A class of novel redox-active hybrid nanostructures comprising of metal platinum and ordered mesoporous carbon (Pt-MSC) was designed as molecular tags for sensitive electrochemical immunoassay (alpha-fetoprotein, AFP, as a model analyte) on the cyclodextrin-functionalized graphene sensing platform. To construct such a molecular tag, a layer of positively charged thionine was initially adsorbed onto the MSC through negatively charged carboxyl groups, and [PtCl6](2-) ions were then conjugated onto the thionine/MSCs, followed by in situ reducing to metal platinum. Finally, horseradish peroxidase-labeled anti-AFP (HRP-anti-AFP) was conjugated onto the metal platinum surface. A sandwich-type immunoassay format was employed for determination of AFP by using the labeled HRP toward the reduction of H2O2 with the aid of thionine in pH 6.5 acetic acid-buffered solution. Under optimal conditions, the developed immunoassay displayed a wide linear range from 2.0 pg/mL to 10.0 ng/mL toward AFP standards with a low detection limit (LOD) of 1.5 pg/mL at 3 sigma. The precision, selectivity and stability were acceptable. Clinical serum specimens were assayed with the method, and the results were received in good accordance with those obtained from the referenced electrochemiluminescent immunoassay method. (C) 2012 Elsevier Ltd. All rights reserved.