Yolk–shell hybrid nanoparticles with magnetic and pH-sensitive properties for controlled anticancer drug delivery

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ISSN 2040-3364

2040-3364(2010)2:1;1-T

COVER ARTICLEGraham et al.Mixed metal nanoparticle assembly and the effect on surface-enhanced Raman scattering

REVIEWLin et al.Progress of nanocrystalline growth kinetics based on oriented attachment

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umber 1 | 2010

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Graphical Abstract

Yolk–shell hybrid nanoparticles with magnetic and

pH-sensitive properties for controlled anticancer drug

delivery

Shunxing Li,*ab

Jianzhong Zheng,ac

Dejian Chen,a Yijin Wu,

a Wuxiang

Zhang,a Fengying Zheng,

ab Jing Cao,

c Heran Ma,

c and Yaling Liu

*c

aDepartment of Chemistry and Environmental Science, MinNan Normal University, Zhangzhou 363000, P. R.

China.

Shunxing Li E-mail: [email protected]; Tel: +86 596 2591395; Fax: +86 596 2591395

bFujian Provincial Key Laboratory of Modern Analytical Science and Separation Technology, Zhangzhou 363000,

P. R. China

cLaboratory for Nanomaterials, National Center for Nanoscience and Technology, Beijing, 100190, P. R. China

Yaling Liu E-mail: [email protected]; Tel: +86 82545603; Fax: +86 62656765

A facile and effective way for preparation of nano-sized

Fe3O4@graphene yolk-shell nanoparticles via hydrothermal method is

developed. Moreover, the targeting properties of the materials for

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View Article OnlineDOI: 10.1039/C3NR04032A


anticancer drug (doxorubicin hydrochloride) delivery are investigated.

Excitingly, these hybrid materials possess favorable dispersibility, good

superparamagnetism (the magnetic saturation value is 45.740 emu/g),

high saturated loading capacity (2.65 mg/mg), and effective loading

(88.3%). More importantly, the composites exhibit strong pH-triggered

drug release response (at the pH value of 5.6 and 7.4, the release rate was

24.86% and 10.28%, respectively) and good biocompatibility over a

broad concentration range of 0.25-100 µg/mL (the cell viability was

98.52% even in the high concentration of 100 µg/mL), which shed light

on bright future for bio-related applications.

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Yolk–shell hybrid nanoparticles with magnetic and

pH-sensitive properties for controlled anticancer drug delivery

Shunxing Li,*ab

Jianzhong Zheng,ac

Dejian Chen,a Yijin Wu,

a Wuxiang Zhang,

a

Fengying Zheng,ab

Jing Cao,c Heran Ma,

c and Yaling Liu

*c

aDepartment of Chemistry and Environmental Science, MinNan Normal University, Zhangzhou 363000, P. R. China.

Shunxing Li E-mail: [email protected]; Tel: +86 596 2591395; Fax: +86 596 2591395

bFujian Provincial Key Laboratory of Modern Analytical Science and Separation Technology, Zhangzhou 363000, P. R. China

cLaboratory for Nanomaterials, National Center for Nanoscience and Technology, Beijing, 100190, P. R. China

Yaling Liu E-mail: [email protected]; Tel: +86 82545603; Fax: +86 62656765


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Abstract

A facile and effective way for preparation of nano-sized Fe3O4@graphene

yolk-shell nanoparticles via hydrothermal method is developed. Moreover, the

targeting properties of the materials for anticancer drug (doxorubicin hydrochloride)

delivery are investigated. Excitingly, these hybrid materials possess favorable

dispersibility, good superparamagnetism (the magnetic saturation value is 45.740

emu/g), high saturated loading capacity (2.65 mg/mg), and effective loading (88.3%).

More importantly, the composites exhibit strong pH-triggered drug release response

(at the pH value of 5.6 and 7.4, the release rate was 24.86% and 10.28%, respectively)

and good biocompatibility over a broad concentration range of 0.25-100 µg/mL (the

cell viability was 98.52% even in the high concentration of 100 µg/mL) which shed

light on bright future for bio-related applications.

Keywords: york-shell nanoparticles; magnetic; graphene oxide; drug delivery


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1. Introduction

Hybrid material, a novel mixture of material has garnered a great deal of attention

due to the exciting properties compared with pure counterparts.1 Thus far, much

attention has been focused on the synthesis of hybrid materials in the application of

anticancer drug delivery, one of the important issues which are crucial to human

health.2 Park et al.

3 have synthesized a hybrid nanoparticles in drug delivery.

However, quantum dots were used in this material, which still make toxicity a serious

problem in bio-related applications. Giri et al.4 have designed a stimuli-responsive

controlled-release delivery system, yet this stimuli-responsive approach needed the

process of the functional groups introduced process. Therefore, it is necessary to

develop a facile method for designing a system in the anticancer drug delivery with

stimuli-responsive drug release, no toxicity, as well as good biocompatibility.

Graphene oxide, a new multi-functional hybrid material has attracted extensive

attention because of its novel properties, such as tunable properties by reduction,5

biocompatibility,6

and potential applications in preparation of graphene7 and

controlled drug release.8 So do the magnetic nanomaterials due to their unique

properties of no toxicity, magnetic responsiveness, targeted monitoring of drug

release, and the potential application in biology.9 Recently, there are many reports

about the hybrids based on graphene oxide and magnetic nanomaterials and the

applications in controlling anticancer drug delivery In an earlier report, Li et al.

10

have reported a Fe3O4-graphene hybrid, which was used as anticancer drug delivery.

Although this material owned the property of pH-activated release, the magnetic

saturation value of this material was just 23.096 emu/g, which was much lower than


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that of bare Fe3O4 nanomaterials. Zhang et al.11

have designed Fe3O4/graphene

composites with three-dimensional hierarchical nanosheet structure and explored the

properties in controlled drug delivery. However, the magnetic saturation value was

only 32.85 emu/g, which was not high enough, and the nanoflower-shaped Fe3O4 had

occupied some surface areas of the graphene nanosheets. Moreover, the authors just

used rhodamine B as a model drug, and did not provide the data of cellular toxicity of

this material, which was an important parameter for application in biology.9

Therefore, it is still a challenge to design a magnet/graphene hybrid system with

effective loading, strong magnetic and stimuli-response, as well as good

biocompatibility for application in controlled anticancer drug delivery. Fabrication of

yolk-shell structures is a facile and important procedure for preparation of the

hybrids.12

That is because thanks to the tailorability of both the shells and the interior

cores13

the yolk-shell structure can exhibit multifunctionality and moreover the cavity

in it presents an efficient way for nanoreactor14

and drug delivery.15

In this paper, a simple and effective way for synthesis of Fe3O4@graphene

yolk-shell nanoparticles via hydrothermal method was developed. Moreover, the

targeting properties of the materials for anticancer drug delivery were explored,

which showed that this material not only owned the favorable dispersibility and

dissolution in aqueous solutions but also behaved good superparamagnetism (with the

magnetic saturation value of 45.740 emu/g). Specially, when the concentration of

doxorubicin hydrochloride (DOX) was 300 µg/mL, the saturated loading capacity of

Fe3O4@graphene was 2.65 mg/mg, with a good effective loading of 88.3%. Moreover,

the Fe3O4@graphene yolk-shell nanoparticles exhibited strong pH-triggered drug


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release response and good biocompatibility, indicating a bright future of this kind of

materials for biorelated applications.

2. Experimental

2.1. Materials

Graphite powder was purchased from National medicine group chemical reagent

Co., Ltd. Sodium nitrate (analytical grade), Potassium permanganate (analytical

grade), Hydrochloric acid (analytical grade), Sulfuric acid (analytical grade), Barium

chloride (analytical grade) and Hydrogen peroxide (30%) were purchased from

Shantou west long chemical Co., Ltd. Iron (ш) chloride anhydrous (98%) was

purchased from Alfa Aesar. DOX was purchased from Beijing Huafeng united

Technology Co., Ltd. All chemicals and solvents were used as received. All aqueous

solutions were prepared using ultrapure water (18 MU) from a Milli-Q system

(Millipore).

2.2. Formation of york-shell architecture

The synthesis procedure of Fe3O4@graphene yolk-shell nanoparticles was shown

in Fig. 1. Firstly, graphene oxide was prepared by the modified Hummer’s method16

as follows. Graphite (1.0 g) was combined with concentrated sulfuric acid (23 mL) in

a 1000 mL round bottom flask and stirred in an ice bath. Then, NaNO3 (0.5 g) and

KMnO4 (3.0 g) were slowly added to the suspension at a constant temperature of (0±

1) °C. After that, the mixture was heated at (35±3) °C for 30 min, and then water (46

mL) was slowly added into the mixture and maintained at 98 °C for 15 min,

following by adding of water (140 mL) and 30% H2O2 (2 mL) to end the reaction.


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Thereafter, the suspension was hot filtered and washed with 5% HCl and water in

turn, and small and highly oxidized graphene oxide debris were produced after

washing under alkaline conditions. After that, NaAc (3.0 g) and a suitable amount of

graphene oxide debris solution were added into the homogeneous solution of FeCl3

(1.0 g) dissolving in diethylene glycol (20 mL). Then, the mixture was aided by

ultrasound for 30 min and transferred to a teflonlined stainless-steel autoclave with

200 °C for 6 h. Finally, the black products were obtained and washed several times

with water and ethanol and then dried at 80 °C. Transmission Electron Microscope

(TEM) was conducted on FEI Tecnai G2 S-TWIN and the accelerating voltage was

200 kV. UV-Vis spectra were conducted on a Hitachi U-3010 Spectrophotometer at

room temperature. Thermogravimetric analysis (TGA) was performed using a

NETZSCH TG 209 F1 thermogravimetric analyzer from room temperature to 800 °C

with the heating rate of 10 °C/min and an N2 flow rate of 50 mL/min. The power

X-ray diffraction (XRD) was conducted on D/MAX-TTRIII (CBO). Fluorescence

spectra were measured on BX51 fluorescence spectrometer (Olympus, Japan). HeLa

cell was treated with DOX loaded Fe3O4@graphene nanoparticles for 12 h incubation,

followed by copious wash steps to remove unbound Fe3O4@graphene nanoparticles

before fixing on coverslips for imaging. Raman spectroscopy was measured on

Renishaw inVia plus using 633 nm laser excitation. Microplate reader: Biocell HT2.

The magnetic properties of magnetite materials were carried on PPMS-9 (Quantum

Design).

Fig. 1


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2.3. Loading of Fe3O4@graphene with DOX and release of DOX

Loading of DOX on Fe3O4@graphene was performed by mixing DOX (5 mg) and

Fe3O4@graphene (20 mg) in the PBS buffered solution (Na2HPO4-KH2PO4, 30 mL,

pH=7.4) under ultrasound and then stirring the solution for 12 h at room temperature

in darkness. After that, the product was collected by centrifugation, washed with the

PBS buffer solution for two or three times, and then freeze-dried. The supernatant

was used to monitor the absorbance at 490 nm (the characteristic absorbance of DOX)

relative to a calibration curve recorded under identical conditions to measure the

amount of unbound DOX. The DOX-loading efficiency was calculated as following:

Loading efficiency (％)＝(minjection DOX－mfree DOX)／minjection DOX×100

To study the in vitro release of DOX on Fe3O4@graphene, freeze-dried DOX

loaded Fe3O4@graphene sample (1 mg) was added to the PBS buffer solution (10 mL)

with pH of 5.6 and 7.4 at the temperature of 37 °C, respectively. At selected time

intervals (1 h to 12 h, with step of 1 h) the above samples was centrifuged at 1400

r/min for 3 min, and the supernatants were used to monitor the absorbance at 490 nm

(the characteristic absorbance of DOX) to detect the release of DOX at different pH

value, respectively.

2.4. Cell viability and in vitro cellular study

The in vitro viability tests was analyzed by the methyl thiazolyl tetrazolium (MTT)

method.17

Rat myocardial Cells from exponential cultures were seeded into 96-well

culture plates at a density of 1.0 × 105 cells/cm

2. After attached, the cells were treated

with series of drug concentrations (every concentration were made in fivetuplicate)


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and incubated for 24 h at 37 °C under 5% CO2 atmosphere. To the experimental

group, the above medium was removed, 180 µL/well of dulbecco's modified eagle

medium (DMEM) containing 20 µL MTT（5.0 mg/mL, 0.5% MTT）was added to the

well, and the plates were incubated for 4 h. Then, the supernatant was aspirated, and

150 µL/well DMSO was added, shaking for 10 min at room temperature to dissolve

the crystal produced. The absorbance was measured at 490 nm using a microplate

reader. The spectrophotometer was calibrated to zero absorbance (culture medium,

MTT and DMSO), and the control wells contained cells, the same concentration

solution of drug, culture medium, MTT, and DMSO. Control cytotoxicity

experiments to confirm the biocompatibility of the drug-free carrier and the in vitro

cellular cytotoxicity to HeLa cell line of DOX alone and DOX loaded

Fe3O4@graphene yolk-shell nanoparticles were carried out by following the same

procedure as described above.

3. Results and discussion

3.1. Preparation of Fe3O4@graphene and the corresponding characterization

The morphologies of the samples were imaged by TEM. As illustrated in Fig. 2a,

after hydrothermal treatment the core-shell Fe3O4@graphene nanoparticles with the

multi-graphene shells were synthesized, the average size of which was about 70 nm.

After treatment with HCl, the core-shell Fe3O4@graphene nanoparticles were

transformed to be those with the yolk-shell structures and meanwhile the size was

decreased to about 10 nm (the core diameter is about 60 nm, Fig. 2b). The high

resolution transmission electron microscopy (HRTEM) image and the corresponding


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selected area electron diffraction (SAED) pattern demonstrated that the core was

Fe3O4 (the lattice spacing was 0.48 nm), which was further confirmed by the X-ray

powder diffraction (XRD) pattern (Fig. 2d).

Fig. 2

Fig. 3a shows the thermal property of Fe3O4@graphene yolk-shell nanoparticles

characterized by thermogravimetric analysis (TGA). The significant weight loss

before 105 °C was due to evaporation of the absorbed water molecules on

Fe3O4@graphene yolk-shell nanoparticles, and the subsequent two steps of mass loss

at 168 and 530 °C were attributed to the loss of CO and CO2 from decomposition of

the oxygen functional groups and carbon oxidation of graphene oxide, respectively.

The mass fraction of Fe3O4 was about 82.6%. The mass loss starting at 168 °C for

graphene shells indicated that the thermal stability of this hybrid material was lower

than that of the natural flake graphite, which was may attributed to the incomplete

reduction of graphene oxide.18

In the UV-Vis spectra, to graphene oxide, there was a

characteristic absorption maximum at about 229 nm (Fig. 3b), which was

corresponded to the sp2 hybridized carbon domain (π-π* transition). After the

treatment of Fe3O4@graphene core-shell nanoparticles with enough HCl, the hollow

graphene sphere without the core of Fe3O4 was acquired (inset of Fig. 3b), and the

peak was red-shifted to 259 nm, revealing the partial repair of the electronic

conjugate structure of graphene oxide.5a

These results could be further confirmed by

the Raman spectrum of Fe3O4@graphene yolk-shell nanoparticles (Fig. 3c). There


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were three typical peaks, G peak 1604 cm-1

, D peak 1356cm-1

and 2D peak 2729 cm-1

,

respectively. The G peak is usually associated with first-order scattering of the E2g

mode for sp2 hybridized carbon domain, and the D and 2D peaks are assigned to the

structural defects.19

Furthermore, the ratio of ID and IG was 0.97, indicating the highly

disordered carbon structure and the partial reduction of graphene oxide.20

As the

magnetic saturation value is an important parameter in the magnetic targeted drug

delivery system,9 the hysteresis loops of Fe3O4@graphene yolk-shell nanoparticles

were measured as shown in Fig. 3d. The magnetic saturation value of

Fe3O4@graphene yolk-shell nanoparticles was 45.740 emu/g, a little lower than that

of Fe3O4 nanocrystal.10, 11

Morevoer, the superparamagnetic behavior revealed that

Fe3O4@graphene yolk-shell nanoparticles had very good dispersibility in water

without aggregation owing to the size of Fe3O4.21

Furthermore, the suspension also

exhibited very good magnetic response to the external magnet (inset of Fig. 6).

Namely, these composites could be separated from the solution effectively, indicating

bright applications in biology.

Fig. 3

3.2. Loading and delivery of DOX

DOX, a widely used anticancer drug,22

is chosen to explore the drug delivery

properties of Fe3O4@graphene yolk-shell nanoparticles. As illustrated in Fig. 4a, to

DOX, there was a peak around 490 nm in the UV-Vis spectra (red line in Fig. 4a).

Before the loading of DOX, there were no peaks at about 490 nm to pure


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Fe3O4@graphene yolk-shell nanoparticles (black line in Fig. 4a), however, after the

loading of DOX, a peak appeared at about 490 nm (blue line in Fig. 4a), revealing the

successfully loading of DOX in Fe3O4@graphene yolk-shell nanoparticles. Herein,

drug loading and delivery of Fe3O4@graphene yolk-shell nanoparticles was assessed

using UV-Vis absorbance of DOX at about 490 nm. Moreover, the loading capacity

of DOX in Fe3O4@graphene yolk-shell nanoparticles increased linearly with the

initial concentration of DOX (blue line in Fig. 4b). Excitingly, when the

concentration of DOX was 300 µg/mL, the saturated loading capacity of

Fe3O4@graphene yolk-shell nanoparticles could reach to 2.65 mg/mg (blue line in

Fig. 4b), with load rate of 88.3% (black line in Fig. 4b), contributing to the york-shell

nanostructure, the high surface area of graphene, and the π-π stacking and hydrogen

bonding interaction between graphene and drug.23

Subsequently, the release of DOX

from Fe3O4@graphene yolk-shell nanoparticles was investigated under different pH

conditions. The release rate at the pH of 5.6 and 7.4 was 24.86% and 10.28%,

respectively (Fig. 5), revealing that the acidic condition was more conductive to

release of DOX. That is because, at the low pH of 5.6, the interaction between DOX

and Fe3O4@graphene yolk-shell nanoparticles is broken more easily,10

and the

solubility of DOX can be increased due to the protonated process.24

In comparison to

the reported Fe3O4-based materials,10,11,23b,25

our designed Fe3O4@graphene yolk-shell

nanoparticles exhibited the high saturated loading capacity, effective loading,

magnetic saturation value, high pH-sensitive, as well as biocompatibility for further

application in controlled anticancer drug delivery (Table 1).


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Fig. 4

Fig. 5

Table. 1

3.3. In vitro biocompatibility and cellular assay

Monitoring the biocompatibility of Fe3O4@graphene yolk-shell nanoparticles is

a key to materials’ application in biological systems. As shown in Fig. 6a, cell

viabilities (rat myocardial cells) in the presence of different concentrations of

Fe3O4@graphene yolk-shell nanoparticles (from 0.25 to 100 µg/mL) were determined

and normalized with the cell viability in cell culture for 24 h at the temperature of

37 °C. Impressively, even in the high concentration of 100 µg/mL, the cell viability

could maintain as high as 98.52%, revealing that the Fe3O4@graphene yolk-shell

nanoparticles exhibited good biocompatibility. In addition, the in vitro cellular

cytotoxicity to HeLa cell line of DOX alone and DOX loaded Fe3O4@graphene

yolk-shell nanoparticles was investigated, as shown in Fig. 6b and 6c. Both of the

above material exhibited the time-dependent and dose-dependent cytotoxicity to

HeLa cells. To further study the interaction between the designed hybrid system and

the HeLa cell, fluorescence spectra was used. As shown in Fig. 6d, red fluorescence

was only observed in the cell nucleus, indicting the designed Fe3O4@graphene

yolk-shell nanoparticles could effectively deliver the anti drug to the HeLa cells

nuclei to interact with DNA.


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Fig. 6

4. Conclusion

In summary, nano-sized Fe3O4@graphene yolk-shell nanoparticles were

synthesized by a facile and effective method on the basis of hydrothermal synthesis.

Impressively, this hybrid material exhibited perfect dispersibility in aqueous solutions,

good superparamagnetism (with the magnetic saturation value of 45.740 emu/g), and

high loading capacity of DOX. Moreover, the composites owned the property of

strong pH-triggered drug release response and good biocompatibility, indicating

potential application in biology. This work will shed light on design and fabrication

of new functional biomaterials with novel structures.

Acknowledgement

This work was supported by the National Natural Science Foundation of China

(40506020, 20775067, 20977074, and 21175115, S.X. L.), the Program for New

Century Excellent Talents in University (NCET-11 0904, S.X. L.), Outstanding

Youth Science Foundation of Fujian Province, China (2010J06005, S.X. L.), and the

Science & Technology Committee of Fujian Province, China (2012Y0065, F.Y. Z.).

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Figure and table captions

Fig. 1 A schematic illustration of the formation process of Fe3O4@graphene

yolk-shell nanoparticles.

Fig. 2 Typical TEM images of (a) Fe3O4@graphene core-shell nanoparticles and (b)

Fe3O4@graphene yolk-shell nanoparticles. (c) HRTEM image and SAED pattern

(inset) of the core of Fe3O4@graphene yolk-shell nanoparticles. (d) XRD pattern of

Fe3O4 and Fe3O4@graphene yolk-shell nanoparticles.

Fig. 3 (a) TGA curve of Fe3O4@graphene yolk-shell nanoparticles. (b) UV-Vis

spectra of graphene (black line) and the hollow graphene spheres without the Fe3O4

cores (red line). Inset is the corresponding TEM image of the hollow graphene

spheres without the Fe3O4 cores. (c) Raman spectrum of Fe3O4@graphene yolk-shell

nanoparticles. (d) Magnetization curve of Fe3O4@graphene yolk-shell nanoparticles

measured at 300 K. Inset is the photograph of the stable dispersion of

Fe3O4@graphene yolk-shell nanoparticles in water and the corresponding magnetic

response of the suspension to a magnet after several minutes.

Fig. 4 (a) UV-Vis spectra of DOX (red line), Fe3O4@graphene yolk-shell

nanoparticles (black line) and DOX loaded Fe3O4@graphene yolk-shell nanoparticles

(blue line). (b) Drug loading (black line) and drug loading efficiency (blue line) of

Fe3O4@graphene yolk-shell nanoparticles with different initial concentration of

DOX.

Fig. 5 Time-dependent release of DOX from the Fe3O4@graphene yolk-shell


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nanoparticles at pH 5.6 and 7.4 under 37 °C in the PBS buffer solution, respectively.

Fig. 6 (a) Cell viability of Fe3O4@graphene yolk-shell nanoparticles against rat

myocardial cells with different concentrations. The survival curves of HeLa cells

after different incubation times with different concentration of (b) DOX and (c) DOX

loaded Fe3O4@graphene yolk-shell nanoparticles and (d) fluorescent microscopic

images of HeLa cells labeled by DOX loaded Fe3O4@graphene yolk-shell

nanoparticles for 12 h (fluorescent images by green light excitation).

Table 1 Comparison of the performances of the reported Fe3O4-based materials

and the Fe3O4@graphene yolk-shell nanoparticles synthesized in our work for drug

delivery.


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Figure captions

Fig. 1 A schematic illustration of the formation process of

Fe3O4@graphene yolk-shell nanoparticles.

Fig. 2 Typical TEM images of (a) Fe3O4@graphene core-shell

nanoparticles and (b) Fe3O4@graphene yolk-shell nanoparticles. (c)

HRTEM image and SAED pattern (inset) of the core of Fe3O4@graphene

yolk-shell nanoparticles. (d) XRD pattern of Fe3O4 and Fe3O4@graphene


Fig. 3 (a) TGA curve of Fe3O4@graphene yolk-shell nanoparticles. (b)

UV-Vis spectra of graphene (black line) and the hollow graphene spheres

without the Fe3O4 cores (red line). Inset is the corresponding TEM image

of the hollow graphene spheres without the Fe3O4 cores. (c) Raman

spectrum of Fe3O4@graphene yolk-shell nanoparticles. (d) Magnetization

curve of Fe3O4@graphene yolk-shell nanoparticles measured at 300 K.

Inset is the photograph of the stable dispersion of Fe3O4@graphene

yolk-shell nanoparticles in water and the corresponding magnetic


Fig. 4 (a) UV-Vis spectra of DOX (red line), Fe3O4@graphene

yolk-shell nanoparticles (black line) and DOX loaded Fe3O4@graphene

yolk-shell nanoparticles (blue line). (b) Drug loading (black line) and

drug loading efficiency (blue line) of Fe3O4@graphene yolk-shell

nanoparticles with different initial concentration of DOX.


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Fig. 5 Time-dependent release of DOX from the Fe3O4@graphene

yolk-shell nanoparticles at pH 5.6 and 7.4 under 37 °C in the PBS buffer

solution, respectively.

Fig. 6 (a) Cell viability of Fe3O4@graphene yolk-shell nanoparticles

against rat myocardial cells with different concentrations. The survival

curves of HeLa cells after different incubation times with different

concentration of (b) DOX and (c) DOX loaded Fe3O4@graphene

yolk-shell nanoparticles and (d) fluorescent microscopic images of HeLa

cells labeled by DOX loaded Fe3O4@graphene yolk-shell nanoparticles

for 12 h (fluorescent images by green light excitation).


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Table captions

Table 1 Comparison of the performances of the reported Fe3O4-based

materials and the Fe3O4@graphene yolk-shell nanoparticles synthesized

in our work for drug delivery.


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Fig. 1 A schematic illustration of the formation process of

Fe3O4@graphene yolk-shell nanoparticles.


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Fig. 2 Typical TEM images of (a) Fe3O4@graphene core-shell

nanoparticles and (b) Fe3O4@graphene yolk-shell nanoparticles. (c)

HRTEM image and SAED pattern (inset) of the core of Fe3O4@graphene

yolk-shell nanoparticles. (d) XRD pattern of Fe3O4 and Fe3O4@graphene



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Fig. 3 (a) TGA curve of Fe3O4@graphene yolk-shell nanoparticles. (b)

UV-Vis spectra of graphene (black line) and the hollow graphene spheres

without the Fe3O4 cores (red line). Inset is the corresponding TEM image

of the hollow graphene spheres without the Fe3O4 cores. (c) Raman

spectrum of Fe3O4@graphene yolk-shell nanoparticles. (d) Magnetization

curve of Fe3O4@graphene yolk-shell nanoparticles measured at 300 K.

Inset is the photograph of the stable dispersion of Fe3O4@graphene

yolk-shell nanoparticles in water and the corresponding magnetic



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Fig. 4 (a) UV-Vis spectra of DOX (red line), Fe3O4@graphene yolk-shell

nanoparticles (black line) and DOX loaded Fe3O4@graphene yolk-shell

nanoparticles (blue line). (b) Drug loading (black line) and drug loading

efficiency (blue line) of Fe3O4@graphene yolk-shell nanoparticles with

different initial concentration of DOX.


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Fig. 5 Time-dependent release of DOX from the Fe3O4@graphene

yolk-shell nanoparticles at pH 5.6 and 7.4 under 37 °C in the PBS buffer

solution, respectively.


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Fig. 6 (a) Cell viability of Fe3O4@graphene yolk-shell nanoparticles

against rat myocardial cells with different concentrations. The survival

curves of HeLa cells after different incubation times with different

concentration of (b) DOX and (c) DOX loaded Fe3O4@graphene

yolk-shell nanoparticles and (d) fluorescent microscopic images of HeLa

cells labeled by DOX loaded Fe3O4@graphene yolk-shell nanoparticles

for 12 h (fluorescent images by green light excitation).


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Table 1 Comparison of the performances of the reported Fe3O4-based

materials and the Fe3O4@graphene yolk-shell nanoparticles synthesized

in our work for drug delivery.

Author material and

structure

saturated

loading

capacity

mg/mg

effective

loading pH-sensitive biocompatibility

magnetic

saturation

value

emu/g

Li et al.10

graphene

intercalated Fe3O4

nanoparticles with

3D layer structure

- - -

5-80 µg/mL cell

viability: above

98% (80 µg/mL)

23.096

Zhang et al.11

three-dimensional

hierarchical

Fe3O4/graphene

nanosheet

* * * no 32.85

Zhu et al.23b

grape-like Fe3O4

on the voile-like

graphene sheets

randomly

no 0.65 no no 45.5

Yang et al.25

GO-Fe3O4

nanohybrid 0.387 no

the release rate

(pH 5, 24%)

(pH 7, 7.5%)

no 8.57

This work

Fe3O4@graphene

yolk-shell

nanoparticles

2.65 0.883

the release rate

(pH 5.6, 24.86%)

(pH 7.4, 10.28%)

0.25-100 µg/mL

cell viability:

98.52% (100

µg/mL)

45.740

* Note that the authors used rhodamine B as a model drug.

- Note that the authors used the 5-fluorouracil as a model drug.


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Documents

Yolk–shell hybrid nanoparticles with magnetic and pH-sensitive properties for controlled anticancer drug delivery