Breast cancer has become one of the most common cancers worldwide, but the effectiveness of the conventional drug chemotherapy is still restricted. Therefore, precision imaging and targeted therapy against breast cancer cells have become a hot research topic. In this study, a dual-responsive nanocarrier system based on multi-functionalized gold nanoparticles (GNP) was developed for simultaneous diagnosis and treatment of breast cancer cells. The nanoparticles were modified with an aptamer which specifically recognizes MUC-1 protein on the surface of the breast cancer cell MCF-7, achieving precise cellular targeting. Upon entry into the cell, the decrease of pH in the intracellular environment causes the detachment of the i-motif sequence from GNP. Cy5 labeled at the end of i-motif, which is previously quenched by GNP thus restores its fluorescence, achieving the imaging of the cancer cells. Additionally, chemotherapeutic drug gemcitabine (GEM) is covalently attached to GNP through a rationally designed oligopeptide linker CGFLG. Cathepsin B, which is overexpressed in MCF-7 cells, can precisely cleave the CGFLG linker and release GEM to the cells, thereby achieving the targeted drug delivery and treatment. When 4 nM nanocarrier was applied, the inhibition rate of MCF-7 cells was approximately 70 %. This dual-responsive nanocarrier system integrates the targeting, imaging and therapeutic functions in a simple GNP platform. The high targeting efficiency of the nanocarrier reduces the non-specific binding and toxic effects on normal cells, while enhances the toxicity toward cancer cells. Therefore, it may have great prospects in medical applications.