Fig. 1 Illustration of activation mechanism of fluorescence signal when F@H presenting in the HClO

Fig. 2 Characterization of the prepared HMPB and F@H (a) Typical TEM image, (b) XRD pattern, and (c) pore-size distribution curve of HMPB with inset showing N2 adsorption-desorption isotherm; (d) UV-Vis spectra of FITC, HMPB and F@H; (e) Fluorescence spectra of free FITC and F@H with inset showing corresponding fluorescence intensity ratio at 520 nm; (f) Fluorescence life of FITC and F@H

Fig. S1 Dynamic light scattering (DLS) result of HMPB with insets showing digital photographs of HMPB suspension standing still for 0 and 12 h.

Fig. S2 Standard curves (a) and the corresponding calibration curve (b) of FITC, UV-Vis spectrum of F@H supernatent (c) ppm: μg/mL

Fig. 3 In vitro detection of HClO and mechanism (a, b) Fluorescence (FL) spectra (a) and the corresponding calibration curve (b) of F@H (50 μg/mL) with the addition of NaClO (0-50 μmol/L) in Tris-HCl (10 mmol/L, pH 5.5). λex=488 nm, λem=520 nm; (c) Absorbance of F@H varied with time before and after addition of NaClO; (d) XPS profiles of F@H without/with addition of NaClO

Fig. S3 Time-dependent fluorescence intensity of F@H (50 μg/mL) upon the addition of 50 μmol/L NaClO in Tris-HCl buffer (10 mmol/L, pH=5.5). λex = 488 nm, λem = 520 nm.

Fig. 4 Fluorescence of F@H in the presence of other ROS (a) Fluorescence spectra (inset of (a)) and the corresponding fluorescence (FL) intensity (a) of F@H (50 μg/mL) with the addition of different interfering substances (500 μmol/L, 1-blank, 2-TBHP, 3-ROO, 4-NO, 5-H2O2, 6- · ·OH, 7-ONOO-, 8-ClO-) in Tris-HCl (10 mmol/L, pH 5.5) λex=488 nm, λem=520 nm; (b) Absorbance change of F@H with addition of different interfering substances (500 μmol/L) Colorful figures are available on website

Fig. S4 Cytotoxicity of F@H on 4T1 cells. Cells were incubated with 0-100 μmol/L F@H in DMEM medium containing 10% fetal bovine serum (FBS) for 24 h. ppm: μg/mL

Fig. 5 Detecting HClO in living cancer cells (a-d) Confocal fluorescence and (e-h) bright field images for detecting exogenous or endogenous HClO in 4T1 cells Blank: without any treatments; Control: 50 μg/mL of F@H and 0 μmol/L NaClO; NaClO: 50 μg/mL of F@H and 100 μmol/L NaClO; Elesclomol: 50 μg/mL of F@H and 50 μmol/L elesclomol. λex=488 nm, λem=520 nm; (i) Statistical analyses of the confocal images