Graphene-supported hemin as a highly active biomimetic oxidation catalyst.

Well supported: stable hemin-graphene conjugates formed by immobilization of monomeric hemin on graphene, showed excellent catalytic activity, more than 10 times better than that of the recently developed hemin-hydrogel system and 100 times better than that of unsupported hemin. The catalysts also showed excellent binding affinities and catalytic efficiencies approaching that of natural enzymes.

Integration of molecular and enzymatic catalysts on graphene for biomimetic generation of antithrombotic species.

The integration of multiple synergistic catalytic systems can enable the creation of biocompatible enzymatic mimics for cascading reactions under physiologically relevant conditions. Here we report the design of a graphene-haemin-glucose oxidase conjugate as a tandem catalyst, in which graphene functions as a unique support to integrate molecular catalyst haemin and enzymatic catalyst glucose oxidase for biomimetic generation of antithrombotic species. Monomeric haemin can be conjugated with graphene through π-π interactions to function as an effective catalyst for the oxidation of endogenous L-arginine by hydrogen peroxide. Furthermore, glucose oxidase can be covalently linked onto graphene for local generation of hydrogen peroxide through the oxidation of blood glucose. Thus, the integrated graphene-haemin-glucose oxidase catalysts can readily enable the continuous generation of nitroxyl, an antithrombotic species, from physiologically abundant glucose and L-arginine. Finally, we demonstrate that the conjugates can be embedded within polyurethane to create a long-lasting antithrombotic coating for blood-contacting biomedical devices.

Laser scribing of high-performance and flexible graphene-based electrochemical capacitors.

Although electrochemical capacitors (ECs), also known as supercapacitors or ultracapacitors, charge and discharge faster than batteries, they are still limited by low energy densities and slow rate capabilities. We used a standard LightScribe DVD optical drive to do the direct laser reduction of graphite oxide films to graphene. The produced films are mechanically robust, show high electrical conductivity (1738 siemens per meter) and specific surface area (1520 square meters per gram), and can thus be used directly as EC electrodes without the need for binders or current collectors, as is the case for conventional ECs. Devices made with these electrodes exhibit ultrahigh energy density values in different electrolytes while maintaining the high power density and excellent cycle stability of ECs. Moreover, these ECs maintain excellent electrochemical attributes under high mechanical stress and thus hold promise for high-power, flexible electronics.

Patterning and electronic tuning of laser scribed graphene for flexible all-carbon devices.

Engineering a low-cost graphene-based electronic device has proven difficult to accomplish via a single-step fabrication process. Here we introduce a facile, inexpensive, solid-state method for generating, patterning, and electronic tuning of graphene-based materials. Laser scribed graphene (LSG) is shown to be successfully produced and selectively patterned from the direct laser irradiation of graphite oxide films under ambient conditions. Circuits and complex designs are directly patterned onto various flexible substrates without masks, templates, post-processing, transferring techniques, or metal catalysts. In addition, by varying the laser intensity and laser irradiation treatments, the electrical properties of LSG can be precisely tuned over 5 orders of magnitude of conductivity, a feature that has proven difficult with other methods. This inexpensive method for generating LSG on thin flexible substrates provides a mode for fabricating a low-cost graphene-based NO(2) gas sensor and enables its use as a heterogeneous scaffold for the selective growth of Pt nanoparticles. The LSG also shows exceptional electrochemical activity that surpasses other carbon-based electrodes in electron charge transfer rate as demonstrated using a ferro-/ferricyanide redox couple.

A one-step, solvothermal reduction method for producing reduced graphene oxide dispersions in organic solvents.

Refluxing graphene oxide (GO) in N-methyl-2-pyrrolidinone (NMP) results in deoxygenation and reduction to yield a stable colloidal dispersion. The solvothermal reduction is accompanied by a color change from light brown to black. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images of the product confirm the presence of single sheets of the solvothermally reduced graphene oxide (SRGO). X-ray photoelectron spectroscopy (XPS) of SRGO indicates a significant increase in intensity of the C=C bond character, while the oxygen content decreases markedly after the reduction is complete. X-ray diffraction analysis of SRGO shows a single broad peak at 26.24 degrees 2theta (3.4 A), confirming the presence of graphitic stacking of reduced sheets. SRGO sheets are redispersible in a variety of organic solvents, which may hold promise as an acceptor material for bulk heterojunction photovoltaic cells, or electromagnetic interference shielding applications.