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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., (Copyright © 2014 Elsevier B.V. All rights reserved.)

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., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reduced graphene oxide nanoplatelets (rGONPs) were synthesized by sonication of covalently PEGylated GO sheets followed by a chemical reduction using hydrazine and bovine serum albumin. Human mesenchymal stem cells (hMSCs), as a fundamental factor in tissue engineering, were isolated from umbilical cord blood (as a recently proposed source for extracting fresh hMSCs) to investigate, for the first time, the size-dependent cyto- and geno-toxic effects of the rGONPs on the cells. The cell viability test showed significant cell destructions by 1.0 μg/mL rGONPs with average lateral dimensions (ALDs) of 11±4 nm, while the rGO sheets with ALDs of 3.8±0.4 μm could exhibit a significant cytotoxic effect only at highconcentration of 100 μg/mL after 1 h exposure time. Although oxidative stress and cell wall membrane damage were determined as the main mechanism involved in the cytotoxicity of the rGO sheets, neither of them could completely describe the cell destructions induced by the rGONPs, especially at the concentrations≤1.0 μg/mL. In fact, the rGONPs showed genotoxic effects on the stem cells through DNA fragmentations and chromosomal aberrations, even at low concentration of 0.1 μg/mL. Our results present essential knowledge for more efficient and innocuous applications of graphene sheets and particularly nanoplatelets in upcoming nanotechnology-based tissue engineering as, e.g., drug transporter and scaffolds., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Graphene oxide nanowalls with extremely sharp edges and preferred vertical orientation were deposited on a graphite electrode by using electrophoretic deposition in an Mg(2+)-GO electrolyte. Using differential pulse voltammetry (DPV), reduced graphene nanowalls (RGNWs) were applied for the first time, in developing an ultra-high-resolution electrochemical biosensor for detection of the four bases of DNA (G, A, T, and C) by monitoring the oxidation signals of the individual nucleotide bases. The extremely enhanced electrochemical reactivity of the four free bases of DNA, single-stranded DNA, and double-stranded DNA (dsDNA) at the surface of the RGNW electrode was compared to electrochemical performances of reduced graphene nanosheet (RGNS), graphite, and glassy carbon electrodes. By increasing the number of DPVs up to 100 scans, the RGNW electrode exhibited an excellent stability with only 15% variation in the oxidation signals, while for the RGNS electrode no detectable signals relating to T and C of 0.1 μM dsDNA were observed. The linear dynamic detection range of the RGNW electrode for dsDNA was checked in the wide range of 0.1 fM to 10 mM, while for the RGNS electrode, it was from 2.0 pM to <10 mM. The lower limits of dsDNA detection of the RGNW and RGNS electrodes were estimated as 9.4 zM (∼5 dsDNA/mL) and 5.4 fM, respectively. The RGNWs were efficient in label-free detection of single nucleotide polymorphisms of 20 zM oligonucleotides (∼10 DNA/mL) having a specific sequence. Therefore, the RGNWs can effectively contribute to the development of ultra-high-sensitive electrochemical biosensors with single-DNA resolutions.

Bioactivity of Escherichia coli bacteria (as a simple model for microorganisms) and interaction of them with the environment were controlled by their capturing within aggregated graphene nanosheets. The oxygen-containing functional groups of chemically exfoliated single-layer graphene oxide nanosheets were reduced by melatonin as a biocompatible antioxidant. While each one of the graphene (oxide) suspension and melatonin solution did not separately show any considerable inactivation effects on the bacteria, aggregation of the sheets in the melatonin-bacterial suspension resulted in trapping the bacteria within the aggregated sheets, i.e., a kind of inactivation. The bacteria trapped within the aggregated sheets were biologically disconnected from their environment, because they could not proliferate in a culture medium and consume the glucose of their environment. However, after removing the sheets from the surface of the microorganisms by using sonication, they could again interact with their environment. The reactivated bacteria consumed glucose and could be proliferated; i.e., they were alive within the aggregated graphene sheets (here, at least for 24 h). The trapped alive bacteria could be photothermally inactivated forever by near-infrared irradiation at 808 nm. These results suggest that graphene nanosheets may potentially serve as an encapsulating material for delivery of such microorganisms and as an effective photothermal agent for inactivation of the graphene-wrapped microorganisms., (© 2011 American Chemical Society)

Bacterial toxicity of graphene nanosheets in the form of graphene nanowalls deposited on stainless steel substrates was investigated for both gram-positive and gram-negative models of bacteria. The graphene oxide nanowalls were obtained by electrophoretic deposition of Mg(2+)-graphene oxide nanosheets synthesized by a chemical exfoliation method. On the basis of measuring the efflux of cytoplasmic materials of the bacteria, it was found that the cell membrane damage of the bacteria caused by direct contact of the bacteria with the extremely sharp edges of the nanowalls was the effective mechanism in the bacterial inactivation. In this regard, the gram-negative Escherichia coli bacteria with an outer membrane were more resistant to the cell membrane damage caused by the nanowalls than the gram-positive Staphylococcus aureus lacking the outer membrane. Moreover, the graphene oxide nanowalls reduced by hydrazine were more toxic to the bacteria than the unreduced graphene oxide nanowalls. The better antibacterial activity of the reduced nanowalls was assigned to the better charge transfer between the bacteria and the more sharpened edges of the reduced nanowalls, during the contact interaction.

Abstract: In this work, aligned and compact Ag nanorods capped by sol–gel mesoporous TiO2 layer were grown on Ti/Si(100) in order to be applied in antibacterial applications. The Ag nanorods with a high effective surface were grown by applying an electric field perpendicular to the surface of the Ag/Ti/Si thin film while it was being heat-treated at 700 °C in an Ar+H2 ambient. The grown silver nanorods had widths and lengths of 20–50 and 250–500 nm with an abundance in {100} facet, respectively. The TiO2 cap layer also had the specific surface area, the total pore volume and the pore diameter of 474 m2/g, 0.49 cm3/g and 8.0 nm, respectively. Antibacterial activities of the TiO2-capped Ag nanorods against E. coli bacteria were examined in the dark and under UV irradiation, and then compared to the corresponding activities of the TiO2-capped Ag thin film and the TiO2-capped Ag nanoparticles grown on the Ti layer. The Ag+ ion release measurements showed that the mesoporous and aqueous TiO2 cap layer can control the silver release process by inter-diffusion of water and silvers thorough its capillary structures, completely different from the ion release behavior of the silver nanorods not capped by the TiO2 layer. The results showed a strong and lasting antibacterial activity for the TiO2-capped Ag nanorods with 2.34 h−1 for the relative rate of reduction of the number of viable bacteria. [Copyright &y& Elsevier]