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Background: Satisfactory prognosis of breast cancer (BC) is limited by difficulty in early diagnosis and insufficient treatment. The combination of molecular imaging and photothermal therapy (PTT) may provide a solution., Methods: Fe 3 O 4 -Au shell nanoparticles (NPs) were prepared by thermal decomposition, seeded growth and galvanic replacement and were comprehensively characterized. After conjugated to PEG, NPs were used as MRI and PTT agents in vitro and in vivo., Results: Fe 3 O 4 -Au shell NPs which had uniform Janus-like morphology were successfully synthesized. The Fe 3 O 4 had a size of 18 ± 2.2 nm, and the Au shell had an outer diameter of 25 ± 3.3 nm and an inner diameter of 20 ± 2.9 nm. The NPs showed superparamagnetism, a saturation magnetization of 36 emu/g, and an optical absorption plateau from 700 to 808 nm. The Fe 3 O 4 -Au shell NPs were determined to possess good biocompatibility. After PEG coating, the zeta potential of NPs was changed from -23.75 ± 1.37 mV to -13.93 ± 0.55 mV, and the FTIR showed the characteristic C-O stretching vibration at 1113 cm -1 . The NPs' MR imaging implied that the T 2 can be shortened by Fe 3 O 4 -Au shell NPs in a concentration-dependent manner, and the Fe 3 O 4 -Au shell NPs coated with PEG at the molar ratio of 160 (PEG: NPs) showed the highest transverse relaxivity ( r 2 ) of 216 mM -1 s -1 . After irradiation at 0.65 W/cm 2 for 5 min, all cells incubated with the Fe 3 O 4 -Au shell -PEG160 NPs (Fe: 30 ppm, Au: 70 ppm) died. After administrated intratumorally, Fe 3 O 4 -Au shell -PEG160 notably decreased the signal intensity of tumor in T 2 WI images. Under the same irradiation, the temperature of tumors injected with Fe 3 O 4 -Au shell -PEG160 quickly rose to 54.6°C, and the tumors shrank rapidly and were ablated in 6 days., Conclusion: Fe 3 O 4 -Au shell -PEG NPs show good r 2 and PTT performance and are promising synergistic theranostic agents of MRI and PTT for BC., Competing Interests: The authors report no conflicts of interest in this work., (© 2021 Kang et al.)

Background: Beyond magnetic resonance imaging (MRI), which has been widely used clinically, molecular MRI (mMRI) can further provide qualitative and quantitative information at the cellular and molecular levels. However, the diagnostic accuracy may not be satisfactory via single-contrast mMRI due to some interferences in vivo. T 1 /T 2 dual-contrast MRI using the same contrast agent (CA) could significantly improve the detection accuracy. Therefore, in this study, we fabricated poly(ethylene glycol) (PEG)-coated, manganese-doped iron oxide nanocomposites (Mn-IONPs@PEG) as T 1 /T 2 dual-contrast CA, and evaluated its feasibility of T 1 /T 2 dual-contrast MRI in vitro and in vivo., Methods: Mn-IONPs were prepared by the thermal decomposition of iron-eruciate and manganese-oleate complexes and were coated with 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy[polyethylene glycol]-2000) (DSPE-PEG 2000). The physicochemical properties and cytotoxicity of the Mn-IONPs were fully characterized, followed by MRI in vitro and in vivo., Results: Ultrasmall 3 nm-sized nanoparticles were successfully prepared and were identified using transmission electron microscopy (TEM), high-resolution TEM, and X-ray diffraction. After coating with DSPE-PEG, the Mn-IONPs@PEG displayed excellent hydrophilicity and good biocompatibility. Due to the manganese-doping and PEG coating, the Mn-IONPs@PEG showed good relaxivity in vitro. Especially, the Mn-IONPs@PEG coated with DSPE-PEG following a mass ratio to Mn-IONPs of 1:20 showed harmonious longitudinal relaxivity ( r 1 = 7.1 mM -1 s -1 ) and transversal relaxivity ( r 2 = 120.9 mM -1 s -1 ), making it a better candidate for T 1 /T 2 dual-contrast mMRI. After administrated via a caudal vein, the Mn-IONPs@PEG can induce significant enhancement in both T 1 -weighted and T 2 -weighted MR images and the time at 10 mins after injection was regarded as a suitable time for imaging because both the T 1 and T 2 enhancement were optimum at that time., Conclusion: The obtained Mn-IONPs@PEG exhibited good r 1 and r 2 and was a reasonable candidate for T 1 /T 2 dual-contrast mMRI., Competing Interests: The authors report no conflicts of interest in this work., (© 2019 Xiao et al.)