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 μM 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.