Photo-induced electric polarizability of Fe3O4 nanoparticles in weak optical fields
© Milichko et al.; licensee Springer. 2013
Received: 23 May 2013
Accepted: 1 July 2013
Published: 9 July 2013
Using a developed co-precipitation method, we synthesized spherical Fe3O4 nanoparticles with a wide nonlinear absorption band of visible radiation. Optical properties of the synthesized nanoparticles dispersed in an optically transparent copolymer of methyl methacrylate with styrene were studied by optical spectroscopy and z-scan techniques. We found that the electric polarizability of Fe3O4 nanoparticles is altered by low-intensity visible radiation (I ≤ 0.2 kW/cm2; λ = 442 and 561 nm) and reaches a value of 107 Å3. The change in polarizability is induced by the intraband phototransition of charge carriers. This optical effect may be employed to improve the drug uptake properties of Fe3O4 nanoparticles.
33.15.Kr, 78.67.Bf, 42.70.Nq
KeywordsMagnetite nanoparticles Electric polarizability Low-intensity visible radiation
Magnetite (FeO*Fe2O3, or Fe3O4) nanoparticles, and materials based on them, have been successfully used to solve applied problems in biology and magneto-optics. Pronounced superparamagnetic [1–4] and ferromagnetic  properties at room temperature enable the use of these nanoparticles in magnetic resonance imaging [6–9] and biosensing  as well as in drug delivery and drug uptake applications [8–13]. Because they possess magneto-optical properties [14, 15], Fe3O4 nanoparticles have also been used to develop tunable filters [16, 17] and optical switches [18, 19] that operate under magnetic fields.
In fact, Fe3O4 nanoparticles have been examined for the presence of unique magnetic properties because magnetite is a narrow-gap semiconductor [20–22] and the optical properties of other semiconductor nanoparticles have been thoroughly studied. Currently, there are several experimental and theoretical works dedicated to studying the optical properties of both bulk magnetite [23–26] and its nanoparticles [27–29]. However, some specific optical properties of Fe3O4 nanoparticles (in particular, the effects of electric polarizability on their biological activity, conductivity, ferroelectricity, and electro-optical properties) as well as the nature of these properties remain virtually unexplored.
In this paper, we demonstrate that Fe3O4 nanoparticles exhibiting a wide nonlinear absorption band of visible radiation (1.7:3.7 eV) are able to significantly change their electric polarizability when exposed to low-intensity visible radiation (I ≤ 0.2 kW/cm2). The observed change in polarizability was induced by the intraband phototransition of nanoparticle charge carriers, and polarizability changes were orders of magnitude greater than those of semiconductor nanoparticles and molecules [30, 31].
Synthesis of nanoparticles
There are several techniques for the synthesis of Fe3O4 nanoparticles with an arbitrary shape and size and for their dispersal in different matrices [4, 5, 11, 12, 27, 29, 32–36]. In this study, we synthesized nanoparticles using co-precipitation method [1, 2, 13–15, 37, 38], dispersed them in monomeric methyl methacrylate with styrene (MMAS), and polymerized this composition using pre-polymerization method.
Oleic acid (in a mass ratio of 0.7:1 with the formed Fe3O4) was added to a 0.5% solution of iron salts (FeSO4/FeCl3 = 1:2.2 molar ratio) in 0.1 M HCl. The aqueous solution of iron salts was heated to 80°C, followed by the addition of concentrated aqueous ammonia (20% excess). The solution was heated and stirred for an hour.
Stabilized nanoparticles were then extracted from the aqueous phase into a nonpolar organic solvent hexane at a ratio of 1:1. The organic layer containing the iron oxide Fe3O4 was separated from the aqueous medium. The sample was centrifuged for 15 min (6,000 rpm) to remove larger particles. Excess acid was removed with ethanol.
The second step (Figure 1b) focused on obtaining a solid composite based on Fe3O4 nanoparticles and MMAS. The organic solvent containing nanoparticles and monomers (methyl methacrylate with styrene) was subjected to stirring and ultrasonic homogenization. To prevent nanoparticle aggregation during the polymerization process, we used the pre-polymerization method at 75°C because the nanoparticles had different affinities to the monomer and polymer.
Finally, the composite was synthesized in situ by radical polymerization. The polymerization of methyl methacrylate with styrene (in the mass ratio of 20:1) proceeded for over 10 h (in a temperature gradient mode that progressed from 55°C to 110°C) in the presence of benzoyl peroxide (10−3 mol/L).
The obtained solid composites had 0.001%, 0.003%, 0.005%, and 0.01% volume concentrations of Fe3O4 nanoparticles in MMAS. Importantly, the synthesized Fe3O4 nanoparticles generally had a thick layer of acids [36, 39] surrounding them to prevent aggregation of the nanoparticle. In our case, the synthesized Fe3O4 nanoparticles had a monolayer of oleic acid that allowed the nanoparticles to exhibit their specific optical properties.
Because they have absorption bands of 380 to 650 nm, Fe3O4 nanoparticles should exhibit an optical response upon external radiation with wavelengths in this band . To detect the optical response of the nanoparticles contained in the composite (0.005% nanoparticle volume concentration), we used the standard z-scan technique . This technique enabled the analysis of changes in the absorption coefficient Δα(I) and refractive index Δn(I) of the composite and pure MMAS, which were induced by weak optical radiation with different intensities 0 to 0.14 kW/cm2.
The experimental curves T(I) and Tpv(I), which contain information about ΔT and ΔTpv, showed that only the reverse saturable absorption of yellow radiation occurred in pure MMAS (Figure 4a). In contrast, the composite manifested the expected optical response: the shape of the experimental curves T(I) and Tpv(I) indicated the saturable absorption of visible radiation in the composite and a negative change in its refractive index (Figure 5), and the values of ΔT(I) and ΔTpv(I) increased linearly with increasing intensities of blue (Figure 5a) and yellow (Figure 5b) radiation.
where the coupling factor ρ = Δα × λ / 4π × Δn and the phase shift due to nonlinear refraction ΔΦ = 2π × Δn × Leff / λ had the following values: ρ = 0.09 and ΔΦ = −0.23 and −0.5 for blue radiation with intensities of 0.019 and 0.054 kW/cm2 and ρ = 0.05 and ΔΦ = −0.7 and −1.45 for yellow radiation with intensities of 0.04 and 0.093 kW/cm2.
where chc was the MMAS heat capacity (0.7 J/g·K), ρd was the MMAS density (1.3 g/cm3), dn/dT was the MMAS thermo-optic coefficient (−10−5 K−1), and ΔE was the energy absorbed by the composite per unit volume per second. The thermal effect of cw low-intensity radiation on the change in the refractive index (red dashed lines in Figure 6b) was relatively small (not more than 20% for blue radiation and 8% for yellow radiation).
where e was the electron charge, c was the speed of light, ϵ0 was the electric constant, m e was the electron mass, and N e was the concentration of excited electrons, which depends on the number of photons in the beam or the radiation intensity I.
Using Equation 4 to approximate the experimentally observed behavior of Δn(I) (Figure 6b, blue dashed lines), we estimated that the concentration of optically excited electrons in Fe3O4 nanoparticles was approximately 1023 m−3, being the radiation intensity of less than 0.14 kW/cm2.
where ϵ was the real part of the dielectric constant, the composite refractive index n(I) = n0 + Δn(I), and n0 was the refractive index of pure MMAS (approximately 1.5). The extinction coefficient k = αλ / 4π was significantly less than n(I) and could be ignored; χ was the nanoparticle susceptibility, and N was the nanoparticle concentration (approximately 2.3 × 1019 m−3). Therefore, the values of Δα (Å3) for Fe3O4 nanoparticle were calculated using the formula Δα (Å3) ≈ 2n × Δn(I) × 1030 / N and are presented in Figure 6b.
The obtained values for the changes in nanoparticle polarizability are orders of magnitude greater than those for semiconductor nanoparticles and molecules [30, 31] in extremely weak optical fields. In addition, the average nanoparticle volume was approximately 2.2 × 106 Å3, and the maximum value of Δα (Å3) was 9 × 106 Å3. Thus, we can conclude that the nanoparticle polarization should be formed by several optical intraband transitions of nanoparticle electrons in weak optical fields.
We used the developed co-precipitation method to synthesize spherical Fe3O4 nanoparticles covered with a monolayer of oleic acid that possessed a wide nonlinear absorption band of visible radiation 1.7 to 3.7 eV. The synthesized nanoparticles were dispersed in the optically transparent copolymer methyl methacrylate with styrene, and their optical properties were studied by optical spectroscopy and z-scan techniques. We report that the electric polarizability of Fe3O4 nanoparticles changes due to the effect of low-intensity visible radiation (I ≤ 0.2 kW/cm2; λ = 442 and 561 nm) and reaches a relatively high value of 107 Å3. The change in polarizability is induced by the intraband phototransition of charge carriers and can be controlled by the intensity of the visible radiation used. This optical effect observed in magnetic nanoparticles may be employed to significantly improve the drug uptake properties of Fe3O4 nanoparticles.
Methyl methacrylate with styrene.
The work was supported by the Programs of Presidium of Russian Academy of Science (12-I-OFN-05, 12-I-P24-05, 12-II-UO-02-002) and by the Program of UB RAS (12-S-Z-1004).
- Gass J, Poddar P, Almand J, Srinath S, Srikanth H: Superparamagnetic polymer nanocomposites with uniform Fe3O4 nanoparticle dispersions. Adv Funct Mater 2006, 16: 71–75. 10.1002/adfm.200500335View Article
- Wan J, Tang G, Qian Y: Room temperature synthesis of single-crystal Fe3O4 nanoparticles with superparamagnetic property. Appl Phys A 2007, 86: 261–264.View Article
- Mürbe J, Rechtenbach A, Töpfer J: Synthesis and physical characterization of magnetite nanoparticles for biomedical application. Mater Chem Phys 2008, 110: 426–433. 10.1016/j.matchemphys.2008.02.037View Article
- Hashimoto H, Fujii T, Nakanishi M, Kusano Y, Ikeda Y, Takada J: Synthesis and magnetic properties of magnetite-silicate nanocomposites derived from iron oxide of bacterial origin. Mater Chem Phys 2012, 136: 1156–1161. 10.1016/j.matchemphys.2012.08.070View Article
- Wang X, Zhao Z, Qu J, Wang Z, Qiu J: Fabrication and characterization of magnetic Fe3O4-CNT composites. J Phys Chem Sol 2010, 71: 673–676. 10.1016/j.jpcs.2009.12.063View Article
- Xie J, Chen K, Lee HY, Xu C, Hsu AR, Peng S, Chen X, Sun S: Ultrasmall c(RGDyK)-coated Fe3O4 nanoparticles and their specific targeting to integrin αvβ3-rich tumor cells. J Am Chem Soc 2008, 130: 7542–7543. 10.1021/ja802003hView Article
- Mi C, Zhang J, Gao H, Wu X, Wang M, Wu Y, Di Y, Xu Z, Mao C, Xu S: Multifunctional nanocomposites of superparamagnetic (Fe3O4) and NIR-responsive rare earth-doped up-conversion fluorescent (NaYF4:Yb, Er) nanoparticles and their applications in biolabeling and fluorescent imaging of cancer cells. Nanoscale 2010, 2: 1141–1148. 10.1039/c0nr00102cView Article
- Chen ZL, Sun Y, Huang P, Yang XX, Zhou XP: Studies on preparation of photosensitizer loaded magnetic silica nanoparticles and their anti-tumor effects for targeting photodynamic therapy. Nanoscale Res Lett 2009, 4: 400–408. 10.1007/s11671-009-9254-5View Article
- Yang C, Wu J, Hou Y: Fe3O4 nanostructures: synthesis, growth mechanisms, properties and application. Chem Commun 2011, 47: 5130–5141. 10.1039/c0cc05862aView Article
- Wang X, Zhang R, Wu C, Dai Y, Song M, Gutmann S, Gao F, Lu G, Li J, Li X, Guan Z, Fu D, Chen B: The application of Fe3O4 nanoparticles in cancer research: a new strategy to inhibit drug resistance. J Biomed Mater Res A 2007, 80A(4):852–860. 10.1002/jbm.a.30901View Article
- Gong P, Li H, He X, Wang K, Hu J, Tan W, Zhang S, Yang X: Preparation and antibacterial activity of Fe3O4@Ag nanoparticles. Nanotechnology 2007, 18: 1–7. 285604 285604
- Liu X, Hu Q, Fang Z, Wu Q, Xie Q: Carboxyl enriched monodisperse porous Fe3O4 nanoparticles with extraordinary sustained-release property. Langmuir Lett 2009, 25(13):7244–7248. 10.1021/la901407dView Article
- Covaliu CI, Berger D, Matei C, Diamandescu L, Vasile E, Cristea C, Ionita V, Iovu H: Magnetic nanoparticles coated with polysaccharide polymers for potential biomedical applications. J Nanopart Res 2011, 13: 6169–6180. 10.1007/s11051-011-0452-6View Article
- Wu KT, Kuo PC, Yao YD, Tsai EH: Magnetic and optical properties of Fe3O4 nanoparticle ferrofluids prepared by coprecipitation technique. IEEE Trans Magn 2001, 37(4):2651–2653. 10.1109/20.951263View Article
- Narsinga Rao G, Yao YD, Chen YL, Wu KT, Chen JW: Particle size and magnetic field-induced optical properties of magnetic fluid nanoparticles. Phys Rev E 2005, 72: 1–6.
- Liu T, Chen X, Di Z, Zhang J: Tunable magneto-optical wavelength filter of long-period fiber grating with magnetic fluids. Appl Phys Lett 2007, 91: 121116. 10.1063/1.2787970View Article
- Li J, Liu X, Lin Y, Bai L, Li Q, Chen X: Field modulation of light transmission through ferrofluid film. Appl Phys Lett 2007, 91: 1–3. 253108 253108View Article
- Chieh JJ, Hong CY, Yang SY, Horng HE, Yang HC: Study on magnetic fluid optical fiber devices for optical logic operations by characteristics of superparamagnetic nanoparticles and magnetic fluids. J Nanopart Res 2010, 12: 293–300. 10.1007/s11051-009-9613-2View Article
- Xia SH, Wang J, Lu ZX, Zhang F: Birefringence and magneto-optical properties in oleic acid coated Fe3O4 nanoparticles: application for optical switch. Int J Nanoscience 2011, 10(3):515–520. 10.1142/S0219581X11008289View Article
- Balberg I, Pankove JI: Optical measurements on magnetite single crystals. Phys Rev Lett 1971, 27(9):596–599. 10.1103/PhysRevLett.27.596View Article
- Park JH, Tjeng LH, Allen JW, Metcalf P, Chen CT: Single-particle gap above the Verwey transition in Fe3O4. Phys Rev B 1997, 55(19):813–817.
- Jordan K, Cazacu A, Manai G, Ceballos SF, Murphy S, Shvets IV: Scanning tunneling spectroscopy study of the electronic structure of Fe3O4 surface. Phys Rev B 2006, 74: 1–6. 085416 085416
- Buchenau U, Müller I: Optical properties of magnetite. Solid State Commun 1972, 11: 1291–1293. 10.1016/0038-1098(72)90845-9View Article
- Muret P: Optical absorption in polycrystalline thin films of magnetite at room temperature. Solid State Commun 1974, 14: 1119–1122. 10.1016/0038-1098(74)90286-5View Article
- Schlegel A, Alvarado SF, Wachter P: Optical properties of magnetite (Fe3O4). J Phys C: Solid State Phys 1979, 12: 1157–1164. 10.1088/0022-3719/12/6/027View Article
- Fontijn WFJ, van der Zaag PJ, Devillers MAC, Brabers VAM, Metselaar R: Optical and magneto-optical polar Kerr spectra of Fe3O4 and Mg2+ - or Al3+-substituted Fe3O4. Phys Rev B 1997, 56(9):5432–5442. 10.1103/PhysRevB.56.5432View Article
- Yasumori A, Matsumoto H, Hayashi S, Okada K: Magneto-optical properties of silica gel containing magnetite fine particles. J Sol–gel Sci Tech 2000, 18: 249–258. 10.1023/A:1008700107415View Article
- Barnakov YA, Scott BL, Golub V, Kelley L, Reddy V, Stokes KL: Spectral dependence of Faraday rotation in magnetite-polymer nanocomposites. J Phys Chem Solids 2004, 65: 1005–1010. 10.1016/j.jpcs.2003.10.070View Article
- Roychowdhury A, Pati SP, Mishra AK, Kumar S, Das D: Magnetically addressable fluorescent Fe3O4/ZnO nanocomposites: structural, optical and magnetization studies. J Phys Chem Solids 2013, 74: 811–818. 10.1016/j.jpcs.2013.01.012View Article
- Evlyukhin AB, Reinhardt C, Seidel A, Luk’yanchuk BS, Chichkov BN: Optical response features of Si-nanoparticle arrays. Phys Rev B 2010, 82(4):1–12. 045404 045404View Article
- Marenich AV, Cramer CJ, Truhlar DG: Reduced and quenched polarizabilities of interior atoms in molecules. Chem Sci 2013, 4: 2349–2356. 10.1039/c3sc50242bView Article
- Kang YS, Risbud S, Rabolt JF, Stroeve P: Synthesis and characterization of nanometer-size Fe3O4 and γ- Fe3O4 particles. Chem Mater 1996, 8: 2209–2211. 10.1021/cm960157jView Article
- Chen L, Yang WJ, Yang CZ: Preparation of nanoscale iron and Fe3O4 powders in a polymer matrix. J Mater Sci 1997, 32: 3571–3575. 10.1023/A:1018613926326View Article
- Long Y, Chen Z, Duvali JL, Zhang Z, Wan M: Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures. Physica B 2005, 370: 121–130. 10.1016/j.physb.2005.09.009View Article
- Banert T, Peuker UA: Preparation of highly filled super-paramagnetic PMMA-magnetite nanocomposites using the solution method. J Mater Sci 2006, 41: 3051–3056. 10.1007/s10853-006-6976-yView Article
- Li D, Jiang D, Chen M, Xie J, Wu Y, Dang S, Zhang J: An easy fabrication of monodisperse oleic acid-coated Fe3O4 nanoparticles. Mater Lett 2010, 64: 2462–2464. 10.1016/j.matlet.2010.08.025View Article
- Gnanaprakash G, Mahadevan S, Jayakumar T, Kalyanasundaram P, Philip J, Raj B: Effect of initial pH and temperature of iron salt solutions on formation of magnetite nanoparticles. Mater Chem Phys 2007, 103: 168–175. 10.1016/j.matchemphys.2007.02.011View Article
- Tural B, Özkan N, Volkan M: Preparation and characterization of polymer coated superparamagnetic magnetite nanoparticle agglomerates. J Phys Chem Solids 2009, 70: 860–866. 10.1016/j.jpcs.2009.04.007View Article
- Lan Q, Liu C, Yang F, Liu S, Xu J, Sun D: Synthesis of bilayer oleic acid-coated Fe3O4 nanoparticles and their application in pH-responsive Pickering emulsions. J Coll Interf Sci 2007, 310: 260–269. 10.1016/j.jcis.2007.01.081View Article
- Milichko VA, Dzyuba VP, Kulchin YN: Unusual nonlinear optical properties of SiO2 nanocomposite in weak optical fields. Appl Phys A 2013, 11(1):319–322.View Article
- Sheik-Bahae M, Said AA, Wei TH, Hagan DJ, Van Stryland EW: Sensitive measurement of optical nonlinearities using a single beam. IEEE J Quantum Electron 1990, 26(4):760–769. 10.1109/3.53394View Article
- Liu X, Guo S, Wang H, Hou L: Theoretical study on the closed-aperture Z-scan curves in the materials with nonlinear refraction and strong nonlinear absorption. Opt Commun 2001, 197: 431–437. 10.1016/S0030-4018(01)01406-7View Article
- Ganeev RA, Ryasnyansky AI, Stepanov AL, Usmanov T: Nonlinear optical response of silver and copper nanoparticles in the near-ultraviolet spectral range. Phys Sol State 2004, 46(2):351–356. 10.1134/1.1649436View Article
- AlL E, Rosen M: Quantum size level structure of narrow-gap semiconductor nanocrystals: effect of band coupling. Phys Rev B 1998, 58(11):7120–7135. 10.1103/PhysRevB.58.7120View Article
- Bennett BR, Soref RA, Del Alamo J: Carrier-induced change in refractive index of InP, GaAs, and InGaAsP. IEEE J Quantum Electron 1990, 26(1):113–122. 10.1109/3.44924View Article
- Veselago VG: The electrodynamics of substances with simultaneously negative values of ϵ and μ . Physics-Uspekhi 1968, 10: 509–514. 10.1070/PU1968v010n04ABEH003699View Article
- Yu ZG, Krishnamurthy S, Guha S: Photoexcited-carrier-induced refractive index change in small bandgap semiconductors. J Opt Soc Am B 2006, 23(11):2356–2360. 10.1364/JOSAB.23.002356View Article
- Akhmanov A, Nikitin SY: Physical Optics. Oxford: Oxford University Press; 1997.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.