Catalytic and SERS activities of tryptophan-EDTA capped silver nanoparticles

Article abstract of DOI:10.1002/zaac.201400056

This report describes the synthesis of silver nanoparticles (AgNPs) by in situ reduction of silver nitrate with designed ethylenediaminetetraacetic acid-tryptophan bioconjugates. Conjugation of EDTA was chosen to augment water solubility of resulting conjugate, which in turn facilitates synthesis of AgNPs in aqueous medium. Various spectroscopic and microscopy techniques were employed to characterize the EDTA-tryptophan capped AgNPs. The nanoparticles show excellent catalytic activity towards reduction of p-nitrophenol to p-aminophenol with a rate constant of 16.43×10^-2 min^-1. In addition, as-synthesized AgNPs show high SERS activity, which was used for low concentration detection of biomolecules. Copyright

Full text of DOI:10.1002/zaac.201400056

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ARTICLE
DOI: 10.1002/zaac.201400056
Catalytic and SERS Activities of Tryptophan-EDTA Capped Silver
Nanoparticles
[a]
[a,b]
Sudipta Mondal and Sandeep Verma*
Dedicated to Professor C. N. R. Rao on the Occasion of His 80th Birthday
Keywords: Silver; Nanoparticles; Peptides; Tryptophan; Catalysis; Surface-enhanced Raman scattering (SERS) spectroscopy
Abstract. This report describes the synthesis of silver nanoparticles
AgNPs) by in situ reduction of silver nitrate with designed ethylenedi-
aminetetraacetic acid-tryptophan bioconjugates. Conjugation of EDTA nophenol with a rate constant of 16.43ϫ10 min . In addition, as-
ize the EDTA-tryptophan capped AgNPs. The nanoparticles show ex-
(
cellent catalytic activity towards reduction of p-nitrophenol to p-ami-
–
2
–1
was chosen to augment water solubility of resulting conjugate, which synthesized AgNPs show high SERS activity, which was used for low
in turn facilitates synthesis of AgNPs in aqueous medium. Various
spectroscopic and microscopy techniques were employed to character-
concentration detection of biomolecules.
Introduction
Silver nanoparticles (AgNPs) are highly useful owing to
their wide spectrum of applications ranging from imaging, op-
change conditions may lead to particle aggregation. Shape,
size, and aqueous solubility also play crucial roles in con-
trolling various properties of metal nanoparticles.[ For exam-
ple, most antibacterial applications of capped AgNPs require
5]
[1]
tical sensing, conductive, diagnostics, and therapeutics.
[6]
optimal water solubility and biocompatibility. To address
AgNPs strongly interact with light causing electrons in the
conduction band, on the metal surface, to collectively oscillate
when irradiated by a lightsource of specific wavelength. This
phenomenon, known as surface plasmon resonance, affords
notable absorption properties leading to varied colors in nano-
particle sols. In the case of AgNPs, it is shown that their ex-
tinction cross sections can exceed ten-fold compared to their
such issues, recent syntheses of AgNPs report the use of amino
acids and peptides, as they provide better control over physico-
chemical properties of nanoparticles, without compromising
[7]
with their biocompatibility. Tryptophan and tyrosine-based
oligopeptides have been employed for in situ preparation of
nanoparticles, thereby eliminating the use of external reducing
agents.[ However, hydrophobic nature of aromatic amino acid
8]
physical cross section. Thus, AgNPs exhibit higher plasmonic required addition of organic co-solvents to solubilize pept-
activity compared to other metallic nanoparticles.[2] Despite ides.[8a–c]
such attractive photophysical properties, synthesis of AgNPs
In this report, we describe an expeditious entry to water-
is considered challenging because of weak chemical and col- soluble AgNPs using an EDTA-tryptophan conjugate, where
loidal stability.[ Established methods of synthesis of AgNPs tryptophan moiety is employed as the reducing agent. In our
3]
(9)
conjugate, EDTA fragment was incorporated to augment water
solubility of the resulting conjugate, thus facilitating synthesis
of AgNPs in aqueous medium without addition of organic co-
solvent. The single amino acid based conjugate is easy to syn-
thesize and provides a cost effective alternative for silver nano-
particles preparation.
are based on the reduction of silver salts with reducing agents
such as citrate, sodium borohydride, ascorbic acid, in the pres-
ence of stable capping agents or via ligand exchange reac-
tions.[4]
Latter approach presents a drawback, where presence of
multiple variables alters reaction conditions and ligand ex-
More specifically, the advantages of reported EDTA-trypto-
phan conjugate are:
*
Prof. S. Verma
Fax: +91-512-2597436
E-Mail: sverma@iitk.ac.in
(1) Conjugation of EDTA renders this conjugate soluble in
aqueous environment without requiring an organic co-solvent,
which is a requirement for other tryptophan-containing pept-
ides.
[
[
a] Department of Chemistry
Indian Institute of Technology Kanpur
Kanpur 208 016
Uttar Pradesh, India
(2) Use of single amino acid based conjugate makes this
b] DST Thematic Unit of Excellence on Soft Nanofabrication
Indian Institute of Technology Kanpur
Kanpur 208 016
procedure simple and synthetically less challenging for wide-
spread use.
Uttar Pradesh, India
(3) The nature of this conjugate confers stability in basic as
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201400056 or from the au-
thor.
well as neutral pH, which complements polyamine-stabilized
nanoparticles that are stable in acidic pH.
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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With this background, we report synthesis, characterization,
and stability studies of such AgNPs and its catalytic potential
towards NaBH -assisted p-nitrophenol reduction. Additionally,
4
these as-synthesized nanoparticles were also applied for SERS-
based detection of adenine nucleobase.
Results and Discussion
Scheme 1 depicts the synthetic scheme for the preparation of
ethylenediaminetetraacetic acid (EDTA)-tryptophan conjugate
(
1). The synthesis of AgNPs starts with the addition of silver
nitrate to an aqueous solution of 1 under basic conditions (pH
1). It is known that the preparation of metal nanoparticles
1
with tryptophan- or tyrosine-containing peptides is supported
under alkaline conditions.[ The resulting solution was stirred
under dark for 72 h, affording color change from colorless
solution to reddish-yellow, indicating formation of AgNPs.
8]
Figure 1. UV/Vis absorption spectra of AgNPs synthesized from dif-
ferent concentrations of silver salt and conjugate 1. Inset: magnified
view of spectra (NP1 broken line ,NP2 dotted line).
AgNPs. This variation in size distributions can also be ex-
plained by considering the rate of reduction leading to the for-
mation of Ag nuclei. The presence of excess amount of ligand
in case of NP1 perhaps results in faster reduction compared to
NP2. Therefore, it is likely that more Ag nuclei are formed at
the early stage of nucleation and higher ligand concentration
shields nascent AgNPs by forming an electrostatic bilayer
membrane, thereby controlling further growth.[
Scheme 1. Synthesis of EDTA-tryptophan conjugate (1).
12]
Two different concentration ratios of 1 and AgNO , 4:1 and
3
These as-synthesized AgNPs were analyzed by transmission
2:1, respectively, were used for reaction optimization
[
13]
electron microscopy (TEM) and EDAX analyses.
Fig-
(Table 1). Figure 1 shows UV/Vis absorption spectra of re-
ure 2a,b show representative TEM micrographs of NP1 and
NP2 nanoparticles. Former consists of spherical or nearly
spherical particles with an average diameter of 20 nm, whereas
sulting products, where NP1 and NP2 show characteristic sur-
face plasmon bands of silver nanoparticles. As shown in Fig-
ure 1, a sharp surface plasmon resonance (SPR) band associ-
ated with each sample is indicative of monodisperse formation
of AgNPs.[
2b,10]
However, the SPR band exhibited slightly dif-
ferent maxima for the two samples: NP1 shows a maximum
at 408 nm, whereas the maximum for NP2 is 411 nm. This
difference may be attributed to the size difference of as-synthe-
sized nanoparticles.[
11]
Table 1. Composition of silver nanoparticles.
Sample name
Composition
AgNO
3
1
NP1
NP2
1 mM
2 mM
4 mM
4 mM
AgNP size distribution was determined by dynamic light
scattering (DLS) measurements. NP1 particles, having a lower
λmax value, show the hydrodynamic radius of 22 nm, whereas
the average radius of NP2 particles is 38 nm (see Supporting
Information). DLS measurement of NP1 also exhibits the pres-
ence of some higher order structures, but careful analysis of
TEM data does not support formation of such larger aggre-
gates. As expected, a subtle variation in the ratio of ligand and
Figure 2. (a) TEM micrographs of (a) NP1; (b) NP2. (c) and (d)
EDAX spectrum and elemental compositions of AgNPs (NP1), respec-
silver concentrations could lead to formation of different sizes tively.
2
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Activities of Tryptophan-EDTA Capped Silver Nanoparticles
the latter had particle sizes with diameter ranging from 30– tical to pH 11 were observed. However, further lowering of
5 nm. These value and distribution pattern were in good pH (pH 5) resulted in slight peak shifting and broadening of
4
agreement with the DLS data. EDAX confirmed the presence the spectrum, suggesting a tendency to aggregate and a pos-
of silver in nanoparticle samples, while additional peaks veri- sible coupling between neighboring plasmons.[19] Acidified
fied the presence of other elements in the selected spot con- solution of NP1 at pH below 7 undergoes further aggregation
firming stabilization of AgNPs by 1 (Figure 2c,d).[14] NP2 also on standing for 24 h, whereas colloidal nature of NP2 re-
exhibited an identical EDAX behavior.
mained intact over a period of 24 h (see Supporting Infor-
Adsorption of ligands on AgNP surface was investigated by mation).
FTIR analysis. Figure 3 shows FTIR spectra of sodium salt of
EDTA-tryptophan conjugate and AgNPs obtained by washing
of the excess ligand with methanol. The spectrum of AgNPs
shows all characteristic bands associated with ligand and inter-
estingly, many bands are red shifted because of the interaction
of the absorbed molecules with the field of the solid sur-
face.[ The 1655 cm peak in Figure 3a is characteristic of
amide I ascribed to C=O stretching, with minor contributions
from the out-of-phase CN stretching and N–H in-plane bend-
15]
–1
–
1
ing vibrations, whereas the peak at 1591 cm may result from
the stretching vibration of carboxylate group and possibly
amide II.[ Two new bands appear at 1459 and 1436 cm
16]
–1
that may be ascribed to symmetric and asymmetric stretching
of carboxylate bound to silver (Figure 3b). The carboxylate
groups can bind to nanoparticles surface either symmetrically
or in a side-on arrangement and can be accounted for appear-
ance in these bands.[ Apart from this, amide I and II peaks
17]
–
1
at 1632 and 1595 cm are also observed in Figure 3b. These
characteristic absorption peaks and the presence of a strong
–
1
band at 1041 cm , due to C–O single bond stretching, indi-
cates that perhaps ligand 1 remains chemisorbed on AgNP sur-
face.[
18]
Figure 4. UV/Vis study of nanoparticle stability as a function of solu-
tion pH. (a) AgNPs from sample NP1, (b) AgNPs from sample NP2.
Tryptophan is a redox-active amino acid, serving crucial role
in electron transfer relay reactions, and is known to reduce
silver and gold salts to their zerovalent state. Its pH-dependent
redox potential is estimated to be ≈1.0 V (pH 7), which is ≈0.1
V above another redox-active amino acid, tyrosine. EDTA was
also utilized for the synthesis and stabilization of silver nano-
particles,[ although drastic conditions are required for such
transformations.[
20]
14b,21]
Figure 3. FTIR spectra: (a) sodium salt of 1; (b) AgNPs stabilized
with EDTA-tryptophan conjugate.
However, control reactions performed with tryptophan or
EDTA alone, under the conditions used in this reaction, failed
Colloidal stability of EDTA-tryptophan stabilized AgNPs to afford synthesis of AgNPs (Figure 5). Thus, these experi-
was studied by recording UV/Vis spectra at various pH values ments demonstrate that neither EDTA nor tryptophan alone
(Figure 4). It is clear that at pH 7 and 9, the absorption maxima could support formation and stabilization of AgNPs under am-
associated with each band does not change and spectra iden- bient conditions.
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Figure 5. UV/Vis absorption spectra of silver salt in presence of tryp-
tophan, mixture of tryptophan and EDTA, and EDTA, respectively
(from top to bottom). Inset: Magnified view of the spectra for the
region 300 nm to 600 nm.
Catalytic Activity
Metal nanoparticles have been used extensively to catalyze
various chemical reactions and the reduction of p-nitrophenol
is one of the well-studied systems. Reduction of aromatic nitro
compounds in the presence of silver nanoparticles has been
reported.[ This process has environmental significance as ni-
trophenol, generated from various source of industrial and ag-
riculture waste, is a known water pollutant.[23] The reduction
of nitro group to amino group could be useful for the synthesis
of fine chemicals.[
22]
24]
Figure 6. Catalytic reduction of p-nitrophenol by AgNPs (NP1): (a)
time-dependent UV/Vis spectra for the catalytic process (Arrow indi-
We decided to investigate the reduction of p-nitrophenol to
p-aminophenol to assess catalytic activity of novel EDTA-tryp- cate progress of reaction). (b) Plots of ln(A) (A is absorption value at
400 nm) vs. reaction time.
tophan capped AgNPs, in conjunction with sodium borohyd-
ride as a reductant (NaBH ) (Scheme 2). It is known that
4
throughout the course of reaction, thus pseudo-first-order ki-
netics can be used to evaluate rate of this reaction. Figure 6
shows a plot of ln(A) (A is absorbance value at 400 nm) vs.
NaBH alone is ineffective to reduce p-nitrophenol (see Sup-
4
porting Information).[
25]
The reduction of p-nitrophenol is as-
sociated with a decrease in the absorbance value at 400 nm
and a concomitant appearance of a peak at 300 nm, character-
istic of p-aminophenolate ion. Figure 6 shows time-dependent
follow-up of the catalytic reaction in the presence of NP1
AgNPs (completion of reaction was observed within 20 min).
2
reduction time and a good linear fitting of the data (R = 0.97)
confirms that the catalysis process indeed follow the pseudo-
first-order kinetics. The apparent rate constant (k) calculated
from this plot is 16.43ϫ10–2 min for NP1 AgNPs, while
NP2 also exhibited pseudo-first-order kinetics, with a rate con-
stant of 9.75ϫ10–2 min (Figure 7). According to literature
reports, k value obtained in this study is amongst highest
–1
–1
rate constants value reported for different silver-based
–1 [12]
nanocomposites
[literature
values:
4.73ϫ10–4 s ,
.15ϫ10–3
s
–1[12,18,21,26]
]. A combination of the presence of
2
[
8a]
indole moieties, size and surface of these nanoparticles may
[
12,27]
account for high catalytic activity observed in this case.
Scheme 2. AgNP assisted borohydride reduction of p-nitrophenol.
SERS Activity
The concentration of NaBH used in this reaction is much
4
higher than other reactants. Under this condition, it is reason-
Surface-enhanced Raman scattering (SERS) spectroscopy is
able to assume that the amount of NaBH remains constant considered as an efficient method for highly sensitive detection
4
4
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Activities of Tryptophan-EDTA Capped Silver Nanoparticles
number of complex hierarchical structures, which exhibit sta-
bility in solid state as well as in solution. This prompted us to
investigate whether novel EDTA-Trp capped AgNPs would
serve as a good substrate for SERS detection of adenine nu-
cleobase as several reports have described viability of SERS-
based adenine detection in biological as well as extraterrestrial
samples.[ A recent study reported reproducible, label-free
detection of adenine molecules at 10 attomol level, with the
help of deep-UV surface-enhanced resonance Raman scat-
tering.[ Such possibilities indicate that near- and far-field
optical nanoparticle arrays could be engineered for ultrasensi-
tive detection of biomolecules. Another recent example re-
ported synthesis of AgNPs via chemical reduction on poly(vi-
nylidene fluoride) coated arrays. This approach resulted in bet-
ter reproducibility and sensitivity for detection of adenine, cy-
tosine, thymine, and uracil at nanomolar level in very small
volumes.[
33]
34]
35]
We probed the efficacy of EDTA-Trp capped AgNPs as
SERS substrates for adenine nucleobase, by Raman spec-
troscopy and Raman mapping measurements. Figure 8 shows
the Raman spectrum of different concentrations of adenine in
the presence of NP2 AgNPs of larger size. As a reference,
Raman spectrum of adenine alone at laser excitation of 532 nm
is compared in Figure 8. Adenine exhibits several characteris-
tic bands, with most prominent bands appearing at 722 and
–1
1
329 cm , corresponding to ring breathing of the molecule,
and stretching and bending of several C–N bonds, respec-
tively.[
36]
Figure 7. Catalytic reduction of p-nitrophenol in presence of AgNPs
of NP2 (Arrow indicate progress of reaction). (a) Time-dependent UV/
Vis spectra for catalytic reduction. (b) Plots of ln(A) (A is absorption
value at 400 nm) versus reaction time.
of Raman-active (bio)analytes at low concentrations. SERS
critically depends on stable interaction of adsorbed analytes
on the surface of plasmonic gold, silver, or copper metallic
nanostructures. Engineered gold and silver surfaces are pre-
ferred over copper, as stability of the latter is often compro-
mised due its air reactivity. Given the constraints, SERS sub-
strate optimization is also crucial in order to enhance sensitiv-
Figure 8. SERS spectra of different concentrations of adenine in the
[28]
ity of this technique for single-molecule detection.
This en- absence and presence of NP2 AgNPs: (a) Raman spectrum of adenine
–
6
–5
–4
alone; SERS spectra of (b) 10 m, (c) 10 m and (d) 10 m of ade-
nine. Solid line represents the normal Raman spectrum bands, whereas
dash line represents SERS bands.
hancement depends on the nature of nanoparticle assembly of-
fering specially identified as hot-spot junctions for optimal
SERS response.[
29,30]
It is established that electromagnetic and
chemical enhancement are primarily responsible for the SERS
effect. The electromagnetic enhancement stems from collective
SERS spectra of adenine in the presence of AgNPs show
oscillation of localized surface plasmons, while chemical en- increased intensity for these characteristic bands along with
hancement of SERS depends primarily on charge-transfer pro- others, while shift of a band at 722 cm–1 to 732 cm is clearly
–1
cesses.[
31]
observable. SERS enhancement could be achieved at micro-
We have been working on interaction of silver with DNA molar concentration of adenine. To understand the localization
[
32]
nucleobase adenine.
During the course of our studies, we of Raman active sites, Raman mapping of two different con-
–7
found that adenine avidly coordinates to silver affording a centrations of adenine (10–6 m and 10 m) was performed
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(
Figure 9). This figure confirms that SERS effects are highly Experimental Section
localized and SERS signal amplification originates from the
hot-spots, which are visible as a bright spot.
low concentration, the appearance of significant Raman band
is clearly observable as shown in Figure 9b and d, correspond-
ing to the signals from spots marked with white circle in Fig-
Synthesis of Silver Nanoparticles: The solutions of compound 1 and
metal salts were prepared in H O. HPLC grade water was used in these
studies. A 40 mM stock solution of AgNO was prepared in water.
Sample NP1 was prepared by dissolving compound 1 in water (4 mM)
followed by addition of AgNO (1 mM). The reaction container was
[37]
Even at this
2
3
3
ure 9. These experiments demonstrate that as-synthesized wrapped with aluminum foil and stirred for 15 min. pH of that solution
AgNPs could very well serve as SERS active materials for was adjusted to 11 with NaOH solution. The solution was kept for
nucleobase sensing.
further stirring and different spectroscopic measurements were per-
formed with these as-synthesized nanoparticles. NP2 was also pre-
pared with identical procedures but with different stoichiometric ratios.
Sample NP2 contains 4 mM of compound 1 and 2 mM AgNO3.
UV/Vis Spectroscopy: Absorption spectra were recorded with a
CARY 100 Bio UV/Vis spectrophotometer, with 10 mm quartz cell at
25Ϯ0.1 °C. HPLC grade water was used for these studies. UV/Vis
spectra were measured by diluting the respective nanoparticles with an
aqueous solution of pH 11. For pH study, solution pH was changed
with NaOH and HNO , and UV/Vis spectra of the resulting solutions
3
were measured immediately and after 24 h. A 5 nm / 5 nm excitation
and absorption slit width was used for all the study.
Catalytic Reduction of p-Nitrophenol: Aqueous solution of p-ni-
trophenol (0.001 m) was taken in a quartz cuvette and freshly prepared
4
aqueous NaBH (0.1 m) was added to this solution to a final volume
–
6
–1
of 2 mL. Sample NP1 (3.5ϫ10 mol·L , based on amount of silver
atoms) was added to this solution and the UV/Vis spectrum was re-
corded at regular intervals to monitor the progress of the reaction.
The catalytic conversion for sample NP2 was followed by identical
–
6
procedures. The amount of NP2 used for this reaction is 5ϫ10
mol·L (based on amount of silver atoms).
–
1
Figure 9. Raman mapping of adenine SERS, showing distribution of
Scanning Electron Microscopy (SEM): Aliquots (20 μL) of the two
–
6
hot spots for two different concentrations of adenine: (a) 10 m and times diluted AgNps solutions were deposited on silicon wafer. The
(
c) 10– m of adenine. These images are obtained by plotting samples were initially dried under light, vacuum dried for 30 min, and
7
7
32 cm–1 vibrational band intensity over scanned surface. (b) SERS
subsequently imaged without gold coating. Field emission scanning
electron microscopy images were acquired on FEI QUANTA 200
microscope, equipped with a tungsten filament gun, operating at WD
spectra of adenine taken from marked hot spot in (a). (d) SERS spectra
of adenine taken from marked hot spot in (c).
10.6 mm and 20 kV.
Transmission Electron Microscopy (TEM): As synthesized AgNPs
was diluted 10 times for recording TEM images. A 2 μL aliquot of
that sample was placed on a 400 mesh carbon coated copper grid. The
Conclusions
A novel EDTA-tryptophan conjugate was synthesized and samples were dried under lamp and the samples were viewed using a
used for in situ synthesis of silver nanoparticles. Preparation JEOL 1200EX electron microscope operating at 80 kV.
of these silver nanoparticles involves ambient approach as the
synthesis was carried out under aqueous conditions and with-
out the presence or involvement of organic solvents or external
Raman Measurements: Raman spectra and images were acquired
with a WiTec CRM 200 Raman spectrometer equipped with a piezos-
canner and a 100ϫ microscope objective (NA = 0.9). Raman mapping
reducing agent. By varying the initial compositions of metal were done with 225 spectraϫ225 line and having an integration time
salts and ligand, the preparation of AgNPs with different size of 0.015 s for each spectrum. The samples were excited with a He-Cd
distributions was achieved. The characteristic of the ligands laser using the 532 nm laser line. SERS spectra were recorded with an
integration time of 10 s. The sample NP2 (100 μL) was added to water
makes as-synthesized AgNPs stable in basic as well as neutral
(
(
1 mL) containing appropriate concentration of adenine. This solution
100 μL) was placed atop a silicon wafer and dried under lamp for
pH and can complement synthesis protocol that produce nano-
particles stable in acidic pH. Moreover, the as-synthesized
AgNPs show excellent catalytic activity towards the reduction
Raman measurement.
of p-nitrophenol to p-aminophenol in water with a rate con- FTIR Spectra: FTIR spectra were recorded with a Perkin-Elmer FTIR
–
2
–1
stant of 16.43ϫ10 min . In addition, the as-synthesized spectrometer (Spectrum Two) on KBr plate. Samples were dried under
reduced pressure and washed with excess methanol to remove unab-
sorbed ligand molecules.
AgNPs show high SERS activity, which can be used for detec-
tion of biomolecules at low concentration. We intend to further
develop these stable, monodisperse, capped silver nanopar-
ticles for select applications in catalysis and single molecule Synthesis details of EDTA-tryptophan conjugate and additional spec-
Supporting Information (see footnote on the first page of this article):
detection.
troscopic data.
6
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Activities of Tryptophan-EDTA Capped Silver Nanoparticles
[
14] a) S. Ghosh, A. Mukherjee, P. J. Sadler, S. Verma, Angew. Chem.
Int. Ed. 2008, 47, 2217; b) E. Hutter, J. H. Fendler, Chem. Com-
mun. 2002, 378.
Acknowledgements
SM thanks CSIR-India and IIT kanpur for financial support. SV thanks [15] L. H. Dubois, B. R. Zegarski, R. G. Nuzzo, Langmuir 1986, 2,
the Department of Science and Technology for continued financial sup-
port and to DST Thematic Unit of Excellence on Soft Nanofabrication
for microscopy facility.
412.
[
[
16] K.-Z. Liu, H. H. Mantsch, Am. J. Obstet. Gynecol. 1999, 180,
696.
17] a) N. Wu, L. Fu, M. Su, M. Aslam, K. C. Wong, V. P. Dravid,
Nano Lett. 2004, 4, 383; b) Y. T. Tao, J. Am. Chem. Soc. 1993,
115, 4350.
[
[
[
18] L. Zhang, R. He, H.-C. Gu, Appl. Surf. Sci. 2006, 253, 2611.
19] A. Henglein, M. Giersig, J. Phys. Chem. B 1999, 103, 9533.
20] a) Y. Lin, W. Jing, P. Kang, Z. Xiaoming, W. Zhouping, X. Wen-
shui, Bull. Korean Chem. Soc. 2011, 32, 1277.
References
[1] a) A. Kumar, P. K. Vemula, P. M. Ajayan, G. John, Nat. Mater.
2
008, 7, 236; b) M. Lv, S. Su, Y. He, Q. Huang, W. Hu, D. Li,
[
21] D. Jiang, J. Xie, M. Chen, D. Li, J. Zhu, H. Qin, J. Alloys Compd.
C. Fan, S. T. Lee, Adv. Mater. 2010, 22, 5463; c) Y. L. Tai, Y. X.
Wang, Z. G. Yang, Z. Q. Chai, Surf. Interface Anal. 2011, 43,
2011, 509, 1975.
[
[
22] N. Pradhan, A. Pal, T. Pal, Colloids Surf. A 2002, 196, 247.
23] M. Nemanashi, R. Meijboom, J. Colloid Interface Sci. 2013, 389,
260.
1480; d) S. Chang, Z. A. Combs, M. K. Gupta, R. Davis, V. V.
Tsukruk, ACS Appl. Mater. Interfaces 2010, 2, 3333; e) M. J.
Sweet, I. Singleton, Adv. Appl. Microbiol. 2011, 77, 115; f) D. R.
Bae, W. S. Han, J. M. Lim, S. Kang, J. Y. Lee, D. Kang, J. H.
Jung, Langmuir 2010, 26, 2181.
[24] R. Fenger, E. Fertitta, H. Kirmse, A. F. Thunemann, K. Radem-
ann, Phys. Chem. Chem. Phys. 2012, 14, 9343.
[25] a) A. Gangula, R. M. R. Podila, L. Karanam, C. Janardhana,
A. M. Rao, Langmuir 2011, 27, 15268; b) P. Hervés, M. Pérez-
Lorenzo, L. M. Liz-Marzán, J. Dzubiella, Y. Lu, M. Ballauff,
Chem. Soc. Rev. 2012, 41, 5577.
[
2] a) J. A. Scholl, A. L. Koh, J. A. Dionne, Nature 2012, 483, 421;
b) D. Steinigeweg, S. Schlücker, Chem. Commun. 2012, 48, 8682;
c) J.-S. Lee, A. K. R. Lytton-Jean, S. J. Hurst, C. A. Mirkin, Nano
Lett. 2007, 7, 2112.
[26] a) A. M. Signori, K. D. O. Santos, R. Eising, B. L. Albuquerque,
F. C. Giacomelli, J. B. Domingos, Langmuir 2010, 26, 17772; b)
Y. Lu, P. Spyra, Y. Mei, M. Ballauff, A. Pich, Macromol. Chem.
Phys. 2007, 208, 254; c) M. H. Rashid, T. K. Mandal, J. Phys.
Chem. C 2007, 111, 16750.
[
[
3] Q. Zhang, J. Xie, Y. Yu, J. Y. Lee, Nanoscale 2010, 2, 1962.
4] a) Q. Zhang, N. Li, J. Goebl, Z. Lu, Y. Yin, J. Am. Chem. Soc.
2011, 133, 18931; b) X. Su, R. Kanjanawarut, ACS Nano 2009,
3, 2751; c) Y. Zheng, Y. Liz, Z. Deng, Chem. Commun. 2012, 48,
6160.
[
27] a) R. Eising, A. M. Signori, S. Fort, J. B. Domingos, Langmuir
2
011, 27, 11860; b) D. Zaramella, P. Scrimin, L. J. Prins, J. Am.
[5] a) A. P. Alivisatos, J. Phys. Chem. 1996, 100, 13226; b) C. J.
Murphy, Science 2002, 298, 2139.
Chem. Soc. 2012, 134, 8396.
[
28] a) J. F. Li, Y. F. Huang, Y. Ding, Z. L. Yang, S. B. Li, X. S. Zhou,
F. R. Fan, W. Zhang, Z. Y. Zhou, D. Y. Wu, B. Ren, Z. L. Wang,
Z. Q. Tian, Nature 2010, 464, 392; b) A. F. Chrimes, K. Khosh-
manesh, P. R. Stoddart, A. A. Kayani, A. Mitchell, H. Daima, V.
Bansal, K. Kalantar-zadeh, Anal. Chem. 2012, 84, 4029; c) Z. Xu,
G. Hu, RSC Adv. 2012, 2, 11404.
29] a) K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, M. S. Feld,
Chem. Rev. 1999, 99, 2957; b) K. A. Stoerzinger, J. Y. Linb, T. W.
Odom, Chem. Sci. 2011, 2, 1435.
[6] a) J. Xie, J. Y. Lee, D. I. C. Wang, Y. P. Ting, ACS Nano 2007, 1,
429; b) R. C. Doty, T. R. Tshikhudo, M. Brust, D. G. Fernig,
Chem. Mater. 2005, 17, 4630.
7] a) C. J. Carter, C. J. Ackerson, D. L. Feldheim, ACS Nano 2010,
[
4, 3883; b) G. Upert, F. Bouillère, H. Wennemers, Angew. Chem.
Int. Ed. 2012, 51, 4231; c) P. Graf, A. Mantion, A. Haase, A. F.
Thünemann, A. Ma sˇ i c´ , W. Meier, A. Luch, A. Taubert, ACS Nano
[
2011, 5, 820; d) I. M. Rio-Echevarria, R. Tavano, V. Causin, E.
Papini, F. Mancin, A. Moretto, J. Am. Chem. Soc. 2011, 133, 8; [30] a) J. Schenk, L. Tröbs, F. Emmerling, J. Kneipp, U. Panne, M.
e) G. Maayan, L.-K. Liu, Pept. Sci. 2011, 96, 679; f) R. Levy,
N. T. K. Thanh, R. C. Doty, I. Hussain, R. J. Nichols, D. J. Schif-
frin, M. Brust, D. G. Fernig, J. Am. Chem. Soc. 2004, 126, 10076.
8] a) S. Si, T. K. Mandal, Chem. Eur. J. 2007, 13, 3160; b) S. Si,
R. R. Bhattacharjee, A. Mukherjee, T. K. Mandal, Chem. Eur. J.
Albrecht, Anal. Methods 2012, 4, 1252; b) M. Futamata, Y. Yu,
T. Yajima, J. Phys. Chem. C 2011, 115, 5271.
[31] J. R. Anema, J.-F. Li, Z.-L. Yang, B. Ren, Z.-Q. Tian, Annu. Rev.
Anal. Chem. 2011, 4, 129.
[
[32] a) S. Khanna, S. Verma, Cryst. Growth Des. 2012, 12, 3025; b)
S. Verma, A. K. Mishra, J. Kumar, Acc. Chem. Res. 2010, 43, 79;
c) R. K. Prajapati, J. Kumar, S. Verma, Chem. Commun. 2010,
2006, 12, 1256; c) S. Bhattacharya, A. K. Das, A. Banerjee, D.
Chakravorty, J. Phys. Chem. B 2006, 110, 10757; d) P. R. Selvak-
annan, S. Mandal, S. Phadtare, A. Gole, R. Pasricha, S. D. Adyan-
thaya, M. Sastry, J. Colloid Interface Sci. 2004, 269, 97; e) S. Si,
E. Dinda, T. K. Mandal, Chem. Eur. J. 2007, 13, 9850.
9] a) Z. Zaheer, M. A. Malik, F. M. Al-Nowaiser, Z. Khan, Colloids
Surf. B 2010, 81, 587; b) R. N. Mitra, P. K. Das, J. Phys. Chem.
C 2008, 112, 8159.
46, 3312; d) J. Kumar, S. Verma, Inorg. Chem. 2009, 48, 6350;
e) C. S. Purohit, S. Verma, J. Am. Chem. Soc. 2007, 129, 3488.
33] a) M. Pagliai, S. Caporali, M. Muniz-Miranda, G. Pratesi, V.
Schettino, J. Phys. Chem. Lett. 2012, 3, 242; b) E. Papadopoulou,
S. E. J. Bell, J. Phys. Chem. C 2010, 114, 22644; c) A. Barhoumi,
D. Zhang, F. Tam, N. J. Halas, J. Am. Chem. Soc. 2008, 130,
[
[
5
523; d) Y. Maruyama, M. Ishikawa, M. Futamata, Chem. Lett.
[
[
10] S. Si, M. Raula, T. K. Paira, T. K. Mandal, ChemPhysChem 2008,
2001, 8, 834.
9, 1578.
[
34] S. K. Jha, Z. Ahmed, M. Agio, Y. Ekinci, J. F. Loffler, J. Am.
Chem. Soc. 2012, 134, 1966.
35] P. Rajapandiyan, J. Yang, Anal. Chem. 2012, 84, 10277.
36] F. Feng, G. Zhi, H. S. Jia, L. Cheng, Y. T. Tian, X. J. Li, Nano-
technology 2009, 20, 295501.
37] H. Liu, L. Zhang, X. Lang, Y. Yamaguchi, H. Iwasaki, Y. Inouye,
Q. Xue, M. Chen, Sci. Rep. 2011, 1, 112.
11] a) K. Belser, T. V. Slenters, C. Pfumbidzai, G. Upert, L. Mirolo,
K. M. Fromm, H. Wennemers, Angew. Chem. Int. Ed. 2009, 48,
[
[
3661; b) L. Li, J. Sun, X. Li, Y. Zhang, Z. Wang, C. Wang, J.
Dai, Q. Wang, Biomaterials 2012, 33, 7547.
[
12] X. Huang, Y. Xiao, W. Zhang, M. Lang, Appl. Surf. Sci. 2012,
[
258, 2655.
[
13] a) C. C. Wang, M. O. Luconia, A. N. Masib, L. P. Fernándeza,
Talanta 2009, 77, 1238; b) X. Li, J. Wang, Y. Zhang, M. Li, J.
Liu, Eur. J. Inorg. Chem. 2010, 1806.
Received: February 5, 2014
Published Online: ᭿
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Job/Unit: Z14056
/KAP1
Date: 06-03-14 16:58:51
Pages: 8
S. Mondal, S. Verma
ARTICLE
S. Mondal, S. Verma* ....................................................... 1–8
Catalytic and SERS Activities of Tryptophan-EDTA Capped
Silver Nanoparticles
8
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