There is great interest in developing a sensitive method being able to quantitatively measure and compare antioxidant potencies of samples of interest against multiple reactive oxygen species (ROS) whose imbalance could cause oxidative stress. Here, a sensitive nanoprobe, double-stranded DNA encased single-walled carbon nanotubes (SWNTs) has been developed to determine antioxidant potencies of selected samples (caffeine, regular coffee, and decaffeinated coffee) against ROS, hydrogen peroxide, and hydroxyl radicals. Antioxidant vitamin C and uric acid are used as standards. The method focuses on unique dual optical sensing capability of SWNTs, the rate of spectral suppression when exposed to ROS, and the magnitude of spectral recovery of the ROS-suppressed SWNTs when an antioxidant is added. It is found that the dual sensing capability of SWNTs is still sustained when reacting with the reactive hydroxyl radicals. The results show that caffeine's antioxidant potency is weak, about one millionth of those of vitamin C and uric acid. It is a better scavenger of hydrogen peroxide and a little less effective for hydroxyl radicals. In comparison, coffee, regardless of regular or decaffeinated, is a more efficient antioxidant than caffeine, having an antioxidant potency about ten thousand times stronger. This work provides a versatile detection method for evaluating the antioxidant potencies of samples of interest against various ROS for chemical, biological, and medical applications.
Platinum thin films with different densities were grown on glassy carbon electrodes by high pressure sputtering deposition and evaluated as oxygen reduction reaction catalysts for polymer electrolyte fuel cells using cyclic voltammetry and rotating disk electrode techniques in aqueous perchloric acid electrolyte. The electrochemically active surface area, ORR mass activity (MA) and specific activity (SA) of the thin film electrodes were obtained. MA and SA were found to be higher for low-density films than for high-density film.
Self-supported nanocolumnar Pt-Ni alloy thin films (TFs) with different Pt:Ni compositions and Pt mass loadings were fabricated by high pressure sputtering (HIPS) on a microporous layer (MPL)-like surface composed of carbon particles in order to mimic the catalyst-coated gas diffusion layer (gas diffusion electrode) in a membrane electrode assembly and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cells. HIPS is a simple physical vapor deposition method that is scalable and easily applicable to industrial sputter deposition systems. At high working gas pressures, columnar and less-dense structures are formed because of angular distribution of sputtered atoms that leads to a shadowing effect. Cauliflower-like microstructures were observed from scanning electron microscopy imaging. X-ray diffraction and quartz crystal microbalance analysis revealed that by simply changing the relative deposition power between Pt and Ni source, different Pt:Ni compositions can be achieved. Benchtop cyclic voltammetry and rotating disk electrode measurements were performed for electrochemical characterization of the Pt:Ni-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area (ECSA) ranged between 22-42 m2/g for varying Pt:Ni compositions. Lower Pt mass loadings showed a higher ECSA likely due to smaller nanocauliflower diameters, while the ORR activity of all compositions increased as the Pt mass loading is increased. The catalytic performance of the Pt:Ni-TFs increased in the order of 3:1 < 1:1 < 1:3 with the 1:3 films exhibiting a specific activity of 1781 µA/cm2 and mass activity of 0.66 A/mg, indicating efficient catalyst utilization. The Pt:Ni-TFs were found to exhibit higher ORR activity than traditional high surface area carbon supported Pt nanoparticles, elemental Pt nanorods, and Pt-Ni nanorods.
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