The FAM-ssDNA probe (10 μL of 20 μM solution) was mixed with 50 μL of NS@DA in HEPES buffer (10 mM, pH 7.4) and 2 mM CaCl2 (total volume 1 mL) for 30 min at room temperature. The obtained probe -NS@DA complex solution (180 μL) was mixed with 20 μL of cDNA or miR-21 at different concentrations and shaken for 30 min at room temperature. The fluorescence intensity of the samples was measured directly with the fluorometer. Other fluorescence assays are described in the supporting information.