The magnetization profile of iron oxide magnetic nanoparticles (MNPs) and the binding ability of MNPs with metal ions in aqueous solutions were investigated by means of the magnetic linear dichroism (MLD) and the magneto-optical Kerr effect (MOKE) measurements. The ultra-visible MLD spectra of the non-modified and surface modified MNPs with -COOH showed a typical magnetization curve for a superparamagnetic
particles. Also, the MLD spectra were changed drastically by the addition of dysprosium(III) ion and showed that MLD spectra can be used for the evaluation of metal-MNPs binding ability. Furthermore, the magnetization of MNPs solution was measured sensitively by the transversal MOKE measurements, where a polarized beam was reflected at the interface of prism/solution of MNPs

Watarai, H.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 4 No 1, 01MFPM02(2pp) (2015)   2304-1862/2015/4(1)01MFPM02(2) 01MFPM02-1  2015 Sumy State University Magneto-Optical Characterization of Binding Ability of Magnetic Nanoparticles in Solution  H. Watarai  Institute for Nano Science, Design, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan   (Received 01 June 2015; published online 26 August, 2015)  The magnetization profile of iron oxide magnetic nanoparticles (MNPs) and the binding ability of MNPs with metal ions in aqueous solutions were investigated by means of the magnetic linear dichroism (MLD) and the magneto-optical Kerr effect (MOKE) measurements. The ultra-visible MLD spectra of the non-modified and surface modified MNPs with -COOH showed a typical magnetization curve for a super-paramagnetic particles. Also, the MLD spectra were changed drastically by the addition of dysprosium(III) ion and showed that MLD spectra can be used for the evaluation of metal-MNPs binding ability. Further-more, the magnetization of MNPs solution was measured sensitively by the transversal MOKE measure-ments, where a polarized beam was reflected at the interface of prism/solution of MNPs.   Keywords: Magneto-optical effect, Magnetic linear dichroism, MOKE, Magnetic nanoparticles.   PACS numbers: 33.57.+c, 78.20.Ls,85.70.Sq   1. INTRODUCTION  Magnetic nanoparticles (MNPs) have been widely used in bio-medical, mechanical and material technolo-gies. Most widely used MNPs are the nanometer sized magnetite or magnetite and maghemite mixtures. Sur-face modified MNPs are also developed and used for various purposes [1,2]. Characterization of MNPs has been carried out usually by magnetometric methods and spectroscopic methods. Recent progress of magneto-optical methods, such as Faraday rotation [3,4], magneto-optical Kerr effect (MOKE)[5,6], magnetic linear dichroism (MLD)[7,8] and magnetic circular dichroism [9,10], opened new possibility to be applied for the characteri-zation of MNPs. Especially, the interaction between the surface modified MNPs and small ions and molecules are fundamentally important subjects. However, these interdisciplinary subjects between chemistry and phys-ics still require intensive study.  In the present study, the MLD spectrometry was applied to the measure-ments of the magnetization of MNPs solution and of the chemical binding between MNPs and dysprosi-um(III) ion.  2. MATERIALS AND METHODS  2.1 Materials  Magnetic nanoparticles (MNPs) used in this study were an aqueous solution of magnetite, W-40 (40% magnetite, 8% oleic acid, 6% sodium dodecyl-benzenesulfonate, 46% water) from Tauhokozai Co. Ltd. Tokyo, Japan and an aqueous solution of anionic sur-factant coated magnetic nanoparticles, EMG707 (ca. 10 nm in diameter, COOH modified, 8.5-11.6% iron oxide, 5.7-7.8% surfactant, 80.6-85.8% water) from Ferrotec, Tokyo, Japan. The aqueous solution of Dy(III) ion was prepared by dissolving DyCl3 with water. Water was purified by a Milli-Q system (Millipore, USA).   2.2 Methods   The magnetization of diluted MNPs and the interaction of the MNPs with metal ions in aqueous solutions have been examined by MLD spectrometry. MLD spectra were measured by a spectropolarimeter (Jasco, J-820E) applying magnetic field with a pair of permanent magnets perpendicular to the propagating light through the sample in a 1 mm quartz cell. The magnetic field was changed in the range of 0-200 mT. The transverse magneto-optical Kerr effect (TMOKE) of MNPs at the glass/solution interface was measured by TMOKE instrument, which was built in our laboratory by incorporating motor driven stage to move a permanent magnet which can apply magnetic field (0-97 mT) in the transversal direction. A vertically polarized green laser beam of 532 nm was incident on the prism/MNPs solution interface with 54.8° and the reflected beam was detected after another vertical analyzer.  3. RESULTS AND DISCSSION   3.1 MLD measurements  of magnetization  The MLD intensity of the diluted W-40 sample was increased with the increase of the magnetic field revers-ibly as shown in Fig. 1. This feature is understood as the typical magnetization curve for superparamagnetic materials. Then, it was concluded that MLD intensity can be used for the measurement of magnetization curve for diluted solution of MNPs.  Fig. 1 – Correlation between the MLD intensity at 410 nm and the magnetic flux density (mT) for 0.1% magnetite (W-40) in aqueous solution with 1 mm cell.  00,020,040,060,080,10,120,140,160,180 50 100 150 200MLD (410 nm) Magnetic field / mT  H. WATARAI PROC. NAP 4, 01MFPM02 (2015)   01MFPM02-2  3.2 Effect of Dy(III) ion on the MLD spectra   Dysprosium(III) ion is known to form the complex with -COOH group [11]. When a small amount of Dy(III) ion less than 10-4 M was added to the solution of EMG707, a drastic decrease of the MLD spectra was observed (Fig. 2).  As the concentration of Dy(III) is increased, the MLD spectra decreased remarkably with the red-shift of the maximum wavelength from 330 nm to 379 nm.  Fig. 2 – Decrease of MLD intensity with the concentration of Dy(III) for 0.0165% EMG707 MNPs solution. The concentra-tions of Dy(III) were, from top figure,  3.3 x 10-5 M, 6.7 x 10-5 M,   1.1 x 10-4 M, 1.5 x 10-4 M and 1.3 x 10-4 M.  In Fig. 2, the spectral decrease was somewhat affected due to the migration of MNPs complex toward the magnets in the higher concentration of Dy(III). Anyway, the decrease of MLD intensity with Dy(III) ion suggests the binding of the MNPs by the complexation of Dy(III) ion with the surface -COOH. Here, the value of pH was almost kept at 7.0 and the hydrolysis of Dy(III) is negligible. Therefore, the observed MLD intensity can be approximated to be the MLD of free MNPs remaining in solution. To analyze the change of MLD spectra, we have postulated a chemical reaction between MNPs and Dy(III) as,   M + nDy = MDy,n (1)  Fig. 3 – Linear correlation between logarismic values of MLD intensity at the maximum wavelength and the concentration of Dy(III) ion  where M and MDy,n refer to the free MNPs and MNPs bound  by n ions of Dy(III). Equation (1) suggests a linear relationship between log ΔMLD and log [Dy(III)], in which ΔMLD means the decrease of MLD due to the addition of Dy(III). Figure 3 shows the plot of the observed data, which supported well the postulated relationship. The result of the present study demonstrated a high potential of MLD spectrometry for the evaluation of the binding ability.  3.3 TMOKE measurement of magnetization  TMOKE signal was measured for the diluted W-40 so-lution and EMG707 MNPs aqueous solution by the re-flected beam of 532 nm at the prism/solution interface. It is interesting that the reflected light at the glass/solution interface gave a magnetization curve very similar to Fig. 1 observed by MLD spectra, and the curve suggested again the superparamagnetic property of W-40 and EMG707.  In these measurements, the required volume was only 50 L, which was put in the gap of a prism and a slide glass. Therefore, the sample volume could be re-duced and it will be adaptable to green chemistry too. The interaction between the functional group bound to the glass surface and MNPs in solution will be measured by this technique. It will be conducted in our next study.  AKNOWLEDGEMENTS  This work was supported by the Grant-in-Aid for Scientific Research (No. 256201120, 262880660) of the Ministry of Education, Culture, Sports, Science and Technology of Japan.  REFERENCES  1. B. Issa, I. M. Obaidat, B. A. Albiss, Y. Haik, Int. J. Mol. Sci. 14, 21266 (2013).  2. H. Watarai, Annual Rev. Anal. Chem. 6, 353 (2013).  3. H. Watarai, P. Gangopadhyay, R.A. Norwood, and  N. Peyghambarian, Chem. Lett. 43 No10, 1651 (2014). 4. M. Suwa, K. Miyamoto, and H. Watarai, Anal. Sci. 29 No1, 113 (2013).  5. C.A. Herreño-Fierro, E. J. Patiño, Phys. Status Solidi B 252 No2), 316 (2015).  6. C.-Y. You, S.-C. Shin, Appl. Phys. Lett. 69 No9, 1315 (1996). 7. A. Butykai, A. Orban, V. Kocsis, D. Szaller, S. Bordacs,  E. Tatrai-Szekeres, L.F. Kiss, A. Bota, B.G. Vertessy,  T. Zelles, I. Kezsmarki, Sci. Rep. 3, 1431 (2013). 8. S. Taketomi, H. Takahashi, N. Inaba, H. Miyajima, J. Phys. Soc. Jpn. 60 No10, 3426 (1991). 9. J.T. Wang, S. Hall, Y. Zhen, D.S. Guo, J. Supercond. Nov. Magn. 23, 1155 (2010). 10. O. Ohno, Y. Kaizu. H. Kobayashi, J. Chem. Phys. 99, 4128 (1993). 11. T. Gushuchina and G. Kotenko, Koord. Khim. 12, 325 (1986). y = 2,3251x + 7,862 R² = 0,971 -4-3-2-101-5,5 -4,5 -3,5log ΔMLD log [Dy(III)]/M 00,010,020,030,040,050,060,070,080,09300 400 500 600 700MLD Wavelength / nm 

Magneto-Optical Characterization of Binding Ability of Magnetic Nanoparticles in Solution

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 4 No 1, 01MFPM02(2pp) (2015) 
 
 
2304-1862/2015/4(1)01MFPM02(2) 01MFPM02-1  2015 Sumy State University 
Magneto-Optical Characterization of Binding Ability of Magnetic Nanoparticles in Solution 
 
H. Watarai 
 
Institute for Nano Science, Design, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan  
 
(Received 01 June 2015; published online 26 August, 2015) 
 
The magnetization profile of iron oxide magnetic nanoparticles (MNPs) and the binding ability of 
MNPs with metal ions in aqueous solutions were investigated by means of the magnetic linear dichroism 
(MLD) and the magneto-optical Kerr effect (MOKE) measurements. The ultra-visible MLD spectra of the 
non-modified and surface modified MNPs with -COOH showed a typical magnetization curve for a super-
paramagnetic particles. Also, the MLD spectra were changed drastically by the addition of dysprosium(III) 
ion and showed that MLD spectra can be used for the evaluation of metal-MNPs binding ability. Further-
more, the magnetization of MNPs solution was measured sensitively by the transversal MOKE measure-
ments, where a polarized beam was reflected at the interface of prism/solution of MNPs.  
 
Keywords: Magneto-optical effect, Magnetic linear dichroism, MOKE, Magnetic nanoparticles. 
 
 PACS numbers: 33.57.+c, 78.20.Ls,85.70.Sq 
 
 
1. INTRODUCTION 
 
Magnetic nanoparticles (MNPs) have been widely 
used in bio-medical, mechanical and material technolo-
gies. Most widely used MNPs are the nanometer sized 
magnetite or magnetite and maghemite mixtures. Sur-
face modified MNPs are also developed and used for 
various purposes [1,2]. 
Characterization of MNPs has been carried out 
usually by magnetometric methods and spectroscopic 
methods. Recent progress of magneto-optical methods, 
such as Faraday rotation [3,4], magneto-optical Kerr 
effect (MOKE)[5,6], magnetic linear dichroism 
(MLD)[7,8] and magnetic circular dichroism [9,10], 
opened new possibility to be applied for the characteri-
zation of MNPs. Especially, the interaction between the 
surface modified MNPs and small ions and molecules 
are fundamentally important subjects. However, these 
interdisciplinary subjects between chemistry and phys-
ics still require intensive study.  In the present study, 
the MLD spectrometry was applied to the measure-
ments of the magnetization of MNPs solution and of 
the chemical binding between MNPs and dysprosi-
um(III) ion. 
 
2. MATERIALS AND METHODS 
 
2.1 Materials 
 
Magnetic nanoparticles (MNPs) used in this study 
were an aqueous solution of magnetite, W-40 (40% 
magnetite, 8% oleic acid, 6% sodium dodecyl-
benzenesulfonate, 46% water) from Tauhokozai Co. Ltd. 
Tokyo, Japan and an aqueous solution of anionic sur-
factant coated magnetic nanoparticles, EMG707 (ca. 10 
nm in diameter, COOH modified, 8.5-11.6% iron oxide, 
5.7-7.8% surfactant, 80.6-85.8% water) from Ferrotec, 
Tokyo, Japan. The aqueous solution of Dy(III) ion was 
prepared by dissolving DyCl3 with water. Water was 
purified by a Milli-Q system (Millipore, USA).  
 
2.2 Methods  
 
The magnetization of diluted MNPs and the 
interaction of the MNPs with metal ions in aqueous 
solutions have been examined by MLD spectrometry. 
MLD spectra were measured by a spectropolarimeter 
(Jasco, J-820E) applying magnetic field with a pair of 
permanent magnets perpendicular to the propagating 
light through the sample in a 1 mm quartz cell. The 
magnetic field was changed in the range of 0-200 mT. 
The transverse magneto-optical Kerr effect (TMOKE) 
of MNPs at the glass/solution interface was measured by 
TMOKE instrument, which was built in our laboratory by 
incorporating motor driven stage to move a permanent 
magnet which can apply magnetic field (0-97 mT) in the 
transversal direction. A vertically polarized green laser 
beam of 532 nm was incident on the prism/MNPs solution 
interface with 54.8° and the reflected beam was detected 
after another vertical analyzer. 
 
3. RESULTS AND DISCSSION  
 
3.1 MLD measurements  of magnetization 
 
The MLD intensity of the diluted W-40 sample was 
increased with the increase of the magnetic field revers-
ibly as shown in Fig. 1. This feature is understood as 
the typical magnetization curve for superparamagnetic 
materials. Then, it was concluded that MLD intensity 
can be used for the measurement of magnetization 
curve for diluted solution of MNPs. 
 
Fig. 1 – Correlation between the MLD intensity at 410 nm and 
the magnetic flux density (mT) for 0.1% magnetite (W-40) in 
aqueous solution with 1 mm cell.  
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0,18
0 50 100 150 200
M
L
D
 (
4
1
0
 n
m
) 
Magnetic field / mT 
 H. WATARAI PROC. NAP 4, 01MFPM02 (2015) 
 
 
01MFPM02-2 
 
3.2 Effect of Dy(III) ion on the MLD spectra  
 
Dysprosium(III) ion is known to form the complex 
with -COOH group [11]. When a small amount of 
Dy(III) ion less than 10-4 M was added to the solution of 
EMG707, a drastic decrease of the MLD spectra was 
observed (Fig. 2).  As the concentration of Dy(III) is 
increased, the MLD spectra decreased remarkably with 
the red-shift of the maximum wavelength from 330 nm 
to 379 nm. 
 
Fig. 2 – Decrease of MLD intensity with the concentration of 
Dy(III) for 0.0165% EMG707 MNPs solution. The concentra-
tions of Dy(III) were, from top figure,  3.3 x 10-5 M, 6.7 x 10-5 M,   
1.1 x 10-4 M, 1.5 x 10-4 M and 1.3 x 10-4 M. 
 
In Fig. 2, the spectral decrease was somewhat 
affected due to the migration of MNPs complex toward 
the magnets in the higher concentration of Dy(III). 
Anyway, the decrease of MLD intensity with Dy(III) ion 
suggests the binding of the MNPs by the complexation 
of Dy(III) ion with the surface -COOH. Here, the value 
of pH was almost kept at 7.0 and the hydrolysis of 
Dy(III) is negligible. Therefore, the observed MLD 
intensity can be approximated to be the MLD of free 
MNPs remaining in solution. 
To analyze the change of MLD spectra, we have 
postulated a chemical reaction between MNPs and 
Dy(III) as, 
 
 M + nDy = MDy,n (1) 
 
Fig. 3 – Linear correlation between logarismic values of MLD 
intensity at the maximum wavelength and the concentration 
of Dy(III) ion 
 
where M and MDy,n refer to the free MNPs and MNPs bound  
by n ions of Dy(III). Equation (1) suggests a linear relationship 
between log ΔMLD and log [Dy(III)], in which ΔMLD means 
the decrease of MLD due to the addition of Dy(III). Figure 3 
shows the plot of the observed data, which supported well the 
postulated relationship. The result of the present study 
demonstrated a high potential of MLD spectrometry for the 
evaluation of the binding ability. 
 
3.3 TMOKE measurement of magnetization 
 
TMOKE signal was measured for the diluted W-40 so-
lution and EMG707 MNPs aqueous solution by the re-
flected beam of 532 nm at the prism/solution interface. It 
is interesting that the reflected light at the glass/solution 
interface gave a magnetization curve very similar to Fig. 
1 observed by MLD spectra, and the curve suggested 
again the superparamagnetic property of W-40 and 
EMG707.  In these measurements, the required volume 
was only 50 L, which was put in the gap of a prism and 
a slide glass. Therefore, the sample volume could be re-
duced and it will be adaptable to green chemistry too. 
The interaction between the functional group bound to 
the glass surface and MNPs in solution will be measured 
by this technique. It will be conducted in our next study. 
 
AKNOWLEDGEMENTS 
 
This work was supported by the Grant-in-Aid for 
Scientific Research (No. 256201120, 262880660) of the 
Ministry of Education, Culture, Sports, Science and 
Technology of Japan. 
 
REFERENCES 
 
1. B. Issa, I. M. Obaidat, B. A. Albiss, Y. Haik, Int. J. Mol. 
Sci. 14, 21266 (2013).  
2. H. Watarai, Annual Rev. Anal. Chem. 6, 353 (2013).  
3. H. Watarai, P. Gangopadhyay, R.A. Norwood, and  
N. Peyghambarian, Chem. Lett. 43 No10, 1651 (2014). 
4. M. Suwa, K. Miyamoto, and H. Watarai, Anal. Sci. 29 
No1, 113 (2013).  
5. C.A. Herreño-Fierro, E. J. Patiño, Phys. Status Solidi B 
252 No2), 316 (2015).  
6. C.-Y. You, S.-C. Shin, Appl. Phys. Lett. 69 No9, 1315 
(1996). 
7. A. Butykai, A. Orban, V. Kocsis, D. Szaller, S. Bordacs,  
E. Tatrai-Szekeres, L.F. Kiss, A. Bota, B.G. Vertessy,  
T. Zelles, I. Kezsmarki, Sci. Rep. 3, 1431 (2013). 
8. S. Taketomi, H. Takahashi, N. Inaba, H. Miyajima, J. 
Phys. Soc. Jpn. 60 No10, 3426 (1991). 
9. J.T. Wang, S. Hall, Y. Zhen, D.S. Guo, J. Supercond. Nov. 
Magn. 23, 1155 (2010). 
10. O. Ohno, Y. Kaizu. H. Kobayashi, J. Chem. Phys. 99, 4128 
(1993). 
11. T. Gushuchina and G. Kotenko, Koord. Khim. 12, 325 
(1986).
 
y = 2,3251x + 7,862 
R² = 0,971 
-4
-3
-2
-1
0
1
-5,5 -4,5 -3,5
lo
g
 Δ
M
L
D
 
log [Dy(III)]/M 
0
0,01
0,02
0,03
0,04
0,05
0,06
0,07
0,08
0,09
300 400 500 600 700
M
L
D
 
Wavelength / nm 


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Magneto-Optical Characterization of Binding Ability of Magnetic Nanoparticles in Solution

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