It is well known that breast cancer can be caused by mutations in the BRCA1, BRCA2, and p53 genes as one of the well-documented cancers. Breast cancer, however, is usually symptom-free in its early stages and causes many difficulties in diagnosis. In addition, breast cancer patients around 20% is triple-negative breast cancer (TNBC). Therefore, diagnosing and tracking TNBC is very important. Human small-breast epithelial mucin (hSBEM), also known as mucin-like protein 1 (MUCL1), is a promising biological marker for diagnosis of TNBC. Herein, we show a novel method for hSBEM detection by integrating target-responsive aptamer modified PtNPs and magnetic graphene oxide (mGO) with TMB/H2O2 reaction for colorimetric read out. Upon target existence, the aptamer modified PtNPs are unbound from mGO so that it can participate in the reduction of H2O2 with TMB　to catalyze the change of solution color from blue to yellow (450 nm). The concentrations of the target can be monitored by naked eye and quantified by UV-Vis spectrometer. This colorimetric aptasensor has simplicity, ultra-sensitivity (0.184 fM), and high selectivity. Thus, it has a great potential to be a general detection tool for breast cancer