br Results and discussion br Synthesis
2. Results and discussion
2.1. Synthesis and characterization of the nanoplatform
Fig. 1a shows a schematic summary of the detailed synthesis of the nanoplatform. Hollow MnSiO3 nanoparticles were synthesized based on well-dispersed Mesoporous silica nanoparticles (MSNs). Then, Fe3O4 nanoparticles were decorated on the surface of MnSiO3, followed by amination (MFN) and grafting PEG (MFNP) on the surface and subse-quently loading cisplatin (CDDP) into the nanoplatform ([email protected]). This well-engineered nanoplatform with pH-re-sponsive ability could be used for dual-mode MRI-guided combinatorial
As seen in the TEM images, the as-prepared MSN presented good dispersity and a uniform size (approximately 127 nm) (Fig. 2a,e). In addition, a hollow structure appeared after etching Mn2+ from MSN, suggesting that MnSiO3 was successfully prepared (Fig. 2b,f). Subse-quently, Fe3O4 nanoparticles with small sizes fabricated by coprecipi-tation were uniformly decorated on the surface of MnSiO3 to form hollow MF (Fig. 2c,g). The distance between two adjacent planes of the nanoparticle was measured to be 0.255 nm (Fig. 2d,h), corresponding to the (311) plane of Fe3O4 nanocrystals. The hydrodynamic size of MSN, MnSiO3, and MF was 289, 344, and 486 nm, which was larger than that of TEM observation (Fig. 1k-m). However, MFNP showed a relatively small size of 198 nm (Fig. S1), indicating that PEG chains could dramatically improve the solubility of particles. In addition, the hydrodynamic size of MFNP appeared to slightly increase with standing time increasing, indicating that MFNP had a good colloidal stability. The scanning TEM and Malonyl Coenzyme A mapping analyses of MF confirmed the uniform distribution of Fe, Si, O, and Mn (Fig. 2i and j), indicating that Fe3O4 nanoparticles were successfully decorated on MnSiO3.
X-Ray Diﬀraction (XRD) peaks of amorphous MnSiO3 and typical spinel-structure Fe3O4 are shown in Fig. 3a. In addition, MF presented overlapping MnSiO3 and Fe3O4 peaks, confirming the successful in-tegration of Fe3O4 and MnSiO3. The nitrogen adsorption-desorption isotherm curves indicated that compared with that of MnSiO3 (277 m2/ g), the specific surface area of MF (167 m2/g) significantly decreased, and the corresponding pore size decreased from 9 to 5 nm. These results suggested that Fe3O4 nanoparticles could eﬀectively obstruct the pore
Fig. 3. (a) XRD patterns, (b) N2 adsorption/desorption isotherms (inset: pore size distribution), (c) zeta potential, and (d) full XPS spectra of diﬀerent samples. (e) M-H curves at 300 K and 3 K and (f) ZFC/FC curves of MF. (g) FT-IR spectra of diﬀerent samples and (h) ESR spectra of diﬀerent samples mixed with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and H2O2 at diﬀerent conditions. (i) UV absorption spectra of MF at diﬀerent concentrations mixed with TMB and H2O2 under pH 5.5 conditions.
channels of MnSiO3 (Fig. 3b). In addition, in the isotherm curve, the typical hysteresis behavior was ascribed to the delay of nitrogen eva-poration from the inner hollow structure blocked by the surrounding mesopores. The zeta potential of MnSiO3 was +11.6 mV (Fig. 3c), but that of MF changed to −21.2 mV, which could be attributed to the decoration of negatively charged Fe3O4. In addition, the surface po-tential of MFNP was +7.9 mV, which was beneficial for the cell uptake and reducing the cell toxicity.
X-ray photoelectron spectroscopy (XPS) analysis of MnSiO3 con-firmed the presence of Mn, O, and Si (Fig. 3d). Compared with MnSiO3, MFNP exhibited the appearance of a new peak at 710.5 eV assigned to the Fe2p peak (Fig. S2), confirming the successful integration of MnSiO3 with Fe3O4. After the nanoplatform was loaded with CDDP, the new peak appearing at 72.7 eV could be assigned to the Pt4f peak, in-dicating the successful loading of CDDP. Field-dependent magnetiza-tion (M-H) curves and standard zero-field cooling (ZFC) and field cooling (FC) curves of MnSiO3 demonstrated typical paramagnetic be-havior (Fig. S3). Nevertheless, MF presented significantly saturated magnetization values (Fig. 3e, 18 emu/g at 300 K and 24 emu/g at 3 K), suggesting the existence of soft-ferromagnetism or super-paramagnetism. Moreover, the ZFC/FC curves further confirmed that MF possessed superparamagnetism according to the overlapping tem-perature (100 K), indicating that Fe3O4 and MnSiO3 were successfully assembled into one nanosystem (Fig. 3f). Subsequently, the composi-tion and modification of the nanoplatform were further characterized by fourier transform infrared (FT-IR) spectroscopy (Fig. 3g). Compared with MnSiO3, MF featured a new peak at 571 cm−1 assigned to the FeeO stretching vibration, demonstrating the presence of Fe3O4. In