O. Akhavan

Sharif University of Technology, Teheran, Tehrān, Iran

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Publications (118)427.7 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Reduced graphene oxide nanomeshes (rGONMs), as p-type semiconductors with band-gap energy of ∼1 eV, were developed and applied in near infrared (NIR) laser stimulation of human neural stem cells (hNSCs) into neurons. The biocompatibility of the rGONMs in growth of hNSCs was found similar to that of the graphene oxide (GO) sheets. Proliferation of the hNSCs on the GONMs was assigned to the excess oxygen functional groups formed on edge defects of the GONMs, resulting in superhydrophilicity of the surface. Under NIR laser stimulation, the graphene layers (especially the rGONMs) exhibited significant cell differentiations, including more elongations of the cells and higher differentiation of neurons than glia. The higher hNSC differentiation on the rGONM than the reduced GO (rGO) was assigned to the stimulation effects of the low-energy photoexcited electrons injected from the rGONM semiconductors into the cells, while the high-energy photoelectrons of the rGO (as a zero band-gap semiconductor) could suppress the cell proliferation and/or even cause cell damages. Using conventional heating of the culture media up to ∼43 °C (the temperature typically reached under the laser irradiation), no significant differentiation was observed in dark. This further confirmed the role of photoelectrons in the hNSC differentiation.
    Colloids and surfaces B: Biointerfaces 02/2015; 126. · 4.28 Impact Factor
  • O. Akhavan
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    ABSTRACT: Bacteriorhodopsin (bR) molecules were utilized as light-driven proton pumps for green as well as effective reduction of single-layer graphene oxide (GO) sheets. The bR molecules and graphene sheets were separated from each other in an aqueous environment by using a polytetrafluoroethylene membrane filter, in order to prevent their direct interactions (including attachment of the bR molecules onto the GO). Although reduction of GO using hydrazine or bR showed similar deoxygenation levels (based on X-ray photoelectron spectroscopy), the former resulted in formation of CN bonds which can substantially decrease the electrical conductivity of the reduced sheets. The electrical characteristics of the single-layer graphene sheets were studied by recording current–voltage curves of the sheets located between two Au electrodes on a SiO2 (300 nm)/Si (100) substrate. The electrical conductivity of the bR-reduced graphene oxide (rGO) sheets was found about one order of magnitude better than that of hydrazine-rGO sheets. The excellent electrical conductivity of the bR-rGO sheets (with sheet resistance of ∼7.1 × 104 Ω/sq) was assigned to the effective deoxygenation (without formation of any CN bonds) and better restoration of the graphitic structure of the GO sheets, using the protons pumped by the bR molecules.
    Carbon 01/2015; 81. · 6.16 Impact Factor
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    ABSTRACT: Nanoparticles of high-Z elements exhibit stronger photoelectric effects than soft tissues under gamma irradiation. Hence, they can be used as effective radiosensitizers for increasing the efficiency of current radiotherapy. In this work, superparamagnetic zinc ferrite spinel (ZnFe2O4) nanoparticles were synthesized by a hydrothermal reaction method and used as radiosensitizers in cancer therapy. The magnetic nanoparticles showed fast separation from solutions (e.g., ~1min for 2mgmL(-1) of the nanoparticles in ethanol) by applying an external magnetic field (~1T). The ZnFe2O4 nanoparticles were applied in an in vitro radiotherapy of lymph node carcinoma of prostate cells (as high radioresistant cells) under gamma irradiation of (60)Co source. The nanoparticles exhibited no significant effects on the cancer cells up to the high concentration of 100μgmL(-1), in the absence of gamma irradiation. The gamma irradiation alone (2Gy dose) also showed no significant effects on the cells. However, gamma irradiation in the presence of 100μgmL(-1) ZnFe2O4 nanoparticles resulted in ~53% inactivation of the cells (~17 times higher than the inactivation that occurred under gamma irradiation alone) after 24h. The higher cell inactivation was assigned to interaction of gamma radiation with nanoparticles (photoelectric effect), resulting in a high level electron release in the media of the radioresistant cells. Our results indicated that ZnFe2O4 nanoparticles not only can be applied in increasing the efficiency of radiotherapy, but also can be easily separated from the cell environment by using an external magnetic field after the radiotherapy. Copyright © 2014 Elsevier B.V. All rights reserved.
    Materials Science and Engineering C 01/2015; 46:394-9. · 2.74 Impact Factor
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    ABSTRACT: tGraphene oxide nanoribbons (GONRs) were synthesized using an oxidative unzipping of multi-walledcarbon nanotubes. The interactions of the GONRs with various concentrations of fetal bovine serumor human plasma serum indicated that the GONRs were functionalized substantially by the albuminoriginated from the two different protein sources. Then, concentration-dependent cytotoxicity of theprotein-functionalized GONRs on human epithelial cells was studied. Although the GONRs with concen-trations ≤50 �g/mL did not exhibit significant cytotoxicity on the cells (with the cell viability >85%), theconcentration of 100 �g/mL exhibited significant cytotoxicity including prevention of cell proliferationand induction of cell apoptosis. These results can provide more in-depth understanding about cytotoxiceffects of graphene nanostructures which can be functionalized by the proteins of media.
    Applied Surface Science 11/2014; · 2.54 Impact Factor
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    ABSTRACT: Export Date: 18 October 2014
    Journal of Alloys and Compounds 11/2014; 612:380-385. · 2.73 Impact Factor
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    ABSTRACT: Graphene oxide nanoplatelets (GONPs) with extremely sharp edges (lateral dimensions ~20–200 nm and thicknesses <2 nm) were applied in extraction of the overexpressed guanine synthesized in cytoplasm of leukemia cells. The blood serums containing the extracted guanine were used in differential pulse voltammetry (DPV) supplied by reduced graphene oxide nanowall (rGONW) electrodes to develop fast and ultra sensitive electrochemical detections of leukemia cells at leukemia fractions (LFs) of ~10-11 (as the lower detection limit). Stability of the DPV signals obtained through oxidation of the extracted guanine on the rGONWs was studied after 20 cycles. Without the guanine extraction, the DPV peaks relating to guanine oxidation of normal and abnormal cells were overlapped at LFs <10-9, and consequently, the performance of alone rGONWs were limited at this level. As a benchmark, the DPV using glassy carbon electrodes was able to detect only LFs ~10-2. The ultra sensitivity obtained by this combination method (guanine extraction by GONPs and then guanine oxidation by rGONWs) is five orders of magnitude better than the sensitivity of the best current technologies (e.g., specific mutations by polymerase chain reaction) which not only are expensive, but also require few days for diagnosis.
    Nanoscale 10/2014; · 6.74 Impact Factor
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    ABSTRACT: Graphene oxide (GO) sheets functionalized by aminopropylsilyl groups (8.0 wt.%) were labeled by 198,199Au nanoparticle radioisotopes (obtained through reduction of HAuCl4 in sodium citrate solution followed by thermal neutron irradiation) for fast in vivo targeting and SPECT imaging (high purity germanium-spectrometry) of tumors. Using instant thin layer chromatography method, the physicochemical properties of the amino-functionalized GO sheets labeled by 198,199Au NPs (198,199Au@AF-GO) were found to be highly stable enough in organic phases, e.g. a human serum, to be reliably used in bioapplications. In vivo biodistribution of the 198,199Au@AF-GO composite was investigated in rats bearing fibrosarcoma tumor after various post-injection periods of time. The 198,199Au@AF-GO nanostructure exhibited a rapid as well as high tumor uptake (with uptake ratio of tumor to muscle of 167 after 4 h intravenous injection) that resulted in an efficient tumor targeting/imaging. Meantime, the low lipophilicity of the 198,199Au@AF-GO caused to its fast excretion (~ 24 h) throughout the body by the kidneys (as also confirmed by the urinary tract). Because of the short half-life of 198,199Au radioisotopes, the 198,199Au@AF-GO with an excellent tumor targeting/imaging and fast washing out from the body can be suggested as one of the most effective and promising nanomaterials in nanotechnology-based cancer diagnosis and therapy.
    Materials Science and Engineering C 09/2014; · 2.74 Impact Factor
  • Omid Akhavan, Elham Ghaderi
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    ABSTRACT: An effective and self-organized differentiation of human neural stem cells (hNSCs) into neurons was developed by pulsed laser stimulation of the cells on graphene films (prepared by drop-casting GO suspension onto quartz substrates). The effects of graphene oxide (GO) and hydrazine-reduced graphene oxide (rGO) sheets on proliferation of hNSCs were examined. The higher proliferation of the cells on the GO was assigned to its better hydrophilicity. On the other hand, the rGO sheets with significantly better electrical conductivity than GO exhibited more differentiation of the cells into neurons. The pulsed laser stimulation not only resulted in accelerated differentiation of the hNSCs into neurons (rather than glia), but also caused self-organization of a radial neuronal network on surface of the rGO sheets, due to a radial stress induced by the surface thermal gradient originated from the center of the laser spot. The higher thermal conductivity of the rGO sheets (as compared to the GO sheets and the quartz substrate) provided better outwards heat flow from the center of laser spot, and consequently, prevented an extra local heating at the position of laser spot. These results can excite more investigations on the advantages of graphene in self-organized differentiation of hNSCs, using pulsed laser stimulation.
    J. Mater. Chem. B. 06/2014;
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    ABSTRACT: A magneto-photothermal therapy for cancer (in vitro photothermal therapy of prostate cancer cells and in vivo photothermal therapy of human glioblastoma tumors in the presence of an external magnetic field) was developed using superparamagnetic zinc ferrite spinel (ZnFe2O4)–reduced graphene oxide (rGO) nanostructures (with various graphene contents). In vitro application of a low concentration (10 μg mL−1) of the ZnFe2O4–rGO (20 wt%) nanostructures under a short time period (1 min) of near-infrared (NIR) irradiation (with a laser power of 7.5 W cm−2) resulted in an excellent destruction of the prostate cancer cells, in the presence of a magnetic field (1 Tesla) used for localizing the nanomaterials at the laser spot. However, in the absence of a magnetic field, ZnFe2O4–rGO and also rGO alone (10 μg mL−1) resulted in only 50% cell destruction at the most in the short photothermal therapy and also in a typical radiotherapy (2 min gamma irradiation with a dose of 2 Gy). The minimum concentrations required for the successful application of the nanostructures in the photothermal and radiotherapeutic methods were found to be 100 and 1000 μg mL−1, while in the proposed magneto-photothermal therapy it was only 10 μg mL−1. The in vivo feasibility of this method was also examined on mice bearing glioblastoma tumors. Furthermore, the localization of the magnetic nanomaterials injected into the tumors was studied in the presence and absence of an external magnetic field. These results will stimulate more applications of magnetic graphene-containing composites in highly efficient photothermal therapy.
    J. Mater. Chem. B. 05/2014; 2(21).
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    ABSTRACT: Cited By (since 1996):1, Export Date: 18 October 2014
    International Journal of Hydrogen Energy 05/2014; 39(15):8169-8179. · 2.93 Impact Factor
  • M. Mazaheri, O. Akhavan, A. Simchi
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    ABSTRACT: Graphene oxide (GO)─chitosan composite layers with stacked layer structures were synthesized using chemically exfoliated GO sheets (with lateral dimensions of ̃1 μm and thickness of ̃1 nm), and applied as antibacterial and flexible nanostructured templates for stem cell proliferation. By increasing the GO content from zero to 6 wt%, the strength and elastic modulus of the layers increased ̃80% and 45%, respectively. Similar to the chitosan layer, the GO─chitosan composite layers showed significant antibacterial activity (>77% inactivation after only 3 h) against Staphylococcus aureus bacteria. Surface density of the actin cytoskeleton fibers of human mesenchymal stem cells (hMSCs) cultured on the chitosan and GO(1.5 wt%)─chitosan composite layers was found nearly the same, while it significantly decreased by increasing the GO content to 3 and 6 wt%. Our results indicated that although a high concentration of GO in the chitosan layer (here, 6 wt%) could decelerate the proliferation of the hMSCs on the flexible layer, a low concentration of GO (i.e., 1.5 wt%) not only resulted in biocompatibility but also kept the mechanical flexibility of the self-sterilized layers for high proliferation of hMSCs.
    Applied Surface Science 04/2014; 301. · 2.54 Impact Factor
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    ABSTRACT: Graphene oxide (GO) sheets were synthesized through a modified Hummers' method. Using high resolution transmission electron microscopy the thickness of the GO sheets in a multilayer structure of stacked GO sheets was found ̃0.8 nm. A nanosecond pulsed laser (with wavelength of 532 nm and average power of 0.3 W) was applied for effective and environment friendly reduction of the GO sheets in an ammonia solution (pH ̃9) at room temperature conditions. The deoxygenation of the GO sheets by the pulsed laser reduction method was confirmed by using UV─visible, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS) and thermo gravimetric analysis. Based on XPS analysis, the O/C ratio of the GO sheets decreased from 49% to 21% after 10 min laser irradiation. This reduction efficiency was comparable with the efficiency achieved by hydrazine which yielded the O/C ratio of 15% at 80 °C after 10 min. Using Raman spectroscopy it was found that the pulsed laser reduction method resulted in nearly no aggregation of the reduced GO sheets in the ammonia solution. These results can help to further promotion and application of pulsed lasers in environment friendly reduction of GO.
    Applied Surface Science 04/2014; 301. · 2.54 Impact Factor
  • Alireza Meidanchi, Omid Akhavan
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    ABSTRACT: Superparamagnetic ZnFe2O4/reduced graphene oxide (rGO) composites containing ZnFe2O4 nanoparticles (with ∼5–20 nm sizes) attached onto rGO sheets (with ∼1 μm lateral dimensions) were synthesized by hydrothermal reaction method. By increasing the graphene content of the composite from 0 to 40 wt%, the size as well as the number of the ZnFe2O4 nanoparticles decreased and the saturated magnetization of the composites reduced from 10.2 to 1.8 emu/g, resulting in lower responses to external magnetic fields. Concerning this, the time needed for 90% separation of ZnFe2O4/rGO (40 wt%) composite from its solution (2 mg/mL in ethanol) was found 60 min in the presence of an external magnetic field (∼1 Tesla), while using ZnFe2O4/rGO (15 wt%), only 2 min was required (comparable to the separation time of pure ZnFe2O4 nanoparticles). Correspondingly, the magnetic separation time of 10 μM methyl orange and rhodamine B from aqueous solutions containing 2 mg/mL ZnFe2O4/rGO (15 wt%) was found <6 min, while using the ZnFe2O4/rGO (40 wt%) only 15–20% of the dyes could be separated after 16 min. Although the pure ZnFe2O4 nanoparticles could magnetically separate nearly whole of the dyes from the solutions, the separation time was too longer (>16 min).
    Carbon 04/2014; 69:230–238. · 6.16 Impact Factor
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    ABSTRACT: Vertically aligned ZnO@CdS nanorod heterostructure films with various loadings of CdS nanoparticle shell were synthesized and applied in photoinactivation of Escherichia coli bacteria under visible light irradiation. While neither the bare ZnO nanorods (with band-gap energy (E g) of 3.28 eV) under visible light irradiation nor the nanorod heterostructures in dark exhibited any significant antibacterial activity, the ZnO@CdS nanorod heterostructures (with E g 2.5–2.6 eV) could successfully inactivate the bacteria under visible light irradiation. Furthermore, it was found that an optimum loading of the CdS shell (corresponding to the effective thickness less than 15 nm) is required to achieve a complete inactivation of the bacteria after 24 h visible light irradiation at room temperature. Using X-ray photoelectron spectros-copy, the lower photoinactivation efficiencies of the ZnO@CdS nanorod heterostructure at CdS thicknesses lower and higher than the optimum one were assigned to lower amounts of CdS nanoparticles and OH bonds (substantially existed on the hydrothermally synthesized ZnO nanorods) which are responsible for absorption of the visible light and production of hydroxyl radicals, respectively. Water contact angle measurements showed that the sample with more surface OH groups has a more hydro-philic surface and so more antibacterial activity.
    Journal of Alloys and Compounds 03/2014; 590:507. · 2.73 Impact Factor
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    ABSTRACT: Asian red ginseng was used for green reduction of chemically exfoliated graphene oxide (GO) into reduced graphene oxide (rGO). The reduction level and electrical conductivity of the ginseng-rGO sheets were comparable to those of hydrazine-rGO ones. Reduction by ginseng resulted in repairing the sp2 graphitic structure of the rGO, while hydrazine-rGO showed more defects and/or smaller aromatic domains. The ginseng-rGO sheets presented a better stability against aggregation than the hydrazine-rGO ones in an aqueous suspension. Whilst the hydrophobic hydrazine-rGO films exhibited no toxicity against human neural stem cells (hNSCs), the hydrophilic GO and ginseng-rGO films (as more biocompatible films) showed proliferation of the stem cells after 3 days. On the other hand, the hydrazine-rGO and especially the ginseng-rGO films exhibited more differentiation of hNSCs into neurons (rather than glia) than the GO film, after 3 weeks. The accelerated differentiation on the rGO films was assigned to their higher capability for electron transfer. Meanwhile, the better differentiation on the ginseng-rGO film (as compared to the hydrazine-rGO film) was attributed to its higher biocompatibility, more hydrophilicity and the π−π attachment of ginsenoside molecules (as powerful antioxidants) on surface of the reduced sheets.
    Carbon 01/2014; 66:395–406. · 6.16 Impact Factor
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    ABSTRACT: Export Date: 18 October 2014
    RSC Advances 01/2014; 4(52):27213-27223. · 3.71 Impact Factor
  • O. Akhavan, K. Bijanzad, A. Mirsepah
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    ABSTRACT: Cited By (since 1996):2, Export Date: 18 October 2014
    RSC Advances 01/2014; 4(39):20441-20448. · 3.71 Impact Factor
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    Applied Surface Science 01/2014; · 2.54 Impact Factor
  • Omid Akhavan, Elham Ghaderi
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    ABSTRACT: Graphene nanogrids (crossed graphene nanoribbons synthesized by the oxidative unzipping of multi-walled carbon nanotubes) on a SiO2 matrix containing TiO2 nanoparticles (NPs) were applied as a photocatalytic stimulator in the accelerated differentiation of human neural stem cells (hNSCs) into two-dimensional neural networks. The hydrophilic graphene nanogrids exhibited patterned proliferations of hNSCs (consistent with patterns of the nanogrids), in contrast with the usual random growths occurring on quartz substrates. The number of cell nuclei differentiated on reduced graphene oxide nanoribbon (rGONR) grid/TiO2 NPs/SiO2 increased 5.9 and 26.8 fold compared to the number of cells on quartz substrates, after three weeks of differentiation, in the dark and under photo stimulation, respectively. The stimulation, originated by the injection of photoexcited electrons from the TiO2 NPs into the cells on the nanogrids, also resulted in changing the number of differentiated neurons and glial cells in the patterned neural network by factors of 1.8 and 0.17, respectively. A higher differentiation on the rGONR grids than rGO sheets was assigned to the physical stress induced by the surface topographic features of the nanogrids. The current–voltage properties of the neural networks differentiated on the electrically disconnected rGONR grids demonstrated effective cell-to-cell and cell-to-rGONR couplings after three weeks of the stimulated differentiation.
    J. Mater. Chem. B. 11/2013; 1(45).
  • Omid Akhavan, Elham Ghaderi
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    ABSTRACT: For the application of human neural stem cells (hNSCs) in neural regeneration and brain repair, it is necessary to stimulate hNSC differentiation towards neurons rather than glia. Due to the unique properties of graphene in stem cell differentiation, here we introduce reduced graphene oxide (rGO)/TiO2 heterojunction film as a biocompatible flash photo stimulator for effective differentiation of hNSCs into neurons. Using the stimulation, the number of cell nuclei on rGO/TiO2 increased by a factor of ∼1.5, while on GO/TiO2 and TiO2 it increased only ∼48 and 24%, respectively. Moreover, under optimum conditions of flash photo stimulation (10 mW cm(-2) flash intensity and 15.0 mM ascorbic acid in cell culture medium) not only did the number of cell nuclei and neurons differentiated on rGO/TiO2 significantly increase (by factors of ∼2.5 and 3.6), but also the number of glial cells decreased (by a factor of ∼0.28). This resulted in a ∼23-fold increase in the neural to glial cell ratio. Such highly accelerated differentiation was assigned to electron injection from the photoexcited TiO2 into the cells on the rGO through Ti-C and Ti-O-C bonds. The role of ascorbic acid, as a scavenger of the photoexcited holes, in flash photo stimulation was studied at various concentrations and flash intensities.
    Nanoscale 09/2013; 5(21). · 6.74 Impact Factor

Publication Stats

3k Citations
427.70 Total Impact Points

Institutions

  • 2000–2014
    • Sharif University of Technology
      • • Department of Physics
      • • Institute for Nanoscience and Nanotechnology
      Teheran, Tehrān, Iran
  • 2005
    • Institute For Trade Studies and Research, Iran
      Dārāb, Fārs, Iran