- Open Access
Biocompatibility of crystalline opal nanoparticles
- Marlen Hernández-Ortiz†1,
- Laura S Acosta-Torres†3,
- Genoveva Hernández-Padrón†4,
- Alicia I Mendieta†6,
- Rodolfo Bernal†7,
- Catalina Cruz-Vázquez†2 and
- Victor M Castaño5, 8Email author
© Hernandez et al.; licensee BioMed Central Ltd. 2012
- Received: 21 May 2012
- Accepted: 1 October 2012
- Published: 22 October 2012
Silica nanoparticles are being developed as a host of biomedical and biotechnological applications. For this reason, there are more studies about biocompatibility of silica with amorphous and crystalline structure. Except hydrated silica (opal), despite is presents directly and indirectly in humans. Two sizes of crystalline opal nanoparticles were investigated in this work under criteria of toxicology.
In particular, cytotoxic and genotoxic effects caused by opal nanoparticles (80 and 120 nm) were evaluated in cultured mouse cells via a set of bioassays, methylthiazolyldiphenyl-tetrazolium-bromide (MTT) and 5-bromo-2′-deoxyuridine (BrdU).
3T3-NIH cells were incubated for 24 and 72 h in contact with nanocrystalline opal particles, not presented significant statistically difference in the results of cytotoxicity. Genotoxicity tests of crystalline opal nanoparticles were performed by the BrdU assay on the same cultured cells for 24 h incubation. The reduction of BrdU-incorporated cells indicates that nanocrystalline opal exposure did not caused unrepairable damage DNA.
There is no relationship between that particles size and MTT reduction, as well as BrdU incorporation, such that the opal particles did not induce cytotoxic effect and genotoxicity in cultured mouse cells.
- Synthetic opal
- BrdU and MTT assay
Technology is now available to produce nanoparticles materials, with a wide range of size distributions, shapes and modified surface functions. Particularly, silicon nanoparticles, are of interest as a biomarker because they are potentially bioinert and do not require a thick protective shell [1–4]. In addition, silica nanoparticles are being developed as a host of biomedical and biotechnological applications such as cancer therapy, DNA transfection, drug delivery and enzyme immobilization [5–7].
The extensive use of nanomaterials has promoted the study of nanotoxicology in parallel to the development of applications. This is due to the fact that the surfaces of biomaterials (e.g., implants and medical devices) are immediately covered by biomolecules (e.g., proteins, natural organic materials, detergents, and enzymes) as they come into contact with a biological medium. Nanoparticles coated with proteins have a conformation that may be disrupted or induced to aggregate, which, in turn, can trigger unexpected cellular responses. The key role of protein-nanoparticle interactions in nanomedicine and nanotoxicity has begun to emerge recently via the identification of the nanoparticle and protein corona. This dynamic layer of proteins and/or other biomolecules adsorbed to the nanoparticle surface determines how a nanoparticle interacts with living systems and thereby modifies the cellular responses [8–11].
The affinity and amount of proteins adsorbed on the surfaces of nanoparticle are highly dependent on the nanomaterial composition, size and surface chemistry . For example, the nano-sized silica can generate adverse effects, like liver injury and inflammation; and the exposure of amorphous spherical silicon dioxide nanoparticles of different sizes induces decreases in viability of human endothelial cells, an expression of its cytotoxicity which was apparently dependent of the particle size. Besides, each organ has different reactions; some studies indicate that nano-silica can cause cytotoxicity and primary damage in DNA but not mutagenicity in cultured mammalian cells [2, 6, 12–16].
Specifically, a polymorphous of the silica, called opal, has not been studied regarding its biocompatibility. Opal is a natural hydrous silica with either amorphous (opal-A) or ordered cristobalite structures (opal-C) and a spherical shape over a wide range of diameters from several tens of nanometers to various micrometers [17–19]. Humans are exposed directly and indirectly to opals. For example, some animals and plants contain opal as a cross-linking agent in connective tissues [20, 21] and the infiltration of biomolecules in photonic crystals to get improved luminescence spectra of DNA infiltrated opal due to the possible formation of new photon-electron bound states . The last study was made in vitro and does not consider toxicity tests. For this reason, the aim of the present work is to investigate in vitro whether nanocrystalline opal synthetized by sedimentation method could induce cytotoxic and genotoxic effects in 3T3-NIH mouse epithelial cells, using MTT and BrdU assays, respectively.
Cytotoxicity of magnetic nanoparticles
Advancements in nanotechnology over the last 20 years have led to the development of novel magnetic nanoparticles. The general theory of nuclear relaxation in the presence of paramagnetic substances is based on a monocrystalline or polycrystalline iron oxide core with a diameter of 5–30 nm embedded within a polymer coating . Superparamagnetic iron oxide nanoparticles (SPIONs) are used in a large variety of biomedical applications, such as cell labeling, hyperthermia, controlled drug delivery, in vivo cell tracking, hyperthermia, treatment of cancer, as magnetic resonance imaging (MRI) contrast agents, including [24–27]. Among all types of nanoparticles, SPIONs are the most promising candidates for use as contrast agents not only for their suitable magnetic saturation and superparamagnetic properties, but also due to their colloidal stability and biocompatibility [23, 24, 26, 28, 29].
In summary, cytotoxity of magnetic nanoparticles is strongly dependent of their chemistries and physics characteristic, cell lines, cell cycle and examined technique. The manner in which SPIONs are chemically modified will indeed impact cytotoxicity outcomes in vitro and also the toxicokinetics and dynamics in vivo . Cytotoxicity of the bare and coated SPIONs has been assessed via various methods such as the cell-life cycle assay, MTT assay, comet assay, TUNEL assay (i.e., for apoptosis detection), and several in vivo models .
The relation with this paper is based in that mesoporous silica is the magnetic carrier in whose pores is adsorbed the drug . Specifically, silica has also received tremendous attention given its long industrial history as an occupational carcinogen. Also nanoscale silica can disrupt nuclear integrity by forming intranuclear protein aggregates that can lead to inhibition of replication, transcription and cell proliferation, as reported by Chen et al. .
Production and characterization of opal nanoparticles
Synthetic opals were produced by Stöber technique . Nanodispersive silica spheres near 80 and 120 nm in diameter were synthesized through the sol-gel process of tetraethyl orthorsilicate (TEOS; Si (OC2H5)4) in a water-ethanol solution with presence of ammonium hydroxide as a catalyst, each particle size corresponds at a batch called O1 and O2, respectively. The colloid solutions were dried at 60°C. Finally, samples were sintered to 1150°C for 2 days with extreme sluggishness.
The structure and the morphology of samples were characterized by X-Ray Diffraction (XRD), using a Rigaku diffractometer, model Miniflex, with Cu Kα radiation, and Scanning Electron Microscopy (SEM) analysis, obtained with a JEOL JSM-6060LV microscope using gold as coater.
The purity of opal nanoparticles was proved with infrared spectroscopy (FTIR), using a Perkin-Elmer Spectrum GX by the KBr pellet method; and a chemical analysis by energy-dispersive spectroscopy (EDS) was developed in a JEOL JSM-5410LV Scanning Microscope.
Preparation of opal nanoparticles
Opals were added into 15 mL acid mixture of H2SO5:HNO3 (3:1) in an ultrasonic bath for 24 h, then in 0.1 M NaOH aqueous solution at 90°C for 2 h, finally in 0.1 M HCl aqueous solution at 90°C for 2 h. Thereafter, the treated opals were washed with distilled water and then centrifuged and dried. After drying, the particles were dissolved in distilled water and the solution was sonicated for 20 min before the cell evaluations.
Cell line and culture
The 3T3-NIH mouse fibroblast were cultured in DMEM (Dulbecco’s Modified-Eagle medium) supplemented with FBS (Fetal Bovine Serum, 10%) and penicillin-streptomycin (1%). The mouse fibroblasts were seeded in 24-well plates (1 x 104 cells) during 24 h, and then the medium was renewed and the experimental opals samples were put in contact with cells.
The cytotoxicity of particles was determined using the MTT assay . Briefly, opal particles were set in contact with cells and incubated in a volume of 500 μL into each well of a 24-well plate during 24 and 72 h. After each period of time, the MTT reagent was added to each well at a final concentration of 0.5 mg/mL and plates were incubated at 37°C for 40 min. Next, a solubilizing solution was added to each well and mixed thoroughly during 5 min. The optical density (OD) was read on a spectrophotometric ELISA plate reader at a wavelength of 570 nm. Cells not in contact with opals nanoparticles were used as control group. The results of the experiments were expressed as percentage of cell viability.
The quantitative determination of DNA synthesis in cells was measured using a modified BrdU test. After the cell incubation for 24 h, the BrdU labeling reagent was added and the cells were incubated again for further 4 h. During this period, the thymidine analogue BrdU is incorporated instead of thymidine into the DNA of proliferating cells. After removing the culture medium, the cells were fixed and the DNA was denatured in one step by adding FixDenat. The quantity of BrdU incorporation was detected by the monoclonal antibody from mouse hybrid cells conjugated with peroxidase (anti-BrdU-POD) which binds to the BrdU in newly synthesized cellular DNA. These immune complexes were detected by the subsequent substrate reaction and after addition of the stop solution (1 mol/L H2SO4) the colorimetric measurement of BrdU was started with the respective wavelength 450 nm in an ELISA microreader. The color intensity and thereby the absorbance directly correlated to the amount of DNA synthesis and hereby to the number of proliferating cells. The percentage of BrdU incorporation was determined by the analysis of cells treated with test substances, compared to controls.
The MTT and BrdU experiments were run using n = 3 on each group. Statistical analysis was carried out using Student’s t-test and Mann Whitney test respectively. Differences were considered significant when the P value was less than 0.05.
Characterization of the opal nanoparticles
Induction of cytotoxicity and of DNA strand breaks by opal
It observed major grade of cytotoxicity and genotoxicity in the O1 opal with less particle size and low concentration of groups OH and H2O molecules (Figure 2). This is important regarding a detailed discussion of the surface area interaction of links OH of the opal with the cellular environment. Some studies support that the smaller silica nanoparticles with greater specific surface area show more toxic effects [5, 40]. Indeed, there is an inverse relationship between particle size and number of surface expressed molecules, because the number of atoms or molecules on the surface of the particle may determine the material reactivity . In addition, silanol (SiOH) groups present on the surface of silica particles are capable of forming hydrogen bonds with oxygen and nitrogen groups found in biologic cell membranes, which then may lead to a loss of membrane structure, lysosomal leakage and tissue damage . On the other hand, Costa et al. showed that smaller silica particles are not as extensively cross-linked, as observed from the large radius increase within liquid, due to swelling with water and ethanol; also, by its lower concentrations of ammonia, used in the synthesis, contain broadly distributed residual ethoxy groups on surfaces but also largely within the particles . In fact, the oxidative state of nanomaterials at the interface is another potential design feature that can be used to mitigate cytotoxicity . This case could be reason that the O1 opal does not present cell damage significant statistically.
Due to practically there are not studies about toxicity of crystalline opal nanoparticles, results observed of this work are compared with different crystalline and amorphous silica materials on distinct types of cells. This comparison indicates similitude in it exhibited [6, 7, 42–44]. Dusts composed of amorphous silica (opal), with the exception of fiberglass, are not generally considered to be harmful to humans. On the other hand, a research data suggests that there is fibrogenic activity of different forms of free silica; the action of fused silica, quartz, cristobalite and tridymite on the liver of mice . More even, crystalline silica shows cytotoxicity and genotoxicity based on in vitro testing , apparently contradicts the work of this paper. Although, the water is considered as active agent, a study shows as the stishovite (crystalline form of silica) diluted in H2O could be even more toxic than quartz . Therefore, the water attached to the surface of crystalline opal nanoparticles is an important factor in the interaction process between cells and particles, which influences to avoid toxicity. Also, the concentration of crystalline opal nanoparticles is an important parameter in biocompatibility studies. In the present study, the concentration of sample used is greater than it what might be used in practice; which indicates no damage cytotoxic or genotoxic in cells. Certainly, the physical and chemical effects observed in the interaction between surface and biological environment requires further investigation in order to provide a good physicochemical explanation for the shown phenomenon.
Within the limitation of the present study we conclude that crystalline opals nanoparticles with 80 to 120 nm in diameter were no cytotoxic and genotoxic to the exposed mouse fibroblast cells.
The authors would like to thank for excellent technical support to: Ph. D. Marina Vega González, Miguel A. Arellano, T. Daniel Mondragón and T. Antonio Prado. M. Hernández-Ortiz is recipient of doctoral fellowship from CONACyT.
- Choi J, Zhang Q, Reip V, Wang NS, Stratmeyer ME, Hitchins VM, Goering PL: Comparison of cytotoxic and inflammatory responses of photoluminescent silicon nanoparticles with silicon micron-sized particles in RAW 264.7 macrophages. J Appl Toxicol 2009, 29: 52–60. 10.1002/jat.1382View ArticleGoogle Scholar
- Barnes CA, Elsaesser A, Arkusz J, Smok A, Palus J, Lesniak A, Salvati A, Hanrahan JP, De Jong WH, Dziubałtowska E, Stepnik M, Rydzynski K, McKerr G, Lynch I, Dawson KA, Howard CV: Reproducible comet assay of amorphous silica nanoparticles detects no genotoxicity. Nano Letters 2008, 8: 3069–3074. 10.1021/nl801661wView ArticleGoogle Scholar
- Sharma HS, Hussain S, Schlager J, Ali SF, Sharma A: Influence of nanoparticles on blood-brain barrier permeability and brain edema formation in rats. Acta Neurochirurgica Supplementum 2010, 106: 359–364. 10.1007/978-3-211-98811-4_65View ArticleGoogle Scholar
- Savage N, Diallo MS: Nanomaterials and water purification: opportunities and challenges. J Nanopart Res 2005, 7: 331–342. 10.1007/s11051-005-7523-5View ArticleGoogle Scholar
- Yu KO, Grabinski CM, Schrand AM, Murdock RC, Wang W, Gu B, Schlager JJ, Hussain SM: Toxicity of amorphous silica nanoparticles in mouse keratinocytes. J Nanopart Res 2009, 11: 15–24. 10.1007/s11051-008-9417-9View ArticleGoogle Scholar
- Choi HS, Kim YJ, Song M, Song MK, Ryu JC: Genotoxicity of Nano-silica in Mammalian Cell Lines. Toxicol Environ Health Sci 2011, 3: 7–13. 10.1007/s13530-011-0072-7View ArticleGoogle Scholar
- Durnev AD, Solomina AS, Daugel-Dauge NO, Zhanataev AK, Shreder ED, Nemova EP, Shreder OV, Veligura VA, Osminkina LA, Timoshenko VY, Seredenin SB: Evaluation of genotoxicity and reproductive toxicity of silicon nanocrystals. B Exp Biol Med+ 2010, 149: 445–449. 10.1007/s10517-010-0967-3View ArticleGoogle Scholar
- Nel A, Xia T, Mädler L, Li N: Toxic potential of materials at the nanolevel. Science 2006, 311: 622–627. 10.1126/science.1114397View ArticleGoogle Scholar
- Nel AE, Mädler L, Velegol D, Xia T, Hoek EMV, Somasundaran P, Klaessig F, Castranova V, Thompson M: Understanding biophysicochemical interactions at the nano-bio interface. Nat Mater 2009, 8: 543–557. 10.1038/nmat2442View ArticleGoogle Scholar
- Mahmoudi M, Lynch I, Ejtehadi MR, Monopoli MP, Bombelli FB, Laurent S: Protein nanoparticle interactions: opportunities and challenges. Chem Rev 2011, 111: 5610–5637. 10.1021/cr100440gView ArticleGoogle Scholar
- Mahmoudi M, Serpooshan V: Large protein absorptions from small changes on the surface of nanoparticles. J Phys Chem C 2011, 115: 18275–18283. 10.1021/jp2056255View ArticleGoogle Scholar
- Kim YJ, Yu M, Park HO, Yang SI: Comparative study of cytotoxicity, oxidative stress and genotoxicity induced by silica nanomaterials in human neuronal cell line. Mol Cell Toxicol 2010, 6: 337–344.Google Scholar
- Lai JCK, Ananthakrishnan G, Jandhyam S, Dukhande VV, Bhushan A, Gokhale M, Daniels CK, Leung SW: Treatment of human astrocytoma U87 cells with silicon dioxide nanoparticles lowers their survival and alters their expression of mitochondrial and cell signaling proteins. Int J Nanomedicine 2010, 5: 715–723. 10.2217/nnm.10.38View ArticleGoogle Scholar
- Wallace WE, Keane MJ, Murray DK, Chisholm WP, Maynard AD, Ong TM: Phospholipid lung surfactant and nanoparticle surface toxicity: Lessons from diesel soots and silicate dusts. J Nanopart Res 2006, 9: 23–38. 10.1007/s11051-006-9159-5View ArticleGoogle Scholar
- Greenberg MI, Waksman J, Curtis J: Silicosis: A Review. Dis Mon 2007, 53: 394–416. 10.1016/j.disamonth.2007.09.020View ArticleGoogle Scholar
- Fanizza C, Ursini CL, Paba E, Ciervo A, Francesco AD, Maiello R, Simonea PD, Cavallo D: Cytotoxicity and DNA-damage in human lung epithelial cells exposed to respirable α-quartz. Toxicol Vitr 2007, 21: 586–594. 10.1016/j.tiv.2006.12.002View ArticleGoogle Scholar
- Jones JB, Segnit ER: Water in sphere-type opal. Mineral Mag 1969, 37: 357–361. 10.1180/minmag.1969.037.287.07View ArticleGoogle Scholar
- Gaillou E, Fritsch E, Aguilar-Reyes B, Rondeau B, Post J, Barreau A, Ostroumov M: Common Gem Opal: An Investigation of Micro- to Nano-Structure. Am Mineral 2008, 93: 1865–1873. 10.2138/am.2008.2518View ArticleGoogle Scholar
- Masalov VM, Sukhinina NS, Emel’chenko GA: Colloidal Particles of Silicon Dioxide or the Formation of Opal-Like Structures. Physics of the Solid State 2011, 53: 1135–1139. 10.1134/S1063783411060229View ArticleGoogle Scholar
- Iler RK: The colloid chemistry of silica and silicates. New York: Cornell University Press; 1955.Google Scholar
- Iler RK: The chemistry of silica: solubility, polymerization, colloid and surface properties, and biochemistry. New York: Wiley-Interscience; 1979.Google Scholar
- Boyko V, Dovbeshko G, Fesenko O, Gorelik V, Moiseyenko V, Romanyuk V, Shvets T, Vodolazkyy P: New optical properties of synthetic opals infiltrated by DNA. Mol Cryst Liq Cryst 2011, 535: 30–41. 10.1080/15421406.2011.537888View ArticleGoogle Scholar
- Mahmoudi M, Hosseinkhani XH, Hosseinkhani M, Boutry S, Simchi A, Journeay WS, Subramani K, Laurent S: Magnetic resonance imaging tracking of stem cells in vivo using iron oxide nanoparticles as a tool for the advancement of clinical regenerative medicine. Chem Rev 2011, 111: 253–280. 10.1021/cr1001832View ArticleGoogle Scholar
- Arruebo M, Fernández-Pacheco R, Ibarra MR, Santamaría J: Magnetic Nanoparticles for Drug Delivery. Nanotoday 2007, 2: 22–32.View ArticleGoogle Scholar
- Mahmoudi M, Laurent S, Shokrgozar MA, Hosseinkhan M: Toxicity Evaluations of Superparamagnetic Iron Oxide Nanoparticles: Cell “Vision” versus Physicochemical Properties of Nanoparticles. ACS Nano 2011, 5: 7263–7276. 10.1021/nn2021088View ArticleGoogle Scholar
- Mahmoudi M, Azadmanesh K, Shokrgozar MA, Journeay WS, Laurent S: Effect of Nanoparticles on the Cell Life Cycle. Chem Rev 2011, 111: 3407–3432. 10.1021/cr1003166View ArticleGoogle Scholar
- Sharifi S, Behzadi S, Laurent S, Forrest ML, Stroevee P, Mahmoudi M: Toxicity of nanomaterials. Chem Soc Rev 2012, 41: 2323–2343. 10.1039/c1cs15188fView ArticleGoogle Scholar
- Laurent S, Dutz S, Häfeli UO, Mahmoudi M: Magnetic fluid hyperthermia: Focus on superparamagnetic iron oxide nanoparticles. Adv Colloid Interfac 2011, 166: 8–23.Google Scholar
- Mahmoudi M, Sahraian MA, Shokrgozar MA, Laurent S: Superparamagnetic iron oxide nanoparticles: promises for diagnosis and treatment of multiple sclerosis. ACS Chem Neurosci 2011, 2: 118–140. 10.1021/cn100100eView ArticleGoogle Scholar
- Stöber W, Fink A, Bohn E: Controlled growth of monodisperse silica spheres in the micron size range. J Coll Inter Sci 1968, 26: 62–69. 10.1016/0021-9797(68)90272-5View ArticleGoogle Scholar
- Uboldi C, Bonacchi D, Lorenzi G, Hermanns M, Pohl C, Baldi G, Unger RE, Kirkpatrick CJ: Gold nanoparticles induce cytotoxicity in the alveolar type-II cell lines A549 and NCIH441. Part Fibre Toxicol 2009, 6: 18–29. 10.1186/1743-8977-6-18View ArticleGoogle Scholar
- Karpov IA, Samarov ÉN, Masalov VM, Bozhko SI, Emel’chenko GA: The Intrinsic Structure of Spherical Particles of Opal. Physics of the Solid State 2005, 47: 347–351. 10.1134/1.1866417View ArticleGoogle Scholar
- Guthrie GD, Bish DL, Reynolds RC: Modeling the X-ray diffraction pattern of opal-C. Am Mineral 1995, 80: 869–872.Google Scholar
- Ilieva A, Mihailova B, Tsintsov Z, Petrov O: Structural state of microcrystalline opals: a Raman spectroscopic study. Am Mineral 2007, 92: 1325–1333. 10.2138/am.2007.2482View ArticleGoogle Scholar
- Hernández-Ortiz M, Hernández-Padrón G, Bernal R, Cruz-Vázquez C, Vega-González M, Castaño VM: Nanostructured Synthetic Opal-C. Dig J Nanomater Bios 2012, 7: 1297–1302.Google Scholar
- Beganskienė A, Sirutkaitis V, Kurtinaitienė M, Juškėnas R, Kareiva A: FTIR, TEM and NMR Investigations of Stöber Silica Nanoparticles. Mater Sci (Medžiagotyra) 2004, 10: 287–290.Google Scholar
- Graetsch H, Gies H, Topalovic I: NMR, XRD and IR study on microcrystalline opals. Phys Chem Minerals 1994, 21: 166–175. 10.1007/BF00203147View ArticleGoogle Scholar
- Hernández-Ortiz M, Hernández-Padrón G, Bernal R, Cruz-Vázquez C, Castaño VM: Nanocrystalline Mimetic Opals: Synthesis and Comparative Characterization. J Ceram-Silikaty 2012. in pressGoogle Scholar
- Cortés Escobedo CA: Caracterización de Ópalos Naturales, Reproducción del Fenómeno de Opalescencia a Partir del Proceso Sol-gel y Diseño de un Sistema de Medición de Opalescencia. Mexico City, México: Unpublished Master dissertation, University Instituto Politécnico Nacional; 2005.Google Scholar
- Napierska D, Thomassen LCJ, Rabolli V, Lison D, Gonzalez L, Kirsch-Volders M, Martens JA, Hoet PH: Size-Dependent Cytotoxicity of Monodisperse Silica Nanoparticles in Human Endothelial Cells. Small 2009, 5: 846–853. 10.1002/smll.200800461View ArticleGoogle Scholar
- Costa CAR, Valadares LF, Galembeck F: Stöber Silica Particle Size Effect on the Hardness and Brittleness of Silica Monoliths. Colloids Surf, A Physicochem Eng Asp 2007, 302: 371–376. 10.1016/j.colsurfa.2007.02.061View ArticleGoogle Scholar
- Wang JJ, Sanderson BJS, Wang H: Cytotoxicity and Genotoxicity of Ultrafine Crystalline SiO 2 Particulate in Cultured Human Lymphoblastoid Cells. Environ Mol Mutagen 2007, 48: 151–157. 10.1002/em.20287View ArticleGoogle Scholar
- Laaksonen T, Santos H, Vihola H, Salonen J, Riikonen J, Heikkilä T, Peltonen L, Kumar N, Murzin DY, Lehto VP, Hirvonen J: Failure of MTT as a Toxicity Testing Agent for Mesoporous Silicon Microparticles. Chem Res Toxicol 2007, 20: 1913–1918. 10.1021/tx700326bView ArticleGoogle Scholar
- Schins RPF, Duffin R, Höhr D, Knaapen AM, Shi T, Weishaupt C, Stone V, Donaldson K, Borm PJA: Surface Modification of Quartz Inhibits Toxicity, Particle Uptake and Oxidative DNA Damage in Human Lung Epithelial Cells. Chem Res Toxicol 2002, 15: 1166–1173. 10.1021/tx025558uView ArticleGoogle Scholar
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