 6 antigen was followed by single frequency impedance (SFI) technique. The resulting biosensor exhibited a linear calibration curve over the 0.02-16 pg/mL IL 6 concentration range, a limit of detection (LOD) of 6.0 fg/mL and a good selectivity against other interference biomarkers. Additionally, an excellent reproducibility, a long storage stability and an acceptable repeatability were found. The proposed impedimetric immunosensor was applied successfully to quantify for the IL 6 biomarker in human serum and it displayed a remarkable response in the real sample analysis with serum samples. In comparison with the commercial ELISA kit, the immunosensor provided a lower LOD and a lower analysis cost. In conclusion, the proposed impedimetric immunosensor could be clinically useful in the early diagnosis of the prostate cancer by detection of the serum samples after only simple dilution with phosphate buffer.