Estudo magnético e magneto-ótico do internalização de nanopartículas magnéticas biocompatíveis de γ-F e2O3 recobertas com dextrana por células tumorais de sarcoma
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2010
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Universidade Federal de Goiás
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In this work we investigated the internalization process of magnetite nanoparticles,
surface coated with dextran, by mice tumour cells of Sarcoma 180 (S180) through the tech-
niques of vibrating sample magnetometer (VSM) and static magnetic birefringence (SMB).
The magnetic fluid sample, stable in physiological conditions, was prepared by the coprecip-
itation method. The growth of nanoparticles occurred in conjunction with the nanoparticle
surface coating process by dextran. The crystal structure was confirmed by X-ray diffraction.
The nanoparticles were characterized by high resolution transmission electronic microscopy.
The Sturges method was used to obtain the polydispersity in diameter, which was fitted by
a lognormal size distribution obtaining a modal diameter of 5.5 ± 0.1 nm and dispersity of
0.18 ± 0.02.The mice tumour cell sarcoma 180 was obtained using protocol established by the
American Type Culture Collection (ATCC, Rockville, MD, USA). Studies of cytotoxicity, using
the MTT method, were obtained for a nanoparticle volumetric fraction of φ = 0.00065 after
one and five hours of exposure of cells S180 to the nanoparticles. In particular, we found a
cellular viability of 87 ± 11 % after one hour of exposure proving that there was no appreciable
cell death in the time interval in which the measurements of MAV and BME were performed.
Magnetization measurements were performed to obtain the volume fraction of nanoparticles.
Tests regarding the effect of centrifugation of nanoparticles suspended in cell culture medium
RPMI 1640 showed a extremely low sedimentation of magnetic nanoparticles. A procedure,
using a acceleration of 260×g for 10 minutes, was used to separate cells containing internalized
nanoparticles from nanoparticles suspended in RPMI 1640. Measurements of magnetization
of S180 cells containing nanoparticles were performed in a wide range of exposure time (100
iv
minutes). Between 10 and 70 minutes the amount of nanoparticles in mass unit increased from
52 ± 20 pg/cell to 110 ± 15 pg/cell. Indeed magnetometry data indicate that the process of
internalization had achieved saturation between 30 to 40 minutes.
Magneto-optical technique of SMB was also used to investigate the process of inter-
nalization of nanoparticles. Firstly, SMB measurements were performed in control samples
consisting of magnetic nanoparticles suspended in RPMI 1640. We investigated the effects of
nanoparticle concentration and aging time (related to the dynamics of nanoparticle agglom-
eration). In particular, the average size of the agglomerate (Q), associated with the number
of nanoparticles forming a linear chain, remained basically constant, Q = 4.8 ± 0.2 for a full-
time of 70 minutes. Magnetic birefringence saturation data also remained stable in this time
interval. Additionally, analysis of the measurements of SMB were also used to estimate the
thickness of the coating layer (dextran), from which we found 1.70 ± 0.02 nm. Unlike VSM
data, SMB measurements were obtained on samples containing both S180 cells and magnetic
nanoparticles inside the RPMI medium 1640. Data were obtained in a wide range of time
(120 min.). Initially it was observed that the SMB signal decreases in a time range and then
increases again (between 30-40 min.). The fit of the experimental data indicate that the mag-
netic birefringence saturation (∆ns) decreases in the first 30 minutes and then increases again
smoothly, while the average size of the cluster has the opposite behavior, i.e. increases in the
first 30 minutes and then decreases. In particular, for a exposure time, t(exp), of 10 min. the
average size of the agglomerate (magnetic birefringence saturation) changed from 4.18 ± 0.04
(∆n(s) = 3.41 ± 0.02 ×1018 cm−3
min. As the birefringence saturation is proportional to the number of nanoparticles contribut-
ing to the magneto-optical signal one can conclude that the decrease in the magneto-optical
signal was due to the process of internalization of magnetic nanoparticles by cells S180. On the
other hand, the analysis of the aging time dependence of the mean size of the agglomerate also
suggests that the process of internalization occurs primarily with anisometric nanoparticles or
nanostructures forming small agglomerates. Finally, after reaching saturation of the process
) to 5.22 ± 0.08 (∆ns = 2.75 ± 0.02 ×1018 cm−3
) at texp = 30
v
of nanoparticle internalization we found a formation of small agglomerates in the RPMI 1640
medium, which is responsible for the increased intensity of the magneto-optical signal, as well
as the decrease of the mean size of the agglomerate for times longer than 30 minutes.
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SILVA, Anderson Costa da. Estudo magnético e magneto-ótico do internalização de nanopartículas magnéticas biocompatíveis de γ-F e2O3 recobertas com dextrana por células tumorais de sarcoma. 2010. 103 f. Dissertação (Mestrado em Ciências Exatas e da Terra) - Universidade Federal de Goiás, Goiânia, 2010.