Small-sized silver nanoparticles for studies of biological effects

Article abstract of DOI:10.1134/S0036024411020324

The influence of the hydration extent, AOT and silver ion concentration on average particle size and size distribution in micellar solution of silver nanoparticles obtained by biochemical synthesis was investigated. Formation and stability of nanoparticles were controlled by measurements of optical absorption spectra. Particle sizes were determined by transmission electron microscopy. Combinations of varied parameters have been found, making it possible to prepare three micellar solutions of spherical silver nanoparticles with a different average size in the range 4.6-10.5 nm and narrow size distribution (the standard deviation does not exceed 2.5 nm). For the water dispersions prepared from such solutions by the specially developed procedure, possible applications for studies of size effects in the biological action of nanoparticles are also discussed.

Full text of DOI:10.1134/S0036024411020324

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2011, Vol. 85, No. 2, pp. 264–273. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.S. Sosenkova, E.M. Egorova, 2011, published in Zhurnal Fizicheskoi Khimii, 2011, Vol. 85, No. 2, pp. 317–326.
PHYSICAL CHEMISTRY
OF NANOCLUSTERS AND NANOMATERIALS
SmallꢀSized Silver Nanoparticles for Studies of Biological Effects1
L. S. Sosenkova and E. M. Egorova
Laboratory of Nanopathology, Institute of General Pathology and Pathophysiology, Russian Academy of Medical Sciences,
ul. Baltiiskaya 8, Moscow, 125315 Russia
eꢀmail: lubasya@inbox.ru
Received January 29, 2010
Abstract—The influence of the hydration extent, AOT and silver ion concentration on average particle size
and size distribution in micellar solution of silver nanoparticles obtained by biochemical synthesis was invesꢀ
tigated. Formation and stability of nanoparticles were controlled by measurements of optical absorption
spectra. Particle sizes were determined by transmission electron microscopy. Combinations of varied paramꢀ
eters have been found, making it possible to prepare three micellar solutions of spherical silver nanoparticles
with a different average size in the range 4.6–10.5 nm and narrow size distribution (the standard deviation
does not exceed 2.5 nm). For the water dispersions prepared from such solutions by the specially developed
procedure, possible applications for studies of size effects in the biological action of nanoparticles are also disꢀ
cussed.
Keywords: silver nanoparticles, biochemical synthesis, reverse micelles.
DOI: 10.1134/S0036024411020324
INTRODUCTION
primarily on the nanoparticle concentration in the
environment. The threshold concentrations, which
marked the beginning of toxic effects, depended on
the object type. It has also been revealed that the
degree of toxicity of nanoparticles is sensitive to their
size and shape: for one and the same way of preparaꢀ
tion and at a given concentration in the environment,
9ꢀnm nanoparticles appeared to be more toxic than
those 60 nm in size [14], and triangular particles are
more toxic than spherical ones [15].
Intensive studies on the properties of nanoparticles
and nanomaterials, as well as the development of variꢀ
ous practical applications, may be regarded as a promꢀ
inent feature of the last decade. Metal nanoparticles
represent one of the most popular objects, which have
already found application in chemistry, engineering,
and medicine. Among medical applications, the most
known are the improvements in diagnostics and healꢀ
ing of various (including oncological) diseases with the
use of gold nanoparticles [1–5], as well as antimicroꢀ
bial means in the form of colloidal solutions, or liquidꢀ
phase and solid materials containing silver nanopartiꢀ
cles [6–9]. Silver nanoparticles exhibit the widest
spectrum of applications, the fact that has stimulated
intensive studies of their biological effects. The main
goal of such studies is accumulation of the data on the
degree of toxicity of these nanoparticles to living
organisms, which makes it possible to define condiꢀ
tions for their safe use.
In our studies of the biological action both of silver
nanoparticles in water solutions and materials modiꢀ
fied by these nanoparticles, it was shown that they
behave as a strong toxic agent suppressing viability of
various microorganisms (bacteria and viruses) [6, 26],
slime mold [27, 28], unicellular alga [29], and plant
seeds and mammalian organisms [29, 30]. The conꢀ
centration ranges where the nanoparticles do not exert
their toxic action were defined.
The experiments were carried out with
9
6 nm
nanoparticles obtained by the biochemical synthesis
[31, 32]. The method is based on reduction of metal
ions by natural plant pigments (flavonoids) in reverse
micelles formed by an anionic surfactant. As shown
earlier [6, 32–34], the method allows us to obtain
nanoparticles of various metals (including silver) small
in size and stable in a reverseꢀmicellar (referred to furꢀ
ther as micellar) solution for a long time. Therefore, it
is possible to carry out systematic investigations of
their properties and develop various ways for their
practical application. From their micellar solutions,
water dispersions of silver nanoparticles are prepared
The biological action of silver nanoparticles was
studied on the objects of different type: on bacteria and
viruses [10–18], algae [19], animal and human culꢀ
tured cells [20–22], fish embryos [23], and animal
organisms [24, 25]. In all cases, silver nanoparticles
manifest themselves as a toxic agent causing more or
less obvious suppression of live functions, up to the
destruction (cells and embryos) or disturbance of the
normal functioning of certain organs (for animal
organisms). The intensity of toxic action depended
1
The article was translated by the authors.
264

SMALLꢀSIZED SILVER NANOPARTICLES FOR STUDIES OF BIOLOGICAL EFFECTS
265
by a specially developed procedure [35]; these water [H2O]/[AOT] = 3.7, 5, or 10. The AOT concentration
dispersions may be used, in particular, for studying in the micellar solution ( AOT) was varied in the range
interaction of nanoparticles with biological objects. It 0.015–0.135 M. The concentration of silver nanoparꢀ
is assumed that development of these studies will be in ticles ( SNP) in the micellar solution was determined
the two main directions: (1) widening the range of bioꢀ from the measured optical densities in the absorption
logical objects and (2) variation of particle parameters band maximum and the extinction coefficient (
C
C
ε
=
(size, shape, and surface charge) essential for their 1.03
×
104 l/(mol cm)) found by us as described in [43].
The absorption spectra of micellar or water soluꢀ
tions were recorded on a Heliosꢀ spectrophotometer
biological action.
α
Here, we report the results of our work aimed at
obtaining silver nanoparticles (SNPs) of different
average diameter with narrow size distribution, in
order to study the dependence of their biological effect
on particle size. It was important, as we believed, to
investigate the region of small sizes (below 20 nm),
where the soꢀcalled “size effects” are most distinctly
expressed [1, 36]. Hence, we may expect that exactly
in this size range the effect of particle size will be most
distinctly expressed. To achieve our goal we varied
three parameters of the reverseꢀmicellar system: the
concentration of stabilizer (AOT), that of silver ions,
(Thermo Electronics, GB) in a 1ꢀmm quartz cell at
room temperature. Either isooctane or distilled water
was used as reference solution. Particle sizes in micelꢀ
lar solutions were determined by transmission electron
microscopy on a LEO912 AB OMEGA microscope
(Carl Zeiss, Germany) at an accelerating voltage
120 kV. From electron micrographs, the particle size
distributions were found for no less than 350 particles.
Average sizes and standard deviations were determined
using the Gauss approximation.
and the hydration extent
w = [H2O]/[AOT]. As
RESULTS AND DISCUSSION
reported earlier in a series of works devoted to the
studies of metal nanoparticles formation in reverse
micelles (e.g., [37–42]), these parameters affect the
sizes of water micelles and/or nanoparticles. As will be
shown below, we managed to find the combinations of
parameters providing that at least two populations of
spherical silver nanoparticles are formed with rather
narrow distribution and large enough difference in the
average sizes, the maximum average size not exceedꢀ
ing 10.5 nm. The formation process and stability of
nanoparticles were controlled by measurements of
optical absorption spectra. Particle sizes were deterꢀ
mined by transmission electron microscopy.
As shown earlier [32, 33, 43], the introduction of
silver salt water solution to the Qr micellar solution
leads to rapid changes in color and absorption specꢀ
trum. The colorless or lightꢀyellow quercetin solution
becomes redꢀbrown or almost black depending on the
nanoparticle concentration. Figure 1 shows the typical
change in the absorption spectra of the Qr micellar
solution after the addition of [Ag(NH3)2]NO3 water
solution in the standard synthesis procedure. Instead
of the twoꢀband spectrum in the UV region characterꢀ
istic of flavonoids [44–46], a new absorption band
appears with Dmax = 420–440 nm, lying in the range
characteristic for silver nanoparticles in reverse
micelles at a low hydration extent [42, 47]. The optical
density in the band maximum (Dmax) allows us to find
the SNP concentration at the given time after the
beginning of synthesis. The completion of nanopartiꢀ
cle formation corresponds to the stationary stage when
the Dmax value remains nearly constant. The rate of
SNP formation depends on the salt silver concentraꢀ
tion. As seen from Fig. 1, at cAg = 7.4 mM the process
is almost fully accomplished within 2 h, when Dmax
reaches its stationary value. After the stationary state is
established, only small changes of optical density take
place, not exceeding 10% of the Dmax. At the smaller
silver concentrations, the process can be slowed down,
but in all investigated cases, the formation of nanoparꢀ
ticles is finished in no more than 1–2 days. The SNP
concentration at the stationary stage (cNP) depends on
the system parameters; in the case shown in Fig. 1,
cNP = 3.84 mgꢀion Ag+/l or 0.40 g/l (recalculated to
metal silver). For the particle size measurements, the
solutions were used taken at the stationary stage, 7 days
after the beginning of synthesis.
EXPERIMENTAL
Silver nitrate (analytical grade) and deionized
water (no less than 10 M ) obtained from Vodolei
Ω
water purification system (Khimelectronika, Moscow,
Russia) were used to prepare the AgNO3 aqueous soluꢀ
tion. The complex silver salt [Ag(NH3)2]NO3 was preꢀ
pared by adding 27% aqueous ammonium hydroxꢀ
yde to the silver nitrate water solution. To prepare
quercetin micellar solutions, AOT (sodium bis(2ꢀ
dioctyl)sulphosuccinate, Aldrich or Acros) ( 96%,
≥
Fluka), isooctane (analytical grade) and quercetin
(3,5,7,3',4'ꢀpentahydroxyflavon, Merck) were used.
The standard procedure for preparing the quercetin
(Qr) micellar solution is described in detail elsewhere
[32, 33, 43]. Briefly, Qr taken as a powder was solubiꢀ
lized in the preliminary prepared AOT solution in
isooctane. The Qr concentration in micellar solution
was determined as described in [43].
For the synthesis of silver nanoparticles, an
[Ag(NH3)2]NO3 water solution was added to the 2.65
×
=
=
The electron micrograph and size distribution in
SNP micellar solutions, obtained at the parameters
given in the legend to Fig. 1, are presented in Fig. 2.
10–4 М Qr micellar solution to the concentration, CAg
(1–7.4)
×
10–3
М and hydration extent, w
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D
4
5
4
3
2
3
2
1
0
1
Qr
300
400
500
600
, nm
λ
Fig. 1. Formation kinetics of Ag nanoparticles. Silver ion concentration in micellar solution, cAg = 7.4 mM;
w
= 3.7,
c
= 0.135 M.
AOT
–4
Quercetin concentration here and in the other experiments,
c
=
2.65
×
10
М. Absorption spectra are measured 5 min (1),
Qr
30 min (
2), 2 h (
3), 1 day (
4), and 7 days (
5) after the addition of silver salt water solution (beginning of synthesis).
(a)
(b)
γ, %
40
20
0
50 nm
6
8
10 l, nm
Fig. 2. Electron micrograph (a) and particle size distribution (b) in micellar solution of Ag nanoparticles at
= 0.135 M. Average particle size; = 9.3 nm, standard deviation, 1.7 nm. Here and in Figs. 4, 6, 8, and 10, the microꢀ
graphs are obtained 7 days after the beginning of synthesis. l—particle size (nm), —fraction of the particles.
w
= 3.7,
c
= 7.4 mM,
Ag
c
d
Δ
=
AOT
av
γ
The nanoparticles are spherical, with average size dav
9.3 nm and standard deviation = 1.7 nm.
To change the particle average size, we varied sucꢀ
=
size because of the changes in the aggregation rate of
the nanoclusters [41, 42].
Δ
The AOT concentration was changed to the smaller
cessively three parameters of the reverseꢀmicellar sysꢀ values as it enabled us further to decrease the surfacꢀ
tem: the AOT concentration (cAOT), that of silver salt tant concentration in the SNP water solutions, this
(
cAg) and the hydration extent w. As known from literꢀ may be essential for the studies of their action on bioꢀ
ature, and value affect the size of the micelle water logical objects in the water media. Figure 3 shows the
core [37, 39, 40], where metal ions are reduced with spectra of SNP micellar solutions, obtained at the
subsequent formation of the particles containing small same and cAg values but at different AOT concentraꢀ
w
w
number of silver atoms (nanoclusters). Variation of silꢀ tions: cAOT = 0.135 M (the standard value), 0.08 and
ver salt concentration causes changes in the particle 0.042 M. It is seen that the decrease of cAOT results in
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D
4
1
2
3
3
2
1
0
300
400
500
600
, nm
λ
Fig. 3. The effect of AOT concentration on formation of Ag nanoparticles. Parameters of micellar solution:
AOT
synthesis.
c
= 7.4 mM, w =
Ag
3.7,
c
(
M
): 0.135 (
1), 0.08 (
2
) and 0.042 (3). Spectra here and in Figs. 5, 7, and 9 are measured 7 days after the beginning of
(a)
(b)
γ, %
40
20
0
50 nm
6
8
10
l, nm
Fig. 4. Electron micrograph (a) and particle size distribution (b) in SNP micellar solution at
= 8.4 nm, 1.6 nm.
w
= 3.7,
c
= 7.4 mM,
c
= 0.08 M,
Ag
AOT
d
Δ
=
av
the insignificant fall of SNP concentration (Dmax valꢀ with cAOT = 0.08 M. Here, the average size appeared to
ues), more noticeable for the smallest AOT concenꢀ
tration. In addition, a small shift of the absorption
band to the long waves (from 433 to 440 nm) is
observed, identical for the two last CAOT values.
According to the known Mie theory, this may indicate
to the increase in the average particle size [47, 48].
be 8.4 nm, that is, somewhat smaller than at cAOT
=
0.135 M (9.3 nm), with almost the same standard
deviation (1.6 and 1.7 nm, respectively). Thus, for an
AOT concentration approximately 1.7 times smaller,
we have obtained a SNP solution with an average size
only slightly different from that in the standard soluꢀ
tion. It is clear also that in this case, the assumption
about the increase in size, issuing from the red shift of
the absorption band, is not confirmed by the electron
To determine particle sizes, we used the solution
with cAOT = 0.08 M, because in this case, at the same
supposed increase in size, there remains a higher
nanoparticle concentration. Figure 4 shows an elecꢀ
tron micrograph and size distribution for the solution microscopy data.
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D
4
438
435
1
3
2
1
434
2
3
425
4
420
5
0
300
400
500
600
, nm
λ
Fig. 5. Effect of silver concentration on the formation of nanoparticles. Parameters of micellar solution:
Ag
w
= 3.7,
c
= 0.08 M,
AOT
c
(mM): 7.4 ( ), 4 ( ), 2.4 M ( ), 1 ( ), 0.5 ( ). Figures on curves show wavelengths of absorption band maxima.
1
2
3
4
5
(a)
(b)
γ, %
40
20
0
100 nm
2
4
6
8
10 l, nm
Fig. 6. Electron micrograph (a) and size distribution (b) in SNP micellar solution at
4.6 nm, 1.8 nm.
w
= 3.7,
c
= 1 mM,
c
= 0.08 M, d =
Ag
AOT av
Δ
=
The decrease of silver salt concentration in the SNP concentration is not too low. The electron microꢀ
range 7.4–0.5 mM leads to the essential decrease of graph and particle size distribution in this SNP micelꢀ
SNP concentration and to a shift in the band maxiꢀ lar solution are shown in Fig. 6. It turned out that here
mum towards short wavelengths (Fig. 5). For electron the decrease in silver concentration (in this case, in
microscopy, we have chosen the SNP synthesized at accordance with the Mie theory) actually leads to a
cAg = 1 mM, since here the noticeable shift of λmax is decrease in the average particle size to 4.6 nm at
observed (hence it is possible to assume the significant almost the same standard deviation ( 1.8 nm). Thus,
decrease of the particle size), and at the same time the we obtained an SNP solution with particles almost
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D
1.2
1
2
3
0.8
4
0.4
0
300
400
500
600
, nm
λ
Fig. 7. Influence of AOT concentration on nanoparticle formation. Parameters of micellar solution:
AOT
c
= 1 mM, w = 3.7,
Ag
c
(M): 0.135 (1), 0.08 (2), 0.04 (3), 0.015 (4).
two times smaller than those in solutions with cAg
7.4 mM.
=
tion; the maximal shift (at
The electron micrograph for the solution with cAOT
0.015 M is given in Fig. 8. From histogram analysis, we
find dav 7.7 1.13 nm, that is, an obvious increase in
the average size in comparison with the solution with
AOT = 0.08 M (Fig. 6). Hence, it follows that the parꢀ
ticle average size can be increased by decreasing the
AOT concentration, but this parameter works at a sufꢀ
ficiently small concentration of silver ions. It is possiꢀ
ble that in this case the shift in the SNP absorption
band position to the long waves reflects the increase in
the particle size, in agreement with the Mie theory
predictions.
cAOT = 0.015 M) is 15 nm.
=
Further we found it useful to elucidate whether the
AOT concentration exerts an influence on the particle
sizes for the solution with cAg = 1 mM, that is, whether
the results of the preceding experiment are condiꢀ
tioned by the fact that the effect of AOT concentration
cannot be revealed at a large concentration of silver
ions. Such a supposition issues from the following reaꢀ
sons. It is obvious that the higher silver ion concentraꢀ
tion, the greater the rate of nanoparticle formation
and aggregation. The influence of AOT concentration
on the aggregation process may manifest itself in the
fact that the AOT molecules adsorbed on the surface of
=
c
Thus, at the given stage of research, we obtain three
nanoparticles prevent them from aggregating and thus SNP solutions with close average particle sizes (7.7–
decrease the particle average size. The rate of AOT 9.3 nm) and one solution with an average size of
adsorption will be higher, the greater its concentraꢀ 4.6 nm, i.e., 1.7–2 times smaller. The standard deviaꢀ
tion; therefore, the increase in AOT concentration tion for all solutions does not exceed 1.8 nm.
should lead to a decrease in the average particle size.
The effect of hydration extent was studied in soluꢀ
However, such an effect can be clearly expressed when
tions with cAg = 1 mM, cAOT = 0.08 M. Figure 9 shows
the AOT adsorption rate is comparable to that of
nanoparticle aggregation, i.e., when the concentration
of silver ions is not too high.
the spectra of SNP solutions prepared at three values
of hydration extent: = 3.7, 5, and 10. It is seen that
the increase in in this range has practically no influꢀ
w
w
Figure 7 shows changes in the absorption spectra ence on the SNP concentration, but it results in a blue
with AOT concentration changes in solutions with shift of the absorption band by 6–7 nm. According to
cAg = 1 mM. Similarly to what is found for the greater the Mie theory, such a shift can be caused by the
concentration of silver ions (Fig. 3), here the shift of decrease in particle size. However, in this case, such a
the absorption band to bigger wavelengths is observed, decrease seems to hardly possible since it is well known
which is the greater, the smaller the AOT concentraꢀ that, in metal nanoparticle synthesis in reverse
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(a)
(b)
γ, %
60
40
20
100 nm
0
2
4
6
8
10 12
l
, nm
Fig. 8. Electron micrograph (a) and size distribution (b) in SNP micellar solution at
w
= 3.7,
c
= 1 mM,
c
= 0.015 M,
d
=
Ag
AOT
av
7.7 nm,
Δ
=
1.13 nm.
D
1.2
0.8
0.4
0
1
2
3
300
400
500
600
, nm
λ
Fig. 9. Effect of hydration extent on nanoparticle formation. Parameters of micellar solution:
3.7 (1), 5 (2), and 10 (3).
c
= 1 mM,
c
= 0.08 M,
w
=
Ag
AOT
micelles, the increase in w, on the contrary, leads to an extent for SNP micellar solutions was also observed by
increase in particle size (e.g., [38, 41, 42, 49]). The
same effect of the increase in the hydration extent is
observed in our case. An electron micrograph and the
other authors [41]. As supposed in [41], this may be
related to the increase in the size of the micelle water
core, which leads to an increase in the fraction of less
rigidly structured water and, consequently, to facilitaꢀ
tion of the exchange of micelle content by impacts. As
a result, the frequency of impacts, mergings, and splitꢀ
tings of micelles increases with nanoparticle growth,
with a corresponding increase in the width of their size
particle size distribution in solution at
sented in Fig. 10. In comparison with the solution at
= 3.7, the average size has become almost three
w = 10 are preꢀ
w
times as large, 10.35 nm; however, the size dispersion
has also increased, since the standard deviation is
2.5 nm. A similar tendency toward an increase in the
degree of polydispersion with an increased hydration distribution.
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271
γ, %
25
20
15
10
5
100 nm
0
6
8
10
12
14
, nm
l
Fig. 10. Electron micrograph (a) and size distribution (b) in SNP micellar solution at
10.35 nm, 2.5 nm..
w
= 10,
c
= 1 mM,
c
= 0.08 M, d =
Ag
AOT av
Δ
=
The whole series of sizes obtained by us, with the
For comparison of action of nanoparticles of difꢀ
relevant nanoparticle concentrations and other ferent size, it is possible to use variants 4 and 2, 4 and
parameters of micellar solutions, are presented in the
table.
5, or 4 and 3. It is also necessary to keep in mind that,
as mentioned above, apart from particle size, an essenꢀ
tial role in SNP biological action can be played by their
adsorption on a cell membrane, which depends on the
numerical concentration of nanoparticles (i.e., the
*
added to the experimental system. Therefore, for corꢀ
rect determination of the effect of particle size, it is
important that, for nanoparticles of different size, the
It is known that, during their transfer to the water
phase, the sizes of nanoparticles do not change and
their concentration appears to be equal or close to that
in the micellar solution [29, 35]. Therefore, from the
data given in the table, it is possible to make concluꢀ
sions on the applicability of various variants of syntheꢀ
sis (N 1–5) for studying biological effects of nanoparꢀ
ticles in water media.
number of particles per unit volume in solution,
)
cNP
*
cNP
values be identical in the experimental system.
Variants 1 and 2 give nanoparticles of both nearly
equal size (with small dispersion) and concentration in
solution. They differ only in AOT concentration. Our
way of preparing SNP water solutions is described in
[35]. Since in the thus obtained water solution the
AOT concentration is the lesser, the smaller its conꢀ
centration in the initial micellar solution [29], the
choice between these two variants can be made judging
from the significance of the value of AOT concentraꢀ
tion for the object studied, when this surfactant is
introduced into the experimental system with the SNP
solution. As follows from our experimental practice [6,
29], in the tests on water suspensions of bacterial cells,
the bactericidal action of silver nanoparticles is maniꢀ
fested at such high dilutions (50 times or more) that
the presence of AOT in both variants cannot have an
effect on the object under study. So it is possible to use
both variants of synthesis. If, for the dilutions used, in
variant 1 the toxic action of AOT is detected in the
control experiments (the introduction of AOT water
solution in the absence of nanoparticles), then variꢀ
ant 2 is preferable. If it is necessary to provide a high
concentration of nanoparticles in the medium and
variant 2 is not applicable because of the toxicity of
AOT, it is possible to use variant 3, where the AOT
concentration in water solution is approximately one
order less than in variant 1.
Correspondingly, if the study is performed with two
water solutions containing nanoparticles of different
*
size and the initial
values, it is necessary to use difꢀ
cNP
ferent degrees of dilution in order to ensure equal
numerical nanoparticles concentration in the experiꢀ
mental system. As seen from the data of our table, if
the effects of solutions 4 and 2, with different particle
*
cNP
sizes and equal initial
values, are compared, for
example, on a cell culture, it is possible to use one and
the same dilution of the initial SNP water solutions.
If the biological effects of variants 4 and 5 are comꢀ
pared, it is necessary to use for solution 5 an SNP
Particle sizes and concentrations, AOT concentrations, and deꢀ
grees of hydration in micellar solutions of silver nanoparticles
*
cNP , parꢀ
ticles/ml
cNP
g/l
,
No.
dav, nm
Δ
, nm
c
AOT, M
w
1
2
3
4
5
9.3
8.4
7.7
4.6
1.7
1.6
1.13
1.8
0.135
0.08
3.7 0.40 9.1E+13
3.7 0.39 1.2E+14
3.7 0.11 4.4E+13
3.7 0.11 2.1E+14
0.015
0.08
10.35 2.5
0.08
10
0.11 1.8E+13
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7. R. P. Evstigneeva and V. P. Pchelkin, Khim.ꢀFarmats.
concentration in the experimental system that is ten
times higher (the dilution, ten times less), since the
initial 1.13 value in solution 5 is ten times smaller
than in solution 4. A similar correction should be
made in comparing solutions 4 and 3.
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To summarize, it is possible to conclude that bioꢀ
chemical synthesis allows one to obtain solutions of
silver nanoparticles with an average size in the range
4.6–10.5 nm with a narrow size distribution (with a
standard deviation = 1.13–2.5 nm). All of the nanoꢀ
Δ
Russian].
particles are approximately spherical and stable in
solution for a long time (up to several years). The
change in particle sizes is achieved by variation of the
parameters of the reverseꢀmicellar system where the
synthesis is conducted, namely, of the AOT and silver
concentration, and of the hydration extent. It is necesꢀ
sary to note that changes in the position of the absorpꢀ
tion band maximum, observed with a change in the
chosen parameter do not always agree with Mie theory
predictions. Hence, it follows that, in the investigated
system, apart from size changes, a shift of the SNP
absorption band can result from the other factors. As
reported in a number works devoted to studies of the
optical properties of silver nanoparticles ([50–52] and
references therein), such factors can be the adsorption
of molecules or ions present in a solution (in our case,
probably, silver ions) on the SNP surface, as well as the
adsorption of nanoparticles on silver oxide microcrysꢀ
tals. Further studies will be devoted to elucidating the
reasons for the nanoparticle band shift in cases when
disagreement with the Mie theory is observed. It is also
supposed that selection of the combinations of system
parameters will make it possible to prepare solutions
with an average particle size in the range of 10–20 nm
and then to implement systematic studies of the role of
particle sizes in the biological effects of silver nanoparꢀ
ticles.
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3
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ACKNOWLEDGMENTS
The authors are grateful to Dr. S.S. Abramchuk
from Moscow State University for his assistance in
making electron micrographs of silver nanoparticles in
micellar solutions.
,
,
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