O. Akhavan

Sharif University of Technology, Teheran, Tehrān, Iran

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Publications (112)311.12 Total impact

  • 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.
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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; · 6.73 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; · 2.40 Impact Factor
  • O Akhavan, E. 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. · 3.55 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.
    04/2014;
  • 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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    R. Azimirad, S. Safa, O. Akhavan, E. Hasani
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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
  • 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; · 6.73 Impact Factor
  • M. Choobtashani, O. Akhavan
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    ABSTRACT: Tungsten oxide thin films (deposited by thermal evaporation or sol gel method) were used for photocatalytic reduction of graphene oxide (GO) platelets (synthesized through a chemical exfoliation method) on surface of the films under UV or visible light of the environment, in the absence of any aqueous ambient at room temperature. Atomic force microscopy (AFM) technique was employed to characterize surface morphology of the GO sheets and the tungsten oxide films. Moreover, using X-ray photoelectron spectroscopy (XPS), chemical state of the tungsten oxide films and the photocatalytic reduction of the GO platelets were quantitatively investigated. The better performance of the sol–gel tungsten oxide films in photocatalytic reduction of GO platelets as compared to the evaporated tungsten oxide films was assigned to lower W5+/W6+ ratio (i.e., a better stoichiometry) and higher surface water content of the sol–gel film. The GO reduction level achieved after 24 h UV-assisted photocatalytic reduction on surface of the sol–gel tungsten oxide film was comparable with the reduction level usually obtainable by hydrazine. The sol–gel tungsten oxide film even showed an efficient photocatalytic reduction of the GO platelets after exposure to the visible light of the environment for 2 days.
    Applied Surface Science 07/2013; 276:628–634. · 2.54 Impact Factor
  • Omid Akhavan, Elham Ghaderi
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    ABSTRACT: Reduced graphene oxide nanomesh (rGONM), as one of the recent structures of graphene with a surprisingly strong near-infrared (NIR) absorption, is used for achieving ultraefficient photothermal therapy. First, by using TiO2 nanoparticles, graphene oxide nanoplatelets (GONPs) are transformed into GONMs through photocatalytic degradation. Then rGONMs functionalized by polyethylene glycol (PEG), arginine-glycine-aspartic acid (RGD)-based peptide, and cyanine 7 (Cy7) are utilized for in vivo tumor targeting and fluorescence imaging of human glioblastoma U87MG tumors having αν β3 integrin receptors, in mouse models. The rGONM-PEG suspension (1 μg mL(-1) ) exhibits about 4.2- and 22.4-fold higher NIR absorption at 808 nm than rGONP-PEG and graphene oxide (GO) with lateral dimensions of ≈60 nm and ≈2 μm. In vivo fluorescence imaging demonstrates high selective tumor uptake of rGONM-PEG-Cy7-RGD in mice bearing U87MG cells. The excellent NIR absorbance and tumor targeting of rGONM-PEG-Cy7-RGD results in an ultraefficient photothermal therapy (100% tumor elimination 48 h after intravenous injection of an ultralow concentration (10 μg mL(-1) ) of rGONM-PEG-Cy7-RGD followed by irradiation with an ultralow laser power (0.1 W cm(-2) ) for 7 min), whereas the corresponding rGO- and rGONP-based composites do not present remarkable treatments under the same conditions. All the mice treated by rGONM-PEG-Cy7-RGD survived over 100 days, whereas the mice treated by other usual rGO-based composites were dead before 38 days. The results introduce rGONM as one of the most promising nanomaterials in developing highly desired ultraefficient photothermal therapy.
    Small 04/2013; · 7.82 Impact Factor
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    ABSTRACT: Green tea-reduced graphene oxide (GT-rGO) sheets have been exploited for high efficiency near infrared (NIR) photothermal therapy of HT29 and SW48 colon cancer cells. The biocompatibility of GT-rGO sheets was investigated by means of MTT assays. The polyphenol constituents of GT-rGO act as effective targeting ligands for the attachment of rGO to the surface of cancer cells, as confirmed by the cell granularity test in flow cytometry assays and also by scanning electron microscopy. The photo-thermal destruction of higher metastatic cancer cells (SW48) is found to be more than 20% higher than that of the lower metastatic one (HT29). The photo-destruction efficiency factor of the GT-rGO is found to be at least two orders of magnitude higher than other carbon-based nano-materials. Such excellent cancer cell destruction efficiency provided application of a low concentration of rGO (3mg/L) and NIR laser power density (0.25W/cm(2)) in our photo-thermal therapy of cancer cells.
    Materials science & engineering. C, Materials for biological applications. 04/2013; 33(3):1498-505.
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    Chemical Reviews 03/2013; · 41.30 Impact Factor
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    ABSTRACT: The promise of graphene for use as a vapor sensor motivated exploration of the vapor responses of graphene nanomesh (GNM) functionalized with single stranded DNA. Devices detected different vapor types, including carboxylic acids, aldehydes, organophosphates, and explosives. As-fabricated GNM field effect transistors (FETs) had larger vapor responses than standard graphene FETs due to the effect of oxidized edges and lattice defects. DNA-GNM devices discriminated between homologous species with detection limits of a few parts per million, with fast response and recovery. Responses varied significantly when the base sequence of the DNA was changed, making the sensor class an intriguing candidate for use in an electronic nose system.
    Applied Physics Letters 01/2013; 103(18):183110-183110-5. · 3.52 Impact Factor