Monodisperse Au-Fe2C Janus Nanoparticles: an Attractive

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Monodisperse Au−Fe2C Janus Nanoparticles: An Attractive Multifunctional Material for Triple-Modal Imaging-Guided Tumor Photothermal Therapy Yanmin Ju,†,‡,# Huilin Zhang,†,⊥,# Jing Yu,*,§ Shiyan Tong,†,‡ Ning Tian,∥ Zhiyi Wang,† Xiaobai Wang,† Xintai Su,⊥ Xin Chu,† Jian Lin,‡,¶ Ya Ding,□ Gongjie Li,∥ Fugeng Sheng,*,∥ and Yanglong Hou*,† †

Beijing Key Laboratory for Magnetoelectric Materials and Devices (BKLMMD), BIC-EAST, Department of Materials Science and Engineering, College of Engineering, ‡College of Life Science, and ¶Synthetic and Functional Biomolecules Center, Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China § Research Center of Magnetic and Electronic Materials, College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China ⊥ Ministry Key Laboratory of Oil and Gas Fine Chemicals, College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China ∥ Department of Radiology, 307 Hospital, PLA, Beijing 100071, China □ State Key Laboratory of Natural Medicines, Department of Pharmaceutical Analysis, China Pharmaceutical University, Nanjing 210009, China S Supporting Information *

ABSTRACT: Imaging-guided photothermal therapy (PTT) by combination of imaging and PTT has been emerging as a promising therapeutic method for precision therapy. However, the development of multicomponent nanoplatforms with stable structures for both PTT and multiple-model imaging remains a great challenge. Herein, we synthesized monodisperse Au−Fe2C Janus nanoparticles (JNPs) of 12 nm, which are multifunctional entities for cancer theranostics. Due to the broad absorption in the near-infrared range, Au−Fe2C JNPs showed a significant photothermal effect with a 30.2% calculated photothermal transduction efficiency under 808 nm laser irradiation in vitro. Owing to their excellent optical and magnetic properties, Au−Fe2C JNPs were demonstrated to be advantageous agents for triple-modal magnetic resonance imaging (MRI)/multispectral photoacoustic tomography (MSOT)/computed tomography (CT) both in vitro and in vivo. We found that Au−Fe2C JNPs conjugated with the affibody (Au−Fe2C−ZHER2:342) have more accumulation and deeper penetration in tumor sites than nontargeting JNPs (Au−Fe2C− PEG) in vivo. Meanwhile, our results verified that Au−Fe2C−ZHER2:342 JNPs can selectively target tumor cells with low cytotoxicity and ablate tumor tissues effectively in a mouse model. In summary, monodisperse Au−Fe2C JNPs, used as a multifunctional nanoplatform, allow the combination of multiple-model imaging techniques and high therapeutic efficacy and have great potential for precision theranostic nanomedicines. KEYWORDS: Au−Fe2C Janus nanoparticles, magnetic resonance imaging, multispectral photoacoustic tomography, computed tomography, photothermal therapy

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absorbed light into thermal energy to ablate localized cancer cells by using light-absorbing agents. Compared to traditional cancer treatment methods such as chemotherapy and radio-

onsiderable efforts have been made in the development of precision medicines, which include precise disease diagnosis, precise treatment, and real-time evaluation during and after the treatment.1−4 Theranostic nanomedicine can provide an attractive avenue for precision medicines as the integration of diagnosis and treatment in one nanoplatform.5−7 Photothermal therapy (PTT) converts © 2017 American Chemical Society

Received: June 26, 2017 Accepted: August 29, 2017 Published: August 29, 2017 9239

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Figure 1. (A) Schematic depiction of the synthetic process of Au−Fe2C JNPs. (B) XRD patterns of Au−Fe heterostructures and Au−Fe2C JNPs. (C) TEM and (D) HRTEM images of Au−Fe heterostructures. (E) TEM and (F) HRTEM images of Au−Fe2C JNPs. (G) UV−vis absorption spectra from 300 to 700 nm of 9 nm Au NPs, Au−Fe heterostructures, and Au−Fe2C JNPs in hexane, respectively.

integral information for diagnosis at the molecular level but also to show excellent prospective applications in the clinic. Many multimodel agents reported were fabricated by encapsulating or conjugating imaging moieties together, which have the risk of escape of individual parts.12,30 Some may hold back the potential for clinical application due to the unstable structure in the biomedical environment.31 Compared with them, Janus nanoparticles (JNPs) can simultaneously present two different materials and surface chemistries and show “all-in-one” theranostic properties with intrinsic imaging and therapeutic capability, which could be more stable in vivo.32−35 Iron carbide nanoparticles (NPs) have been reported by our group as an excellent candidate for imaging-guided PTT with no systemic side effects.36−39 Here, based on the previous results, we further optimized their performance as MR/MSOT/ CT imaging agents with high photothermal transduction efficiency relying on their intrinsic properties, which can both provide accurate information for precision diagnosis and ablate tumors for therapy. The use of Au in heterostructure NPs has attracted much attention in recent years due to its excellent optical properties, which have rendered it as a classic component of nanocomposites.40−42 For example, dumbbelllike Au−Fe3O4 NPs have been reported to show both optical and magnetic properties in one unit, which means Au− magnetic JNPs are an extremely attractive composite system for theranostics. Thus, JNPs can be rendered with both optical and magnetic properties.43,44 Herein, we designed 12 nm monodisperse Au−Fe2C JNPs with a broad absorption band in the near-infrared region and excellent magnetic properties. The material exhibited strong PTT effects with a 30.2% calculated photothermal transduction efficiency in vitro. Meanwhile, the ability of triple-modal MR/ MSOT/CT imaging agents was demonstrated both in vitro and

therapy, PTT is highly effective in tumor ablation with minimal damage to normal tissues.8−10 However, the poor accuracy of PTT leads to unsatisfactory therapeutic effects without using imaging contrast agents. Hence, imaging-guided PTT is a promising therapeutic method for precision therapy, as it can visualize the size and location of tumors before therapy and evaluate the treatment efficiency during and after therapy.11,12 There are various imaging modalities that have been utilized for cancer diagnosis such as optical imaging, magnetic resonance imaging (MRI), computed tomography (CT), and position emission tomography (PET).13−19 Among them, MRI is one of the most reliable clinical tools due to its capability to detect anatomy information on biological tissues with high resolution and excellent depth in vivo.20−23 Multispectral photoacoustic tomography (MSOT) is a new emerging and promising hybrid imaging technique based on the detection of ultrasonic waves around the tissue surface induced by biological tissue absorption of photons, which possesses an excellent penetration depth and spatial resolution to visualize tissue structures and functions at the molecular level.6,24−26 CT imaging is currently the most convenient imaging tool in hospitals because of its high efficiency, reasonable cost, and superior spatial and higher resolution.16,27,28 However, these techniques all have their own limitations. For example, MRI and CT are only efficient in detecting tumors and metastases larger than 0.5 cm, while MSOT is largely limited by the penetration depth of light.15,29 In addition, these techniques can provide deep penetration and high spatial resolution only in specific tissues; for instance, MRI is mainly used for soft tissue diseases and early detection of inflammatory disease. Therefore, developing a nanoplatform as contrast agents for MR/MSOT/ CT imaging is highly demanded not only for providing more 9240

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Figure 2. (A) TEM and HRTEM (inset) images of Au−Fe2C−PEG JNPs. (B) UV−vis absorption spectrum from 300 to 900 nm of Au−Fe2C− PEG JNPs in water. (C) MSOT imaging phantoms of various concentrations of Au−Fe2C−PEG JNPs embedded in agar gel cylinders. (D) Photoacoustic signal spectra of Au−Fe2C−PEG JNPs at various concentrations. (E) Linear relationship between photoacoustic signal intensities and concentrations of Au−Fe2C−PEG JNPs. (F) T2 relaxation rate (1/T2) as a function of Fe concentration for the Au−Fe2C−PEG JNPs.

lateral dimension of ∼12 nm (Figures 1E and S3). The HRTEM image of a single Au−Fe2C JNP in Figure 1F showed a lattice spacing of 2.04 Å for the darker region and a spacing of 1.32 Å for the lighter region, corresponding to the (200) and (111) planes of Au and Fe2C, respectively, also confirmed by Xray photonic spectroscopy (XPS) (Figure S4). Intriguingly, the morphology of Au and Fe2C domains in Au−Fe2C JNPs all change to irregular spheres compared with Au−Fe NPs. The growth process of Au−Fe2C JNPs showed distinct optical properties. As shown in Figure 2G, the peak centered at 526 nm comes from the surface plasmon resonance (SPR) absorption of Au NPs. Compared with 9 nm Au seeds, a 39 nm red-shifted SPR peak of Au−Fe NPs was observed after the growth of Fe, while a 12 nm blue-shifted SPR peak of Au−Fe2C JNPs was detected after the carburization. This could result from the charge variation of the Au moiety in Au−Fe heterostructures and Au−Fe2C JNPs. According to previous studies, an electron deficiency on the Au moiety can shift the plasmon absorption to a longer wavelength, whereas an excess of electrons can shift the absorption to a shorter wavelength.45,46 Therefore, the red shift on the SPR of Au−Fe heterostructures indicated that Fe domains produced a deficient electron population on the Au domain, while the blue shift showed that the Fe2C domain caused an excess electron population on the Au moiety. Meanwhile, the amount of oleylamine (OAm) influenced the extent of the interaction between the Fe domain and the Au surface (Figure S5). Modification and Properties of Au−Fe2C JNPs. For biomedical applications, these hydrophobic Au−Fe2C JNPs were transferred to an aqueous environment through encapsulation by the amphiphilic polymer 1,2-distearoyl-snglycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG-NH2), as the modified method previously reported.6,36 The coating amount of DSPE-PEGNH2 (Figure S6) used to form Au−Fe2C−PEG JNPs was about 10.97% (wt). TEM results (Figure 2A) confirmed that the uniform size, spherical morphology, and crystal lattice of the Au−Fe2C JNPs were all well maintained. The corresponding hydrodynamic diameter of the Au−Fe2C−PEG JNPs (Figure

in vivo. After being conjugated by the affibody ZHER2:342, Au− Fe2C−ZHER2:342 JNPs showed more accumulation and deeper penetration in the tumor sites and were able to selectively ablate tumors without side effects in tumor-bearing mice under laser irradiation. Thus, Au−Fe2C JNPs have successfully been evaluated as a multifunctional nanoplatform capable of MR/ MSOT/CT triple-modal imaging-guided PTT in tumor ablation.

RESULTS AND DISCUSSION Synthesis and Characterization of Au−Fe2C JNPs. The synthesis of Au−Fe2C JNPs comprises three steps: the preparation of Au seeds, the formation of Au−Fe heterostructures, and the carburization process of Au−Fe2C JNPs (Figure 1A). According to the optimized conditions (described in the Methods section), monodisperse Au−Fe2C JNPs were obtained using a Au/Fe mass ratio of 1.86 through elemental analysis by inductively coupled plasma (ICP), indicating a Au/ Fe molar ratio of ∼1:2. Other ratios would cause large amounts of isolated Au or Fe2C NPs to form (see Figure S1). Au NPs of 4 nm (Figure S2A) were obtained by reduction of gold chloride trihydrate (HAuCl4·3H2O). The formation of 9 nm Au NPs (Figure S2B) followed the seeded growth synthesis of Au seeds previously prepared. The thermal decomposition of Fe(OA)5 was then performed for the growth of Fe on the Au seed surface. X-ray diffraction (XRD) patterns (Figure 1B) confirmed the composition of Au and body centered cubic (bcc)-Fe heterostructures, also supported by the transmission electron microscope (TEM) results in Figure 1C, showing that Au cores were semisurrounded by the lighter 14 nm Fe domains. The high-resolution TEM (HRTEM) image depicted in Figure 1D shows a lattice spacing between two (111) adjacent planes in Au of 2.36 Å and a distance of 1.32 Å corresponding to the (200) planes of bcc-Fe (α-Fe). The internal Fe core was protected from further oxidization by a ∼2 nm Fe3O4 shell with a spacing of 2.97 Å between the (220) planes of magnetite. After carburization, the XRD analyses (Figure 1B) showed that monodisperse Au−Fe2C JNPs with obvious Janus morphology were obtained, with an overall 9241

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Figure 3. (A) Temperature elevation of deionized water and Au−Fe2C−PEG JNP solutions at different concentrations under 1 W/cm2 laser irradiation. (B) Plot of temperature change versus Fe concentration after laser exposure for 5 min; 0 μg/mL stands for deionized water. (C) Temperature elevation profiles of 100 μg/mL Au−Fe2C−PEG JNP solutions under different laser power densities. (D) Monitored temperature profile over 1200 s of 100 μg/mL Au−Fe2C−PEG JNP solution irradiated by a 1 W/cm2 laser for 600 s, followed by natural cooling after the laser light was turned off.

of 88.2 emu/g.47 The reduction of the Ms value for Au−Fe2C− PEG JNPs is caused by the weight contribution of the nonmagnetic Au part. T2-weighted MRI of Au−Fe2C−PEG JNPs was taken on a 3 T clinical MRI scanner. The value of transverse relaxivity (r2), which is proportional to the iron concentration, was calculated as 210.6 mM−1 s−1 for Au− Fe2C−PEG JNPs (Figure 2F), which was higher than that of the commercially available T2-weighted MRI contrast agent Resovist (174 mM−1 s−1) and 14 nm Fe2C and Au−Fe3O4 NPs (Figure S13, Table S2).36 These findings demonstrated the potential of Au−Fe2C−PEG JNPs as theranostic nanomedicines with multiple imaging ability. Photothermal Property of Au−Fe2C−PEG JNPs. Due to their previously observed ability of photon absorption in the NIR region, Au−Fe 2C−PEG JNPs can be used as a photothermal agent, which converts photons into local heat. The photothermal effect of Au−Fe2C−PEG JNPs in vitro was studied by monitoring the temperature change of 200 μL of a Au−Fe2C−PEG JNP solution at various concentrations (0− 200 μg/mL) under 808 nm laser irradiation. With the NP concentration varied from 6.25 to 200 μg/mL, the elevation temperature of the solutions increased from 4.99 to 49.95 °C after 5 min of laser irradiation, while no obvious temperature increase was observed in the control sample of water (Figure 3A). In Figure 3B, the temperature increase at the end of the laser irradiation was plotted versus the Fe concentration from the JNPs. The temperature elevation profile flattened out with increasing JNP concentration due to the logarithmic dependence of the absorbance on the fraction of incident radiation. In Figure 3C, a clear power-density-dependent temperature

S7) was measured to be 39.87 nm compared with the diameter of 33.83 nm of bare Au−Fe2C JNPs. In order to show the biomedical stability of Au−Fe2C−PEG JNPs, the JNPs were dispersed in phosphate-buffered saline (PBS) solution, cell culture medium, and cell culture medium with 10% fetal bovine serum (FBS). It was found that they remained stable for at least 1 week (Figure S8A). The TEM and zeta potential results of Au−Fe2C−PEG JNPs dispersed in PBS showed their original morphology and surface potential, which all demonstrated the stability of the JNPs (Figure S8B and Table S1). XRD data in Figure S9 also demonstrated the stability of the Au−Fe2C− PEG JNPs. The ultraviolet−visible (UV−vis) absorption spectrum was not affected by the corresponding modification, and it exhibited an appreciable absorbance band in the visible region (400−800 nm) (Figures 2B, S10), suggesting potential photoacoustic (PA) imaging ability. Furthermore, we explored PA signals in vitro at various NP concentrations presented in Figure 2C by an MSOT imaging system. The results in Figure 2D revealed that the PA signal was related to the excitation light wavelength and the concentration of Au−Fe2C JNPs. With shorter wavelengths in the near-infrared (NIR) region and a higher concentration, a stronger signal could be achieved, which corresponds to the optical absorption spectrum in Figure 2B. Quantitative analysis showed that the PA intensity and optical absorption were linearly correlated with the Au−Fe2C JNPs’ concentration (Figures 2E, S11). Magnetization measurements showed that Au−Fe2C−PEG JNPs possess a paramagnetic feature with a saturation magnetization (Ms) of 52.8 emu/g at room temperature (Figure S12), in contrast with our previous study on monoclinic Fe2C NPs, which exhibit an Ms 9242

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Figure 4. (A) Viabilities of the MDA-MB-231 and NIH3T3 cells determined by CCK8 assay after incubation with various concentrations of Au−Fe2C−PEG JNPs for 24 h. (B) Viabilities of MDA-MB-231 cells after incubation with various concentrations of Au−Fe2C−PEG and Au− Fe2C−ZHER2:342 JNPs induced photothermal therapy under 808 nm 1 W/cm2 laser irradiation. (C) Fluorescence microscopy images of (left) live cells, stained with calcein-AM; (middle) necrotic or apoptotic cells, stained with PI; (right) merged, incubated with Au−Fe2C−ZHER2:342 JNPs and irradiated with laser; MDA-MB-231 cells incubated with Au−Fe2C−PEG JNPs and irradiation; MDA-MB-231 cells incubated with Au−Fe2C−ZHER2:342 only; MDA-MB-231 cells irradiated with laser only; and MDA-MB-231 cells without any treatment, respectively (from top to bottom). Scale bars: 100 μm. In all the laser irradiation experiments, irradiation was at a power density of 1 W/cm2 for 5 min. Error bars: mean ± SD.

fluorescence spectrum analysis.30 Figure 4A showed the cell viability of NIH3T3 and MDA-MB-231 cells after being incubated with different concentrations of Au−Fe 2 C− ZHER2:342 JNPs for 24 h by CCK8 assays. No obvious cytotoxicity was observed for both cell lines with NP concentration up to 400 μg/mL. Subsequently, we examined the viability of MDA-MB-231 cells treated with Au−Fe2C− ZHER2:342 JNPs or Au−Fe2C−PEG JNPs after exposure to an 808 nm laser (1 W/cm2 for 5 min). Compared to Au−Fe2C− PEG JNPs, Au−Fe2 C−ZHER2:342 JNPs showed a more significant laser-induced therapeutic effect. Meanwhile, in Au−Fe2C−ZHER2:342 JNPs alone or laser alone group, no obvious cytotoxicity was observed (Figure 4B). Fluorescent live/dead cell staining experiments were performed to further visualize this photothermal ablation process. Live cells were stained with calcein-AM (green fluorescence), while dead cells were differentiated using propidium iodide (PI) (red fluorescence) after laser treatment under a confocal microscope (Figure 3C). In the Au−Fe2C−ZHER2:342 JNPs alone or the laser-only group, almost all cells displayed green fluorescence, illustrating that both of them had little effect on the viability of the cells. When the cells were incubated with Au−Fe2C−PEG JNPs and exposed to laser, the number of dead cells slightly increased. A clear cell death was observed when treated with Au−Fe2C−ZHER2:342 JNPs with laser irradiation. As predicted, these results were in agreement with the CCK8 assay results presented in Figure 4B, demonstrating that Au−Fe2C− ZHER2:342 JNPs can induce more efficient photothermal ablation of cancer cells than Au−Fe2C−PEG JNPs under laser irradiation.

elevation could be seen at a concentration of 100 μg/mL of Au−Fe2C−PEG JNPs. To further study the photothermal transduction efficiency, the Au−Fe2C−PEG JNP solution (100 μg/mL, 200 μL) was continuously illuminated by a 1 W/cm2 laser until reaching a steady-state temperature, at which point the laser was removed and the solution was allowed to cool naturally. The temperature change during the process was monitored to achieve a heat generation−dissipation curve, depicted in Figure 3D. On the basis of the method first developed by Roper and co-workers (detailed in the Supporting Information) the photothermal transduction efficiency of Au− Fe2C−PEG JNPs was calculated as 30.2%. Compared with reference nanoparticles, including 9 nm Au NPs, 9 nm Au nanoparticles, 14 nm Fe2C nanoparticles, and about 18 nm Au−Fe3O4 nanoparticles shown in Figure S14 (all modified with PEG after), Au−Fe2C JNPs exhibited superior photothermal property (Figure S15), which corresponded to the results of their calculated photothermal transduction efficiency shown in Figure S16 and Table S3. These results demonstrated that Au−Fe2C−PEG JNPs are highly efficient PTT agents. In Vitro Photothermal Cell Ablation. Encouraged by the promising photothermal efficiency of the materials, we continued to evaluate the cytotoxicity and PTT efficacy of the Au−Fe2C JNPs in vitro with mouse normal fiber NIH3T3 cells and human mammary carcinoma MDA-MB-231 cells. As MDA-MB-231 cells overexpress HER2 receptors, affibody proteins (ZHER2:342) that can selectively bind to the extracellular domain of HER2 were conjugated to the surface of Au−Fe2C JNPs for mammary-cancer targeting. As shown in Figures S17 and S18, the conjugation of affibody ZHER2:342 attached to the NPs was demonstrated by the infrared spectral (IR) and 9243

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Figure 5. (A) Real-time T2-weighted MR images of MDA-MB-231 tumor-bearing mice at various time points before and after intravenous injection of Au−Fe2C−ZHER2:342 JNPs and Au−Fe2C−PEG JNPs. (B) Relative MR signal intensity in the tumor at different time points postinjection. (C) In vivo MSOT images of tumors in mice taken at different times after intravenous injection of Au−Fe2C−ZHER2:342 JNPs and Au−Fe2C−PEG JNPs. Enlarged views of tumors are also presented. (D) 3D reconstructed CT images before (D1) and after the intratumor injection (D2) of Au−Fe2C−PEG JNPs with 10 μL at a dosage of 10 mg/mL. Error bars: mean ± SD.

Figure 6. (A) Thermal IR imaging of MDA-MB-231 tumor-bearing mice after intravenous injection of Au−Fe2C−ZHER2:342 JNPs and Au− Fe2C−PEG JNPs and exposure to 808 nm laser irradiation. (B) Temperature change curves of MDA-MB-231 tumors in mice treated with Au−Fe2C−ZHER2:342 JNPs and Au−Fe2C−PEG JNPs under laser irradiation. (C) Growth curves of tumor volume in mice from the different treatment groups, which were normalized to their initial sizes. (D) Body weight curves of mice in the different treatment groups. (E) Digital photos of tumor tissues harvested from mice in the different groups at the end of treatment. (F) H&E staining of tumors collected from different groups of mice 5 days post-treatment: (F1) Au−Fe2C−ZHER2:342 JNP injection and laser irradiation; (F2) Au−Fe2C−PEG JNPs and laser irradiation; (F3) Au−Fe2C−ZHER2:342 JNP injection only; (F4) laser irradiation only; and (F5) saline. Error bars represent the standard deviations of 3 mice per group.

In Vivo MRI/MSOT/CT Imaging of Au−Fe2C JNPs. On the basis of the favorable in vitro results, we next evaluated the accumulation and penetration of Au−Fe2C JNPs in the tumor site. When the tumor volume reached 100−200 mm3, T2weighted MRI and MSOT imaging were done before and after the intravenous (i.v.) injection of Au−Fe2C−PEG JNPs and Au−Fe2C−ZHER2:342 JNPs (2 mg/mL, 200 μL) on nude mice

bearing the MDA-MB-231 tumor model, respectively. As shown in Figure 5A and B, enhancement of the negative signal in the tumor sites could be clearly observed in mice treated with Au−Fe2C−ZHER2:342 JNPs for 12 and 24 h postinjection, respectively. The signal from the Au−Fe2C−PEG JNP group was not evident. These results suggested that the accumulation of Au−Fe2C−ZHER2:342 JNPs in the tumor site was more than 9244

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ZHER2:342 JNPs and laser irradiation, whereas the tumors in the other four groups all increased in size. These results demonstrated the efficient PTT efficacy of Au−Fe2C− ZHER2:342 JNPs in vivo. The tumors from each group were harvested at the end of the experimental period (Figure 6E). One mouse from each group was sacrificed on the fifth day post-treatment, and hematoxylin and eosin (H&E) staining was carried out on the tumors (Figure 6F). The histochemical analysis suggested that extensive necrosis appeared in the mouse from the Au−Fe2C−ZHER2:342 JNP injection and laser irradiation group with severe cell shrinkage and loss of contact, whereas fewer necrotic areas were observed in the mouse treated with Au−Fe2C−PEG and laser irradiation. No obvious necrosis was observed in the other three groups. Also, there were no obvious differences between the temperature elevation curve of Au−Fe2C−PEG and Au−Fe2C−ZHER2:342 solutions under laser irradiation (Figure S21). These results demonstrated that Au−Fe2C−ZHER2:342 JNPs are efficient and selective targeting nanomaterials with PTT effects in HER2-overexpressed mice models. Since the Au−Fe2C−ZHER2:342 JNPs were designed for biomedical applications, it is imperative to assess their biosafety. Thus, in vivo toxicity of Au−Fe2C JNPs to major organs was evaluated by investigating viscera index and H&E staining after the sacrifice of all the mice (Figures S22, S23). The H&E-stained slides and viscera index data all showed no obvious abnormality in major organs. Taken together, our results verified that Au−Fe2C JNPs had low side effects in vivo in the therapeutic period and could serve in multiple-imaging guided photothermal therapy in theranostic nanomedicines.

Au−Fe2C−PEG JNPs, as the former ones gradually accumulated in the tumor site through both the enhanced permeability and retention (EPR) effect and the selective targeting relying on the combination of affibody ZHER2:342 with the HER2 receptor. Consequently, we carried out MSOT imaging for the Au−Fe2C JNPs with selective targeting-dependent tumor-site distribution in mice. As shown in Figure 5C, the contrast around the tumor site was detected 4 h after injection, indicating the MSOT imaging ability of Au−Fe2C JNPs in vivo. From 0 to 24 h postinjection, the photoacoustic signal increase in the tumor sites could be observed in Au−Fe2C−PEG and Au−Fe2C−ZHER2:342 JNP groups. On the other hand, the signal enhancement from the selective targeting group was more significant, suggesting more accumulation of Au−Fe2C− ZHER2:342 JNPs. Subsequently, the periphery of the tumor showed significant photoacoustic signals. Weak signals were detected from the internal area of the tumor. Nevertheless, intense photoacoustic signals were clearly monitored in the case of Au−Fe2C−ZHER2:342 JNPs. These results showed a deeper penetration and more uniform distribution of Au−Fe2C− ZHER2:342 JNPs than Au−Fe2C−PEG JNPs in vivo. The results of biodistribution of Au−Fe2C−PEG and Au−Fe2C−ZHER2:342 JNPs after i.v. injection also showed more accumulation of JNPs in the active-targeting group (Au−Fe2C−ZHER2:342 JNPs) (Figure S19). Besides acting as MRI/MSOT imaging agents, Au−Fe2C JNPs could also be candidates for contrast enhancement in CT imaging. The Hounsfield unit (HU) value of Au−Fe2C JNPs was proportional to the concentration of JNPs (Figure S20). Furthermore, Figure 5D shows reconstructed three-dimensional (3D) CT images of the mouse and exhibited enhanced contrast in the tumor site after intratumoral administration of Au−Fe2C−PEG JNPs, revealing that Au−Fe2C JNPs can be a contrast-enhancing agent for CT imaging. Taken together, the above evidence demonstrated that Au−Fe2C−ZHER2:342 JNPs have more accumulation and deeper penetration at the tumor sites and Au−Fe2C JNPs can be agents for MR/MSOT/CT imaging. In Vivo Phototherapy Efficacy and Toxicity Assessment. Encouraged by the selective accumulation of Au− Fe2C−ZHER2:342 JNPs in tumor sites, we next monitored their PTT efficacy on tumor-bearing mice. When the tumor volumes reached about 100−200 mm3, mice were randomly divided into five groups (n = 3): Au−Fe2C−ZHER2:342 JNP injection and laser irradiation; Au−Fe2C−PEG JNPs and laser irradiation; Au−Fe2C−ZHER2:342 JNP injection only; laser irradiation only; and a control group with saline administration. Twenty-four hours after injection with JNPs at a dose of 20 mg/kg, treated mice were exposed to an 808 nm laser (1 W/cm2) for 8 min. The temperature elevation profiles of tumor sites were analyzed in Figure 6A and B. After irradiation for 5 min, mice tumor sites injected with PBS and laser irradiation only showed an increase in temperature of 7.5 °C. However, the temperature of the tumor area of the mice treated with Au−Fe2C−ZHER2:342 JNPs and laser irradiation rapidly increased to 27.21 °C within 8 min, which is sufficient to ablate the tumors. In contrast, Au−Fe2C− PEG JNP-treated and laser-irradiated mice showed an increase of 17.31 °C. As tumor cells are killed when their local temperature achieves higher than 42 °C, Au−Fe2C−PEG JNPs treated with laser for 5 min can ablate tumors completely. The tumor volumes and body weights of each group of mice were monitored for 27 days with an interval of 3 days (Figure 6C,D). A remarkable growth inhibition and elimination of the tumor volume was observed in 27 days after injection of Au−Fe2C−

CONCLUSION In summary, Au−Fe2C JNPs were successfully synthesized and demonstrated as multifunctional entities with triple-modal MRI/MSOT/CT imaging-guided PTT effects for precise diagnosis and efficient tumor treatment. They had broad absorption patterns in the range of 600−800 nm for MSOT imaging and showed a strong photothermal effect under 808 nm laser irradiation. It was found, through MRI/MSOT imaging technologies, that the affibody-conjugated Au−Fe2C JNPs (Au−Fe2C−ZHER2:342) have a larger tumor accumulation and deeper tumor penetration than the nontargeted JNPs (Au− Fe2C−PEG). Meanwhile, our results verified that Au−Fe2C− ZHER2:342 JNPs can target tumor cells with low cytotoxicity in the therapeutic period and selectively kill them through laser radiation. Moreover, Au−Fe2C−ZHER2:342 JNPs achieved efficient tumor ablation against tumors in vivo. No evident side effect was observed from our experiments. Therefore, monodisperse Au−Fe2C JNPs had great potential as a multifunctional nanoplatform for precision theranostic nanomedicines. METHODS Reagents. All chemicals were used without further purification. Octadecene (ODE, tech. 90%) was purchased from Alfa Asear. NH4Br (99%) and borane-tert-butylamine complex (TBAB) were purchased from J&K Chemicals. Oleylamine (tech. 70%),1-ethyl-3-(3(dimethylamino)propyl)carbodiimide (EDC), sulfo-(N-hydroxysulfosuccinimide) (sulfo-NHS), calcein-AM, and propidium iodide were purchased from Sigma-Aldrich. Iron pentacarbonyl (Fe(CO)5) was from Tianyi Co. Ltd. (Jiangsu, China). DSPE-PEG-NH2 was purchased from Seebio Ltd. (Shanghai, China). Deionized water (18.2 MΩ·cm resistivity at room temperature) was used for all tests. Synthesis of Au−Fe Heterostructures. Typically, 1 mL of 9 nm Au NPs (15 mg/mL), 8 mg of NH4Br, 15 mL of ODE, and 100 μL of 9245

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ACS Nano OAm were mixed and stirred in a 100 mL four-neck flask under the standard gas (5% H2 in Ar) atmosphere. The system was heated to 100 °C and degassed for 2 h. When the temperature was raised to 180 °C, 100 μL of Fe(CO)5 was injected into the solutions. After 30 min, the system was cooled to room temperature and Au−Fe heterostructures were washed three times and redispersed in hexane. Synthesis of Au−Fe2C JNPs. The carbonization process was carried out with a process similar to that in our published paper.46 ODE (5 mL) and OAm (10 mL) were mixed and stirred in a fourneck flask. Subsequently, the above materials, in 10 mL of hexane, were injected via a syringe and degassed at 120 °C for 30 min, and the system was raised up to 300 °C for another 30 min. The solution was cooled to room temperature and redispersed in hexane after washing three times. Modification of Au−Fe2C JNPs. The modification was carried out according to our previous paper.30 Briefly, 100 mg of DSPE-PEGNH2 was dissolved in 15 mL of chloroform and added dropwise into 30 mL of chloroform containing 25 mg of Au−Fe2C JNPs. The mixed solution was stirred under an Ar atmosphere until the chloroform evaporated totally. Deionized water was added to disperse the Au− Fe2C−PEG JNPs, and then the mixture was dialyzed for 24 h to remove excess DSPE-PEG-NH2. In order to make the heterostructures selectively target the HRE2-overexpressing cells, HER2 binding affibody ZHER2:342 was linked to the Au−Fe2C−PEG JNPs. A 1 × 10−4 mmol amount of ZHER2:342 (provided by J. Lin) was added into 10 mL of PBS solution and activated by EDC and sulfo-NHS for 1 h. Then, the above Au−Fe2C−PEG JNPs were added and stirred for 4 h. The Au−Fe2C−ZHER2:342 JNPs conjugates were washed with deionized water three times and dialyzed for 24 h. In Vivo MRI. When the tumor volume reached about 100−200 mm3, mice were randomly allocated into two groups, and 200 μL of 20 mg/kg Au−Fe 2 C−ZHER2 JNPs or Au−Fe 2C−PEG JNPs was administered via tail vein, respectively. MR images were acquired before and 2, 4, 8, 12, and 24 h after injection. The T2-weighted images were obtained in a clinic 3 T MRI scanner (SIEMRNS, Germany), and the sequence was TR = 1200 ms, TE = 30.2 ms, slice thickness = 2.5 mm. In Vivo Photoacoustic Tomography. Mice with tumor volumes (on the right side of the back) of 100−200 mm3 were used for in vivo photoacoustic imaging by a multispectral optical tomography system (MSOT inVision 128, iThera Medical, Germany). Mice were randomly allocated into two groups, and 200 μL of 20 mg/kg Au− Fe2C−ZHER2 JNPs or Au−Fe2C−PEG JNPs was administered via tail vein, respectively. Photoacoustic signals were detected at a wavelength of 700 nm. The two excitation wavelengths were used to measure oxygenated and deoxygenated hemoglobin at 850 and 750 nm, respectively. MSOT signals before injection were recorded as a control. In Vivo Temperature Measurement during NIR Irradiation and Photothermal Therapy. Solutions of 200 μL of 20 mg/kg Au− Fe2C−ZHER2 JNPs, Au−Fe2C−PEG JNPs, and a saline solution were administered by i.v. injection to the MDA-MB-231 tumor-bearing mice, respectively. The mice received NIR irradiation (808 nm, 1 W/ cm2) for 5 min 24 h after injection. A thermographic map of the tumor tissues before and after illumination was imaged by a thermal imaging camera (FLIR SC7100, USA).48 The temperature was noted as the highest one in the tumor center. Photothermal ablation was performed when the tumors reached about 100−200 mm3. The mice were divided into 5 groups with 3 mice in each group: (1) Au−Fe2C−ZHER2 JNPs with laser; (2) Au−Fe2C−PEG JNPs with laser; (3) Au−Fe2C− ZHER2 JNPs only; (4) laser only; (5) control (saline). Laser irradiation at 808 nm was carried out 24 h after injection at a power 1 W/cm2 for 5 min. Tumor sizes and body weights were measured every 3 days during the treatment. Tumor volume was calculated according to the formula (a × b2)/2, where a and b are the long and short diameters of the tumor, respectively.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.7b04461. Additional experimental details (PDF)

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected] (Yu). *E-mail: [email protected] (Sheng). *E-mail: [email protected] (Hou). ORCID

Xintai Su: 0000-0002-2832-7406 Yanglong Hou: 0000-0003-0579-4594 Author Contributions #

Y. Ju and H. Zhang contributed equally to this work.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (51672010, 51631001, 81421004, 51590882, 51602285, 21575161), the Research Fellowship for International Young Scientists of the National Natural Science Foundation of China (51550110502), the Interdisciplinary Project of Beijing New Star Plan of Science and Technology, the State Key Project of Research and Development of China (2017YFA0206301, 2016YFA0200102), and the Key Laboratory of Biomedical Effects of Nanomaterials and Nanosafety, National Center for Nanoscience and Technology, Chinese Academy of Sciences (No. NSKF201607). The authors acknowledge Jesus M. Lopez Baltazar for his help in polishing the writing. REFERENCES (1) Collins, F. S.; Varmus, H. A New Initiative on Precision Medicine. N. Engl. J. Med. 2015, 372, 793−795. (2) Jameson, J. L.; Longo, D. L. Precision Medicine-Personalized, Problematic, and Promising. Obstet. Gynecol. Surv. 2015, 70, 612−614. (3) Mirnezami, R.; Nicholson, J.; Darzi, A. Preparing for Precision Medicine. N. Engl. J. Med. 2012, 366, 489−491. (4) Ashley, E. A. The Precision Medicine Initiative: a New National Effort. JAMA 2015, 313, 2119−2120. (5) Janib, S. M.; Moses, A. S.; MacKay, J. A. Imaging and Drug Delivery Using Theranostic Nanoparticles. Adv. Drug Delivery Rev. 2010, 62, 1052−1063. (6) Lv, G.; Guo, W.; Zhang, W.; Zhang, T.; Li, S.; Chen, S.; Eltahan, A. S.; Wang, D.; Wang, Y.; Zhang, J. Near-Infrared Emission CuInS/ ZnS Quantum Dots: All-in-One Theranostic Nanomedicines with Intrinsic Fluorescence/Photoacoustic Imaging for Tumor Phototherapy. ACS Nano 2016, 10, 9637−9645. (7) Lammers, T.; Aime, S.; Hennink, W. E.; Storm, G.; Kiessling, F. Theranostic Nanomedicine. Acc. Chem. Res. 2011, 44, 1029−1038. (8) Liang, C.; Diao, S.; Wang, C.; Gong, H.; Liu, T.; Hong, G.; Shi, X.; Dai, H.; Liu, Z. Tumor Metastasis Inhibition by Imaging-Guided Photothermal Therapy with Single-Walled Carbon Nanotubes. Adv. Mater. 2014, 26, 5646−5652. (9) Sun, M.; Xu, L.; Ma, W.; Wu, X.; Kuang, H.; Wang, L.; Xu, C. Hierarchical Plasmonic Nanorods and Upconversion Core-Satellite Nanoassemblies for Multimodal Imaging-Guided Combination Phototherapy. Adv. Mater. 2016, 28, 898−904. 9246

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