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.