Colorimetric detection: The RCA was extended to 20 h to synthesize the HRPloaded DNA flowers. The DNA flowers were collected by magnetic separation, then washed with 100 μL water to remove excess HRP. Finally, the DNA flower was re-suspended in 30 μL water. For colorimetric detection, the DNA flower (10 μL) was mixed with 80 μL acetate buffer (pH 5, 0.1 M), then added to 5 μL 35% H2O2 (w/w aqueous solution) and 5 μL TMB (0.025 mM). The mixture was put on a rocking table at room temperature for 10 min. After adding 50 μL of stop solution (0.2 M H2SO4) into the mixture, the particles were removed by magnetic separation. The absorbance of the supernatant at 450 nm was measured using a UV-vis spectrophotometer. All data were obtained from triplicate experiments.