Ionic liquid functionalized graphene based immunosensor for sensitive detection of carbohydrate antigen 15-3 integrated with Cd(2+)-functionalized nanoporous TiO2 as labels.

A novel electrochemical immunosensor for sensitive detection of carbohydrate antigen 15-3 (CA15-3) based on dual signal amplification strategy of ionic liquid functionalized graphene and Cd(2+)-functionalized nanoporous TiO2 (f-TiO2-Cd(2+)) has been developed. Ionic liquid functionalized graphene was used to anchor primary CA15-3 antibody (Ab1). f-TiO2-Cd(2+) was employed to immobilize secondary cancer antigen 15-3 (CA15-3) antibody (Ab2) and the resulting nanocomposite (Ab2-f-TiO2-Cd(2+)) was used as trace tag for signal amplification. The fabricated immumosensor displayed a wide range of linear response (0.02-60 U/mL), ultra-low detection limit (0.008 U/mL), good reproducibility, selectivity and stability towards CA15-3. The good performance of the immunosensor can be attributed to (1) high surface-to-volume ratio of graphene which allows high-level immobilization of Ab1, (2) excellent biocompatibility and electron transfer rate originating from ionic liquid functionalized graphene, (3) a highly specific surface area of nanoporous TiO2 that facilitates the adsorption of high amount of Cd(2+) for signal amplification.