Cyclin A2 is a prognostic indicator in early-stage cancer. However, since most of peptide-protein bindings do not produce an easily measurable output signal, this severely hinders homogeneous detection of protein using peptide as detection probe. Cyclin A2 can be detected as low as 0.6 μM using a well-known p21(WAF-1) consensus senquence for a specific cyclin A2 binding motif, which is incorporated into a Tb3+ chelating macrocycle by chemical modification at the N-terminus of CMB. Herein, a simple, ultra-sensitive, and selective signal-on fluorescence assay is developed for detection of a prognostic indicator in early-stage cancer, cyclin A2. Graphene oxide (GO) is even superior to SWNTs for cyclin A2 detection. The direct detection limit using graphene oxide is 0.5 nM, 10-fold better than using SWNTs, and 1200-fold better than the latest reported value of 0.6 μM using the Tb3+ chelating macrocycle modified p21(WAF-1) peptide.