Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

Article abstract of DOI:10.1039/c5ra08009f

A surface-enhanced Raman scattering (SERS) sensor of mercury ions based on the coordinated catalytic reaction of Hg²⁺-Ag nanoparticles (NPs) has been designed and constructed for water quality monitoring. We combined Ag NPs (average particle size is 49 nm) with mercury ions to form Hg²⁺-Ag NPs in aqueous phase by electrostatic interactions. The formed Hg²⁺-Ag particles can catalyze a redox reaction between o-phenylendiamine (OPD) and dissolved oxygen to form 2,3-diaminephenazine (DAP), which is Raman-active and possesses a strong SERS signal due to the adherence to Ag NPs. Therefore we can trace the SERS intensity of DAP to determine mercury ions and the lowest detectable concentration of mercury is 1.0 nM using this method. This sensor displays higher sensitivity and selectivity and it possesses a certain value in terms of water quality detection.

Full text of DOI:10.1039/c5ra08009f

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Highly sensitive SERS sensor for mercury ions based
on the catalytic reaction of mercury ion decorated
Ag nanoparticles†
Cite this: RSC Adv., 2015, 5, 49759
a
a
Guohua Qi,a Cuicui Fu,a Gang Chen,ab Shuping Xu and Weiqing Xu
*
A surface-enhanced Raman scattering (SERS) sensor of mercury ions based on the coordinated
catalytic reaction of Hg2+–Ag nanoparticles (NPs) has been designed and constructed for water
quality monitoring. We combined Ag NPs (average particle size is 49 nm) with mercury ions to form
Hg2+–Ag NPs in aqueous phase by electrostatic interactions. The formed Hg2+–Ag particles can
catalyze a redox reaction between o-phenylendiamine (OPD) and dissolved oxygen to form 2,3-
diaminephenazine (DAP), which is Raman-active and possesses a strong SERS signal due to the
adherence to Ag NPs. Therefore we can trace the SERS intensity of DAP to determine mercury ions
and the lowest detectable concentration of mercury is 1.0 nM using this method. This sensor
displays higher sensitivity and selectivity and it possesses a certain value in terms of water quality
detection.
Received 1st May 2015
Accepted 26th May 2015
DOI: 10.1039/c5ra08009f
www.rsc.org/advances
Surface-enhanced Raman spectroscopy (SERS) that
employs molecules adsorbed on the surface of noble metal
1 Introduction
nanoparticle (NP) to enhance their Raman signals has exten-
sive applications in various elds such as drug identication,
catalysis monitoring the reaction process, the treatment of
disease and so on.23 SERS not only can realize qualitative
research, but also can be used for quantitative study in the
eld of analytical chemistry.24,25 It is quite applicable in
aqueous phase and easily identiable due to the ngerprint
characters of probes.
In this work, we propose an indirect SERS sensing method
for mercury ions by a catalytic oxidation reaction. Hg2+–Ag NPs
composed of Ag NPs and mercury ions were used as catalysts
and prepared in water through the electrostatic assembly (A in
Scheme 1), which can catalyze a redox reaction of o-phenyl-
endiamine (OPD) and dissolved oxygen to produce 2,3-dia-
minophenazineand (DAP). The SERS sensing of the growing
DAP can indirectly response for the amount of mercury ions (B
in Scheme 1). The results show that the lowest detectable
concentration of mercury ion is as low as 1.0 nM and this sensor
displays a good selectivity for mercury ions.
Mercury ions are toxic heavy metal ions. They can easily
combine with negatively charged groups (e.g. sulfydryl of
enzymes and proteins in the body),1–6 and alter or destroy
physiological activities by changing their chemical structures.
For living cells, mercury ions can cause metabolic disorder.7–9
Mercury ion poisoning is an accumulation process of mercury
ions in the body through the food chain and drinking water.10,11
The United States of America Environmental Protection Bureau
(EPA) standard code states that inorganic mercury can't exceed
2.0 nM in drinking water.10–12 Therefore, to develop a simple and
selective quantitative determination approach of mercury in
water is of signicance. There are many methods to detect
mercury ions, such as dithizone colorimetric method,13,14
atomic emission spectrometry,15,16 absorption spectrometry,17,18
stripping voltammetry,19,20 and so on. These methods have
disadvantages on that they require long cycle and the complex
pre-treatment of samples. The lowest detectable concentration
is 2.0 nM for dithizone colorimetric method21 and is 11 nM for
stripping voltammetry method.22 So a huge challenge is put
forward to develop a fast respond, high selectivity and sensi-
tivity method for the trace detection of mercury ions.
2 Experimental section
2.1 Material
aState Key Laboratory of Supramolecular Structure and Materials, Institute of
Theoretical Chemistry, Jilin University, 2699 Qianjin Ave., Changchun, People's
Republic of China. E-mail: xuwq@jlu.edu.cn
OPD (reagent grade) was obtained from Tianjin Guang Fu Fine
Chemical Research Institute. Mercury nitrate (reagent grade)
was purchased from Taixing Chemical Reagent Factory. Sodium
citrate (C6H5Na3O7$2H2O, reagent grade) and citric acid
(C6H8O7$H2O, reagent grade) were purchased from Beijing
Chemical Corp. Silver nitrate (reagent grade) was purchased
bCollege of Chemistry, Jilin University, 2699 Qianjin Ave., Changchun, People's
Republic of China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra08009f
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 49759–49764 | 49759

View Article Online
RSC Advances
Paper
Scheme 1 Schematic diagram of the formation of Hg2+–Ag NPs (A) and the SERS sensing for mercury ions by a catalytic oxidation reaction (B).
(C) shows the experimental procedures.
from Shanghai Chemical company. Calcium acetate, barium
acetate, lead acetate, nickelous acetate, tin acetate, cupric
acetate, cobalt acetate, zinc acetate, manganese acetate and
cadmium acetate were obtained from Beijing Chemical Corp.
Deionized water used throughout the experiments was puried
by a Millipore system.
2.2 Synthesis of Hg2+–Ag NPs and their catalytic reaction
First, Ag NPs were synthesized using Lee's method as described
previously.26 From transmission electron microscopic (TEM)
image and size distribution (Fig. 1(a)), we can nd the Ag NPs
synthesized is basically spherical and the average particles size
is 49 nm (Fig. S1b in ESI†). The maximum of the absorbance
wavelength of the Ag NPs is 418 nm (Fig. S1a†). Second, we
mixed 100 mL of Ag NPs and 100 mL of mercury ions solution for
10 min incubated time at room temperature to prepare the
Hg2+–Ag NPs. The Hg2+–Ag NPs were formed via the electrostatic
assembly of mercury ions on the surface of Ag NPs (Scheme 1A)
and their TEM images are shown in Fig. 1(b). It can be found
that the shape and size of the Hg2+–Ag NP has no obvious
difference to the Ag NPs.
To carry out the catalytic reaction, the synthesized Hg2+–Ag
NPs (200 mL with the particle concentration is 3.0 nM) were
added to 100 mL of the freshly prepared 0.02 M OPD in citrate
buffer and then 700 mL of citrate buffer solution (0.1 M) were
ꢀ
added above solution. The mixed solution was heated to 50 C
in water bath for 35 min to complete the transformation of
target OPD.
In order to identify the product of reaction between the OPD
Fig. 1 (a) and (b) TEM images of the Ag NPs and Hg2+–Ag NP. (c)–(e)
and dissolved oxygen, we centrifuged the reaction solution at a
speed of 10 000 rpm. The precipitates were Hg2+–Ag NPs and the TEM mappings of Hg2+–Ag NP prepared by adding 100 mL of Ag NPs
and 100 mL of Hg2+ ion solution (1.0 ꢁ 10ꢂ6 M). (d) and (e) show Hg and
suspension solution obtained through cooling crystallization,
centrifugation and desiccation (Scheme 1C). There are many
needle-like crystals formed in the suspension solution and they
were identied by Fourier transform infrared (FT-IR), mass (MS)
Ag element distribution in this individual Hg2+–Ag nanoparticle (c),
respectively. (f) The elements analysis of an Hg2+–Ag NPs above a
copper grid under TEM.
and SERS spectroscopies.
49760 | RSC Adv., 2015, 5, 49759–49764
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
gas; N2 (30 psi), gas 1; N2 (55 psi), gasꢀ; N2 (50 psi), ion spray
voltage; 5000 V, and temperature; 400 C. The data collection
was carried out in enhanced MS (EMS) mode. For the product,
the protonated molecular ion, [M + H]+, and two conrming
ions were obtained.
2.4 SERS measurements
The reaction solutions were dropped on the 1 cm ꢁ 1 cm silicon
pellet to form a spot with a diameter of 1.5 mm (Scheme 1C and
Fig. S4†).
Then, SERS spectra of the dried solutions were measured
by a confocal Raman system (LabRAM ARAMIS, HORIBA Jobin
Yvon, USA) with a 5 mW/785 nm laser as an excitation source
and actualized by Synapse Thermoelectric cooled charge-
coupled device (CCD) camera (HORIBA Jobin Yvon, USA).
Since the produced DAP has uorescence in the range of 450–
700 nm,27 we chose 785 nm wavelength as the excitation laser
to avoid the uorescence interference (see a comparison of
SERS spectra of DAP under different excitation wavelength,
Fig. S3 in ESI†). Laser excitation and Raman scattering light
collection were through a ꢁ50 microscope objective lens
(numerical aperture ¼ 0.5, LMLFLN, Olympus, Japan). The
outstretched scan spectra with a spectral range from 550 to
1600 cmꢂ1 were obtained with an integration time of 20 s and
two accumulations. The 520.7 cmꢂ1 vibrational band of
silicon wafer was used as a reference for the wave number
calibration. The SERS spectra of the DAP produced from the
redox reaction between OPD and dissolved oxygen were
detected. The signal intensities of DAP at 997 cmꢂ1 were
recorded for different concentrations of mercury ions to make
a working curve.
Fig. 2 (a) Time-resolved extinction spectra of DAP solution without
the Hg2+–Ag NPs while 1.0 ꢁ 10ꢂ5 M of Hg2+ was used. Inset in (a)
shows a plot of UV-vis absorption intensity with the reaction time. (b)
UV-vis and fluorescent emission spectra of the produced DAP solution
without the Hg2+–Ag NPs while 1.0 ꢁ 10ꢂ5 M of Hg2+ was used. Inset
(b) is a photograph of DAP solution under UV light (365 nm).
2.5 Selectivity
We selected other metal ions, such as, Ca2+, Ba2+, Pb2+, Ni2+,
Sn2+, Cu2+, Ag+, Co2+, Zn2+, Mn2+ and Cd2+ to investigate the
selectivity of Ag NPs to Hg2+ (Fig. S2†). Under the optimal
2.3 Characterization
A Shimadzu UV-3600 spectrophotometer was used to record conditions that 6.0 of pH, 50 ꢀC of temperature, 100 mL of Ag NP
ultraviolet-visible (UV-vis) spectra of the produced DAP solu- volume and 35 min of reaction time, the concentrations of the
tions in a 1.0 cm light path quartz cuvette. The uorescence interference ions including Ca2+, Ba2+, Pb2+, Ni2+, Sn2+, Co2+,
emission spectrum of the DAP solutions was obtained on a Zn2+, Mn2+, Cd2+ were all 1.0 ꢁ 10ꢂ3 M except the concentra-
Shimadzu RF-5301PC spectrophotometer. To avoid the inter- tions of Cu2+ and Ag+ were 1.0 ꢁ 10ꢂ4 M and concentration of
ference from the Hg2+–Ag NPs, we centrifuged the reaction the target (Hg2+ ions) was 1.0 ꢁ 10ꢂ6 M. The intensities of the
solution at a speed of 10 000 rpm. The precipitates of Hg2+–Ag peak at 997 cmꢂ1 were obtained from the SERS spectra of all the
NPs were removed before we carried out UV-vis and uores- metal ions and they were plotted for comparison.
cence measurements (the results are shown in Fig. 2).
FT-IR spectrum was measured with a Bruker Vertex 80v
spectrometer. TEM images were obtained by a JEM-2100 F eld-
emission transmission electron microscope (JEOL, Tokyo,
3 Result and discussion
3.1 Characterization of Hg2+–Ag NPs
Japan). The sample was loaded above a polymer lm modied
copper grid for TEM measurement. Mass spectrum (MS) was
recorded on a Q-Trap MS (Applied Biosystems/MDS Sciex,
Concord, ON, Canada) which equipped with an electrospray
ionization source. The product was dissolved by methanol and
As we known, Ag NPs synthesized by the citrate reduction are
coated with a layer of citrate ions, displaying negative charges.
Moreover, mercury ions own two positive charges, which can
attach to Ag NP surface due to the electrostatic force. As shown
in the Fig. 1(a) and (b), the TEM images of Ag NPs and Hg2+–Ag
which show the shape and size of the Hg2+–Ag NPs has no
obvious difference to the Ag NP. Fig. 1(c)–(e) shows the TEM
mapping of Hg2+–Ag NP. From Fig. 1(c)–(e), we can nd that
introduced into the MS detector at a ow rate of 0.01 mL minꢂ1
.
The analyte was monitored in positive mode, and the detection
parameters were as follows: collision gas; N2 (medium), curtain
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 49759–49764 | 49761

View Article Online
RSC Advances
Paper
Fig. 3 The IR (a), MS (b) and Raman spectra (c) of the product of needle-like DAP. Inset in (c); a photograph of needle-like DAP.
mercury ions have been assembled on the surface of Ag NP to emission spectra of the produced solution aer removing the
form a Hg2+–Ag NP. At the same time, we can nd mercury ions Hg2+–Ag NPs (optical photograph 5 in Scheme 1C). At the same
only occupy a very limited surface area of an Ag NP, which can time, we also nd a strong uorescent emission band is located
leave enough large surface area for DAP adsorption. Fig. 1(f) at 554 nm when the production solution is excited at 440 nm,
shows the elemental analysis, in which we also can identify a also proving that the product of reaction is DAP.2 The product
certain amount of mercury in the combined NPs.
solution under UV light (365 nm) shows an obvious yellow
3.2 The OPD-oxidized reaction under the catalysis of Hg2+
Ag NPs
–
We used the Hg2+–Ag NPs to catalyze the reaction between the
OPD solution and dissolved oxygen. The OPD solution was
colourless before the Hg2+–Ag NPs added (optical photograph 1
in Scheme 1C). When the Hg2+–Ag NPs were added into the OPD
solution, the solution colour became yellow at 35 min (optical
photograph 3 in Scheme 1C) and the UV-vis maximum
absorption intensity of the product aer the Hg2+–Ag NPs were
separated from solution gradually increased with time from
bottom to top as shown in Fig. 2(a). There is a strong absorption
peak at 417 nm, which is in accordance with previously reported
that this band belongs to DAP.28 The inserted spectrum of
Fig. 2(a) shows the relationship of UV-vis maximum absorption
intensity with reaction time, indicating the growth of the col-
oured product. Fig. 2(b) records the UV-vis and uorescent
Table 1 The assignments of Raman vibration modes of the producta
Wave number (cmꢂ1
)
Vibrational assignments
596
626
bC–N–C + bC–C–C
bC–C–C
725
767
850
gC–C–C + gC–N–C
uNH2 + gC–C–C
gC–H
997
bC–C–C + nC–C
bC–H + nC–N + nC–C
bC–H + nC–N
nC–N + bC–H + nC–C
nC–N + nC–C
nC–C + nC–NH2
nC–N + bC–H + nC–C
nC–C + dNH2
1125
1246
1342
1385
1448
1512
1557
Fig. 4 (a) SERS spectra for sensing different concentrations of Hg2+
(from top to bottom 1.0 ꢁ 10ꢂ5, 1.0 ꢁ 10ꢂ6, 1.0 ꢁ 10ꢂ7, 1.0 ꢁ 10ꢂ8 and
1.0 ꢁ 10ꢂ9 M, respectively). (b) The dependence of SERS intensity at
997 cmꢂ1 on the concentration of Hg2+ probed by this designed
sensor.
a
b, in plane bending; g, out plane bending; u, wagging; n, stretching
vibration; d, scissoring.
49762 | RSC Adv., 2015, 5, 49759–49764
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
colour (inset in Fig. 2(b), revealing that the DAP exhibits yellow
uorescence. This OPD-oxidized reaction can be expressed as
follows:
3.3 Identication of the OPD-oxidized product
The oxidized product of OPD is still amphibolous in the
reported literatures. For example, C. Hempen's and many
reports27–31 referred that the product was DAP. However, in W. Z.
Sheng's paper,32 they stated that the main product was azoani-
line. To conrm our product, we characterized it by IR, MS, and
Raman spectroscopies. Before characterizations, the nal
product that was separated from reaction solution by centrifu-
gation was carried out through cooling crystallization, centri-
fugation and desiccation to form a needle-like crystal (Scheme
1C). Fig. 3(a) shows the IR spectrum of the crystal. The char-
acteristic absorption band at 3434, 3414, 3180 and 2996 cmꢂ1
are assigned to the N–H stretching vibration of the adjacent two
amino group on phenazine. The band of C]N stretching
vibration and primary amine deformation vibration are at 1643
and 1562 cmꢂ1. The band at the 1498 cmꢂ1 is aromatic ring.
Four adjacent hydrogens of ring deformation vibration are at
763 cmꢂ1 and the peak at 586 cmꢂ1 attributes to aromatic plane
and out-of-plane bending vibration. From Fig. 3(a), it proves
that the product of the OPD-oxidized reaction is DAP, which is
similar to the previously reported DAP molecules.33,34 Fig. 3(b)
displays the MS of the product. A strong ion peak at 211.3 shows
that the DAP has formed an OPD dimer (the mass of DAP plus a
H+) in this method.2 To further conrm the structure of the
oligomer, the Raman spectrum of the needle-like crystal was
recorded. Fig. 3(c) shows the Raman spectrum of the product
and the band assignments are listed in Table 1.34 Based on
above characterizations, we can identify that the obtained
product is DAP.
Fig. 5 SERS intensities at 997 cmꢂ1 response to common metal ions
(1.0 ꢁ 10ꢂ3 M) apart from Hg2+ (1.0 ꢁ 10ꢂ6 M), Ag+ (1.0 ꢁ 10ꢂ4 M) and
Cu2+ (1.0 ꢁ 10ꢂ4 M) under the optimal conditions.
relationship between the concentration of mercury ions and the
intensities of the peak at 997 cmꢂ1 aer subtracting the blank.
The linear relationship is y ¼ 7.4 ꢁ 108x + 673.7 with a corre-
lation coefficient of 0.988. The minimum detection concentra-
tion is 1.0 nM with the noise to signal ratio is 4 : 1. We also have
researched the reproducibility of SERS detection (Fig. S5†) and
the relative standard deviations (RSDs) of SERS intensities are
less than 10%, which can meet the standard of a high-
performance SERS substrate (RSDs < 20%).35,36
3.5 Selectivity
As shown in Fig. 5, the SERS intensity of DAP produced by the
catalysis of the Hg2+–Ag NPs is much stronger while Ca2+, Ba2+,
Pb2+, Ni2+, Sn2+, Co2+, Zn2+, Mn2+ and Cd2+ provide much
weaker signals. In addition, we nd the Ag+ and Cu2+ cause a
little stronger interference than the other cations, because OPD
can be oxidized by Cu2+ and Ag+ in presence of Ag NPs, which is
in accordance with previous literature.31 These results indicate
that this sensor has excellent selectivity for mercury ions among
heavy metal ions.
3.4 Detection of mercury ions
3.6 SERS detection of real sample
We employed this Hg2+–Ag NPs catalyzed redox reaction
between OPD and dissolved oxygen to trace the concentration of
mercury ions (B in Scheme 1). Since Hg2+–Ag NPs play a role of a
catalyst, more Hg2+–Ag NPs will produce more DAP in the same
reaction time. OPD has a weak Raman behaviour, however, the
produce DAP is Raman-active. In addition, the Raman signal of
the produced DAP can be greatly enhanced by the contained Ag
NPs (Fig. S6†). Therefore we can trace the SERS intensity of the
produced DAP to determine mercury ions and the detection
sensitivity in this “turn on” sensing mechanism can also be
improved by the enhancement activity of Ag NPs. The different
concentrations of mercury ions were measured from 10 mM to 1
nM and the SERS spectra of produced DAP in different
concentrations of mercury ions in casting lms over a silicon
slide are shown in Fig. 4(a). Fig. 4(b) shows the linear
In order to test the application of our sensor for Hg2+ in real
sample, we adopted tap water from the campus of Jilin
University with standard addition of mercury ions.
The results are listed in Table 2. We can nd the recovery rate
of mercury ion range from 90–95%, which proves that our
Table 2 The recovery rate of Hg2+ in local drinking water. Each
sample was measured five times
Sample no.
Real value
Measured value
Recovery (%)
1
2
3
2.00 mM
40.0 mM
8.00 nM
1.90 ꢃ 0.400 mM
36.5 ꢃ 0.300 mM
7.30 ꢃ 0.100 nM
94.5 ꢃ 2.00
91.2 ꢃ 0.800
90.6 ꢃ 1.30
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 49759–49764 | 49763

View Article Online
RSC Advances
Paper
sensor is practical in real samples and it displays strong anti- 11 S. Chen, D. Liu, Z. Wang, X. Sun, D. Cui and X. Chen,
interference ability.
Nanoscale, 2013, 5, 6731.
12 Y. Du, R. Liu, B. Liu, S. Wang, M. Y. Han and Z. Zhang, Anal.
Chem., 2013, 85, 3160.
13 Y. Takahashi, S. Danwittayakul and T. M. Suzuki, Analyst,
2009, 134, 1380.
14 J. Zhang, L. Mao, G. Yang, X. Gao and X. Tang, Spectrosc.
Spectral Anal., 2010, 30, 1979.
15 Q. Li, Z. Zhang and Z. Wang, Anal. Chim. Acta, 2014, 845, 7.
16 H. Matusiewicz, J. Fish and T. Malinski, Anal. Chem., 1987,
59, 2264.
17 A. Q. Shah, T. G. Kazi, J. A. Baig, H. I. Afridi and M. B. Arain,
Food Chem., 2012, 134, 2345.
18 I. Seramovski, I. Karadjova, T. Stalov and J. Cvetkovic,
Microchem. J., 2008, 89, 42.
19 R. Fukai and L. Huynh-Ngoc, Anal. Chim. Acta, 1976, 83, 375.
20 M. Hatle, Talanta, 1987, 34, 1001.
4 Conclusions
In summary, we adopted electrostatic assembly method to form
Hg2+–Ag NPs, which can be used not only for accelerating a
redox reaction between OPD and dissolved oxygen, but also for
enhancing the Raman signal of the produced DAP. We used the
good catalytic ability of the Hg2+–Ag NPs to develop a “turn on”
SERS detection method for tracing Hg2+. The lowest concen-
tration of mercury ion is as low as 1.0 nM. Compared with other
mercury ion sensing approaches, our sensor has merits not only
in the aspects of simple operation and low cost, but also in its
sensing behaviours of high sensitivity and good selectivity.
These merits indicate that this SERS sensor has applicable
potential in water samples.
21 Y. Takahashi, S. Danwittayakul and S. M. Toshishige,
Analyst, 2009, 134, 1380.
22 E. Punrat, S. Chuanwatanakwl, T. Kaneta, S. Motomizu and
O. Chailapakul, J. Electroanal. Chem., 2014, 727, 78.
23 S. Qiao, Y. Ding, D. Tian, Y. Li and G. Yang, Appl. Spectrosc.
Rev., 2014, 9, 11746.
24 Y. Du, R. Liu, B. Liu, S. Wang, M. Y. Han and Z. Zhang, Anal.
Chem., 2013, 85, 3160.
25 L. Zhang, H. Chang, A. Hirata, H. Wu, Q. K. Xue and
M. Chen, ACS Nano, 2013, 7, 4595.
Acknowledgements
This work was supported by the National Instrumentation
Program (NIP) of the Ministry of Science and Technology of
China (Grant no. 2011YQ03012408), National Natural Science
Foundation of China (Grant nos 21373096) and Innovation
Program of the State Laboratory of Supramolecular Structure
and Materials, Jilin University.
26 P. C. Lee and D. Meisel, J. Phys. Chem. C, 1982, 86, 3391.
27 L. Yan, Z. Chen, Z. Zhang, C. Qu, L. Chen and D. Shen,
Analyst, 2013, 138, 4280.
28 S. Fornera and P. Walde, Anal. Biochem., 2010, 407, 293.
29 G. Roman-Gusetu and K. C. Waldron, J. Chromatogr. A, 2009,
1216, 8270.
Notes and references
1 H. Tan, Q. Li, C. Ma, Y. Song, F. Xu and S. Chen, Biosens.
Bioelectron., 2015, 63, 566.
2 S. Liu, X. Qin, J. Tian, L. Wang and X. Sun, Sens. Actuators, B,
2012, 171–172, 886.
3 M. Yang, W. Meng, X. Liu, N. Su, J. Zhou and B. Yang, RSC
Adv., 2014, 4, 22288.
30 H. Wang, W. Jiang, Y. Wang, X. Liu, J. Yao and L. Yuan,
Langmuir, 2013, 29, 3.
4 S. J. L. Billinge, E. J. McKimmy, M. Shatnawi, H. J. Kim,
V. Petkov and D. Wermeille, J. Am. Chem. Soc., 2005, 127,
8492.
5 S. Yoon, A. E. Alber, A. P. Wong and C. J. Chang, J. Am. Chem.
Soc., 2005, 127, 16030.
31 X. Yang and E. Wang, Anal. Chem., 2011, 83, 5005.
32 Z. Wu, G. Zhou, J. Jiang, G. Shen and R. Yu, Talanta, 2006, 70,
533.
33 P. D. Zhou, H. Liu, S. C. Chen, L. Lucia, H. Y. Zhan and
S. Y. Fu, Molbank., 2011, M730.
6 G. K. Darbha, A. Ray and P. C. Ray, ACS Nano, 2007, 1, 208.
7 M. Zhu, Y. Wang, Y. Deng, L. Yao, S. B. Adeloju and D. Pan,
Biosens. Bioelectron., 2014, 61, 14.
8 Z. Mohammadpour, A. Safavi and M. Shamsipur, Chem. Eng.
J., 2014, 255, 1.
34 S. Sylvestre, S. Sebastian, K. Oudayakumar, T. Jayavarthanan
and N. Sundaraganesan, Spectrochim. Acta, Part A, 2012, 96,
401.
35 M. J. Natan, Faraday Discuss., 2006, 132, 321.
36 X.-M. Lin, Y. Cui, Y.-H. Xu, B. Ren and Z.-Q. Tian, Anal.
Bioanal. Chem., 2009, 394, 1729.
9 Y. J. Long, Y. F. Li, Y. Liu, J. J. Zheng, J. Tang and C. Z. Huang,
Chem. Commun., 2011, 47, 11939.
10 V. Bhalia, R. Tejpal, M. Kumar and A. Sethi, Inorg. Chem.,
2009, 48, 11677.
49764 | RSC Adv., 2015, 5, 49759–49764
This journal is © The Royal Society of Chemistry 2015