Immobilization of iron hydroxide/oxide on reduced graphene oxide: Peroxidase-like activity and selective detection of sulfide ions

Article abstract of DOI:10.1039/c4ra05047a

We prepared nanocomposites of amorphous iron hydroxide/oxide immobilized on reduced graphene oxide (FeO_xH-rGO) with peroxidase-like activity for the detection of sulfide (S^2-) ions. FeO_xH-rGO nanocomposites were prepared by reaction of GO (size ～ 300 nm) partially reduced by ultraviolet irradiation with Fe²⁺in Tris-borate solution (5.0 mM, pH 7.0). The amorphous FeO(OH) and Fe(OH)₂were immobilized on rGO to form FeO_xH-rGO nanocomposites. The as-prepared FeO_xH-rGO nanocomposites exhibited peroxidase-like catalytic activity in the H₂O₂-mediated oxidation of Amplex Red (AR) to fluorescent resorufin. Our AR/FeO_xH-rGO probe allowed the detection of H₂O₂down to 50 nM within 10 min under microwave irradiation (170 W). The catalytic activity of FeO_xH-rGO was significantly suppressed in the presence of S^2-because of the formation of FeS on the FeO_xH-rGO nanocomposites' surfaces. The H₂O₂/AR-FeO_xH-rGO probe provided a limit of detection (signal-to-noise ratio = 3) of 50 nM for S^2-with high selectivity (>100-fold) with respect to other anions. Taking advantage of their high stability and selectivity, we employed our H₂O₂/AR-FeO_xH-rGO probe for the detection of S^2-in hot spring samples (75.1-619.5 μM) and the results showed good correlation (r = 0.98) with results from inductively coupled plasma mass spectrometry. This label-free, rapid, and simple sensing system shows great potential for the detection of S^2-ions in real samples. This journal is

Full text of DOI:10.1039/c4ra05047a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Immobilization of iron hydroxide/oxide on reduced
graphene oxide: peroxidase-like activity and
selective detection of sulfide ions†
Cite this: RSC Adv., 2014, 4, 37705
a
b
c
b
Kuang-I Hsu, Chia-Wen Lien, Chia-Hua Lin, Huan-Tsung Chang*
ade
and Chih-Ching Huang*
We prepared nanocomposites of amorphous iron hydroxide/oxide immobilized on reduced graphene
2ꢀ
oxide (FeO
x x
H–rGO) with peroxidase-like activity for the detection of sulfide (S ) ions. FeO H–rGO
nanocomposites were prepared by reaction of GO (size ꢁ 300 nm) partially reduced by ultraviolet
2+
irradiation with Fe in Tris–borate solution (5.0 mM, pH 7.0). The amorphous FeO(OH) and Fe(OH)
were immobilized on rGO to form FeO H–rGO nanocomposites. The as-prepared FeO H–rGO
nanocomposites exhibited peroxidase-like catalytic activity in the H -mediated oxidation of Amplex
Red (AR) to fluorescent resorufin. Our AR/FeO H–rGO probe allowed the detection of H down to 50
nM within 10 min under microwave irradiation (170 W). The catalytic activity of FeO H–rGO was
significantly suppressed in the presence of S because of the formation of FeS on the FeO H–rGO
nanocomposites' surfaces. The H /AR–FeO H–rGO probe provided a limit of detection (signal-to-
noise ratio ¼ 3) of 50 nM for S with high selectivity (>100-fold) with respect to other anions. Taking
advantage of their high stability and selectivity, we employed our H /AR–FeO H–rGO probe for the
detection of S in hot spring samples (75.1–619.5 mM) and the results showed good correlation (r ¼
.98) with results from inductively coupled plasma mass spectrometry. This label-free, rapid, and simple
2
x
x
2
O
2
x
2 2
O
x
2
ꢀ
x
O
2 2
x
2ꢀ
Received 28th May 2014
Accepted 12th August 2014
2
O
2
x
2ꢀ
DOI: 10.1039/c4ra05047a
0
2ꢀ
www.rsc.org/advances
sensing system shows great potential for the detection of S ions in real samples.
nanomaterials, specically bimetallic nanoparticles (NPs) and
hybrid nanomaterials. For example, it has been found that
1
Introduction
3
–5
Natural enzymes possess high substrate specicity and high many noble metal-based NPs, including AuBi, AuPt, AuHg,
catalytic efficiency, and have been extensively investigated in AuPb, AgAu, and AgPt bimetallic alloy NPs, exhibit high catalytic
3
many applications such as medicine, environmental analysis, activity. The enzyme-like activity (oxidase, peroxidase, and
1
and food processing. However, the catalytic activities of natural catalase) of Au NPs can be tuned by reaction of different metal
4
3+
+
2+
enzymes are easily affected by environmental conditions such ions. For example, Au NPs in the presence of Bi , Ag , and Hg
as pH, temperature, ionic strength, surfactants, and organic exhibit peroxidase-, oxidase-, and catalase-like activities by
2
solvents. In recent years, great attention has been paid to the forming AuBi, AuAg, and AuHg alloy nanolayers on particle
4
construction and discovery of novel enzyme mimetic surfaces, respectively. Furthermore, it has been demonstrated
that graphene-based carbon materials promote electron trans-
fer between the substrate and catalytic NPs, and improve their
Institute of Bioscience and Biotechnology, National Taiwan Ocean University, 2, dispersibility. Many graphene-supported metal NPs or metal
5
a
Pei-Ning Road, Keelung, 20224, Taiwan. E-mail: huanging@ntou.edu.tw; Fax: +886- oxide NP hybrid nanomaterials, including Au@Pd nano-
2
-24622034; Tel: +886-2-24622192 ext. 5517
particle–graphene hybrids, graphene oxide–Fe O magnetic
3
4
b
Department of Chemistry, National Taiwan University, 1, Section 4, Roosevelt Road,
Taipei 10617, Taiwan. E-mail: changht@ntu.edu.tw; Fax: +886-2-33661171; Tel:
nanocomposites, Co O -reduced graphene oxide (rGO) nano-
3
4
composites, and CoFe
2
O
4
immobilized on rGO nano-
+
886-2-33661171
c
composites, have been shown to act as peroxidase mimics for
H O -mediated reactions. Furthermore, these graphene-based
2 2
Key Laboratory for Nano-Bio Interface Research, Suzhou Key Laboratory for
Nanotheranostics, Division of Nanobiomedicine, Suzhou Institute of Nano-Tech and
Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
6
hybrid nanomaterials have been employed for the detection of
d
6,7
Center of Excellence for Marine Bioenvironment and Biotechnology (CMBB), National
glucose and DNA, and cancer cells and degradation of dyes.
Taiwan Ocean University, 2, Pei-Ning Road, Keelung, 20224, Taiwan
e
2ꢀ
The sulde anion (S ) is a traditional toxic pollutant found
School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, 100, Shih-
in water owing to not only industrial wastewater but also
microbial reduction of sulfate by anaerobic bacteria and the
Chuan 1st Road, Kaohsiung 80708, Taiwan
†
Electronic supplementary information (ESI) available. Fig. S1–S9. See DOI:
8
sulfur-containing amino acids in meat proteins. Once
1
0.1039/c4ra05047a
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 37705–37713 | 37705

View Article Online
RSC Advances
Paper
x
Scheme 1 Schematic representation of the preparation of peroxidase-like FeO H–rGO nanocomposites for the detection of sulfide ions based
on the inhibition of enzymatic activity.
protonated, H
Continuous and high concentration exposure to H
2
S is even more toxic than the sulde itself. sulde, and graphite (7–11 mm) were obtained from Alfa Aesar
S can cause (Ward Hill, MA, USA). Hydrogen peroxide was purchased from
2
various physiological and biochemical problems such as SHOWA (Tokyo, Japan). Sulfuric acid and phosphoric acid were
Down's syndrome, Alzheimer's disease, diabetes, respiratory purchased from J. T. Baker (Phillipsburg, NJ, USA). Milli-Q
9
paralysis, and liver cirrhosis. Thus, a rapid and sensitive ultrapure water (Millipore, Billerica, MA, USA) was used in all
2
ꢀ
method for the detection of S is essential for environmental experiments. The buffer used in this study was a solution
protection, clinical diagnostics, and microbial infestations. So of Tris–borate (50 mM, pH 7.0 adjusted Tris with 200 mM boric
far, many methods have been employed for the determination acid).
2
ꢀ
of S concentrations, including titration, spectroscopy, elec-
10
trochemistry, chromatography, and combinations thereof.
2
.2 Preparation of FeO
GO was synthesized using an improved Hummers' method.
Briey, a mixture of graphite akes (0.75 g) and KMnO (4.5 g)
and H PO
x
H–rGO
However, these probing systems are time-consuming, compli-
cated procedures, requiring large sample volumes and special-
ized skills. Thus, there is a need to develop sensitive and simple
probes not only for qualitative analysis but also for determina-
1
2
4
was added to a 9 : 1 mixture of concentrated H
(100 mL). The mixture was then heated to 50 C and stirred for
2
SO
4
3
4
ꢂ
2
ꢀ
tion of S in real samples at trace levels.
1
2 h. The reaction was cooled to room temperature in an ice
bath, and then poured into 100 mL of deionized (DI) water
containing 3 mL of 30% H . The aqueous mixture was then
In this study, we immobilized iron hydroxide/oxide on rGO
from rGO (size ꢁ 300 nm; prepared from irradiation of GO with
2
+
O
2 2
UV light for 5 h) and iron ions (Fe ) in 5.0 mM Tris–borate
centrifuged at a relative centrifugal force of 35 000g for 1 h, and
the supernatant was decanted. The remaining pellet was
repeatedly washed with 200 mL of DI water until the washings
reached a pH of 7.0. The aqueous solution was then sonicated
for 1 h and centrifuged at a relative centrifugal force of 25 000g
for 0.5 h. The GO solution was collected and the remaining
pellet was discarded. The GO concentration in the supernatant
solution (pH 7.0). The iron(III) oxide-hydroxide [FeO(OH)] and
iron(II) hydroxide [Fe(OH) ] were immobilized on rGO to form
2
FeO H–rGO nanocomposites. The FeO H–rGO nanocomposites
x
x
exhibited high catalytic activity for the H
of Amplex Red (AR; 10-acetyl-3,7-dihydroxyphenoxazine) to
uorescent resorun (7-hydroxy-3H-phenoxazin-3-one)
Scheme 1). To demonstrate the practicality of FeO H–rGO,
the as-prepared FeO H–rGO nanocomposites were rst
employed for the rapid detection of H O assisted with micro-
2 2
O -mediated oxidation

11
(
x
ꢀ1
was determined to be ꢁ1.2 g L
(denoted as the 100ꢃ
x
concentration for simplicity) using the freeze-drying method.
The reduced graphene oxide (rGO) was prepared from irradia-
tion of 10ꢃ GO in 5.0 mM Tris–borate solution (pH 7.0) with a
2
2
wave irradiation. We further applied the AR/H O –FeO H–rGO
2
2
x
2
ꢀ
system for the sensing of S based on the analyte-induced
inhibition of the catalytic activity of FeO H–rGO nano-
composites (Scheme 1). The practicality of this approach was
ꢀ2
hand-held UV lamp (365 nm; 140 mW cm ) for 5 h. For prep-
x
aration of FeO
in a Tris–borate solution (5.0 mM, pH 7.0) and reacted for 1 h.
The resulting FeO(OH) and Fe(OH) were immobilized on rGO
to form the FeO H–rGO nanocomposites.
x
H–rGO, FeCl
2
(100 mM) was mixed with GO (1ꢃ)
2
ꢀ
validated through the detection of S in stream water, lake
water, tap water, and hot springs.
2
x
2
Experimental
2
.3 Characterization
Transmission electron microscope (TEM) images of the rGO
Tris(hydroxymethyl)aminomethane (Tris), hydrochloric acid, and FeO H–rGO nanocomposites were recorded using a Hitachi
2.1 Chemicals
x
boric acid, and all metal salts used in this study were purchased H7100 TEM, operated at 75 kV. Samples for TEM and energy-
from Mallinckrodt Baker (Phillipsburg, NJ, USA). AR was dispersive X-ray spectroscopy (EDS) measurements were
purchased from Invitrogen (Eugene, Oregon, USA). Sodium prepared by placing aliquots (20 mL) of the rGO or FeO H–rGO
x
cyanide, sodium thiocyanate, sodium acetate, sodium bromide, solutions on a carbon-coated copper grid (copper 200 mesh).
sodium chloride, sodium carbonate, sodium iodide, sodium Aer standing for 2 h at ambient temperature, the solution of
nitrate, sodium phosphate, potassium permanganate, sodium rGO or FeO H–rGO was removed. EDS analysis of FeO H–rGO
x x
37706 | RSC Adv., 2014, 4, 37705–37713
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
using a 0.7 nm diameter electron probe was employed to with
a
constant AR concentration (10 mM) were also
determine their chemical identities. X-ray diffraction (XRD) investigated.
samples were prepared by depositing FeO H–rGO on a Si(100)
x
wafer, and XRD measurements were performed at room
temperature using a Rigaku 18 kW rotating anode source X-ray
2.7 Analysis of real samples
Water samples collected from a stream near the National Tai-
wan Ocean University campus, a lake on the National Taiwan
University campus, and local tap water were ltered through a
diffractometer (The Woodlands, Texas, USA) with the Cu Ka1
˚
line (l ¼ 1.54 A, energy ¼ 8.8 keV) operated at 50 kV, 100 mA,
2
and slits set at 10 ꢃ 2 mm . X-ray photoelectron spectroscopy
2
ꢀ
0
.22 mm membrane. For the detection of S , aliquots (300 mL)
of the Tris–borate solution (5.0 mM, pH 7.0) containing
FeO
H–rGO (0.167ꢃ) were equilibrated at room temperature for
0 min. The 2-fold diluted water samples were spiked with S
0–5.0 mM) in a Tris–borate solution (100 mL, 5.0 mM, pH 7.0)
and then separately added to the FeO H–rGO nanocomposite
solutions. Aer reacting for 30 min, the Tris–borate solution
(XPS) was performed using a VG ESCA scientic theta probe
spectrometer (Uppsala, Sweden) in the constant analyzer energy
mode with a pass energy of 28 eV and Al Ka (1486.6 eV) radiation
as the excitation source. Raman spectra were recorded using a
Raman spectrometer (DongWoo 500i; KyungGiDo, Korea)
equipped with a 50ꢃ objective Nd:YAG laser (532 nm) and a
charge-coupled detector. The signal collection time for each
sample was 30 s. A Zetasizer 3000HS analyzer (Malvern Instru-
ments, Malvern, UK) was used for analysis of dynamic light
x
2ꢀ
1
(
x
(
100 mL, 5.0 mM, pH 7.0) containing AR (50 mM) and H O2
2
(50 mM) was added to each of the mixtures and le for 2 h before

uorescence measurements with excitation at 530 nm.
scattering and zeta potential of rGO and FeO H–rGO
x
Hot spring water samples collected from Yangmingshan
nanocomposites.
National Park were ltered through a 0.22 mm membrane. For
2
ꢀ
the detection of S , aliquots (300 mL) of the Tris–borate solu-
tion (5.0 mM, pH 7.0) containing FeO
H–rGO (0.167ꢃ) were
Aliquots (400 mL) of Tris–borate solutions (5.0 mM, pH 7.0) equilibrated at room temperature for 10 min. The 40-fold
2.4 Peroxidase-like activity assay
x
2
+
containing Fe (125 mM), GO (1.25ꢃ), FeO
x
H–GO (1.25ꢃ), rGO diluted hot spring water samples were prepared in a Tris–borate
(
1.25ꢃ), or FeO H–rGO (1.25ꢃ) were equilibrated at room solution (100 mL, 5.0 mM, pH 7.0) and then separately added to
x
temperature for 1 h. Tris–borate solution (100 mL, 5.0 mM, pH the FeO H–rGO nanocomposite solutions. Aer reacting for 30
x
7
.0) containing AR (50 mM) and H O (500 mM) was then added min, the Tris–borate solution (100 mL, 5.0 mM, pH 7.0) con-
2 2
to each of the mixtures and le for 2 h before uorescence taining AR (50 mM) and H O (50 mM) was added to each of the
2
2
measurements with excitation at 530 nm (Synergy 4 mono- mixtures and le for 2 h before uorescence measurements
chromatic microplate spectrophotometer, Biotek Instruments, with excitation at 530 nm. Moreover, all samples were analyzed
Winooski, VT, USA).
by inductively coupled plasma-mass spectrometry (ICP-MS;
700 Series, Agilent Technologies, California, USA); the samples
were prepared in 2% HNO3.
7
2
ꢀ
2
.5 Catalytic sensing of S
Aliquots (350 mL) of the Tris–borate solution (5.0 mM, pH 7.0)
containing FeO
temperature for 10 min. Tris–borate solution (50 mL, 5.0 mM,
x
H–rGO (0.143ꢃ) were equilibrated at room 3 Results and discussion
3
.1 Peroxidase-like activity of FeO H–rGO
x
2ꢀ
pH 7.0) containing S (0–15 mM) was separately added to each
of the FeO H–rGO nanocomposite solutions and le for an
additional 30 min. Tris–borate solution (100 mL, 5.0 mM, pH
.0) containing AR (50 mM) and H O (50 mM) was then added to
The peroxidase-like activity of the FeO H–rGO nanocomposites
x
x
was evaluated using the typical peroxidase substrate AR in the
presence of H
2 2 2 2
O . H O acted as an electron acceptor of the
7
2
2
FeO H–rGO nanocomposites for the catalytic oxidation of AR
x
each of the mixtures and le for 2 h before uorescence
measurements with excitation at 530 nm.
with a 1 : 1 stoichiometry, which yielded a highly uorescent
and colored product, resorun (quantum yield: 0.83; absorption
4
ꢀ1
ꢀ1
13
coefficient: 5.4 ꢃ 10 cm
M
at 570 nm). The AR was
2.6 Enzyme kinetic analysis
selected as the substrate based on the stability of its oxidized
Kinetic measurements were conducted with a black 96-well product (resorun) at pH values greater than 5.0 and its high
microplate using a Synergy 4 monochromatic microplate spec- quantum yield (>80%) as well as long excitation and emission
trophotometer. The AR/H
180 mL, pH 7.0) were separately added to each well of a much sensitive (>100-fold) than colorimetric ones, we expected
microtiter plate, and aliquots (20 mL) of peroxidase-like our H /AR–FeO H–rGO probe to provide a comparatively
FeO
H–rGO nanocomposite solutions (1ꢃ) were then added to lower LOD values for S . In our previous study, we found that
the plate. The reaction progress was monitored every 30 s for 2 h 3,3 ,5,5 -tetramethylbenzidine (TMB) was not
2 2
O substrates in Tris–borate solution wavelengths. Moreover, uorescence-based sensors are typically
(
2
O
2
x
2
ꢀ
14
x
0
0
a
suitable
by recording the uorescence of the reaction product, resorun, substrate for nanoparticles-mediated catalytic oxidation of AR
at 585 nm with an excitation wavelength of 530 nm. Variable in the presence of H O in neutral solution, mainly because
2
2
concentrations (0.5–25 mM) of AR with a constant H O
TMB could only react with H O by natural peroxidase and
2 2
2
2
concentration (10 mM) were investigated in the catalytic reac- peroxidase mimic nanoparticles at low pH values (3.0–5.0). The
tions. In addition, variable H
2
O
2
concentrations (100–7500 mM) FeO
x
H–rGO nanocomposites likely catalyzed a one-electron
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 37705–37713 | 37707

View Article Online
RSC Advances
Paper
oxidation of a nonuorescent AR to form a nonuorescent AR measurement further revealed the FeO(OH) (43.2%) and
15
radical. Subsequently, these two AR radicals underwent an Fe(OH)2 (50.4%) are the major species in the FeO H–rGO
x
enzyme-independent dismutation reaction to form uorescent nanocomposite (Fig. S3, ESI†). Moreover, no crystalline FeO H
x
2
+
resorun. The Fe , GO, and rGO exhibited relatively low cata- was found in the XRD image (data not shown), suggesting that
lytic activity for the H -mediated AR reaction (curves a, b, and the deposited FeO(OH) and Fe(OH) are amorphous. Recently,
d in Fig. 1A). In contrast, the FeO H–GO and FeO H–rGO (curves amorphous FeOOH and Fe(OH) nanostructures have been
2
O
2
2
x
x
2
c and e in Fig. 1A) relative to GO and rGO exhibited 70- and 770- employed as catalysts for photoelectrochemical water splitting,
fold uorescence intensity at 585 nm when excited at 530 nm. electrode materials for lithium-ion batteries, and degradation
17,18
Our results indicated that FeO
x
H–rGO nanocomposites have of dye pollutants.
To our knowledge, however, amorphous
high peroxidase-like activity. The catalytic mechanism of FeOOH and Fe(OH) used as enzyme-like materials in solution
2
FeO H–rGO nanocomposites may follow Fenton-like reactions have not been attempted, although its specic surface area is
x
2
+
3+
16
due to Fe /Fe in deposited FeO H. When FeCl2 was higher than crystalline iron oxide (such as Fe O and Fe O ).
x
2
3
3 4
2
prepared in Tris–borate solution (5.0 mM, pH 7.0), the iron(III) FeOOH and Fe(OH) are merely used as catalysts in homoge-
2
+
+
oxide-hydroxide (4Fe + O
2
+ 6H
2
O / 4FeO(OH) + 8H ) and nous aqueous solution, probably because their nanostructures
2
+
+
iron(II) hydroxide (Fe + 2H
and immobilized on GO or rGO. As shown in Fig. 2B and C, the suspended in the solution. Another disadvantage of amorphous
FeO H nanostructures were randomly distributed on the FeOOH and Fe(OH) is their tendency to form crystalline iron
surface of GO and rGO. oxides or dissolve in preparation or storage, which may greatly
2
O / Fe(OH) + 2H ) were formed are difficult to conne; they easily exist as gel-like structures
2
16
x
2
The Raman spectra of FeO H–rGO revealed that the FeO(OH) reduce their catalytic activity as their surface area is greatly
x
and Fe(OH) species were dominant on rGO (Fig. S1, ESI†). The diminished. We noted that our rGO-supported FeO(OH) and
2
ꢀ
1
peaks at 210, 272, 384, and 995 cm were assigned to FeO(OH), Fe(OH)
2
were stable in aqueous solution at room temperature
. In for at least two months. This phenomenon is presumably due to
H was evalu- the strong association of FeO(OH) and Fe(OH) with rGO,
ated by the EDS measurement to be about 1.98 : 1, consistent improving their stability.
with that of FeOOH or Fe(OH) (Fig. S2, ESI†). The XPS We noted that the peroxidase-like activity of FeO
curve e in Fig. 1) was about 10-fold higher than that of
ꢀ
1
while the bands at 580 cm were attributed to Fe(OH)
addition, the atomic ratio of O to Fe of bare FeO
2
x
2
2
x
H–rGO
(
FeO H–GO (curve c in Fig. 1). This may be attributed to the fact
x
that rGO has a stronger adsorption ability to AR and higher
19
conductivity. The UV-vis absorption spectra of GO show a
broad absorption band with a shoulder in the UV region. The
absorption band (230 nm) was attributed to the p / p* tran-
2
sition of the C]C bond in the sp hybrid region. The shoulder
at ꢁ300 nm was caused by the n / p* electronic transition of
20
peroxide and/or epoxide functional groups in GO. The slightly
stronger absorption of rGO indicated that some oxygen-con-
taining carbons were reduced to C]C, which can provide more
p orbitals for adsorption of AR molecules via p–p stacking and
transfer of electrons to oxidize AR. Relative to GO, the higher
ratio of C]C/C–C (86.2% versus 56.9%; Fig. S4, ESI†) of rGO
further supports our reasoning. We also noted that at constant
concentrations of AR (500 nM) and GO or rGO (1ꢃ), about 70%
and 95% of AR molecules were adsorbed on GO and rGO,
respectively. It has been reported that enzyme-mimicking
nanoparticles transfer electrons between pairs of different
3
–5
oxidation states of metal ions to drive their catalytic activity.
2
+
3+
Therefore, the various valence states of Fe /Fe on particle
surfaces and high conductivity of rGO accounted for the
nanocomposites' high peroxidase-like activity.
Fig. 1 (A) Fluorescence spectra of 5.0 mM Tris–borate (pH 7.0) con-
2
+
taining AR (10 mM) and H
mM), (b) GO (1ꢃ), (c) FeO
mM) in Tris–borate solution], (d) rGO (1ꢃ), and (e) FeO
2 2
O (100 mM) in the presence of (a) Fe (100
2
+
x
H–GO [prepared from GO (1ꢃ) and Fe (100
H–rGO
prepared from rGO (1ꢃ) and Fe (100 mM) in Tris–borate solution]. (B) We demonstrated that rGO plays an important role in
UV-vis absorption spectra of 5.0 mM Tris–borate (pH 7.0) in the
presence of (a) GO, (b) FeO H–GO, (c) rGO, and (d) FeO H–rGO. Inset
to (A): photograph of the fluorescence of the solutions upon excitation
under a hand-held UV lamp (365 nm). The fluorescence intensity (I
3
.2 Effect of irradiation
x
2+
[
x
enhancing the catalytic activity of FeO H. Fig. 3 shows that the
catalytic activity of FeO H–rGO nanocomposites was increased
with increasing UV-irradiation time in the preparation of rGO.
The uorescence intensity of resorun at 585 nm increased
initially on increasing the irradiation time before reaching a
x
x
x
F
)
and absorption (Abs) are plotted in arbitrary units (a. u.). The excitation
wavelength in (A) was set at 530 nm.
37708 | RSC Adv., 2014, 4, 37705–37713
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 2 (A–C) Low-magnification TEM images of 5.0 mM Tris–borate (pH 7.0) containing (A) rGO (1ꢃ), (B) FeO
x
H–GO (1ꢃ), and (C) FeO
x
H–rGO
H–rGO (1ꢃ). Other
(
1ꢃ) and (D and E) high-magnification TEM images of 5.0 mM Tris–borate (pH 7.0) containing (D) FeO
x
H–GO (1ꢃ) and (E) FeO
x
conditions were the same as those described in Fig. 1.
AR–FeO H–rGO probe allowed detection of H O concentra-
x
2 2
tions down to 1.0 mM under the catalytic reaction time of 2 h
curve a in Fig. S6, ESI†). To shorten the analysis time (<10 min),
(
we employed microwave irradiation to aid the catalytic reaction.
Microwave heating is one type of electroheating technique that
21
utilizes specic wavelengths of electromagnetic energy. When
applying microwave irradiation to metallic and metal oxide
nanomaterials, the electric and magnetic components change
rapidly, and the molecules cannot respond quickly to the
change in direction, giving rise to friction and therefore causing
22
them to quickly warm up. The acceleration of the catalytic
reaction rate of H /AR–FeO H–rGO under microwave irradi-
ation is probably due to the superheating effect produced in a
2
O
2
x
23
microwave eld. The heat and electron transfer of FeO
x
H–rGO
Fig. 3 Fluorescence response (IF585) of 5.0 mM Tris–borate (pH 7.0)
was strongly inuenced aer GO interacted with the microwave
containing AR (10 mM), H
2
O
2
(100 mM), and FeO
x
H–rGO [prepared
24

eld. It has been demonstrated that metal oxide–rGO nano-
2+
from Fe (100 mM) and UV-irradiated (0–10 h) GO (1ꢃ)]. Error bars
composites have better dielectric constants due to the signi-
represent the standard deviations from three repeated experiments.
24
The fluorescence intensities at 585 (IF585) are plotted in arbitrary units cantly increased conductivity from rGO.
Metal oxides
(
a. u.). Other conditions were the same as those described in Fig. 1.
incorporated with rGO could have enhanced microwave-
25
absorbing properties. In addition, the different dielectric
properties of the liquid and FeO H–rGO nanocomposites might
x
plateau at ꢁ5 h. This result is consistent with the UV-vis result in localized temperature differences, creating strong
absorption of rGO, which was prepared from GO with different convection currents at the surface of the microwaved
2
4,25
UV-irradiation times (0–10 h; Fig. S5, ESI†). The color of GO FeO H–rGO nanocomposites.
(
Therefore, diffusions of the
rGO) solutions changed from light brown to dark black and reaction products were rapidly promoted away from the surface.
absorbance became stronger with increasing UV-irradiation Under the assistance of microwave irradiation (170 W), our
time, from 0 to 10 h. Under optimized conditions for the AR–FeO H–rGO probe allowed the detection of H with a
preparation of rGO (irradiation of GO with UV light for 5 h), our limit of detection (LOD; signal-to-noise (S/N) ratio ¼ 3) of
x
x
2 2
O
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 37705–37713 | 37709

View Article Online
RSC Advances
Paper
ꢁ
50 nM within 10 min (curve b in Fig. S5, ESI†). One of the Table 1 Comparison of the apparent Michaelis constant (K
M
) and
maximal velocity (vmax) between FeO
x
H–rGO nanocomposites (0.1ꢃ)
possible factors for this ultrahigh sensitivity for H O is the
2
2
2
ꢀ
in the absence and presence of S (10 mM)
microwave temperature; under microwave irradiation of 170 W,
ꢂ
the reaction temperature was raised to ꢁ75 C. However, we
ꢀ1
Catalyst
Substrate
K
M
(mM)
v
max (mM s
)
noted that the reaction time needed to reach completion was
ꢀ3
ꢂ
2
h even at 75 C (data not shown). In another control experi- FeO
x
x
x
x
H–rGO
H–rGO + S
H–rGO
AR
AR
3.67
5.16
1.3 ꢃ 10
7.1 ꢃ 10
5.6 ꢃ 10
2.2 ꢃ 10
2
ꢀ
ꢀ4
FeO
FeO
FeO
ment, we noted the microwave irradiation caused negligible
ꢀ4
H
H
2
O
O
2
2
326
166

uorescence change to 5.0 mM Tris–borate (pH 7.0) solution
containing AR (10 mM)–H (10 mM). This microwave-assisted
catalytic reaction not only shortened the analysis time to
0 min, but also provided near one order of magnitude greater
sensitivity than the above results. Compared with other GO- equation (1/n ¼ K /v
2ꢀ
ꢀ4
H–rGO + S
2
2 2
O
1
M
max
(1/[S] + 1/K )), the kinetic data,
based nanocomposites with peroxidase-like activities, the including the Michaelis constant (K ) and maximal velocity
M
M
preparation of FeO
x
x
H–rGO is relatively simple and cost-effective (vmax) of FeO H–rGO nanocomposites in the absence and
2
ꢀ
and the AR–FeO H–rGO probe shows comparable sensitivity for presence of S , were calculated and are listed in Table 1. From
x
6,7
H
2
O
2
detection.
the double reciprocal plots of catalytic velocity against one of
the substrate concentrations when the other substrate was xed
at three concentration levels, we demonstrated that the catalytic
3.3 Sensing of sulde
reaction of H
2 2 x
O /AR–FeO H–rGO followed a ping-pong mecha-
Fig. 4A (curve b) reveals the poorly developed uorescence
intensity of the H O /AR–FeO H–rGO (0.1ꢃ) system in the
nism because the slopes of the lines were parallel (Fig. S7,
2
2
x
26
ESI†). This result revealed that, like HRP, the FeO H–rGO
2
ꢀ
x
presence of S (10 mM) in Tris–borate solution (5.0 mM, pH
nanocomposites bind and react with the rst substrate (AR or
7
S
.0). The low catalytic activity of FeO
x
H–rGO in the presence of
is presumably because of the formation of FeS and Fe on
H–rGO due to the strong affinity of S for surface iron
H O ) and then release the rst product before reacting with the
2
ꢀ
2 2
2 3
S
other substrate. K
catalyst NPs for the substrates. By comparing the apparent
kinetic parameters, the
composites in the presence of S with AR as the substrate was
M
is oen associated with the affinity of the
2
ꢀ
the FeO
ions on nanocomposites Fe (Ksp (FeS) ꢁ 6 ꢃ 10 ) and Fe
x
2
+
ꢀ19
3+
K
M
value of FeO
x
H–rGO nano-
ꢀ
88
(K
sp (Fe
2
S
3
) ꢁ 1 ꢃ 10 ). The formation of FeS and Fe
2 3
S
2
ꢀ
may block the active sites of FeO H–rGO and diminish their
x
2ꢀ
slightly higher than that in the absence of S , revealing that
peroxidase-like activity. The EDS (Fig. 4B) and Raman
spectra (Fig. 4C) further supported that sulde was
FeO H–rGO nanocomposites have a lower affinity with AR when
x
FeS and/or Fe S were deposited on their surfaces. The K value
2
3
M
ꢀ
deposited on FeO
quantify that about 95% of S (10 mM) ions were binding to
FeO
H–rGO (0.1ꢃ). According to the Michaelis–Menten
x
H–rGO. In addition, we used ICP-MS to
2
of FeO H–rGO nanocomposites in the presence of S with
2
ꢀ
x
H
2
O
2
as the substrate was slightly lower than that for
x
FeO
that FeS and Fe
FeO H–rGO nanocomposites in the presence of S have a lower
for H
, the ꢁ2.5-fold lower vmax value indicated that the
deposited FeS and Fe S did not promote the catalytic reaction.
x
H–rGO nanocomposites alone, which agrees with reports
27
2 3 2 2
S have a strong affinity with H O . Although
2
ꢀ
x
K
M
2 2
O
2
3
We further investigated the selectivity and sensitivity of the
H O (10 mM)/AR (10 mM)–FeO H–rGO (0.1ꢃ) probe for sensing
2
2
x
2
ꢀ
S
x
. The catalytic activity of FeO H–rGO was signicantly
2ꢀ
reduced by S at room temperature, when compared with other
tested anions, including CH
NO
Fig. 5A, the concentration of each anion was 10 mM). In addi-
tion, tolerance concentrations of the other anions (within a
ꢀ
3ꢀ
2ꢀ
2ꢀ
43ꢀ
3
COO , PO
4
, S
2
O
3
, SO
4
,
ꢀ ꢀ ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3 2 2
, Cl , Br , I , NO , CN , SCN , AsO , and AsO
(
2
ꢀ
relative error of ꢄ5%) during the sensing of S (10 mM) with the
H O /AR–FeO H–rGO probe were at least 100 times higher than
2
2
x
ꢀ
2
that of the S (Fig. S8, ESI†). The uorescence response of the
H
2
O
2
/AR–FeO
x
H–rGO probe decreased on increasing the
2
ꢀ
concentration of S
ions (Fig. 5B). We obtained a linear
)/IF0 against the
response in the plot of the expression (IF0 ꢀ I
F
2ꢀ
concentration of S over the range 0.1–1.5 mM (r ¼ 0.99), where
IF0 and I represent the uorescence intensities of the mixtures
F
2
ꢀ
in the absence and presence, respectively, of the added S . The
H O /AR–FeO H–rGO probe provided an LOD for S
Fig. 4 (A) Fluorescence spectra of 5.0 mM Tris–borate (pH 7.0)
containing AR (10 mM), H (10 mM), and FeO H–rGO (0.1X) in the (a)
absence and (b) presence of S (10 mM). (B) EDS and (C) Raman
2
ꢀ
ions
2
2
x
2
O
2
x
2
ꢀ
2ꢀ
(
S/N ¼ 3) of ꢁ50 nM. This LOD for S was comparable to those
2ꢀ
28,29
spectra of FeO
x
H–rGO (10X) in the presence of S (1.0 mM).
using other optical sensors with functional nanoparticles.
37710 | RSC Adv., 2014, 4, 37705–37713
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 6 Comparison between ICP-MS and the H
2
O
2
/AR–FeO
x
H–rGO
2
ꢀ
probe for detection of S in hot spring water samples. There was a
2ꢀ
linear correlation between the S concentrations in five hot spring
waters determined using ICP-MS and H /AR–FeO H–rGO assays.
2
O
2
x
Error bars represent the standard deviations from three repeated
experiments.
2
ꢀ
sensing approach could detect the presence of any S ions in
these original water samples. We further applied the
2
ꢀ
H O /AR–FeO H–rGO probe to determine the S ions in ve
2
2
x
sulfur spring waters collected from Yangmingshan National
Park (Taipei, Taiwan). Fig. shows the good linear
correlation (r ¼ 0.98) between the results obtained using the
/AR–FeO H–rGO probe and ICP-MS over concentrations
2
ꢀ
2 2 x
Fig. 5 (A) Selectivity of the H O /AR–FeO H–rGO probe toward S
6
ions. Fluorescence response (IF585) of 5.0 mM Tris–borate solution (pH
.0) containing AR (10 mM), H (10 mM), and FeO H–rGO nano-
composites (0.1ꢃ) in the absence or presence of anions (10 mM) at 585
nm. (B) Validation of the use of H /AR–FeO H–rGO probe for the
detection of S (0–1.5 mM). The inset to (B): values of (IF0 ꢀ I )/IF0 were
represent the fluores-
cence intensities of the solutions at 585 nm in the absence and
presence of S , respectively. Error bars in the inset represent the
standard deviations from three repeated experiments. Other condi-
tions were the same as those described in Fig. 4.
7
2
O
2
x
H
2
O
2
x
O
2 2
x
ranging from 75.1 to 619.5 mM, suggesting that our probe is
2
ꢀ
F
2ꢀ
useful for screening S concentrations in hot spring waters.
2ꢀ
plotted against S concentration. IF0 and I
F
Therefore, the proposed methods are applicable for practical
2
ꢀ
2ꢀ
analysis of S in environmental samples.
4
Conclusions
In summary, nanocomposites of amorphous FeO H immobi-
x
Although the sensitivities of some chemosensors are higher
lized on rGO (FeO H–rGO) were successfully synthesized by the
x
2 2 x
than the H O /AR–FeO H–rGO probe, those chemosensors
simple reaction of GO partially reduced by ultraviolet irradia-
require complicated and multistep complicated synthesis and
2
+
tion with Fe in aqueous solution. We demonstrated that
FeO H–rGO nanocomposites exhibit intrinsic peroxidase-like
activity. With the assistance of microwave irradiation, our AR/
FeO H–rGO probe allowed detection of H down to 50 nM
within 10 min. In the presence of S , the catalytic activity of
FeO H–rGO became lower because the formation of FeS and
Fe2S3 may block the active sites of FeO H–rGO. The H O /
30
use of sophisticated equipment.
x
2
ꢀ
3
.4 Detection of S in real samples
x
2 2
O
2ꢀ
To validate that our proposed sensing strategy could have
2
ꢀ
x
practical application for S
analysis in water samples, we
x
2 2
applied the H /AR–FeO H–rGO sensor to determine the levels
2
O
2
x
2
ꢀ
2
ꢀ
AR–FeO
high selectivity (>100-fold). Owing to the high stability and
selectivity of the nanocomposites, the H /AR–FeO H–rGO
probe allowed the detection of S in hot spring waters (75.1–
19.5 mM) and the results showed good correlation (r ¼ 0.98)
with ICP-MS. This label-free, low cost, and rapid nanosensor
x
H–rGO probe provided an LOD of 50 nM for S with
of S in stream, lake, and tap water samples. Before analysis,
each of the three samples were ltered through a 0.22 mm
membrane and diluted 10-fold in 5.0 mM Tris–borate solution
2
O
2
x
2
ꢀ
(
pH 7.0). Here, we obtained linear correlations (r ¼ 0.98–0.99)
between the relative uorescence changes ((IF0 ꢀ I )/IF0) and the
concentration of spiked S (Fig. S9, ESI†), where IF0 and I
represent the uorescence intensities of the mixtures in the
6
F
2
ꢀ
F
2
ꢀ
holds great potential for screening S in real water samples.
2ꢀ
absence and presence, respectively, of the spiked S . In these
measurements, the probe provided recoveries of 104.2–107.3%
Acknowledgements
2
ꢀ
2ꢀ
for S ions (0.5 mM). The minimum concentration of S ions
detectable by our H /AR–FeO
samples was ꢁ100 nM. Neither an ICP-MS-based system nor our Technology of Taiwan under contracts NSC 101-2628-M-019-
2
O
2
x
H–rGO probe in these water This study was supported by the Ministry of Science and
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 37705–37713 | 37711

View Article Online
RSC Advances
01-MY3, 102-2113-M-019-001-MY3 and 102-2627-M-019-001-
Paper
0
B. Zhang and J. Tang, ACS Appl. Mater. Interfaces, 2013, 5,
3809–3815; (i) Z. Xing, J. Tian, A. M. Asiri, A. H. Qusti,
A. O. Al-Youbi and X. Sun, Biosens. Bioelectron., 2014, 52,
MY3.
452–457.
Notes and references
8
(a) C. L. Corkhill and D. J. Vaughan, Appl. Geochem., 2009, 24,
2342–2361; (b) M. J. Hawkesford and L. J. De Kok, Plant, Cell
Environ., 2006, 29, 382–395; (c) E. Pouokam, J. Steidle and
M. Diener, Biol. Pharm. Bull., 2011, 34, 789–793; (d)
P. F. Lito, J. P. S. Aniceto and C. M. Silva, Water, Air, Soil
Pollut., 2012, 223, 6133–6155.
9 (a) Q. Li and J. R. Lancaster Jr, Nitric Oxide Biol. Chem., 2013,
35, 21–34; (b) D. J. Polhemus and D. J. Lefer, Circ. Res., 2014,
114, 730–737; (c) S. Mani, A. Untereiner, L. Wu and R. Wang,
Antioxid. Redox Signaling, 2014, 20, 805–817; (d)
G. K. Kolluru, X. Shen, S. C. Bir and C. G. Kevil, Nitric
Oxide Biol. Chem., 2013, 35, 5–20.
1
2
(a) L. M. Podust and D. H. Sherman, Nat. Prod. Rep., 2012, 29,
251–1266; (b) J. A. Gerlt and P. C. Babbitt, Curr. Opin. Chem.
Biol., 2009, 13, 10–18; (c) R. Masella, R. Di Benedetto, R. Var `ı ,
C. Filesi and C. Giovannini, J. Nutr. Biochem., 2005, 16, 577–
1
586.
(a) M. Naushad, Z. A. ALOthman, A. B. Khan and M. Ali, Int. J.
Biol. Macromol., 2012, 51, 555–560; (b) P. V. Iyer and
L. Ananthanarayan, Process Biochem., 2008, 43, 1019–1032;
(
c) C. Mateo, J. M. Palomo, G. Fernandez-Lorente,
J. M. Guisan and R. Fernandez-Lafuente, Enzyme Microb.
Technol., 2007, 40, 1451–1463; (d) G. Feller, J. Phys.:
Condens. Matter, 2010, 22, 323101; (e) S. Yabuki, Anal. Sci., 10 (a) S. K. Pandey, K.-H. Kim and K.-T. Tang, TrAC, Trends Anal.
2
014, 30, 213–217.
Chem., 2012, 32, 87–99; (b) P. Nagy, Z. P ´a link ´a s, A. Nagy,
B. Budai, I. T ´o th and A. Vasas, Biochim. Biophys. Acta, Gen.
Subj., 2014, 1840, 876–891; (c) X. Hu and B. Mutus, Rev.
Anal. Chem., 2013, 32, 247–256; (d) V. S. Lin and
C. J. Chang, Curr. Opin. Chem. Biol., 2012, 16, 595–601; (e)
H. Peng, W. Chen, S. Burroughs and B. Wang, Curr. Org.
Chem., 2013, 17, 641–653.
3
(a) C.-W. Lien, C.-C. Huang and H.-T. Chang, Chem.
Commun., 2012, 48, 7952–7954; (b) W. He, Y. Liu, J. Yuan,
J.-J. Yin, X. Wu, X. Hu, K. Zhang, J. Liu, C. Chen, Y. Ji and
Y. Guo, Biomaterials, 2011, 32, 1139–1147; (c) C.-I. Wang,
C.-C. Huang, Y.-W. Lin, W.-T. Chen and H.-T. Chang, Anal.
Chim. Acta, 2012, 745, 124–130; (d) C.-I. Wang, W.-T. Chen
and H.-T. Chang, Anal. Chem., 2012, 84, 9706–9712; (e) 11 M. Zhou, Z. Diwu, N. Panchuk-Voloshina and
H. You, Z. Peng, J. Wu and H. Yang, Chem. Commun., 2011,
R. P. Haugland, Anal. Biochem., 1997, 253, 162–168.
7, 12595–12597; (f) Y. Chen, H. Cao, W. Shi, H. Liu and 12 (a) W. S. Hummers Jr and R. E. Offeman, J. Am. Chem. Soc.,
4
Y. Huang, Chem. Commun., 2013, 49, 5013–5015.
C.-W. Lien, Y.-C. Chen, H.-T. Chang and C.-C. Huang,
Nanoscale, 2013, 5, 8227–8234.
1958, 80, 1339; (b) D. C. Marcano, D. V. Kosynkin,
J. M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L. B. Alemany,
W. Lu and J. M. Tour, ACS Nano, 2010, 4, 4806–4814.
4
5
(a) J. Zhu, M. Chen, Q. He, L. Shao, S. Wei and Z. Guo, RSC 13 B. Zhao, F. A. Summers and R. P. Mason, Free Radical Biol.
Adv., 2013, 3, 22790–22824; (b) B. F. MacHado and P. Serp, Med., 2012, 53, 1080–1087.
Catal. Sci. Technol., 2012, 2, 54–75; (c) G. Blanita and 14 C.-W. Lien, Y.-T. Tseng, C.-C. Huang and H.-T. Chang, Anal.
M. D. Lazar, Micro Nanosyst., 2013, 5, 138–146; (d) Y. Liang,
Chem., 2014, 86, 2065–2072.
Y. Li, H. Wang and H. Dai, J. Am. Chem. Soc., 2013, 135, 15 (a) J. V. Rodrigues and C. M. Gomes, Free Radical Biol. Med.,
2
013–2036.
2010, 49, 61–66; (b) H. H. Gorris and D. R. Walt, J. Am. Chem.
Soc., 2009, 131, 6277–6282.
6
(a) H. Chen, Y. Li, F. Zhang, G. Zhang and X. Fan, J. Mater.
Chem., 2011, 21, 17658–17661; (b) Y.-L. Dong, H.-G. Zhang, 16 (a) S. Wang, Dyes Pigm., 2008, 76, 714–720; (b) E. G. Garrido-
Z. U. Rahman, L. Su, X.-J. Chen, J. Hu and X.-G. Chen,
Nanoscale, 2012, 4, 3969–3976; (c) J. Xie, H. Cao, H. Jiang,
Y. Chen, W. Shi, H. Zheng and Y. Huang, Anal. Chim. Acta,
Ram ´ı rez, B. K. G. Theng and M. L. Mora, Appl. Clay Sci., 2010,
47, 182–192; (c) J. V. Coelho, M. S. Guedes, R. G. Prado,
J. Tronto, J. D. Ardisson, M. C. Pereira and
L. C. A. Oliveira, Appl. Catal., B, 2014, 144, 792–799; (d)
N. A. Zubir, C. Yacou, J. Motuzas, X. Zhang and J. C. Diniz
da Costa, Sci. Rep., 2014, 4, 4594.
2
013, 796, 92–100; (d) J. Hao, Z. Zhang, W. Yang, B. Lu,
X. Ke, B. Zhang and J. Tang, J. Mater. Chem. A, 2013, 1,
352–4357.
4
7
(a) G. Nie, L. Zhang, X. Lu, X. Bian, W. Sun and C. Wang, 17 (a) F. Peng, T. Luo, L. Qiu and Y. Yuan, Mater. Res. Bull.,
Dalton Trans., 2013, 42, 14006–14013; (b) X. Chen, X. Tian,
B. Su, Z. Huang and M. Oyama, Dalton Trans., 2014, 43,
2013, 48, 2180–2185; (b) K. Zhang, V. Dwivedi, C. Chi and
J. Wu, J. Hazard. Mater., 2010, 182, 162–168; (c)
M.-L. Chen, L.-M. Shen, S. Chen, H. Wang, X.-W. Chen and
J.-H. Wang, J. Mater. Chem. B, 2013, 1, 2582–2589; (d)
G. Huang, C. Zhang, Y. Long, J. Wynn, Y. Liu, W. Wang
and J. Gao, Nanotechnology, 2013, 24, 395601; (e) Y. Sun,
X. Hu, W. Luo, H. Xu, C. Hu and Y. Huang, ACS Appl.
Mater. Interfaces, 2013, 5, 10145–10150.
7449–7454; (c) Y. Ye, T. Kong, X. Yu, Y. Wu, K. Zhang and
X. Wang, Talanta, 2012, 89, 417–421; (d) M. I. Kim,
M. S. Kim, M.-A. Woo, Y. Ye, K. S. Kang, J. Lee and
H. G. Park, Nanoscale, 2014, 6, 1529–1536; (e) Y. Tao,
Y. Lin, Z. Huang, J. Ren and X. Qu, Adv. Mater., 2013, 25,
2594–2599; (f) L.-N. Zhang, H.-H. Deng, F.-L. Lin, X.-W. Xu,
S.-H. Weng, A.-L. Liu, X.-H. Lin, X.-H. Xia and W. Chen, 18 (a) W. D. Chemelewski, H.-C. Lee, J.-F. Lin, A. J. Bard and
Anal. Chem., 2014, 86, 2711–2718; (g) L. Deng, C. Chen,
C. Zhu, S. Dong and H. Lu, Biosens. Bioelectron., 2014, 52,
C. B. Mullins, J. Am. Chem. Soc., 2014, 136, 2843–2850; (b)
J. Jung, K. Song, D. R. Bae, S. W. Lee, G. Lee and
Y.-M. Kang, Nanoscale, 2013, 5, 11845–11849; (c) Z. Xu,
324–329; (h) Z. Zhang, J. Hao, W. Yang, B. Lu, X. Ke,
37712 | RSC Adv., 2014, 4, 37705–37713
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
M. Zhang, J. Wu, J. Liang, L. Zhou and B. Lǚ, Water Sci.
RSC Advances
M. Zong and Y. Wang, Mater. Sci. Eng., B, 2013, 178, 1403–
1409; (d) L. Wang, Y. Huang, X. Sun, H. Huang, P. Liu,
M. Zong and Y. Wang, Nanoscale, 2014, 6, 3157–3164.
Technol., 2013, 68, 2178–2185; (d) M. Mohapatra and
S. Anand, Int. J. Eng. Sci. Technol., 2010, 2, 127–146.
19 (a) Y. Liu, G.-Q. Qi, C.-L. Liang, R.-Y. Bao, W. Yang, B.-H. Xie 26 (a) Y. L. Liu, X. J. Zhao, X. X. Yang and Y. F. Li, Analyst, 2013,
and M.-B. Yang, J. Mater. Chem. C, 2014, 2, 3846–38540; (b)
K. H. Lee, B. Lee, S.-J. Hwang, J.-U. Lee, H. Cheong,
O.-S. Kwon, K. Shin and N. H. Hur, Carbon, 2014, 69, 327–
138, 4526–4531; (b) G. Reginald and C. M. Grisham, in
Biochemistry, Cengage Learning, Belmont, 4th edn, 2010,
part 2, ch. 13, pp. 406–407; (c) F. Deyhimi and F. Nami, Int.
J. Chem. Kinet., 2012, 44, 699–704; (d) L. S. Zamorano,
N. F. Cuadrado, P. P. Galende, M. G. Roig and
V. L. Shnyrov, J. Biophys. Chem., 2012, 3, 16–28.
3
35; (c) A. T. U. Nugrahenny, J. Kim, S.-K. Kim, D.-H. Peck,
S.-H. Yoon and D.-H. Jung, Carbon Lett., 2014, 15, 38–44;
d) J.-H. Yun, Y. H. Ng, R. J. Wong and R. Amal,
(
ChemCatChem, 2013, 5, 3060–3067.
0 (a) X. Tian, S. Sarkar, A. Pekker, M. L. Moser, I. Kalinina,
E. Bekyarova, M. E. Itkis and R. C. Haddon, Carbon, 2014,
27 (a) Z. Dai, S. Liu, J. Bao and H. Ju, Chem.–Eur. J., 2009, 15,
4321–4326; (b) A. K. Dutta, S. K. Maji, D. N. Srivastava,
A. Mondal, P. Biswas, P. Paul and B. Adhikary, ACS Appl.
Mater. Interfaces, 2012, 4, 1919–1927.
2
72, 82–88; (b) F. T. Thema, M. J. Moloto, E. D. Dikio,
N. N. Nyangiwe, L. Kotsedi, M. Maaza and M. Khenfouch, 28 (a) X. Hou, F. Zeng, F. Du and S. Wu, Nanotechnology, 2013,
J. Chem., 2013, 150536.
1 A. K. Datta and V. Rakesh, Compr. Rev. Food Sci. Food Saf.,
24, 335502; (b) A. Hatamie, B. Zargar and A. Jalali, Talanta,
2014, 121, 234–238; (c) A. H. Gore, S. B. Vatre,
P. V. Anbhule, S.-H. Han, S. R. Patil and G. B. Kolekar,
Analyst, 2013, 138, 1329–1333; (d) Z.-X. Wang, C.-L. Zheng,
Q.-L. Li and S.-N. Ding, Analyst, 2014, 139, 1751–1755.
2
2
2
2
2013, 12, 24–39.
2 C. Qiang, J. Xu, Z. Zhang, L. Tian, S. Xiao, Y. Liu and P. Xu, J.
Alloys Compd., 2010, 506, 93–97.
3 P. Kl ´a n, J. Liter ´a k and S. Relich, J. Photochem. Photobiol., A, 29 (a) J. Zhang, X. Xu and X. Yang, Analyst, 2012, 137, 1556–
2001, 143, 49–57.
1558; (b) Z.-X. Wang, C.-L. Zheng and S.-N. Ding, RSC Adv.,
2014, 4, 9825–9829; (c) A. Pandya, K. V. Joshi, N. R. Modi
and S. K. Menon, Sens. Actuators, B, 2012, 168, 54–61; (d)
L.-X. Chen, D.-W. Li, L.-L. Qu, Y.-T. Li and Y.-T. Long, Anal.
Methods, 2013, 5, 6579–6582.
4 (a) P. Liu and Y. Huang, J. Polym. Res., 2014, 21, 430; (b)
G. M. Barbosa, M. M. Mosso, C. Vilani, D. R. G. Larrud ´e ,
E. C. Romani and L. F. Fernando Jr, Microw. Opt. Technol.
Lett., 2014, 56, 560–563; (c) J. A. Men ´e ndez, A. Arenillas,
B. Fidalgo, Y. Fern ´a ndez, L. Zubizarreta, E. G. Calvo and 30 (a) X. Cao, W. Lin and L. He, Org. Lett., 2011, 13, 4716–4719;
J. M. Berm u´ dez, Fuel Process. Technol., 2010, 91, 1–8.
5 (a) J. Zheng, H. Lv, X. Lin, G. Ji, X. Li and Y. Du, J. Alloys
Compd., 2014, 589, 174–181; (b) X. Zhao, Z. Zhang,
L. Wang, K. Xi, Q. Cao, D. Wang, Y. Yang and Y. Du, Sci.
Rep., 2013, 3, 3421; (c) L. Wang, Y. Huang, X. Ding, P. Liu,
(b) L. Zhang, X. Lou, Y. Yu, J. Qin and Z. Li, Macromolecules,
2011, 44, 5186–5193; (c) C. Kar and G. Das, J. Photochem.
Photobiol., A, 2013, 251, 128–133; (d) M.-Q. Wang, K. Li,
J.-T. Hou, M.-Y. Wu, Z. Huang and X.-Q. Yu, J. Org. Chem.,
2012, 77, 8350–8354.
2
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 37705–37713 | 37713