Characterization of MS NPs

The morphology of MS NPs was characterized by TEM (Hitachi HT7700) with an acceleration voltage of 200 kV. The size distribution of MS NPs was measured by Zetasizer (Malvern Instruments). FTIR, fluorescence spectrophotometer and UV-visible spectrophotometer were used to confirm the successful self-assembly of Met and SN38. Sakaguchi reaction was conducted as described below. Different samples (Met, SN38, Met/SN38 and MS NPs) were mixed with the mixture of DDW and 1% α-naphthol ethanol solution, respectively, then hypobromite solutions were added with shaking. After 1 min, 10% NaOH was inhaled to the above solution, and color changes were observed. A dark-box UV analyzer was used to visualize the fluorescence of SN38-containing samples. The drug loading ratio of Met and SN38 were measured using HPLC and HPLC-MS, respectively. Standard curves of Met and SN38 have been showed in Figure S5-S6.