Carbon nanospheres-promoted electrochemical immunoassay coupled with hollow platinum nanolabels for sensitivity enhancement

Two nanostructures including carbon nanospheres-graphene hybrid nanosheets (CNS-GNS) and hollow platinum nanospheres (HPtNS) were first synthesized by using direct electrolytic reduction and wet chemistry methods, respectively. Thereafter, a specific sandwich-type electrochemical immunoassay was designed for determination of carcinoembryonic antigen (CEA) by using HPtNS-labeled horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA) as molecular tags and anti-CEA-assembled CNS-GPS as sensing probes. Compared with pure graphene nanosheets, the presence of carbon nanospheres on the graphene increased the surface coverage of the substrate, and enhanced the immobilized amount of primary antibodies. Several labeling protocols, such as HRP-anti-CEA, solid platinum nanoparticle-labeled HRP-anti-CEA, and hollow platinum nanospheres-labeled HRP-anti-CEA, were investigated for determination of CEA and improved analytical features were obtained with hollow platinum nanosphere labeling. With the HPtNS labeling method, the effects of incubation time and pH on the current responses of the immunosensors were also studied. The strong attachment of biomolecules to the CNS-GPS and HPtNS resulted in a good repeatability and intermediate precision down to 10.2%. The dynamic concentration range spanned from 0.001 ng mL(-1) to 100 ng mL(-1) CEA with a detection limit of 1.0 pg mL(-1) at the 3S(blank) level. No significant differences at the 0.05 significance level were encountered in the analysis of 10 clinical serum samples between the developed immunoassay and the commercially available electrochemiluminescent method for determination of CEA. (C) 2012 Elsevier B.V. All rights reserved.