Ultrasensitive sandwich-type electrochemical immunosensor based on a novel signal amplification strategy using highly loaded toluidine blue/gold nanoparticles decorated KIT-6/carboxymethyl chitosan/ionic liquids as signal labels

An ultrasensitive sandwich-type electrochemical immunosensor for the quantitative detection of carcinoembryonic antigen (CEA) was designed based on a novel signal amplification strategy. Gold nanoparticles decorated mesoporous silica KIT-6 (Au@KIT-6) with large specific surface area and good adsorption properties was used as a label matrix to immobilize both the secondary antibodies (Ab2) and the electron transfer mediator toluidine blue (TB). Ab2 was loaded on KIT-6 due to the presence of gold nanoparticles (Au NPs) and TB was loaded on KIT-6 by physical adsorption. Ionic liquids (ILs) doped carboxymethyl chitosan (CMC) was used to prevent the leak of TB and facilitate the electron transfer. For the immobilization of primary antibodies (Ab1), gold nanoparticles decorated 3-aminopropyltriethoxysilane functionalized graphene sheets (Au@APTES-GS) were used as transducing materials to modify glassy carbon electrodes (GCE). High sensitivity was achieved for the designed immunosensor based on this novel signal amplification strategy. Under optimal conditions, the immunosensor exhibited an extremely low detection limit of 3.3  fg/mL and wide liner range from 10−5  ng/mL to  102 ng/mL for CEA. Moreover, it exhibited good selectivity, acceptable reproducibility and stability, indicating potential application promising in clinical monitoring of tumor biomarkers.