Xinmei Zho,Leyong Zeng,Nryn Hosmne,Yn Gong,Aiguo Wu,*

a CASKey Laboratory of Magnetic Materials and Devices&Division of Functional Materials and Nanodevices,Ningbo Institute of Materials Technology and Engineering,Chinese Academy of Sciences,Ningbo 315201,China

b Zhejiang Pharmaceutical College,Ningbo 315100,China

c Department of Chemistry&Biochemistry,Northern Illinois University,DeKalb,Illinois 60115-2862,United States

d Ningbo Eye Hospital,Ningbo 315040,China

Key words:Fe3O4/Au MRI SERS Cell detection MCF-7

ABSTRACT The development of multifunctional contrast agents contributes signi fi cant character in the diagnosis of cancer.However,still efforts are required to design and improve the biocompatibility of contrast agents for early detection of cancer.Herein,we synthesized splat shape Fe3O4/Au nanocomposites for multimode biomedical applications.Transmission electron microscopy(TEM)results showed that the splat-like Fe3O4/Au structure was in the range of 130 nm and homogeneously distributed in the aqueous medium.The nanocomposites were incubated with MCF-7 cells to investigate the magnetic resonance imaging(MRI)and surface-enhanced Raman scattering(SERS)activities.The excellent T2 MRI and enhanced SERSproperties were obtained without any cytotoxicity.These results demonstrated that assynthesized splat-shaped Fe3O4/Au nanocomposites may be a promising MRI/SERS dual probe for the tumor detection.

Cancer,unrestrained development of abnormal cells in the body,is a serious health threatening disease which has been defeating many important lives every year.Early diagnosis with appropriate treatment can overcome this fatal disease to increase the survival rate of the patients.Presently,nanotechnology produces several multifunctional contrast agents in the form of nanoparticles(NPs)for imaging,such as magnetic resonance imaging/computed tomography(MRI/CT)[1],MRI/photo-acoustic[2],MRI/near infrared ray(NIR)[3]and MRI/optical/thermal imaging[4].However,the control synthesis of solution based multimode nanoparticles with enhanced MRIand biocompatibility are exiting challenges.To improve the sensitivity in cancer diagnosis,surface enhanced Raman scattering(SERS)is one of the best for tumor detection,because(1)the detection limit is lower than the fluorescence method,(2)the effect by autofluorescence of the tumor can be avoided,and(3)SERShas high selectivity for the Raman reporter,so that the impurities in complex samples do not have any influence on the signal collection.Thus,the SERStechnology is one of important analytical methods in biomolecular identi fi cation,and,therefore,it has been w idely utilized in tumor detection and resection[5,6].Thus,combination of SERSand MRItechniques improves the accuracy of cancer diagnosis and therapy.Now days,researchers have been show ing interest to fabricate the novel nanomaterials and nanostructures with dual MRI/SERSimaging applications.

The compositescombined with MRI-active super-paramagnetic iron oxide nanoparticles and SERS-active gold substrates were prepared in 2011,in order for in vivo magnetic resonance imaging and Raman spectroscopy[7].In 2012,a distinct triple-modality Au@SiO2@DOTA-Gd composite was synthesized and explored in brain tumor imaging and resection[8].But,the smaller size and aggregation problems related to super-paramagnetic iron oxide nanoparticles restrict their usage in nanomedicine.The toxicity and nephrogenic systemic fi brosis(NSF)are also associated with commercially available Gd complex.For SERS application,silver nanoparticles are good SERSsubstrates,but they are toxic and easy to be oxidized.Gold nanoparticles have better stability and biocompatibility,therefore,gold nanopartilcles are often used as SERS substrate[9,10].The gold nanoparticles has excellent SERS property in biodetection[11,12].To resolve these issues,we designed new MRI/SERS probe consisting of Fe3O4/Au nanocomposites.Recently,gold-coated Fe3O4nanorose clusters were synthesized for cancer cell targeting,imaging and therapy[13,14].But these studies were not focused on the fields of MRI/SERS applications.In 2014,a new type of magneto-plasmonic Au-Fe alloy nanoparticles was designed for multimode SERS/MRI/CT imaging[15].However,the studies about MRI/SERSproperties of Fe3O4/Au were infancy.

In this work,Fe3O4microspheres with an average size of?130 nm were used to design splat-shaped Fe3O4/Au nanocomposites for MRI/SERSmultimode imaging applications.There are some advantages of this prepared material such as the Fe3O4are composed of tiny nanoparticles with super-paramagnetic nature and the gold nanoparticles can be grow n on the modified surfaces of these microspheres uniformly.The uniform gold nanoparticles have more SERS “hot pot”to enhance the SERS property.The results of this investigation demonstrate the effectiveness of these unique splat-shaped nanocomposites as an excellent combined MRIand SERSagent for cancer detection.

In the experiments,tw o steps are employed to fabricate the splat-like Fe3O4/Au nanocomposites.Firstly,simple hydrothermal method is used to prepare the spherical Fe3O4NPs in which FeCl3?6H2O,sodium 2-hydroxypropane tricarboxylate,and NaOAc?3H2O were mixed in ethylene glycol(EG)and resulting mixture was heated at 200?C for 10 h[16].To enhance the solubility of as-synthesized NPs,the surfaces of Fe3O4microspheres are modified with polyetherimide(PEI)containing lots of amino group,which was improved by zeta potential study of Fe3O4and Fe3O4/PEI microsphere(Fig.S1 in Supporting information).Finally,the seed mediated grow th method is used to grow the gold nanoparticles onto the surface of the modified Fe3O4microspheres[17].The synthesis procedure for Fe3O4/Au composites is show n in Scheme 1.

Fig.1 show s the transmission electron microscopy(TEM)images and UV–vis absorption characteristics of the Fe3O4and Fe3O4/Au nanostructures.It is clear from the TEM images that the microspheres are composed of tiny nanoparticles,and the average size is about 130 nm(Fig.1a).Fig.1b illustrates the gold nanoparticles with an average size of 10 nm that is grow n on the surface of Fe3O4microsphere uniformly shaped NPsin the form of splat-like structure,which can be indicated by energydispersive X-ray spectroscopy(EDS)spectra inserted in Fig.1b.Compared with the UV–vis absorption spectra of Fe3O4microspheres in Fig.1c,an additional absorption peak is observed at 532 nm for Fe3O4/Au nanocomposites,which is attributed to the gold plasmonic oscillations indicating the formation of gold nanoparticles[18].All the X-ray pow der diffraction(XRD)peaks of the Fe3O4/Au composites(Fig.1d)are well indexed to the structure of gold nanoparticles or Fe3O4[19].

To examine the feasibility of the composites in the bioapplications,the toxicity of the nanoparticles was assessed with human breast cancer cells(MCF-7)by using the 3-(4,5-dimethyliazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)method as described before[20].A 2.0 m L sample of MCF-7 in complete Dulbecco’s modified eagle medium(DMEM)were seeded into each well at 6?105cells per well and allowed to adhere at 37?C.After 24 h,the DMEM medium was then changed to a fresh medium containing different amounts of the nanoparticles(0.115,0.229,0.343 mol of Fe)in 2 m L of the DMEM medium,and cells were incubated for 24 h.As show n in Fig.2,no signi fi cant cell death or proliferation defects are recorded with different concentrations(corresponding to the weight concentration of Fe3O4/Au composites).This result suggests that Fe3O4/Au nanocomposites do not pose any considerable toxicity problem to the cells.

The magnetic hysteresis(Fig.S2 in Supporting information)and MRIrelaxavitiesvalues(Fig.S3 in Supporting information)of splatlike Fe3O4/Au nanostructures are show n in Supporting information.The magnetic properties of the samples were measured at 298 K with the magnetic fi eld sweeping from?30 k Oe to+30 k Oe.The magnetization saturation values are about 69.6,58.7 and 33.6 emu/g for Fe3O4,Fe3O4/PEI and Fe3O4/Au,respectively.Compared to Fe3O4,the PEI and gold are the nonmagnetic materials.Therefore,the magnetization saturation value decreases with the addition of nonmagnetic materials[21].The slope of the Fe3O4/Au is 64 and 1 L mmol?1s?1for r2and r1,respectively,which is better than that reported[22].This result suggested that synthesized material can be an excellent T2contrast agent for MRI application.

Schem e 1.Synthetic process of Fe3O4/Au nanocomposites.

Fig.2.The MCF-7 cell viability data for unmodified Fe3O4/Au nanocomposites(1#)and folic acid modified Fe3O4/Au nanocomposites(2#).

Fig.1.TEM images of Fe3O4(a)and Fe3O4/Au nanocomposites(b).(c)UV–vis spectra of Fe3O4 and Fe3O4/Au nanocomposites.(d)XRD pattern of Fe3O4/Au nanocomposites.

Fig.3.(a)Raman spectrum collected on MCF-7 cell(show n in inset image of Fig.3a).(b)MRIimagesof the Fe3O4/Au nanocompositesdispersed in agarose gel(left)and MCF-7 cells incubated with different concentration of Fe3O4/Au nanocomposites(right).

The in vitro MRI and SERS detection in the MCF-7 cells were studied(Fig.3).For the SERS in vitro experiment,0.229 mol(corresponding to the Fe concentration)of the Fe3O4/Au nanocomposites was dispersed in 2 m L of DMEM and incubated with the cells for 4 h at 37?C.Tw o peaks were observed in Fig.3a at 1078 cm?1and 1583 cm?1,which are attributed to the C??S and C??C band shift of the 4-ATP,respectively[23].The good SERS property was also studied without cells,which is show n in Fig.S4(Supporting information).For MRI detection,the 1%low-melting point agarose gels were prepared to simulate the human living tissue.The cells were removed from the wells,washed with phosphate buffer saline(PBS)tw ice and detached with trypsin-EDTA.The cells were centrifuged tw ice and were dispersed in 1%low-melting agarose gel at a density of 5?106cells/m L.A signi fi cant dark contrast is obtained which is also increasing with Fe concentrations(Fig.3b).All the images were obtained at the same clinical magnetic resonance imager with the same sequence.These results revealed that the Fe3O4/Au nanocomposites can be used as SERSand T2-weighted MRIcancer detection.

In conclusion,unique splat-shaped Fe3O4/Au nanostructures were synthesized by using the seed grow th mechanism of secondary particle(Au)onto the primary particle(Fe3O4).Effective T2-weighted MRIand SERSdata were obtained after incubation for 4 h with MCF-7 cancer cells without any toxicity.These results clearly demonstrated that as-synthesized splat-like Fe3O4/Au nanocomposites are a promising MRI/SERSmultifunctional agent for the tumor detection.

Ack now led gm ents

This work was fi nancially supported by the National Natural Science Foundation of China(Nos.21305148,U1732127,U1432114,51303196), the Ningbo Natural Science Foundation(Nos.2014A610159, 2014B82010, 2015C50004, 2015B11002,2016A610013, 2017C110022), Zhejiang Province (Nos.Bsh1202031, 2017C33129, 2017C03042, 2018KY737 and LY18H180011), Zhejiang Pharmaceutical College (No.ZPCSR2015013),Hundred Talents Program of Chinese Academy of Sciences(No.2010-735).The authors also thank Dr.Juan Li from our group for the fruitful discussion.N.Hosmane thanks the Chinese Academy of Science for the Visiting Professorship for Senior International Scientists and Northern Illinois University for granting the leave of absence.

Appendix A.Supplem entary data

Supplementary data associated with thisarticle can be found,in the online version,at https://doi.org/10.1016/j.cclet.2018.01.028.