As a new family of adsorbent materials, porous metal-organic frameworks (MOFs) have attracted enormous attention over the past decade.[1] Having a large surface area, [2] tunable pore size and shape, [3] adjustable composition and functionalizable pore surface, [4] MOFs show unique advantages and promises for potential applications in adsorption-based storage and separation technologies for small gas molecules such as H 2 , CO 2 , and CH 4 . [1b,d, 5] CO 2 capture from flue gases is of particular importance in reducing greenhouse gas emissions and in preserving environmental health. A flue gas mixture is composed of nitrogen, carbon dioxide, water vapor, oxygen, and other minor components such as carbon monoxide, nitrogen oxides, and sulfur oxides.[1b, 6] Separation of low-concentration CO 2 (about 10-15 %) from nitrogen-rich streams remains a challenging task at the present time. Adsorption-based CO 2 capture and separation is considered an effective way and may have a real potential if adsorbents with both high CO 2 selectivity and capacity near room temperature (up to 50 8C) and in the lowpressure range can be developed. [7] Recent studies have revealed a number of MOFs that show a high performance in capturing and separating CO 2 from N 2 and other small gases under conditions mimicking power plant flue gas mixtures. [8]
Here, we report on a novel superoxide anion (O2(*-)) biosensor based on direct electron transfer of copper, zinc-superoxide dismutase (Cu, Zn-SOD) at zinc oxide nanodisks surface for in vivo tracking of O2(*-) in bean sprouts. Direct electron transfer of SOD is achieved at ZnO nanodisks film prepared by a one-step electrodeposited method, with a high heterogeneous electron rate constant of 17 +/- 2 s(-1). Spectroscopic data demonstrate that SOD strongly immobilized onto the nanostructured ZnO surfaces processes its inherent activity toward O2(*-) dismutation. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SOD substantially provides a dual electrochemical approach to determination of O2(*-) with high selectivity, wide linear range, long stability, and good reproducibility. In particular, SOD adsorbed on the ZnO nanodisks film is capable of sensing O2(*-) cathodically at a very positive potential, 0 mV (vs Ag|AgCl), where the common interfering species such as hydrogen peroxide, uric acid, ascorbic acid, and 3,4-dihydroxyphenylacetic acid were effectively avoided. The excellent analytical performance of the present O2(*-) biosensor, combined with the remarkable characteristics of nanostructured ZnO films, such as biocompatibility, ease of preparation, and facile to miniaturize, paves an electrochemical way for reliable and durable in vivo determination of O2(*-) in bean sprouts.
The morphology-dependent electrochemistry and electrocatalytical activity of cytochrome c (cyt. c) were investigated at pyramidal, rodlike, and spherical gold nanostructures directly electrodeposited onto sputtered gold surfaces. Direct, reversible electron transfer of cyt. c, for the first time, was realized at nanorod-like and nanopyramidal gold surfaces without any mediators or promoters, while no redox reaction was observed at the nanospherical gold electrode. The electrochemical properties of cyt. c vary with the shape of gold nanostructures with respect to the reversibility of electrode reactions, kinetic parameters, the formal potentials (E0'), and charge-transport resistance (Rct), suggesting shape-dependent mechanisms for the electrode reactions of cyt. c. The experimental results manifest that cyt. c was stably immobilized on the nanostructured gold electrodes with different conformational changes of the heme microenvironment. Consequently, not only the electroactivity, but also the inherent biological activity of the immobilized cyt. c strongly depended on the shape of the electrode surfaces. The facilitated electron transfer combined with the intrinsic catalytical activity of cyt. c substantially constructed a third-generation H2O2 biosensor with high selectivity, quick response time, large linear range, and good sensitivity. The electrocatalytical activity of the immobilized cyt. c toward H2O2 was also found to be morphology dependent, and the linear range of H2O2 detection could be tuned by means of employing the nanostructured gold surfaces with different shapes.
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