Electrochemical immuno-bioanalysis for carcinoma antigen 125 based on thionine and gold nanoparticles-modified carbon paste interface

A novel electrochemical immunosensor for the determination of carcinoma antigen 125 (CA125) was developed by means of immobilizing CA125 antibody (anti-CA125) on gold nanoparticles (Au) and thionine (Thi)-modified carbon paste interface. To avoid the leak of hydrophilic gold nanoparticles and thionine from carbon paste interface, the Au-Thi-modified carbon paste electrodes (CPEs) were first treated in the mixture solution containing 10% HNO₃ and 2.5% K₂Cr₂O₇ for 1.5 min at +1.5 V to make the carbon surface with -COOH groups, which can react with -NH₂ groups on the thionine molecule, in the meantime, gold nanoparticles were absorbed on the thionine surface. Subsequently, CA125 antibodies were assembled onto the surface of gold nanoparticles. The fabrication process of the immunosensor was characterized by fourier transform infrared spectroscopy (FTIR) and UV-vis absorption spectroscopy. The performance and factors influencing the performance of the immunosensor were studied in detail. A direct electrochemical immunoassay format was employed to detect CA125 antigen based on the current change before and after the antigen-antibody reaction. The current change was proportional to CA125 concentration ranging from 10 to 30 U/ml with a detection limit of 1.8 U/ml (at 3δ). The immunosensors were used to analyze CA125 in human serum specimens. Analytical results of clinical samples show that the developed immunoassay has a promising alternative approach for detecting CA125 in the clinical diagnosis.