DOI 10.1007/s10527-016-9574-6
Biomedical Engineering, Vol. 49, No. 6, March, 2016, pp. 394397. Translated from Meditsinskaya Tekhnika, Vol. 49, No. 6, Nov.Dec., 2015, pp. 5255.
Original article submitted September 11, 2015.
Depolarization of Light Scattered in Water Dispersions
of Nanoparticles of Different Shapes
S. A. Dolgushin1*, I. K. Yudin2, V. K. Deshabo2, P. V. Shalaev1, and S. A. Tereshchenko1
The results of measurement of depolarization of light scattered in water dispersions of nanospheres and nanorods
are presented. The influence of the nanoparticle shape on the degree of depolarization of the scattered light is
demonstrated.
Introduction
Presently, nano and microparticles are widely used
in medicine, biology, and pharmacology for development
of new effective methods of diagnosis and therapy [17].
Nanoparticles are also used in chemistry, petrochemistry,
and hydrocarbon extraction [8, 9]. Thus, the problem of
measurement of the geometric parameters of nanoparti
cles is rather important.
In recent years there has been considerable progress
in methods of measurement of the geometric parameters
of nanoparticles. These methods include electron and
probe microscopy, acoustic spectroscopy, light scattering
methods, etc. [1012]. It should be noted that light scat
tering methods are especially useful because they are
nondestructive and do not require expensive equipment.
These methods make it possible to measure the size of
nanoparticles in liquid dispersions, e.g., in technological
media. Light scattering methods allow rheological and
morphological properties of dispersion nanosystems to be
estimated, which is an additional advantage of these
methods. The methods based on light scattering are
preferable for the analysis of properties of nanoparticles.
In the case of static light scattering, the scattering
intensity is measured at various scattering angles. The
Zimm or Debye methods of data processing allow the
molecular weight of dispersed particles, their radius of
1
National Research University of Electronic Technology, Moscow,
Russia; Email: dolgushin.sergey@gmail.com
2
Oil and Gas Research Institute, Russian Academy of Sciences,
Moscow, Russia.
* To whom correspondence should be addressed.
gyration, and the second virial coefficient to be estimated
[11].
In the case of dynamic light scattering (DLS), the
time correlation function is measured, which allows the
diffusion coefficient and the radius of spherical nanopar
ticles to be determined [11]. Measurements can be per
formed at different scattering angles, which provides
additional information about nanoparticles (e.g., using a
dynamic Zimm plot [11]).
Modifications of the light scattering method
described above are based on the theory of a single scat
tering event, which assumes the absence of multiple scat
tering events. Therefore, the dependence of the light scat
tering intensity on the scattering angle can be considered
as the scattering indicatrix.
Presently, devices using static and dynamic light
scattering are commercially available. In these devices,
the data on the size of particles is obtained under the
assumption of particle sphericity. The estimation of geo
metric parameters of nonspherical particles is a more
sophisticated problem that should be solved on the basis
of additional research. A promising medical application
of the DLS method is the blood cell count in hemotrans
fusion. For example, it can be used for evaluating throm
bocyte viability in blood plasma [13]. Presently, there are
no rapid, reliable, and inexpensive methods for monitor
ing the degradation of stored thrombocytes due to spon
taneous activation, aggregation, etc. [14]. However, the
DLS method allows fast estimation of the geometric
parameters of aggregates of many cells with high accura
cy [13].
An effective approach to the estimation of the geo
metric parameters of particles is based on the measure
394
00063398/16/49060394 © 2016 Springer Science+Business Media New York
Depolarization of Light Scattered in Water Dispersions
ment of the polarization parameters of scattered light. In
such experiments vertically (VV) and horizontally (VH)
polarized components of scattered light are most fre
quently used. The autocorrelation function of the verti
cally polarized component of the scattered light provides
information about the translational diffusion coefficient
and thus the particle radius. The autocorrelation function
of the horizontally polarized component of the scattered
light allows the rotational diffusion coefficient to be esti
mated in the case of nonspherical particles. This pro
vides information about the aspect ratio and the form fac
tor of the nanoparticles. The modification of the light
scattering method that enables measurement of rotation
al diffusion of nonspherical particles is called depolarized
dynamic light scattering (DDLS) [14].
We suggest use of the DDLS method for evaluating
the geometric shape of nonspherical particles. The
application of the DDLS method to medicine would
increase the accuracy of estimation of the geometric
parameters of thrombocytes, because presently available
methods are based on the assumption of particle spheric
ity [13].
In this work, the preliminary results of polarization
measurements of nanoparticles of colloidal gold (spheres
and rods) are presented. The results of this work demon
strated that, as expected in earlier works, light scattering
depolarization is absent in spherical particles. Small
nonzero values of this parameter observed in experiments
were due to small deviations of the particle shape from
spherical. In the case of nanorods, the depolarization
component is rather significant and depends on the
aspect ratio of the samples.
Materials and Methods
Measurements were performed using a Photocor
Complex analyzer of particle size (Photocor Ltd., Russia)
intended to monitor static and dynamic light scattering in
liquids. The range of measured particle sizes was 0.5 nm 10 μm.
Three samples of dispersed nanosize particles of col
loidal gold of various shapes were monitored: 1) nano
spheres with diameter d = 90 nm, 2) nanorods with aspect
ratio a = 3.6, and 3) nanorods with aspect ratio a = 4.9.
The typical rod length was 90 nm. The experimental sam
ples were synthesized at the Laboratory of Nanobiotech
nology, Institute of Biochemistry and Physiology of
Plants and Microorganisms, Russian Academy of
Sciences [15]. In the experiments, the samples were
placed into thermostated containers with working tem
perature (24 ± 0.1)°C.
395
In the experiments, the scattered radiation intensity
I was detected at scattering angles 20°140° with step 10°.
At each scattering angle the scattered radiation intensity
was measured at various positions of the axis of the polar
izer located before the detector. The rotation angle of the
polarizer ranged from 0° to 150° with step 10° relative to
the vertical polarization plane of linearly polarized radia
tion of the diode laser (l = 657 nm).
The photodetector, operating in the photon counting
mode, employed a Hamamatsu R635810 photoelectron
multiplier.
In spherical particles depolarization was absent. The
scattered light intensity dependence on the polarizer
angle α was
I(α) = I0(θ)cos2(α),
(1)
where θ is the scattering angle and I0(θ) is the maximal
intensity at α = 0. In the case of depolarization, the depo
larized component is added:
I(α) = Ip(θ)cos2(α) + Id (θ),
(2)
where Ip(θ) is the maximal intensity of the polarized com
ponent and Id(θ) is the intensity of the depolarized com
ponent.
It is convenient to measure the degree of polarization
in normalized values. In this case the normalized intensi
ty of scattered light for spherical particles is
.
(3)
In the case of depolarization, the normalized inten
sity is
(4)
The degree of depolarization pd is assumed to be
(5)
Results
Curves of scattered radiation intensity I detected by
the photodetector vs. the polarizer angle α are shown in
396
Dolgushin et al.
b
I, a.u.
I, a.u.
a
α, deg
α, deg
Fig. 1. Curves of scattered radiation intensity I vs. polarizer angle α for (a) nanospheres and (b) nanorods with the aspect ratio 4.9 at scatter
ing angles 30° (squares), 50° (triangles), 70° (empty circles), and 90° (filled circles).
b
In, a.u.
In, a.u.
a
α, deg
α, deg
Fig. 2. Curves of normalized scattered light intensity In vs. polarizer angle α for (a) nanospheres and (b) nanorods with the aspect ratio 4.9 at
scattering angles 30° (squares), 50° (triangles), 70° (empty circles), and 90° (filled circles).
Figs. 1a and 1b. The curves were measured for the nano
spheres and nanorods with the aspect ratio 4.9 at the scat
tering angles θ = 30°, 50°, 70°, and 90°.
The curves of normalized scattered light intensity are
shown in Fig. 2. It can be seen that the degree of scattered
light depolarization for nonspherical particles is high and
virtually independent of the scattering angle. The degree of
the depolarization of scattered light is characterized by the
ratio of minimal to maximal intensity, which is 0.056 ±
0.002 for spheres and 0.55 ± 0.02 for rods. The deviation
in the depolarization degree for spheres from zero is due to
small deviations of tested particles from spherical form
(within ±5%). In the case of nonspherical particles, the
depolarization degree is an order of magnitude larger.
Curves of normalized scattered light intensity vs. the
polarizer angle α for nanorods and nanospheres at scat
tering angles 30° and 90° are shown in Figs. 3a and 3b,
respectively.
Conclusion
The shape of nanosize particles was shown to modify
the depolarization degree of single scattered light. For ideal
spherical particles, the depolarization component of scat
tered light is zero. However, in the case of actual spherical
samples, the shape of the tested particles insignificantly dif
fers from the ideal shape, thereby causing a nonzero degree
Depolarization of Light Scattered in Water Dispersions
397
b
In, a.u.
In, a.u.
a
α, deg
α, deg
Fig. 3. Curves of normalized scattered light intensity In vs. polarizer angle α for nanorods with the aspect ratios 3.6 (empty squares) and 4.9
(filled squares) and nanospheres (circles) at scattering angles 30° (a) and 90° (b).
of depolarization (0.056 ± 0.002). For nonspherical parti
cles (nanorods) the depolarization component increases sig
nificantly (by an order of magnitude): for rods with the
aspect ratios 3.6 and 4.9 it is an average of 0.51 ± 0.02 and
0.55 ± 0.02, respectively. In this case, the dependence of the
depolarization degree on the scattering angle is insignificant.
The results obtained in this work can be used in
developing methods for estimation of the geometric shape
of nonspherical particles, e.g., the geometric parameters
of thrombocytes.
This work was supported by the Ministry of Educa
tion and Science of the Russian Federation (Project No.
14.575.21.0090, identifier RFMEFI57514X0090).
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