Biogenic Silver Nanoparticles by Cacumen Platycladi Extract

ARTICLE
pubs.acs.org/IECR
Biogenic Silver Nanoparticles by Cacumen Platycladi Extract:
Synthesis, Formation Mechanism, and Antibacterial Activity
Jiale Huang,†,§ Guowu Zhan,†,§ Bingyun Zheng,†,‡ Daohua Sun,*,† Fenfen Lu,† Yuan Lin,† Huimei Chen,†
Zhouding Zheng,† Yanmei Zheng,† and Qingbiao Li*,†
†
Department of Chemical and Biochemical Engineering, and National Laboratory for Green Chemical Productions of Alcohols, Ethers
and Esters, and Key Lab for Chemical Biology of Fujian Province, College of Chemistry and Chemical Engineering, Xiamen University,
Xiamen 361005, P. R. China
‡
Department of Environment & Life Sciences, Putian University, Putian 351100, P. R. China
bS Supporting Information
ABSTRACT: Biosynthesis of Ag nanoparticles (AgNPs) by Cacumen Platycladi extract was investigated. The AgNPs were
characterized by ultravioletvisible absorption spectroscopy (UVvis), transmission electron microscopy (TEM), selected-area
electron diffraction (SAED), and X-ray diffraction (XRD). The results showed that increasing the initial AgNO3 concentration at 30
or 60 °C increased the mean size and widened the size distribution of the AgNPs leading to red shift and broadening of the Surface
Plasmon Resonance absorption. The conversion of silver ions was determined by atomic absorption spectroscopy (AAS) and to
discuss the bioreductive mechanism, the reducing sugar, flavonoid, saccharide, protein contents in the extract, and the antioxidant
activity were measured using 3,5-dinitrosalicylic acid colorimetric; Coomassie brilliant blue; phenol-sulfuric acid; rutin-based
spectrophotometry method; and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assay methods. The results showed
that the reducing sugars and flavonoids were mainly responsible for the bioreduction of the silver ions and their reductive capability
promoted at 90 °C, leading to the formation of AgNPs (18.4 ( 4.6 nm) with narrow size distribution. Finally, the antibacterial
activity of the AgNPs against E. coli and S. aureus was assessed to determine their potential applications in silver-loaded antibacterial
materials. This work provides useful technical parameters for industrialization of the biosynthetic technique and further antibacterial
application of the AgNPs. Furthermore, the elucidation of bioreductive mechanism of silver ions by measuring the change of the
biomolecular concentrations in plant extract exemplifies understanding the formation mechanism of such biogenic AgNPs.
1. INTRODUCTION
Proliferation of nanotechnology has opened up novel fundamental and applied frontiers in materials science and engineering
in the past decade. As building blocks in nanotechnology, nanostructures of well-defined compositions, shapes, and sizes have
been synthesized through various methods. However, conventional physical and chemical methods are not only energy intensive (because of stringent conditions) but equally environmentally unfriendly, due to the use of toxic solvents or additives.
Compared with the conventional methods, bioreduction methods (based on microorganisms or plants) have been demonstrated (in recent years) to be cost-effective and environmentally
benign and yet produce highly stable nanoparticles (NPs).
Driven by this growing impetus (of green chemistry), considerable
efforts have been directed toward the biosynthesis of inorganic
nanoparticles (NPs). such as Ag,13 Au,4,5 Pd,5,6 CaCO3,7,8
BaCO3,8 SrCO3,9 ZrO2,10 TiO2,11 SiO2,11,12 PbCO3,13 CdCO3,13
BaTiO3,14,15 Fe3O4,16 CuAlO2,17 CdS18,19 and Sb2O320 using microorganisms. The use of bacteria,13,5,6 fungi,4,718 actinomycete,8 and
genetically engineered E. coli19 have been exploited in the intracellular
and extracellular assembly of stabilized NPs under mild conditions
without auxiliary capping agents.21 However, the processing of NPs
by intracellular biosynthesis is generally difficult21 despite the use of
bacteria-supported Pd catalysts, and the screening of extracellular
biosynthesis with microorganisms is extensive. In contrast, living
r 2011 American Chemical Society
plants, plant extracts, and plant biomass have recently attracted
attention as alternative candidates that are simple but effective for the
extracellular synthesis of metal NPs.22,23 For example, alfalfa has been
used to prepare Ag nanoparticles (AgNPs),24 and broths of
geranium,25 neem,26 and Emblica officinalis fruit27 as well as Aloe
vera leaves28 have been employed to synthesize AgNPs. Some studies
broadened the scope by using extracts of Chlorella vulgaris,29
Capsicum annuum L.,30 coffee,31 tea,31 Camellia sinensis,32 Eclipta
leaf33 and Azadirachta indica leaf,34 and sundried Cinnamomum
camphora leaf.35,36 Very recently, in our study, single crystalline
Ag nanowires were synthesized using broth of Cassia fistula
leaf.37
Mostly, biosyntheses of AgNPs using plant extracts are carried
out at room temperature, resulting in low reaction rates and conversions of silver ions. Rapid biosynthesis of metal NPs by plant
extract has hitherto received less reportage. Song et al. demonstrated the rapid biosynthesis of AgNPs using several plant
extracts.38 However, detailed reports on the effect of reaction
temperature and initial AgNO3 concentration on the shape and
size of AgNPs have not been demonstrated. Furthermore, the
Received: November 22, 2010
Accepted: June 21, 2011
Revised:
May 31, 2011
Published: June 21, 2011
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Figure 1. UVvis absorption spectra of the AgNPs over reaction time by reducing (a) 1, (b) 3, and (c) 5 mM aqueous AgNO3 with the C. Platycladi
extract at 30 °C, respectively. (d) shows the change of SPR absorption intensity over reaction time. All samples were measured without dilution.
formation mechanism of biologically synthesized AgNPs is currently
not fully understood.38 In this work, we synthesized AgNPs by
reducing aqueous AgNO3 of various concentrations at different
temperatures with Cacumen Platycladi (C. Platycladi) extract as
reducing and protecting agents without any additive protecting
the AgNPs from aggregating or template shaping the AgNPs. In
contrast to microorganisms, the use of the C. Platycladi extract
previously unexploited for bioreduction of silver ions and based
on rapid pretreatment procedures can circumvent laborious biological screening and cultivation. The C. Platycladi extract was
readily available for the bioreduction as it was obtained from
arborvitae that is widely naturalized in Asia. The effects of reaction
temperature, reaction time, and initial concentration of AgNO3,
etc., on the conversion of silver ions, morphology, mean size, and
size distribution were investigated. Ultravioletvisible absorption spectroscopy (UVvis), transmission electron microscopy
(TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD) were used to characterize the AgNPs and atomic
absorption spectroscopy (AAS) was adopted to determine the
concentration of the residual silver ions (after the reaction). To
elucidate the formation mechanism the extracts before and after
the reaction were analyzed by Fourier transform infrared spectroscopy (FTIR). The contents of the reducing sugars, flavonoids, saccharides, proteins, and antioxidant activity before and
after the reaction were also measured by 3,5-dinitrosalicylic acid
colorimetric, rutin-based spectrophotometry, phenol-sulfuric,
and Coomassie brilliant blue methods as well as 2,2-diphenyl1-picrylhydrazyl (DPPH) free radical-scavenging assay.
Besides the synthesis of different metal nanostructures, applications of such nanostructures have received tremendous attention recently. AgNPs have been recognized as new generation
antimicrobials due to their excellent antimicrobial property and
stability3942 and the increase of bacterial resistance to antibiotics. It was demonstrated that AgNPs exhibit more efficient
antimicrobial activity than silver ions and other silver salts,43 and
the bactericidal properties of AgNPs are size-dependent.44 As a
novel approach to AgNPs, plant-based biosynthesis has been
explored to produce AgNPs with antibacterial activity. Several
antibacterial evaluations of such biogenic AgNPs have been carried
out very recently using standard paper disk or broth medium
methods.4548 However, the antibacterial effect of silver ions was
not ruled out as incomplete reduction of silver ions toxic to the
tested strains was neglected at room temperature in the previous
studies.4548 Therefore, to explore the potential application of
the biogenic AgNPs in the development of antimicrobial materials,
the antibacterial activity of the AgNPs was evaluated by agar plate
and broth medium methods with E. coli (gram-negative bacteria)
and S. aureus (gram-positive bacteria) as test strains.49
Shape and size of the AgNPs, which may affect their downstreaming applications, by the biosynthesis using the C. Platycladi
extract were closely associated with the biochemical components
in the extract. To our knowledge, this is the first report on
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Figure 2. UVvis absorption spectra of the AgNPs over reaction time by reducing (a) 1, (b) 3, and (c) 5 mM aqueous AgNO3 with the C. Platycladi
extract at 60 °C, respectively. (d) shows change of SPR absorption intensity over reaction time. All samples were diluted with 30 deionized water before
taking spectra.
elucidation of bioreductive mechanism of silver ions by measuring the change of the total concentrations of reducing sugars,
flavonoids, saccharides, and proteins in plant extract and the
antioxidant activity of plant extract, which therefore exemplifies
understanding the formation mechanism of such biogenic AgNPs.
Importantly, synthesis of the AgNPs by rapid bioreduction of
silver ions by the C. Platycladi extract and their antibacterial test
in this work may provide useful technical parameters for industrialization of the biosynthetic technique and further antibacterial
application of the AgNPs.
2. EXPERIMENTAL SECTIONS
2.1. Preparation of exrtact. Sundried C. Platycladi was purchased from Xiamen Jiuding Drugstore, China. The biomass (for
the reduction) was milled, and the powder was screened with a
20 mesh sieve. 6.0 g of the powdered extract was dispersed in
200 mL of deionzied water with a blender (Philip) for 9 min to
obtain the extract, which was then centrifuged at 5000 rpm for
another 9 min to remove residual insoluble biomass. Then the
supernatant solution was reserved in a refrigerator (6 °C) and
0.03 g/mL used for the synthesis.
2.2. Synthesis of Silver Nanoparticles. Silver nitrate
(AgNO3) was purchased from Sinopharm Chemical Reagent
Co. Ltd., China and was used as received. Ten mL of the
C. Platycladi extract in a double necks round flask (25 mL), with a
condenser for refluxing the reaction solution, was first heated (at
constant temperature) in an oil bath under vigorous magnetic
stirring for 10 min with subsequent intermittent addition of
0.101, 0.309, or 0.525 mL of 0.1 M aqueous AgNO3 until the end
of the reaction.
2.3. TEM Analysis. AgNPs samples for TEM were prepared by
placing a drop of silver hydrosol on carbon coated copper grids
and allowing for the complete evaporation of water. The images
were taken, and SAED analysis was performed on a Tecnai F30
microscope. The average size and size distribution of the
nanoparticles were estimated with the same method as in our
previous work.35
2.4. AAS Analysis. To completely precipitate the AgNPs,
silver hydrosol was centrifuged at 14000 rpm for 20 min and the
concentration of the residual silver ions in the supernatant
measured by atomic absorption spectrophotometer (Pgeneral,
China); with the conversion of silver ions calculated by
Q ¼
C0 Cf
100%
C0
ð1Þ
where Q denotes the conversion of silver ions; C0 is the initial
concentration of aqueous AgNO3; and Cf is the final concentration of silver ions.
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Figure 3. UVvis absorption spectra of the AgNPs over reaction time by reducing (a) 1, (b) 3, and (c) 5 mM aqueous AgNO3 with the C. Platycladi
extract at 90 °C, respectively. (d) shows change of SPR absorption intensity over reaction time. All samples were diluted with 30 deionized water before
taking spectra.
2.5. UVVis Analysis. UVvis analysis of the reaction solutions was carried out at room temperature on UNICAM UV-300
spectrophotometer (Thermo Spectronic, USA) at a resolution
of 1 nm.
2.6. FTIR Analysis. The extract before and the resulting
solution after the reaction was completely dried at 60 °C, and
the dried biomass was analyzed by an FTIR spectrophotometer
(Avatar 660, Nicolet, USA).
2.7. Biomolecular Components. The following methods
were adopted to measure the contents of biomolecular components in the C. Platycladi extract before and after 1 h reaction.50
The content of the reducing sugars was determined using the 3,5dinitrosalicylic acid colorimetric method, the flavonoids by the
spectrophotometry method (with rutin as the standard sample),
and the saccharides by the phenol-sulfuric acid method; the proteins
were assayed by the Coomassie brilliant blue method; and the
antioxidant activity was investigated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assay in a process regulated by its discoloration5052 (each parameter was assayed in
duplicates).
2.8. Antibacterial Performance. The antibacterial activity of
the AgNPs was evaluated against E. coli (gram-negative) and
S. aureus (gram-positive) bacteria by culturing in Muller Hinton
(MH) broth medium and used as inoculums for the study. Agar
plate and broth medium methods were adopted to test the
antibacterial activity of the AgNPs. For the former method, an
appropriate amount of E. coli and S. aureus were inoculated on
agar plates and exposed to the AgNPs with different concentrations. The plates were later incubated at 37 °C for 24 h, the
number of colonies were counted, and the results of three plates
were averaged. In the latter method, the (two test) strains were
inoculated with 109 CFU, added to several MH broth media
flasks (100 mL), and supplemented with 0; 5; 15; 35; and 50 ppm of
AgNPs. The growth rates were determined by measuring the
optical density at 600 nm intervals (UNICAM UV-300 spectrophotometers).
3. RESULTS AND DISCUSSION
3.1. Biosyntheses of Silver Nanoparticles. 3.1.1. UVVis
Absorption. Comparative study was carried out to investigate the
effect of initial AgNO3 concentration and the reaction temperature on the shape and size disperity of the AgNPs, with the same
extract. It is generally recognized that UVvis absorption spectroscopy could be used to examine the shape and size of metal
NPs.53 Figure 1(ac) shows the UVvis absorption spectra of
the AgNPs as a function of reaction time produced by the reduction of 1, 3, and 5 mM aqueous AgNO3 with the extract at
30 °C. The frequency and width of the Surface Plasmon Resonance
(SPR) absorption depend on the shape and size of the metal
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Figure 4. TEM images of the AgNPs by reducing (ab) 1, (cd) 3, and (ef) 5 mM aqueous AgNO3 with the C. Platycladi extract for 24 h at 30 °C,
respectively.
NPs as well as the dielectric constant and the surrounding
medium of the metal NPs.54 The figure also indicates that the
SPR peaks of the AgNPs are centered respectively on 433, 445,
and 455 nm, implying that the AgNPs were mainly spheroidal
and that their SPR spectra broadened with the increase of the
initial AgNO3 concentration (C0). The evolution of the SPR
absorption intensity as a function of reaction time is presented in
Figure 1d, revealing that the absorption intensity increased over
time until stability. In addition, given the same reaction time, the
intensity increased with the increase of the initial AgNO3
concentration as higher AgNO3 concentration resulted in higher
concentration of the AgNPs.
Figure 2(ac) shows the evolution of the UVvis absorption
spectra at 60 °C (with the same reaction time and reducing
agents as before), indicating SPR peaks at 418, 425, and 429 nm,
respectively; with Figure 2d shows the changes of the SPR
absorption intensity over time at different initial AgNO3 concentration (C0). It took only 30 min to reach a stable SPR
absorption intensity for C0 = 1 mM but 240 min for both C0 = 3
and 5 mM (Figure 2d). Comparing the SPR absorption spectra
for the same initial AgNO3 concentration at 30 and 60 °C, the
peaks at 60 °C are sharper and significantly underwent blue shift
from 30 to 60 °C. Obviously, the concentrations of the AgNPs
synthesized at 60 °C were much higher than 30 °C as the
bioreduction of silver ions was greatly accelerated by switching
reaction temperature from 30 to 60 °C. Moreover, the SPR peaks
of the AgNPs significantly underwent blue shift, suggesting that
the same particle shape, medium dielectric constant, and mean
diameter of metal NPs strongly influence the SPR band in the
aqueous solution.55 The size reduction of the metal NPs may
have also induced the blue shift leading to the narrow size distribution at 60 °C.
The UVvis absorption spectra of the AgNPs synthesized at
90 °C are shown in the Figure 3(a—c) with the SPR peaks at 411,
425, and 431 nm for C0 = 1, 3, and 5 mM, respectively. Given the
same reaction time, the concentrations of the AgNPs synthesized
at 90 °C were also much higher than 30 °C and slightly higher
than 60 °C. In addition, the absorption intensity tended to increase
as the reaction time prolonged, and the intensity increased with
the increase of the initial AgNO3 concentration. The wavelengths
of the maximum absorption peak indicate AgNPs with spheroidal
shape, and Figure 3d shows the correlation curves of the SPR
absorption intensity over reaction time. For C0 = 1 mM, it took
only 30 min for the SPR absorption intensity to stabilize, but the
SPR absorption intensity for C0 = 3 and 5 mM did not increase
after 150 min. Comparing the SPR absorption peaks (30 and
90 °C), those at 90 °C exhibited notable blue shift at about
20 nm; and there is a slight blue shift between the peaks at 60 and
90 °C, elucidated with detailed characterization of the AgNPs by
TEM and the statistics of size distribution.
3.1.2. Size Distribution. Figure 4 is the TEM images of the
AgNPs at 30 °C, with a—b being the images of the AgNPs
synthesized with C0 = 1 mM. The AgNPs are almost spheroidal
in shape with a wide size distribution (between 50 and 100 nm,
although many are less than 10 nm), and c—d are the images for
C0 = 3 mM which also indicate almost spheroidal shapes with
broad size distribution (but with some observed silver plates);
nevertheless, the proportion of AgNPs between 50 and 100 nm
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Figure 5. TEM images of the AgNPs by reducing (ab) 1, (cd) 3, and (ef) 5 mM aqueous AgNO3 with the C. Platycladi extract for 6 h at 60 °C,
respectively.
in diameter increased, compared with those in a—b. Parts e—f of
Figure 4 are the images for C0 = 5 mM that are predominantly
spheroidal and plate-like shapes with wide size distribution still
(some larger than 100 nm and others smaller than 10 nm). These
results are consistent with that of the UVvis spectra in Figure 1
(a—c). Increasing the initial AgNO3 concentration increased the
mean size and widened the size distribution of the AgNPs leading
to red shift and broadening of the SPR absorption.
Figure 5 shows the images at 60 °C with a—b being the images
of the AgNPs synthesized at C0 = 1 mM, manifesting that most of
them was spheroidal. The insert SAED pattern of the AgNPs in
Figure 5b indicates that they are polycrystalline. By comparison
(reactions at 30 and 60 °C), the proportion of AgNPs between
50 and 100 nm largely decreased for the higher temperature
(60 °C) with Figure 5c—d also showing a low proportion of
AgNPs (in the same range) at 60 °C for C0 = 3 mM; while parts
e—f of Figure 5 are the images for C0 = 5 mM, indicating that the
formation of Ag nanoplates and relatively larger AgNPs are suppressed at 60 °C. The results of Figures 4 and Figures 5 were
consistent with the UVvis spectra (Figures 1 and Figures 2),
revealing that increasing the reaction temperature leads to AgNPs
with narrow size distribution.
Figure 6 represents the TEM images of the AgNPs from
aqueous AgNO3 with different initial concentrations (C0 = 1, 3,
and 5 mM) at 90 °C. The insert SAED patterns (in b, d, and f)
indicate that they were polycrystalline; XRD analysis was thus
carried out to determine the crystallinity of the AgNPs. The
typical XRD pattern shows distinct Bragg reflections (Figure S1
in the Supporting Information) which may be indexed on the
basis of the face-centered cubic (fcc) structure of silver, implying
essentially, crystalline AgNPs. Figure 6 shows that AgNPs prepared at 90 °C are evidently smaller with narrower size distribution and uniform spheroidal shape, which is validated by Figure 7
(representing the size distribution of AgNPs at 60 and 90 °C).
3.1.3. Conversion of Silver Ions. Figure 8 (a-c) represents the
variation in the conversion of silver ions with reaction time at 30,
60, and 90 °C, respectively, with Figure 8a representing 80.8%,
27.8%, and 19.1% conversions of silver ions within 1 h at 30 °C
for C0 = 1, 3, and 5 mM, respectively. The conversions increased
to 94.1%, 89.1%, and 83.6%, respectively, with prolonged reaction time of 24 h, showing that the incomplete reduction of silver
ions within 24 h at 30 °C, even for C0 = 1 mM. From an engineering
perspective, this is one disadvantage of the biosynthetic protocol
of the AgNPs (at room temperature) that needs to be addressed.
Furthermore (as mentioned above), the AgNPs synthesized at
30 °C possessed wide size distribution and polydispersed shapes,
leading to heterogeneous nucleation (a characteristic of a secondary nucleation); allowing for the formation of spheriodal
nanoparticles with wide size distribution for C0 = 1 mM, but for
C0 = 3 and 5 mM, the Ostwald ripening effect was promoted,
resulting in anisotropic silver nanostructures.
When the reaction temperature was raised from 30 to 60 °C
(as shown in Figure 8b), the conversions were 83.6% for
C0 = 1 mM, 52.6% for C0 = 3 mM, and 32.6% for C0 = 5 mM
after 10 min, increasing to 98.2%, 91.3%, and 82.0%, respectively, in
6 h. The conversions after 10 min at 90 °C were 91.5% for C0 =
1 mM, 84.4% for C0 = 3 mM, and 46.4% for C0 = 5 mM (Figure 8c),
and the conversion at all the initial concentrations would reach 100%
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Figure 6. TEM images of the AgNPs by reducing (ab) 1, (cd) 3, and (ef) 5 mM aqueous AgNO3 with the C. Platycladi extract for 3 h at 90 °C,
respectively.
Figure 7. Statistic size of the AgNPs by reducing aqueous AgNO3 with
the C. Platycladi extract at 60 and 90 °C, respectively.
after 3 h. Therefore, the reaction temperature was a very critical
factor for the bioreduction. The TEM results and size distribution
statistics show that AgNPs with narrow size distribution were
synthesized at 90 °C for the same initial AgNO3 concentrations,
suggesting that higher temperature not only leads to AgNPs with
uniform sizes but also ensures higher conversion in a short time.
Therefore, for rapid synthesis of the AgNPs, a reaction temperature of 90 °C was used.
3.2. Formation Mechanism of the Silver Nanoparticles.
Since the bioreduction of silver ions and the formation of AgNPs
are closely related with the biomolecular components of the
extract, four main categories of the biomolecules (reducing
sugars, flavonoids, saccharides and proteins) before and after
the reaction were quantitatively examined to explore the formation mechanism of the AgNPs. The contents of the reducing
sugars and saccharides before the reaction were much higher
than those of the flavonoids and proteins (Figure 9), but the
contents of both the reducing sugars and flavonoids decreased
significantly after the reaction, while those of the saccharides and
proteins changed only slightly (Figure 9) in most cases. Therefore, the reducing sugars and flavonoids were the two main
components responsible for the bioreduction of the silver ions,
compared with the saccharides and proteins. It is worth noting
that the difference in the contents of the reducing sugars and
flavonoids before and after the reaction were affected by initial
AgNO3 concentration (C0) and reaction temperature (Figure 9).
In the case of C0 = 1 mM, the two components (flavonoids and
reducing sugars) were again responsible for the bioreduction
except that the content of the reducing sugars changed a little
after 1 h reaction at 30 °C; with similar behavior observed for
C0 = 3 and 5 mM at 30 and 60 °C. The bioreduction of the silver
ions by flavonoids and reducing sugars was promoted at higher
temperature (90 °C), and for C0 = 5 mM, the difference in the
content of the flavonoids before and after the reaction at 30 and
60 °C was much less significant than that at 90 °C. Some
flavonoids such as amentoflavone, cupressuflavone, 7,700 -di-Omethylcupressuflavone, hinokiflavone, etc. in C. Platycladi have
been identified (Figure S2 in the Supporting Information).56
Moreover, it is well-known that reducing sugars widely exist in
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Figure 8. Change of Ag+ conversion over reaction time by reducing
aqueous AgNO3 with the C. Platycladi extract at (a) 30, (b) 60, and
(c) 90 °C, respectively.
plant materials.52 Therefore, the flavonoids and some reducing
sugars might play an important role in reducing silver ions to
silver atoms in the bioreduction by the C. Platycladi extract.
Natural antioxidants with strong reductive ability for the removal of free radicals (such as DPPH radicals) have already been
extracted from a number of plants.57 In a previous study, we showed
that the capability of plant extracts to reduce chloroaurate ions
increased with the enhancement of their ability for free radical
removal,52 which we regarded as antioxidant activity.51 Similarly
therefore, antioxidant activity can be used to evaluate the reductive
ability of the extract for the bioreduction of the silver ions. The
extract exhibited very high initial antioxidant activity before the
reaction (Figure 10). For C0 = 1 and 3 mM, the bioreduction of
the silver ions at 60 and 90 °C were curbed by insufficient AgNO3
precursor; consequently, the antioxidant activity was not changed (notably) after 1 h reaction time (Figure 10). In contrast, the
difference in the antioxidant activity of the extract before and
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after the reaction for C0 = 5 mM in the same reaction time was
significant with the increase in temperature (60 to 90 °C), but the
antioxidant activity of the extract was not changed significantly in
1 h reaction at 30 °C for C0 = 1, 3, and 5 mM due to the very slow
reaction at room temperature. In this work, the soluble biomolecules were extracted by the intensified mixing of the C. Platycladi
biomass and deionized water. Measurement of the antioxidant
activity indicated that the extract exhibited excellent reductive ability
for bioreduction of silver ions with facile biosynthesis of well dispersed AgNPs with narrow size distribution. Therefore, the pretreatment procedures for the biomass (C. Platycladi) and the
biosynthesis of the AgNPs could be extended to other biomasses
for mass-production of metal NPs.
Figure 11, the FTIR spectrum of the extract, gives information
regarding the chemical transformation of the functional groups
involved in the reduction of the silver ions. Some pronounced
absorbance bands centered at 640, 1059, 1420, 1610, 2925, and
3402 cm1 were observed in the region 5004000 cm1. Among
them, the absorbance bands at 640, 1059, 1420, 1610, 2925, and
3402 cm1 were associated with the stretch vibration of CO,
CH, C=C, CH2, and OH, respectively.58 These absorbance bands could be attributed to the reducing sugars, flavonoids (amentoflavone, cupressuflavone, 7, 700 -di-O-methylcupressuflavone, hinokiflavone, etc.), saccharides, and proteins in the
extract, while the absorbance band at 640 cm1 could be regarded as a ‘fingerprint’ of the biomolecules.58 In our previous
study,35 the disappearance of the band at 1109 cm1 after the
bioreduction showed that polyols (from the sundried Cinnamomum camphora) were mainly responsible for the reduction of the
silver and chloroaurate ions. In this present study, the band at
1059 cm1 may be the result of the CO groups of the reducing sugars, flavonoids, saccharides, and proteins in the extract.
The reducing sugars among the saccharides acted as reductants
while the other saccharides as protecting agents. Undoubtedly,
the flavonoids, i.e. amentoflavone, cupressuflavone,56 7,700 -di-Omethylcupressuflavone,56 hinokiflavone,56 were also excellent
reductants for reduction of silver ions. The proteins in the
C. Platycladi extract did not work in the reduction of silver ions
as they were much weaker than the reducing sugars and flavonoids.
Our previous research excluded the possibility for proteins to be
reductants in the biosynthesis of Au NPs by foliar broths.52
Therefore, the band at 1059 cm1 weakened after the bioreduction as the reducing sugars and flavonoids were involved in the
reduction of silver ions.
Based on the FTIR spectra and the biomolecular components
of the extract, our interest was in understanding the effect of the
extract on the formation mechanism of the AgNPs especially, due
to the pronounced differences in shapes at different initial AgNO3
concentrations (C0) and reaction temperature. In the polyol
synthesis (extensive study of silver nanostructures), both oxygen
and nitrogen atoms (of the pyrrolidone unit) facilitated the
protection of the silver nanostructures by the adsorption of PVP
onto their surfaces.59 Similarly, the oxygen atoms of the biomolecular components in our extract facilitated the stabilization of
the AgNPs by the adsorption of the components onto the particle
surface; in which the reducing sugars, flavonoids, saccharides, and
proteins played a dual role as reducing and protecting agents
(biomolecules). At 30 °C and for C0 = 1 mM, the flavonoids were
mainly responsible for the reduction of the silver ions implying
that the other components might largely have acted as protecting
agents of the AgNPs, producing well protected (during the growth
process) and spheroidal AgNPs as Ag atoms were slowly but
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Figure 9. (a) Reducing sugar, (b) flavonoid, (c) saccharide, and (d) protein contents in the extract before reaction and after 1 h reaction.
Figure 10. Antioxidant activity of the extract before reaction and after
1 h reaction.
limitedly produced. However, for C0 = 3 and 5 mM, the accelerated reduction of the silver ions was by the reducing sugars;
the flavonoids showed strong reductive ability, while the other
components exhibited slightly changed protecting ability resulting
in the excessive production of Ag atoms and the anisotropic
growth of the AgNPs, leading to the formation of plate-like
AgNPs due to, perhaps, the capping action of the proteins on
the silver nuclei.29 Silver nuclei may form through homogeneous
nucleation at 90 °C. Remarkable activation of the reducing
Figure 11. Typical FTIR spectra of the biomass (a) before and (b) after
bioreduction of silver ions.
sugars and flavonoids at 90 °C led to the rapid reduction and
the subsequent homogeneous nucleation of the silver nuclei
which was formed simultaneously at the commencement of
the bioreduction(with little subsequent nucleation) leading to
the formation of AgNPs with narrow size distribution. The silver
nuclei produced at 60 °C were more homogeneous than those at
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30 °C but less homogeneous than those at 90 °C. Therefore,
with the same initial AgNO3 concentrations at 30, 60, and 90 °C,
the AgNPs produced at 90 °C possessed the narrower size
distribution.
3.3. Antibacterial Activity of the Silver Nanoparticles. 3.3.1.
Solid Agar Plate Test. The AgNPs were prepared by reducing
aqueous AgNO3 (5 mM) with the extract at 90 °C. The mean
diameter of the AgNPs, which were well dispersed in silver hydrosol, was 18.4 ( 4.6 nm. AAS analysis indicates that the
conversion of silver ions was 100% ruling out the possible effect
of silver ions on the antibacterial properties. The inhibitory percentage of the AgNPs against E. coli and S. aureus at different Ag
concentrations (in the agar plates) shows that the higher the Ag
concentration, the higher the inhibitory (Figure 12). Against
E. coli, the minimal inhibitory concentration (MIC) was 1.4 ppm
and minimal bactericidal concentration (MBC) of 27 ppm, while
the MIC against S. aureus was 5.4 ppm. Figure S3 (in the Supporting Information) shows the growth of fewer colonies grew
on the agar plate with the addition of more AgNPs. Obviously,
the growth of E. coli was completely inhibited in the presence of
the AgNPs with Ag concentration (CAg) of 27 ppm. Sondi et al.
prepared approximately 12 nm AgNPs by reducing AgNO3
Figure 12. Correlative curves between Ag concentration and inhibitory
percentage of the AgNPs against E. coli (2) and S. aureus (4),
respectively.
ARTICLE
solutions with ascorbic acid with Daxad 19 as a stabilizing agent
and obtained an inhibitory of about 95% (comparable with our
results of 100%) against E. coli with the same Ag concentration
(CAg = 27 ppm) in the agar plates.60 In contrast, the AgNPs had
an insignificant effect on the growth of S. aureus (gram-positive
bacteria) with a MIC of 5.4 ppm, almost 5 times less than that
against E. coli. The antibacterial activity was more pronounced
against E. coli than S. aureus; at CAg = 27 ppm, the inhibitory to
E. coli was 100% and 16.1% to S. aureus. Even for CAg = 54 ppm,
the inhibitory against S. aureus was only 46.3% (Figure S4 in the
Supporting Information indicates this phenomenon). The color
of the AgNPs hydrosol was dark brown which made it extremely
difficult to count the S. aureus colonies (the color covered the
colonies) with the increased Ag concentration.
3.3.2. Broth Medium Test. Figure 13 shows the growth curves
of E. coli and S. aureus in MH broth medium in the presence of
the AgNPs at different Ag concentrations. It indicates that the
bacterial growth strongly depended on the Ag concentration in
the broth medium; for CAg = 5 ppm, the value of OD600 was close
to zero implying ineffective bacterial growth inhibition. However, strong inhibitory action against E. coli was observed at high
Ag concentration; for CAg = 15 ppm, the inhibitory time was 10 h
and 11 h for CAg = 35 ppm (Figure 13a). For CAg = 50 ppm, the
OD600 remained close to zero suggesting that all the bacteria were
killed (similar results were obtained against S. aureus) (Figure 13b).
Sathishkumar et al. also demonstrated that the E. coli strain could
be completely killed by the AgNPs (CAg = 50 ppm) synthesized
by Cinnamon zeylanicum bark extract and powder.45 The AgNPs
might adsorb onto the E. coli strain through interaction between
the nanoparticles and negatively charged functional groups.49
Shrivastava et al. reported that the interaction of AgNPs was
much less with the S. aureus strain.49 However, in this work, the
strong antibacterial effect of the biogenic AgNPs showed that
they also dramatically interacted with the S. aureus strain in broth
medium.
In recent years, antibacterial materials impregnated with AgNPs
such as coatings,61,62 textiles,63 and wood flooring64 have attracted
much interest. The antibacterial activity of the biogenic AgNPs
showed the AgNPs might have potential application in such
antibacterial materials. Immobilization of the AgNPs onto the
materials might be achieved by sonochemical, solgel methods,
etc.6164 The biosynthesis by C. Platycladi extract endows the
AgNPs with low-cost and green route for production of antibacterial materials.
Figure 13. Growth curves of (a) E. coli and (b) S. aureus in the presence of the AgNPs at different Ag concentrations, respectively.
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4. CONCLUSIONS
The synthesis of Ag nanoparticles (AgNPs) by reducing AgNO3
with the C. Platycladi extract was investigated; the formation
mechanism was discussed, and the antibacterial activities were
evaluated. Increasing the initial AgNO3 concentration at
30 or 60 °C increased the mean size and widened the size distribution of the AgNPs leading to red shift and broadening of the
SPR absorption. The biomolecules (reducing sugars, flavonoids,
saccharides, and proteins in the extract) played a dual role as
reducing and protecting agents; the reducing sugars and flavonoids
were mainly responsible for the bioreduction of silver ions,
compared with saccharides and proteins. Moreover, bioreduction
of silver ions by flavonoids and reducing sugars could be promoted
at higher temperature, especially at 90 °C and resulting in the
formation of AgNPs (18.4 ( 4.6 nm) with narrow size distribution
through homogeneous nucleation. The AgNPs exhibited excellent
antibacterial activity against E. coli and S. aureus at the Ag
concentration of 50 ppm; we therefore propose their potential
application in fabricating silver-loaded antibacterial materials. This
work provides useful technical parameters for industrialization of
the biosynthetic technique and further antibacterial application of
the AgNPs. Furthermore, the elucidation of bioreductive mechanism of silver ions by measuring the change of the biomolecular
concentrations in plant extract exemplifies understanding the
formation mechanism of such biogenic AgNPs.
’ ASSOCIATED CONTENT
bS
Supporting Information. Figures S1S4. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Authors
*Phone: (+86) 592-2189595. Fax: (+86)592- 2184822. E-mail:
[email protected] (Q.L.) and [email protected] (D.S.).
Author Contributions
§
The first two authors contributed equally to this work.
’ ACKNOWLEDGMENT
This work was supported by the national Natural Science
Foundation of China (Nos. 21036004, 20776120, and 20976146),
the national 863 Program of China (No. 2007AA03Z347), the
Natural Science Foundation of Fujian Province of China (Grant
Nos. 2010J05032 and 2010J01052), and the Fundamental Research Funds for Central Universities (No.2010121051). We
thank Dr. Abdul-Rauf Ibrahim for editing the English.
’ REFERENCES
(1) Klaus, T.; Joerger, R.; Olsson, E.; Granqvist, C. G. Silver-based
crystalline nanoparticles, microbially fabricated. Proc. Natl. Acad. Sci. U.S.A.
1999, 96, 13611.
(2) Fu, J. K.; Liu, Y. Y.; Gu, P. Y.; Tang, D. L.; Lin, Z. Y.; Yao, B. X.;
Weng, S. Z. Spectroscopic characterization on the biosorption and
bioreduction of Ag(I) by Lactobacillus sp. A09. Acta Phys.-Chim. Sin.
2000, 16, 779.
(3) Mukherjee, P.; Ahmad, A.; Mandal, D.; Senapati, S.; Sainkar,
S. R.; Khan, M. I.; Parishcha, R.; Ajaykumar, P. V.; Alam, M.; Kumar, R.;
Sastry, M. Fungus-mediated synthesis of silver nanoparticles and their
immobilization in the mycelial matrix: A novel biological approach to
nanoparticle synthesis. Nano Lett. 2001, 1, 515.
ARTICLE
(4) Mukherjee, P.; Ahmad, A.; Mandal, D.; Senapati, S.; Sainkar,
S. R.; Khan, M. I.; Ramani, R.; Parischa, R.; Ajayakumar, P. V.; Alam, M.;
Sastry, M.; Kumar, R. Bioreduction of AuCl4 ions by the fungus,
Verticillium sp. and surface trapping of the gold nanoparticles formed.
Angew. Chem., Int. Ed. 2001, 40, 3585.
(5) Yong, P.; Rowson, N. A.; Farr, J. P. G.; Harris, I. R.; Macaskie,
L. E. Bioreduction and biocrystallization of palladium by Desulfovibrio
desulfuricans NCIMB 8307. Biotechnol. Bioeng. 2002, 80, 369.
(6) De Windt, W.; Aelterman, P.; Verstraete, W. Bioreductive
deposition of palladium (0) nanoparticles on Shewanella oneidensis with
catalytic activity towards reductive dechlorination of polychlorinated
biphenyls. Environ. Microbiol. 2005, 7, 314.
(7) Rautaray, D.; Ahmad, A.; Sastry, M. Biosynthesis of CaCO3
crystals of complex morphology using a fungus and an actinomycete.
J. Am. Chem. Soc. 2003, 125, 14656.
(8) Rautaray, D.; Ahmad, A.; Sastry, M. Biological synthesis of metal
carbonate minerals using fungi and actinomycetes. J. Mater. Chem. 2004,
14, 2333.
(9) Rautaray, D.; Sanyal, A.; Adyanthaya, S. D.; Ahmad, A.; Sastry,
M. Biological synthesis of strontium carbonate crystals using the fungus
Fusarium oxysporum. Langmuir 2004, 20, 6827.
(10) Bansal, V.; Rautaray, D.; Ahmad, A.; Sastry, M. Biosynthesis of
zirconia nanoparticles using the fungus Fusarium oxysporum. J. Mater.
Chem. 2004, 14, 3303.
(11) Bansal, V.; Rautaray, D.; Bharde, A.; Ahire, K.; Sanyal, A.;
Ahmad, A.; Sastry, M. Fungus-mediated biosynthesis of silica and titania
particles. J. Mater. Chem. 2005, 15, 2583.
(12) Bansal, V.; Ahmad, A.; Sastry, M. Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica. J. Am.
Chem. Soc. 2006, 128, 14059.
(13) Sanyal, A.; Rautaray, D.; Bansal, V.; Ahmad, A.; Sastry, M.
Heavy-metal remediation by a fungus as a means of production of lead
and cadmium carbonate crystals. Langmuir 2005, 21, 7220.
(14) Bansal, V.; Poddar, P.; Ahmad, A.; Sastry, M. Room-temperature biosynthesis of ferroelectric barium titanate nanoparticles. J. Am.
Chem. Soc. 2006, 128, 11958.
(15) Jha, A. K.; Prasad, K. Ferroelectric BaTiO3 nanoparticles:
Biosynthesis and characterization. Colloids Surf., B 2010, 75, 330.
(16) Bharde, A.; Rautaray, D.; Bansal, V.; Ahmad, A.; Sarkar, I.;
Yusuf, S. M.; Sanyal, M.; Sastry, M. Extracellular biosynthesis of magnetite
using fungi. Small 2006, 2, 135.
(17) Ahmad, A.; Jagadale, T.; Dhas, V.; Khan, S.; Patil, S.; Pasricha,
R.; Ravi, V.; Ogale, S. Fungus-based synthesis of chemically difficult-tosynthesize multifunctional nanoparticles of CuAlO2. Adv. Mater. 2007,
19, 3295.
(18) Ahmad, A.; Mukherjee, P.; Mandal, D.; Senapati, S.; Khan,
M. I.; Kumar, R.; Sastry, M. Enzyme mediated extracellular synthesis of
CdS nanoparticles by the fungus, Fusarium oxysporum. J. Am. Chem. Soc.
2002, 124, 12108.
(19) Kang, S. H.; Bozhilov, K. N.; Myung, N. V.; Mulchandani, A.;
Chen, W. Microbial synthesis of CdS nanocrystals in genetically engineered
E-coli. Angew. Chem., Int. Ed. 2008, 47, 5186.
(20) Jha, A. K.; Prasad, K.; Prasad, K. A green low-cost biosynthesis
of Sb2O3 nanoparticles. Biochem. Eng. J. 2009, 43, 303.
(21) Mandal, D.; Bolander, M. E.; Mukhopadhyay, D.; Sarkar, G.;
Mukherjee, P. The use of microorganisms for the formation of metal
nanoparticles and their application. Appl. Microbiol. Biotechnol. 2006, 69, 485.
(22) Mohanpuria, P.; Rana, N. K.; Yadav, S. K. Biosynthesis of
nanoparticles: technological concepts and future applications. J. Nanopart. Res. 2008, 10, 507.
(23) Kumar, V.; Yadav, S. K. Plant-mediated synthesis of silver and
gold nanoparticles and their applications. J. Chem. Technol. Biotechnol.
2009, 84, 151.
(24) Gardea-Torresdey, J. L.; Gomez, E.; Peralta-Videa, J. R.; Parsons,
J. G.; Troiani, H.; Jose-Yacaman, M. Alfalfa sprouts: A natural source for
the synthesis of silver nanoparticles. Langmuir 2003, 19, 1357.
(25) Shankar, S. S.; Ahmad, A.; Sastry, M. Geranium leaf assisted
biosynthesis of silver nanoparticles. Biotechnol. Prog. 2003, 19, 1627.
9105
dx.doi.org/10.1021/ie200858y |Ind. Eng. Chem. Res. 2011, 50, 9095–9106
Industrial & Engineering Chemistry Research
(26) Shankar, S. S.; Rai, A.; Ahmad, A.; Sastry, M. Rapid synthesis of
Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem
(Azadirachta indica) leaf broth. J. Colloid Interface Sci. 2004, 275, 496.
(27) Ankamwar, B.; Damle, C.; Ahmad, A.; Sastry, M. Biosynthesis
of gold and silver nanoparticles using Emblica officinalis fruit extract, their
phase transfer and transmetallation in an organic solution. J. Nanosci.
Nanotechnol. 2005, 5, 1665.
(28) Chandran, S. P.; Chaudhary, M.; Pasricha, R.; Ahmad, A.;
Sastry, M. Synthesis of gold nanotriangles and silver nanoparticles using
Aloe vera plant extract. Biotechnol. Prog. 2006, 22, 577.
(29) Xie, J. P.; Lee, J. Y.; Wang, D. I. C.; Ting, Y. P. Silver nanoplates:
From biological to biomimetic synthesis. ACS Nano 2007, 1, 429.
(30) Li, S. K.; Shen, Y. H.; Xie, A. J.; Yu, X. R.; Qiu, L. G.; Zhang, L.;
Zhang, Q. F. Green synthesis of silver nanoparticles using Capsicum
annuum L. extract. Green Chem. 2007, 9, 852.
(31) Nadagouda, M. N.; Varma, R. S. Green synthesis of silver and
palladium nanoparticles at room temperature using coffee and tea
extract. Green Chem. 2008, 10, 859.
(32) Vilchis-Nestor, A. R.; Sanchez-Mendieta, V.; Carnacho-Lopez,
M. A.; Gomez-Espinosa, R. M.; Camacho-Lopez, M. A.; ArenasAlatorre, J. A. Solventless synthesis and optical properties of Au and
Ag nanoparticles using Camellia sinensis extract. Mater. Lett. 2008, 62, 3103.
(33) Jha, A. K.; Prasad, K.; Kumar, V.; Prasad, K. Biosynthesis of
silver nanoparticles using Eclipta leaf. Biotechnol. Prog. 2009, 25, 1476.
(34) Prathna, T. C.; Chandrasekaran, N.; Raichur, A. M.; Mukherjee,
A. Kinetic evolution studies of silver nanoparticles in a bio-based green
synthesis process. Colloids Surf., A 2011, 377, 212.
(35) Huang, J. L.; Li, Q. B.; Sun, D. H.; Lu, Y. H.; Su, Y. B.; Yang, X.;
Wang, H. X.; Wang, Y. P.; Shao, W. Y.; He, N.; Hong, J. Q.; Chen, C. X.
Biosynthesis of silver and gold nanoparticles by novel sundried Cinnamomum camphora leaf. Nanotechnology 2007, 18, 105104.
(36) Huang, J. L.; Lin, L. Q.; Li, Q. B.; Sun, D. H.; Wang, Y. P.; Lu,
Y. H.; He, N.; Yang, K.; Yang, X.; Wang, H. X.; Wang, W. T.; Lin, W. S.
Continuous-flow biosynthesis of silver nanoparticles by lixivium of
sundried Cinnamomum camphora leaf in tubular microreactors. Ind.
Eng. Chem. Res. 2008, 47, 6081.
(37) Lin, L. Q.; Wang, W. T.; Huang, J. L.; Li, Q. B.; Sun, D. H.;
Yang, X.; Wang, H. X.; He, N.; Wang, Y. P. Nature factory of silver
nanowires: Plant-mediated synthesis using broth of Cassia fistula leaf.
Chem. Eng. J. 2010, 162, 852.
(38) Song, J. Y.; Kim, B. S. Rapid biological synthesis of silver
nanoparticles using plant leaf extracts. Bioproc. Biosyst. Eng. 2009, 32, 79.
(39) Rai, M.; Yadav, A.; Gade, A. Silver nanoparticles as a new
generation of antimicrobials. Biotechnol. Adv. 2009, 27, 76.
(40) Sharma, V. K.; Yngard, R. A.; Lin, Y. Silver nanoparticles: Green
synthesis and their antimicrobial activities. Adv. Colloid. Interface 2009,
145, 83.
(41) Martinez-Castanon, G. A.; Nino-Martinez, N.; MartinezGutierrez, F.; Martinez-Mendoza, J. R.; Ruiz, F. Synthesis and antibacterial activity of silver nanoparticles with different sizes. J. Nanopart.
Res. 2008, 10, 1343.
(42) Panacek, A.; Kvitek, L.; Prucek, R.; Kolar, M.; Vecerova, R.;
Pizurova, N.; Sharma, V. K.; Nevecna, T.; Zboril, R. Silver colloid
nanoparticles: Synthesis, characterization, and their antibacterial activity.
J. Phys. Chem. B 2006, 110, 16248.
(43) Lok, C. N.; Ho, C. M.; Chen, R.; He, Q. Y.; Yu, W. Y.; Sun,
H. Z.; Tam, P. K. H.; Chiu, J. F.; Che, C. M. Proteomic analysis of the
mode of antibacterial action of silver nanoparticles. J. Proteome Res. 2006,
5, 916.
(44) Morones, J. R.; Elechiguerra, J. L.; Camacho, A.; Holt, K.;
Kouri, J. B.; Ramirez, J. T.; Yacaman, M. J. The bactericidal effect of silver
nanoparticles. Nanotechnology 2005, 16, 2346.
(45) Sathishkumar, M.; Sneha, K.; Won, S. W.; Cho, C. W.; Kim, S.;
Yun, Y. S. Cinnamon zeylanicum bark extract and powder mediated green
synthesis of nano-crystalline silver particles and its bactericidal activity.
Colloids Surf. B-Biointerf. 2009, 73, 332.
(46) Krishnaraj, C.; Jagan, E. G.; Rajasekar, S.; Selvakumar, P.;
Kalaichelvan, P. T.; Mohan, N. Synthesis of silver nanoparticles using
ARTICLE
Acalypha indica leaf extracts and its antibacterial activity against water
borne pathogens. Colloids Surf., B 2010, 76, 50.
(47) Nabikhan, A.; Kandasamy, K.; Raj, A.; Alikunhi, N. M. Synthesis
of antimicrobial silver nanoparticles by callus and leaf extracts from
saltmarsh plant, Sesuvium portulacastrum L. Colloids Surf., B 2010, 79, 488.
(48) Veerasamy, R.; Xin, T. Z.; Gunasagaran, S.; Xiang, T. F. W.;
Yang, E. F. C.; Jeyakumar, N.; Dhanaraj, S. A. Biosynthesis of silver
nanoparticles using mangosteen leaf extract and evaluation of their
antimicrobial activities. J. Saudi Chem. Soc. 2011, 15, 113.
(49) Shrivastava, S.; Bera, T.; Roy, A.; Singh, G.; Ramachandrarao,
P.; Dash, D. Characterization of enhanced antibacterial effects of novel
silver nanoparticles. Nanotechnology 2007, 18, 225103.
(50) Xu, J. Experiment and guide for biochemistry; China Medical
Science and Technology Press: Beijing, 2009.
(51) Chen, F. A.; Wu, A. B.; Shieh, P.; Kuo, D. H.; Hsieh, C. Y.
Evaluation of the antioxidant activity of Ruellia tuberosa. Food Chem.
2006, 94, 14.
(52) Zhou, Y.; Lin, W. S.; Huang, J. L.; Wang, W. T.; Gao, Y. X.; Lin,
L. Q.; Li, Q. B.; Lin, L.; Du, M. M. Biosynthesis of gold nanoparticles by
foliar broths: roles of biocompounds and other attributes of the extracts.
Nanoscale Res. Lett. 2010, 5, 1351.
(53) Wiley, B. J.; Im, S. H.; Li, Z. Y.; McLellan, J.; Siekkinen, A.; Xia,
Y. A. Maneuvering the surface plasmon resonance of silver nanostructures through shape-controlled synthesis. J. Phys. Chem. B 2006, 110,
15666.
(54) Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chemistry and properties of nanocrystals of different shapes. Chem. Rev. 2005,
105, 1025.
(55) Daniel, M. C.; Astruc, D. Gold nanoparticles: Assembly,
supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology. Chem. Rev. 2004,
104, 293.
(56) Zhou, J. J.; Xie, G. R.; Yan, X. J. Traditional Chinese medicines:
Molecular structures, natural sources and applications; Chemical and
Industrial Press: Beijing, P. R. China, 2004.
(57) Mc Carthy, T. L.; Kerry, J. P.; Kerry, J. F.; Lynch, P. B.; Buckley,
D. J. Assessment of the antioxidant potential of natural food and plant
extracts in fresh and previously frozen pork patties. Meat Sci. 2001,
57, 177.
(58) Stuart, B. Infrared spectroscopy: fundamentals and applications;
Wiley-VCH Verlag Gmbh & Co. KGaA: Weinheim, 2004.
(59) Xiong, Y. J.; Washio, I.; Chen, J. Y.; Cai, H. G.; Li, Z. Y.; Xia,
Y. N. Poly(vinyl pyrrolidone): A dual functional reductant and stabilizer
for the facile synthesis of noble metal nanoplates in aqueous solutions.
Langmuir 2006, 22, 8563.
(60) Sondi, I.; Salopek-Sondi, B. Silver nanoparticles as antimicrobial agent: a case study on E-coli as a model for Gram-negative bacteria.
J. Colloid Interface Sci. 2004, 275, 177.
(61) Gottesman, R.; Shukla, S.; Perkas, N.; Solovyov, L. A.; Nitzan,
Y.; Gedanken, A. Sonochemical coating of paper by microbiocidal silver
nanoparticles. Langmuir 2011, 27, 720.
(62) Mahltig, B.; Textor, T. Silver containing sol-gel coatings on
polyamide fabrics as antimicrobial finish-description of a technical application process for wash permanent antimicrobial effect. Fiber Polym.
2010, 11, 1152.
(63) Zhang, F.; Wu, X. L.; Chen, Y. Y.; Lin, H. Application of silver
nanoparticles to cotton fabric as an antibacterial textile finish. Fiber
Polym. 2009, 10, 496.
(64) Kim, S.; Kim, H. J. Anti-bacterial performance of colloidal silvertreated laminate wood flooring. Int. Biodeter. Biodegr. 2006, 57, 155.
9106
dx.doi.org/10.1021/ie200858y |Ind. Eng. Chem. Res. 2011, 50, 9095–9106