Fig. 2
The Fenton reaction activity, drug loading, and T2-MRI performance. a, UV-vis spectra of the MSPION3 solutions at pH 5.0 with TMB and/or H2O2 to testify the •OH generation. b, c, UV-vis spectra of the MSPION3 solutions with TMB and H2O2 to measure the •OH generation at different pH values (pH 5.0, 6.5, or 7.4) for 70 h (b), or at pH 5.0 for different times (0, 3.0, 8.0, 25, 50, or 70 h) (c). d, Schematic illustration of the mechanism of the pH-activated Fe release from MSPION3 and the TMB colorimetric method for the measurement of •OH generation. e, ESR spectra measured by using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as •OH trapping agent, indicating Fenton reaction induced •OH generation at pH 5.0, 6.5, or 7.4 for MSPION3. f, Fe ions release profiles (n = 3) in PBS solutions with pH 5.0, 6.5, or 7.4 from MSPION3. g, Representative HPLC chromatograms of the mixture of SFN and BQR, measured at 265 nm–254 nm. h, i, N2 adsorption-desorption isotherms (h), and pore-size distributions (i) of MSPION3 and SFN/BQR1@MSPION3 measured by the BET method. j, T2-weighted MR images of SFN/BQR1@MSPION3 solutions with various CFe (0 ∼200 µM) incubated at different pH values (5.0, 6.5, or 7.4) for 24 h observed by a 7.0 T MRI system. k, l, T2 relaxation rate (1/T2) plotted as a function of CFe for SFN/BQR1@MSPION3 in magnetic field of 7.0 T (k) and 3.0T (l). For T2 relaxation rates in magnetic field 7.0 T: TR = 6000 ms, TE = 120 ms. For T2 relaxation rates in magnetic field 3.0 T: TR = 5000 ms, TE = 80 ms