Highly sensitive immunosensing of prostate-specific antigen based on ionic liquid-carbon nanotubes modified electrode: application as cancer biomarker for prostate biopsies.

A novel and highly sensitive electrochemical immunosensor was developed for detection of prostate specific antigen (PSA) based on immobilization of PSA-antibody (anti-PSA) onto robust nano composite containing multiwalled carbon nanotubes (MWCNTs) and ionic liquid (IL)1-buthyl-methylpyrolydinium bis (trifluromethyl sulfonyl) imide [C₄mpyr][NTf₂]. Thionine was used as redox system for electrochemical probe. The adsorbed thionine displayed a surface-controlled electrode process with electron transfer rate constant of 6.5 s⁻¹ and surface coverage of 3.1×10⁻¹¹ mol cm⁻². The PSA antibody (anti-PSA) was immobilized or entrapped in the nanocomposite and used in a sandwich type complex immunoassay with anti-PSA labeled with horseradish peroxidase (HRP) as secondary antibody and H₂O₂ as the substrate. Under optimal conditions, the DPV peak current of the immunosensor increased linearly with increasing PSA concentration in two concentration ranges, 0.2-1.0 and 1-40 ng ml⁻¹ with detection limit 20 pg ml⁻¹. The intra-assay and inter-assay coefficients of variation (CVs) for five replicate determinations were 2% and 1.35% at 5 ng ml⁻¹ PSA. The immunosensor has been used for PSA detection in serum samples and the accuracy of the method was demonstrated by comparison to the standard ELISA assay. Furthermore, the immunosensor can be used for detection of PSA in prostate tissue samples. The simple one-step fabrication method, high sensitivity, good reproducibility and repeatability as well as acceptable accuracy for PSA detection in human serum samples are the main advantages of this immunosensor. Furthermore, the results indicate that differences in PSA concentration can be detected with the proposed immunosensor for cancer tissue samples which holds great promise in clinical screening of cancer biomarkers.