Enhanced thermal stability and pH behavior of glucose oxidase on electrostatic interaction with polyethylenimine

Electrostatic interactions, mediated by ionic-exchange, between polyethylenimine (PEI) and glucose oxidase (GOx) were used to form GOx-PEI macro-complex, which were evaluated for pH and thermal stability of GOx. Under the experimental conditions, the complex had a dominant GOx presence on its surface and a hydrodynamic diameter of 205 ± 16 nm. Activity was evaluated from 40 to 75 °C, and at pH from 2 to 12. GOx activity in complex was maintained up to 70 °C and it was lost at 75 °C. In contrast, free GOx showed a maximum activity at 50 °C, which was completely lost at 70 °C. This difference, observed by fluorescence analysis, was associated with the compact unfolded structure of GOx in the complex. This GOx stability was not observed under pH variations, and complex formation was only possible at pH ≥ 5 where enzymatic activity was diminished by the presence of PEI.

Super-stretchable graphene oxide macroscopic fibers with outstanding knotability fabricated by dry film scrolling

Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young's moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large-area GO thin films (e.g., 800-1200 cm(2) or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76%), high toughness (up to 17 J/m(3)), and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple, and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of ca. 0.48 V/μm and high current densities (5.3 A/cm(2)). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared with bar coating followed by dry film scrolling.

ROS evaluation for a series of CNTs and their derivatives using an ESR method with DMPO

Carbon nanotubes (CNTs) are important materials in advanced industries. It is a concern that pulmonary exposure to CNTs may induce carcinogenic responses. It has been recently reported that CNTs scavenge ROS though non-carbon fibers generate ROS. A comprehensive evaluation of ROS scavenging using various kinds of CNTs has not been demonstrated well. The present work specifically investigates ROS scavenging capabilities with a series of CNTs and their derivatives that were physically treated, and with the number of commercially available CNTs. CNT concentrations were controlled at 0.2 through 0.6 wt%. The ROS scavenging rate was measured by ESR with DMPO. Interestingly, the ROS scavenging rate was not only influenced by physical treatments, but was also dependent on individual manufacturing methods. Ratio of CNTs to DMPO/ hydrogen peroxide is a key parameter to obtain appropriate ROS quenching results for comparison of CNTs. The present results suggest that dangling bonds are not a sole factor for scavenging, and electron transfer on the CNT surface is not clearly determined to be the sole mechanism to explain ROS scavenging.