Facile and feasible conductometric immunoanalytical assay for alpha-fetoprotein using platinum-functionalized graphitic carbon nitride nanosheets

A simple and feasible conductometric immunoanalytical method was developed for the sensitive detection of a liver cancer biomarker (alpha-fetoprotein, AFP) on an interdigitated comb-like transducer, using platinum (Pt)-functionalized graphitic carbon nitride (g-C3N4) nanosheets. To construct such an immunosensing platform, platinum nanoparticles were initially loaded on the g-C3N4 nanosheets by the aid of a ethylene glycol reduction method. Thereafter, the as-prepared Pt-g-C3N4 nanohybrids were used as the affinity support for the immobilization of anti-AFP antibodies on the interdigitated electrode. Upon addition of AFP, the analyte reacted with the immobilized antibody to form the antigen-antibody immunocomplex, which was coated on the surface of the modified electrode, thereby partly decreasing the electrocatalytic efficiency of Pt-g-C3N4 towards the reduction of hydrogen peroxide (H2O2) in the presence of iodine ions (I-). The variation in the local conductivity by iodine ions could be detected by using an external conductometer on the basis of the Pt-g-C3N4 electrocatalytic reaction in 10 mM phosphate buffer (pH 6.5) containing 80 M H2O2, 50 mM KI and 0.1 M NaCl. Under optimum conditions, the immunosensor exhibited good conductometric responses for the detection of AFP within the dynamic linear range of 0.1-100 ng mL(-1) at a detection limit of 0.097 ng mL(-1). The strong attachment of anti-AFP antibodies to the Pt-g-C3N4 brought good repeatability and intermediate precision down to +/- 12.7%. Importantly, no significant differences at the 0.05 significance level were encountered for the analysis of 12 human serum samples between the developed immunoassay and human AFP ELISA kit for AFP determination.