Silver nanoparticles as highly efficient and selective optical probe for sulphide via dendrimer formation in aqueous medium

Article abstract of DOI:10.1039/c5ra25625a

We herein report a highly efficient, cost effective, convenient as well as selective colorimetric probe for sulphide (S^2-) in the form of silver nanoparticles (AgNPs) capped by an azonaphthol viz. 1-[(4-nitrophenyl)azo]-2-naphthol. A naked eye color change from bright yellow to colorless was observed upon the addition of S^2- to the AgNPs. A remarkable feature of this probe is the unique morphological transition of spherical AgNPs to dendritic architecture induced by S^2-. Although dendritic AgNPs have been reported previously also by many workers through various methods. Here we are presenting a probe that not only selectively recognises S^2- colorimetrically but at the same time paves the way for the self-assembled dendritic structure of AgNPs. The lowest detection limit for S^2- was found to be 67 nM which is much lower than the maximum endurable level (15 μM) of S^2- in drinking water by World Health Organisation (WHO).

Full text of DOI:10.1039/c5ra25625a

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PAPER
Silver nanoparticles as highly efficient and selective
optical probe for sulphide via dendrimer formation
in aqueous medium†
Cite this: RSC Adv., 2016, 6, 14563
*
Isha Sanskriti and K. K. Upadhyay
We herein report a highly efficient, cost effective, convenient as well as selective colorimetric probe for
sulphide (S2ꢀ) in the form of silver nanoparticles (AgNPs) capped by an azonaphthol viz. 1-[(4-
nitrophenyl)azo]-2-naphthol. A naked eye color change from bright yellow to colorless was observed
upon the addition of S2ꢀ to the AgNPs. A remarkable feature of this probe is the unique morphological
transition of spherical AgNPs to dendritic architecture induced by S2ꢀ. Although dendritic AgNPs have
been reported previously also by many workers through various methods. Here we are presenting
a probe that not only selectively recognises S2ꢀ colorimetrically but at the same time paves the way for
the self-assembled dendritic structure of AgNPs. The lowest detection limit for S2ꢀ was found to be 67
nM which is much lower than the maximum endurable level (15 mM) of S2ꢀ in drinking water by World
Health Organisation (WHO).
Received 2nd December 2015
Accepted 24th January 2016
DOI: 10.1039/c5ra25625a
www.rsc.org/advances
Detection of S2ꢀ is important from environmental point of
view as the same is toxic and gets converted into obnoxious H2S
at physiological pH in the living systems.16 Natural as well as
Introduction
Metal nanoparticles have successfully been explored for their
applications in biological, biomedical, chemical and analytical
elds.1,2 On one hand they are utilized for diagnosis, thera-
peutics3 and imaging4,5 purposes, while on the other hand they
have also been widely used in perceiving a wide spectrum of
analytes ranging from ions, small molecules to biomolecules.6,7
Their applicability as chemical sensors is widely been exploited
due to their size, shape and morphology dependent optical
properties.8 The occurrence of a Surface Plasmon Resonance
(SPR) band in the UV-visible range and its modulation by
different analyte in their characteristic way paved the way for
their uses in analyte sensing.8–10
Among metal nanoparticles, gold (Au) and silver (Ag) nano-
particles (NPs) have widely been used in the eld of analyte
recognition as their sensing response can be easily observed
through naked eye.11 Furthermore, AgNPs being less obnoxious
with additional features of simple manageability, biocompati-
bility, high selectivity and sensitivity have attracted a number of
researchers towards their use as optical sensors.8,12–14 We have
concentrated on AgNPs as the same have high extinction coef-
cient as compared to AuNPs of the same size,11,12,14,15 as well as
exhibit better naked eye response.15 At the same time they are
cost effective also as compared to AuNPs.15
waste water are very common sources of S2ꢀ
.
Humans are
16–18
vulnerable to high concentration of S2ꢀ increasing the risks of
respiratory arrest, loss of consciousness and discomfort in
mucous membranes.19 So its detection has become a matter of
serious concern for environment as well as for human health.
Various colorimetric and uorescent molecular probes for
sulphide have been reported in the literature but most of them
suffer with one or other bottlenecks. The biggest bottleneck is
the tedious synthesis of molecular probes and their detection
limits.20–27 Only a few worthy probes are available till date.28,29 In
this context the NPs are better candidates and a number of such
types of probes for sulphide have been reported till date. A few
among these are CuNPs, Cu@AuNPs, glutathione modied
AuNPs, Au/Ag core/shell NRs (nanorods), unmodied Au@Ag
nanoclusters, and citrate capped AuNPs.16,30–34 The LOD's of
these probes were of micromolar level. Hence they are not very
promising ones. A DNA-templated CuNPs and a citrate capped
AuNPs with nanomolar detection limit have also been reported
in literature.35,36 Hence, under these circumstances the AgNPs
being reported through this communication as a sensor for S2ꢀ
with LOD of 67 nM is certainly a worth full report. The non-
interference with a large number of anions further makes our
report even more worthy and lucrative.
A further literature survey related to NPs revealed that their
morphology also affect their properties a lot.37,38 Hence a variety
of nanostructures like nanotrees, nanopines, nanopalms,
nanoleaves, nanoforests, nanobushes, nanomushrooms,
nanoowers, nanobouquets, nanomulberry, nanograss,
Department of Chemistry (Centre of Advanced Study), Faculty of Science, Banaras
Hindu University, Varanasi 221005, India. E-mail: drkaushalbhu@yahoo.co.in;
kku@bhu.ac.in; Tel: +91-542-6702488
† Electronic supplementary information (ESI) available: Synthesis, 1H & 13C NMR,
IR and HRMS of CA has been given. See DOI: 10.1039/c5ra25625a
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nanokelps, nanocorns, nanocactus, nanospines, nanosheafs
have been synthesised.39 Dendritic AgNPs with multidirectional
branches and showing association between different parts have
attracted a lot of interest.37 Furthermore a number of dendritic
nanostructures have also been synthesized by involving
a number of reductant/surfactant38,40 and also through various
synthetic protocols.41–45 None of these methods served the
purpose of analyte sensing.
On the contrary to above reports, our present report incor-
porates the S2ꢀ specic aggregation of AgNPs as dendrimer
which also served the purpose of S2ꢀ sensing through the naked
eye color change.
Fig. 1 Structure of the capping agent (CA).
CA was characterized by 1H, 13C NMR, IR and mass spectral
studies (ESI; Fig. S1–S4†); yield: 88%; 1H NMR (300 MHz, CDCl3,
298 K, TMS): d ppm ¼ 16.13 (s, 1H, OH), 8.42–8.40 (d, 2H, Ar–H),
8.33–8.30 (d, 1H, Ar–H), 7.70–7.43 (m, 6H, Ar–H), 6.71–6.67 (d,
1H, Ar–H); 13C NMR (75 MHz, CDCl3, 298 K, TMS): d ppm ¼
180.22, 173.93, 155.23, 147.92, 143.55, 129.79, 129.17, 128.63,
127.59, 126.35, 125.79, 125.69, 122.58, 122.47, 116.36, 102.91;
IR/cmꢀ1: 3427, 3113, 2922, 1624, 1594, 1575, 1554, 1502, 1453,
1401, 1370, 1332, 1258, 1226, 1204, 1153, 1106, 985, 859, 836,
748, 686, 670, 614, 508, 489, 425; HRMS (ESI): m/z calculated for
Experimental
Materials and methods
All the reagents and solvents were of AR-grade quality and were
used as received. The para-nitroaniline, b-naphthol, NaNO2,
and AgNO3 were purchased from Sigma Aldrich. Stock solutions
of the anions and cations were prepared freshly in Milli-Q water.
All the spectroscopic studies were made aer appropriate
dilution. All the glasswares were properly cleaned with freshly
prepared aqua regia (3 : 1, (v/v) HCl–HNO3) and nally rinsed
many times with Milli-Q water prior to their uses.
C
16H11N3O3 + H [M + H]+ ¼ 294.0873, found ¼ 294.0872.
Synthesis of silver nanoparticles (AgNPs)
The 300 mL of 1.0 M NaOH was diluted with 3.0 mL water and
the same was used in the synthesis. 40 mL of Milli-Q water was
taken in a round bottom ask. Then, 400 mL of CA (4 mM)
prepared in chloroform was added to it with continuous stir-
ring. This was followed by the addition of 400 mL of prepared
NaOH and 800 mL of AgNO3 (8 mM) to it. Then 800 mL of the
same NaOH was added to the stirring mixture at room
temperature which corresponds to pH 14. Slight appearance of
yellow color reects the onset of formation of AgNPs. Aer an
hour, yellow color brightens. The stirring at room temperature
was continued for overnight for complete functionalization of
AgNPs. The functionalized AgNPs were observed as bright
yellow in color with no turbidity. The same was centrifuged
prior to use and were stored in round bottom ask at room
temperature (ESI; Fig. S5†).
Physical measurements
The 1H NMR and 13C NMR spectra for the same were recorded
in CDCl3 with a JEOL AL 300 FT NMR spectrometer. The IR
spectra was recorded with a Perkin-Elmer spectrometer. High
resolution mass spectroscopy (HRMS) was recorded on
a Thermo Scientic Q-Exactive, Accela 1250 pump. Electronic
spectra were recorded at room temperature (298 K) on a UV-
1800 Pharmaspec spectrophotometer with quartz cuvette
(path length ¼ 1 cm). TEM (transmission electron microscope)
studies were carried out using FEI, TECNAI 20 G2 operating at
200 kV. SEM (scanning electron microscope) studies were done
using FEI, Quanta-200. AFM (atomic force microscope) studies
were carried out using NT-MDT, Solver Next.
A pH variation study was also done in order to have an idea
about the optimum pH suitable for AgNPs synthesis. For this
purpose we carried out the synthesis of AgNPs at 6, 8, 10 and 14
pH's (ESI; Fig. S6†). We didn't observe any shi in SPR band of
AgNPs in terms of lmax which was a clear indication about no
signicant change in their size.46,47 Nevertheless the intensity of
SPR band as well as peak area got increased with increase in pH
indicating increase in the concentration (in terms of number) of
AgNPs.
Synthesis of the capping agent 1-[(4-nitrophenyl)azo]-2-
naphthol, (CA)
Para-nitroaniline (1.38 g, 0.01 mol) was dissolved in a mixture of
concentrated HCl (5.0 mL) and distilled water (20 mL) in
a round bottom ask. A cold solution of (NaNO2) sodium nitrite
(0.83 g, 0.012 mol) in distilled water (5.0 mL) was added drop-
wise to the acidic solution of para-nitroaniline maintained at
ꢁ
0 C over a time period of ꢂ5 min. The reaction mixture was
further stirred at 0 ꢁC for ꢂ40 min followed by addition of
cooled solution of b-naphthol (1.44 g, 0.01 mol) in 20 mL of
NaOH (4 g, 0.1 mol). The reaction mixture was further stirred for
Photophysical studies of AgNPs with different analyte
1 hour. An orange colored product was precipitated and was A variety of anionic analytes were screened separately for their
ltered on suction pump, washed several times with water and photophysical (sensing) studies against freshly prepared AgNPs.
nally dried over anhydrous CaCl2 in a desiccator (ESI; Scheme The photophysical studies were done through naked eye fol-
1†). The structure of the capping agent (CA) thus synthesized is lowed by UV-visible studies. The UV-visible titration was per-
shown in Fig. 1.
formed aer each aliquot addition of much lower i.e. 1.0 ꢃ 10ꢀ4
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M concentration of S2ꢀ to the 3 mL of AgNPs prepared by
diluting 1 mL of AgNPs with 2 mL of Milli-Q water. The colori-
metric sensing ability of AgNPs was investigated by separate
addition of much higher concentration i.e. 10 mL of 1.0 ꢃ 10ꢀ1
M of anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, S2ꢀ, (C6H5COOꢀ) BzOꢀ, (CH3-
COOꢀ) AcOꢀ, SO32ꢀ, SO42ꢀ, HSO4ꢀ, S2O52ꢀ, S2O32ꢀ) to 1 mL of
AgNPs diluted with 2 mL of Milli-Q water.
Interference study
The interference study for the anions was performed at their
individual level. To a solution of 1.0 mL AgNPs diluted with 2.0
mL of Milli-Q water, the 10 mL of 1.0 ꢃ 10ꢀ1 M of different
anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, S2ꢀ, BzOꢀ, AcOꢀ, SO32ꢀ, SO42ꢀ, HSO4
,
ꢀ
Fig. 3 Naked eye response and the corresponding UV-visible spec-
trum of capped AgNPs in absence and presence of different anions (10
mL of 1.0 ꢃ 10ꢀ1 M).
S2O52ꢀ, S2O32ꢀ) were added separately followed by addition of
the 10 mL of 1.0 ꢃ 10ꢀ1 M sulphide to each case. The matrix
studies with the mixture (10 mL of 1.0 ꢃ 10ꢀ1 M) of anions and
cations (Na+, K+, Ba2+, Cr3+, Zn2+, Cd2+, Hg2+, Fe3+, Co2+, Ni2+,
Cu2+) separately were also performed to see the effect of
sulphide over AgNPs.
No interference was observed by any anion in the presence of
S2ꢀ either in naked eye or in the UV-visible spectrum pattern
(ESI; Fig. S8†). The plot of A409 of capped AgNPs in the mixture
of S2ꢀ with other anions reects the interference study (Fig. 4).
In the matrix studies of anions, the addition of all anions to
AgNPs resulted in almost insignicant visual change. The
addition of S2ꢀ to this mixture led to bleaching of yellow color of
AgNPs. The same was also reected in the UV-visible spectral
studies. This clearly proves the efficient applicability of this
probe for the visual sensing of sulphide in the mixture of a vast
number of anions (ESI; Fig. S9†).
Results and discussion
UV-visible characterization of the CA and AgNPs stabilised by
it
The absorption spectra of the capping agent (CA) showed
a sharp band at 328 nm and broad band at 429 nm and 461 nm.
The capped AgNPs as synthesised above appeared bright yellow
colored with a corresponding sharp SPR band at 409 nm (Fig. 2).
Addition of the mixture of a large number of cations to
AgNPs resulted in bleaching of yellow color of AgNPs. Never-
theless, addition of S2ꢀ to the same mixture lead to revival of
slight yellow color with its reection in the UV-visible spectrum
(ESI; Fig. S10†).
Interaction of AgNPs with analytes
The above AgNPs were also interacted with a set of cations (10
mL of 1.0 ꢃ 10ꢀ1M) viz. Na+, K+, Ba2+, Cr3+, Zn2+, Cd2+, Hg2+,
Fe3+, Co2+, Ni2+, Cu2+ for their possible photochemical interac-
tion. No conclusive changes were observed either colorimetri-
cally or in its UV-visible spectrum (ESI; Fig. S7†). So, we switched
on to checking the response of AgNPs with anions (Fꢀ, Clꢀ, Brꢀ,
Iꢀ, S2ꢀ, BzOꢀ, AcOꢀ, SO32ꢀ, SO42ꢀ, HSO4ꢀ, S2O52ꢀ, S2O32ꢀ) and
found that the bright yellow colored AgNPs underwent bleach-
ing upon the interaction of S2ꢀ only and the corresponding UV-
visible spectrum showed the disappearance of SPR band at 409
nm and slight broadening of the band is also observed (Fig. 3).
Detection of S2ꢀ and analytical data
The UV-visible titration was performed with S2ꢀ at different
concentration (0 to 43.89 mM) showing gradual disappearance
of SPR band at 409 nm and slow broadening of the same. Same
Fig. 4 Interference study of AgNPs with various anions; blue bars:
Fig. 2 UV-visible spectrum of the capping agent (CA) and AgNPs.
AgNPs + anions, purple bars: AgNPs + anions + S2ꢀ
.
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was translated in the form of bleaching of color of AgNPs
(Fig. 5).
The calibration curve was plotted which was linear in the
range from 0.33 mM to 2.64 mM and follows the linear equation,
y ¼ 0.0242x + 0.0075 with the value of R2 equal to 0.9948 (Fig. 6).
LOD was calculated from three times the standard deviation of
blank signal. The LOD of capped AgNPs for S2ꢀ was calculated
to be 67 nM.
Stability of AgNPs and its sensing action with respect to pH
As evident from the photographs (ESI; Fig. S11a†) there was
slight effect on the bright yellow color of AgNPs at pH 2 and 3.
From pH 4 to 10, the color and the SPR band was maintained.
So, the AgNPs are very stable within the pH range 4 to 10 with
slight less stability at pH 2 and 3. The effectiveness of AgNPs for
colorimetric sensing of S2ꢀ is in good agreement within the pH
range 4 to 10 (ESI; Fig. S11b†). The plot of Absorbance vs. pH
reects the same result as discussed (Fig. 7).
Fig. 7 Stability of AgNPs and its response for sensing S2ꢀ from pH 1 to
13.
a tail to stabilize the monodispersed AgNPs. The resulting
AgNPs were stable upto 5–6 months at the room temperature.
Thus capping agent serves the dual purpose i.e. reduction of Ag+
to Ag as well as stabilizing the AgNPs by getting adsorbed over
them. This proposed mechanistic pathway has been given in
Scheme 1.
Probable mechanism of formation of capped AgNPs
Azonaphthol capped AgNPs appeared bright yellow in color
and are spherical in shape and well dispersed as is evident from
their TEM image (Fig. 8a). The average size of particle calculated
from the TEM image was found to be 10–15 nm. Moreover the
SEM and AFM images (Fig. 8b and c) also support the spherical
morphology of AgNPs.
The reducing action of phenolic moiety in basic medium is
supposed to be responsible for the conversion of Ag+ to Ag.13,14,48
The subsequent conversion of naphthoxide ion into naphthoxyl
radical in its quinone type structure leads to formation of
numerous dimeric structures which are ultimately adsorbed
over AgNPs.13,14 The presence of nitro and diazo groups serve as
Probable mechanism of colorimetric sensing of S2ꢀ through
AgNPs
The capping agent itself doesn't give any response upon the
addition of sulphide to it which is very clearly reected in the
UV-visible spectrum of CA (ESI; Fig. S12†). On the other hand
Fig. 5 UV-visible spectrum of AgNPs at different concentration (0 to
43.89 mM) of S2ꢀ
.
Scheme 1 Probable mechanistic pathway of formation and stabiliza-
tion of AgNPs by capping agent.
Fig. 6 The calibration curves for capped AgNPs in presence of S2ꢀ
.
Fig. 8 (a) TEM, (b) SEM, (c) AFM images of capped AgNPs.
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the capped AgNPs got transformed into a dendritic architecture
which was reected in the corresponding TEM (Fig. 9a–f) and
SEM (Fig. 10a–f) images at their different magnications.
Visually this process was translated in terms of change in color
of AgNPs from bright yellow to colorless which was further
supported from the AFM studies also (Fig. 11a and b).
The solution of Na2S is itself highly alkaline and there is
presence of S2ꢀ along with HSꢀ due to hydroxylation of S2ꢀ. The
latimer diagram for sulphur in basic medium49 (Fig. 12)
suggests an spontaneous conversion of HSꢀ to S. This sulphur
oxidizes metallic silver into silver ion getting itself reduced into
sulphide ion. Now the so–so interaction between Ag+ and S2ꢀ
leads to precipitation of Ag2S.50 This mechanism clearly
explains the microscopic images of majority of spherical
capped-AgNPs coming close together and their some parts
getting dissolved in the form of Ag2S which serves as connec-
tivity between the particles which are arranged in dendritic
Fig. 11 (a) AFM image of sulphide induced dendrimer formation of
AgNPs and (b) 3-D image.
fashion (Fig. 9f, inset). The EDX studies of the AgNPs (ESI;
Fig. S13a†) and its ensemble with sulphide (ESI; Fig. S13b†)
clearly indicated the peaks for Ag and Ag as well as sulphur
respectively.
Fig. 9 TEM images of sulphide induced dendrimer formation of AgNPs from lower to higher magnification (a–f).
Fig. 10 SEM images of sulphide induced dendrimer formation of AgNPs from lower to higher magnification (a–f).
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10 X. Yuan, S. Wen, M. Shen and X. Shi, Anal. Methods, 2013, 5,
5486–5492.
11 Y. Lin, C. Chen, C. Wang, F. Pu, J. Ren and X. Qu, Chem.
Commun., 2011, 47, 1181–1183.
Fig. 12 Latimer diagram of sulphur in basic medium.
12 S. Chen, H. Gao, W. Shen, C. Lu and Q. Yuan, Sens. Actuators,
B, 2014, 190, 673–678.
13 Y.-r. Ma, H.-y. Niu, X.-l. Zhang and Y.-q. Cai, Chem. Commun.,
2011, 47, 12643–12645.
Conclusion
14 Y. Ma, H. Niu, X. Zhang and Y. Cai, Analyst, 2011, 136, 4192–
4196.
15 W. Leesutthiphonchai, W. Dungchai, W. Siangproh,
N. Ngamrojnavanich and O. Chailapakul, Talanta, 2011,
85, 870–876.
16 A. Hatamie, B. Zargar and A. Jalali, Talanta, 2014, 121, 234–
238.
17 W.-Y. Chen, G.-Y. Lan and H.-T. Chang, Anal. Chem., 2011,
83, 9450–9455.
18 A. Baciu, M. Ardelean, A. Pop, R. Pode and F. Manea, Sensors,
2015, 15, 14526–14538.
19 X. Lou, D. Ou, Q. Li and Z. Li, Chem. Commun., 2012, 48,
8462–8477.
20 M. Li, Q. Liang, M. Zheng, C. Fang, S. Peng and M. Zhao,
Dalton Trans., 2013, 42, 13509–13515.
21 M.-Q. Wang, K. Li, J.-T. Hou, M.-Y. Wu, Z. Huang and
X.-Q. Yu, J. Org. Chem., 2012, 77, 8350–8354.
22 Y. Fu, Q.-C. Feng, X.-J. Jiang, H. Xu, M. Li and S.-Q. Zang,
Dalton Trans., 2014, 43, 5815–5822.
Thus 1-[(4-nitrophenyl)azo]-2-naphthol capped AgNPs were
conveniently synthesised, characterized and exploited for
effective colorimetric sensing of S2ꢀ with LOD of 67 nm which is
much lower than the sustainable level (15 mM) of S2ꢀ in
drinking water accepted by WHO.25 Additional feature of this
probe is the beautiful arrangement of spherical AgNPs in
dendritic fashion induced by S2ꢀ. Moreover our approach does
not deal with complex or specic procedures for sensing as well
as in the assembly of AgNPs in dendritic architecture. This
probe showed a naked eye color change from bright yellow to
colorless for S2ꢀ. Applicability of the probe in the wide pH range
from 4 to 10 makes it more worthy and lucrative. As all the
sensing studies were performed in water, hence our probe can
successfully be applied in the naked eye sensing of S2ꢀ in
aqueous medium in the presence of a group of a large number
of similar types of anions. The detailed study and utilisation of
this mechanism can be used for both sensing as well as for the
genesis of even better architecture.
23 M. Sun, H. Yu, H. Li, H. Xu, D. Huang and S. Wang, Inorg.
Chem., 2015, 54, 3766–3772.
24 B. Sen, M. Mukherjee, S. Pal, K. Dhara, S. K. Mandal,
A. R. Khuda-Bukhsh and P. Chattopadhyay, RSC Adv., 2014,
4, 14919–14927.
Acknowledgements
I. S. is thankful to UGC-BSR/RFSMS/432 for fellowship. We
acknowledge Prof. O. N. Srivastava, Department of Physics,
Faculty of Science, Banaras Hindu University for providing the
TEM and SEM facility.
25 Y. Huang, D. Ou, C. Wang, C. Huang, Q. Li and Z. Li, Polym.
Chem., 2014, 5, 2041–2049.
26 X. Cao, W. Lin and L. He, Org. Lett., 2011, 13, 4716–4719.
27 M. G. Choi, S. Cha, H. Lee, H. L. Jeon and S.-K. Chang, Chem.
Commun., 2009, 7390–7392.
28 W. Zhang, J. Kang, P. Li, H. Wang and B. Tang, Anal. Chem.,
2015, 87, 8964–8969.
29 G.-J. Mao, T.-T. Wei, X.-X. Wang, S.-y. Huan, D.-Q. Lu,
J. Zhang, X.-B. Zhang, W. Tan, G.-L. Shen and R.-Q. Yu,
Anal. Chem., 2013, 85, 7875–7881.
Notes and references
1 S. Bothra, J. N. Solanki and S. K. Sahoo, Sens. Actuators, B,
2013, 188, 937–943.
2 T. Asefa, C. T. Duncan and K. K. Sharma, Analyst, 2009, 134,
1980–1990.
3 J. Yang, C. Zhou, C. Liu, Y. Li, H. Liu, Y. Li and D. Zhu, 30 J. Zhang, X. Xu, Y. Yuan, C. Yang and X. Yang, ACS Appl.
Analyst, 2012, 137, 1446–1450.
Mater. Interfaces, 2011, 3, 2928–2931.
4 A. Alizadeh, M. M. Khodaei, Z. Hamidi and 31 J. Zhang, X. Xu and X. Yang, Analyst, 2012, 137, 1556–1558.
M. B. Shamsuddin, Sens. Actuators, B, 2014, 190, 782–791.
5 V. V. Kumar and S. P. Anthony, Sens. Actuators, B, 2014, 191,
31–36.
6 J. Zhang, X. Wang and X. Yang, Analyst, 2012, 137, 2806–
2812.
7 Y. Zhang, Y. Leng, L. Miao, J. Xin and A. Wu, Dalton Trans.,
2013, 42, 5485–5490.
8 J. A. Jacob, H. S. Mahal, N. Biswas, T. Mukherjee and
S. Kapoor, Langmuir, 2008, 24, 528–533.
32 H. Huang, Q. Li, J. Wang, Z. Li, X.-F. Yu and P. K. Chu,
Plasmonics, 2014, 9, 11–16.
33 Z.-X. Wang, C.-L. Zheng and S.-N. Ding, RSC Adv., 2014, 4,
9825–9829.
34 H.-H. Deng, G.-W. Wu, X.-Q. Lin, X.-W. Xu, A.-L. Liu,
X.-H. Xia and W. Chen, RSC Adv., 2015, 5, 58574–58579.
35 J. Liu, J. Chen, Z. Fang and L. Zeng, Analyst, 2012, 137, 5502–
5505.
36 Q. Gao, Y. Zheng, C. Song, L.-Q. Lu, X.-K. Tian and A.-W. Xu,
RSC Adv., 2013, 3, 21424–21430.
9 J. M. Abad, M. Revenga-Parra, T. Garcia, M. Gamero,
E. Lorenzo and F. Pariente, Phys. Chem. Chem. Phys., 2011, 37 M. H. Rashid and T. K. Mandal, J. Phys. Chem. C, 2007, 111,
13, 5668–5678.
16750–16760.
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Paper
RSC Advances
38 X. Wang, K. Naka, H. Itoh, S. Park and Y. Chujo, Chem. 44 X. Sun and M. Hagner, Langmuir, 2007, 23, 9147–9150.
Commun., 2002, 1300–1301. 45 L. Fan and R. Guo, Cryst. Growth Des., 2008, 8, 2150–2156.
39 O. V. Kharissova and B. I. Kharisov, Ind. Eng. Chem. Res., 46 L. M. Liz-Marzan, Langmuir, 2006, 22, 32–41.
2010, 49, 11142–11169. 47 M. Li, S. K. Cushing and N. Wu, Analyst, 2015, 140, 386–406.
40 S. Pang, T. Kondo and T. Kawai, Chem. Mater., 2005, 17, 48 K. Yoosaf, B. I. Ipe, C. H. Suresh and K. G. Thomas, J. Phys.
3636–3641. Chem. C, 2007, 111, 12839–12847.
41 Q. Zhou, S. Wang, N. Jia, L. Liu, J. Yang and Z. Jiang, Mater. 49 B. M. Mahan and R. J. Myers, University Chemistry, Benjamin
Lett., 2006, 60, 3789–3792. Cummings, Menlo Park, CA, 1987.
42 J. Fang, H. You, P. Kong, Y. Yi, X. Song and B. Ding, Cryst. 50 C. Levard, B. C. Reinsch, F. M. Michel, C. Oumahi,
Growth Des., 2007, 7, 864–867.
43 L. Gou, M. Chipara and J. M. Zaleski, Chem. Mater., 2007, 19,
1755–1760.
G. V. Lowry and G. E. Brown, Environ. Sci. Technol., 2011,
45, 5260–5266.
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