| 1. |
- Beal, Jacob, et al.
(author)
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Robust estimation of bacterial cell count from optical density
- 2020
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In: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Journal article (peer-reviewed)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
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| 3. |
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- 2019
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Journal article (peer-reviewed)
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| 4. |
- Klionsky, Daniel J., et al.
(author)
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Guidelines for the use and interpretation of assays for monitoring autophagy
- 2012
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In: Autophagy. - : Informa UK Limited. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
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Research review (peer-reviewed)abstract
- In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
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| 5. |
- Qiu, Chun-Yu, et al.
(author)
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Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in-operando approach
- 2022
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In: Chinese Journal of Catalysis. - 1872-2067. ; 43:7, s. 1918-1926
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Journal article (peer-reviewed)abstract
- To evaluate the H2O2-tolerance of non-Pt oxygen reduction reaction (ORR) catalysts as well as investigate the H2O2-induced decay mechanism, the selection of an appropriate H2O2 concentration is a prerequisite. However, the concentration criterion is still unclear because of the lack of in-operando methods to determine the actual concentration of H2O2 in fuel cell catalyst layers. In this work, an electrochemical probe method was successfully established to in-operando monitor the H2O2 in non-Pt catalyst layers for the first time. The local concentration of H2O2 was revealed to reach 17 mmol/L, which is one order of magnitude higher than that under aqueous electrodes test conditions. Powered by the new knowledge, a concentration criterion of at least 17 mmol/L is suggested. This work fills in the large gap between aqueous electrode tests and the real fuel cell working conditions, and highlights the importance of in-operando monitoring methods.
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| 6. |
- Wang, Yu-Cheng, et al.
(author)
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Porous Carbon Membrane-Supported Atomically Dispersed Pyrrole-Type Fe-N-4 as Active Sites for Electrochemical Hydrazine Oxidation Reaction
- 2020
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In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 16:31
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Journal article (peer-reviewed)abstract
- The rational design of catalytically active sites in porous materials is essential in electrocatalysis. Herein, atomically dispersed Fe-N-x sites supported by hierarchically porous carbon membranes are designed to electrocatalyze the hydrazine oxidation reaction (HzOR), one of the key techniques in electrochemical nitrogen transformation. The high intrinsic catalytic activity of the Fe-N-x single-atom catalyst together with the uniquely mixed micro-/macroporous membrane support positions such an electrode among the best-known heteroatom-based carbon anodes for hydrazine fuel cells. Combined with advanced characterization techniques, electrochemical probe experiments, and density functional theory calculation, the pyrrole-type Fe-N-4 structure is identified as the real catalytic site in HzOR.
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| 7. |
- Xu, Hui, et al.
(author)
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Impact of Pore Structure on Two-Electron Oxygen Reduction Reaction in Nitrogen-Doped Carbon Materials : Rotating Ring-Disk Electrode vs. Flow Cell
- 2022
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In: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 15:5
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Journal article (peer-reviewed)abstract
- The impact of pore structure on the two-electron oxygen reduction reaction (ORR) in nitrogen-doped carbon materials is currently under debate, and previous studies are mainly limited to the rotating ring-disk electrode (RRDE) rather than the practical flow cell (FC) system. In this study, assisted by a group of reliable pore models, the impact of two pore structure parameters, that is, Brunauer–Emmett–Teller surface area (SBET) and micropore surface fraction (fmicro), on ORR activity and selectivity are investigated in both RRDE and FC. The ORR mass activity correlates positively to the SBET in the RRDE and FC because a higher SBET can host more active sites. The H2O2 selectivity is independent of fmicro in the RRDE but correlates negatively to fmicro in the FC. The inconsistency results from different states of the electrode in the RRDE and the FC. These insights will guide the design of carbon materials for H2O2 synthesis.
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| 8. |
- Xu, Weicheng, et al.
(author)
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Nitrogen doping to accelerate the phase transition to ordered intermetallic Pt3Co catalyst for the oxygen reduction reaction in fuel cells
- 2023
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 11:8, s. 4078-4087
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Journal article (peer-reviewed)abstract
- Ordered intermetallic Pt–M alloys are foreseen to be promising as next-generation low-Pt catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) due to their high catalytic activity and stability. Nevertheless, the disorder-to-order intermetallic phase transition often needs to proceed at elevated annealing temperature for a long time, which leads to severe particle agglomeration. Herein, an efficient nitrogen (N)-doping strategy is developed to speed up such phase transition in an intermetallic Pt3Co alloy catalyst, which shortens the annealing duration by 3–5 fold at a temperature of 600–800 °C. Such a strategy can not only minimize the particle agglomeration but also effectively optimize the electronic structure of surface Pt atoms with the incorporated N. The prepared N-doped ordered intermetallic Pt3Co catalyst exhibits high ORR activity among the best of the state-of-the-art, with mass activities of 1.21 and 1.20 A mgPt−1 at 0.90 V in rotating disk electrode (RDE) and proton exchange membrane fuel cell (PEMFC) tests, respectively. Moreover, with the total Pt loading of 0.15 mgPt cm−2, the H2–air PEMFC delivers a power density of 1.27 W cm−2 at 150 kPaabs and 0.6 V, corresponding to a high Pt utilization of 0.118 gPt kW−1 that has surpassed the DOE 2025 target (0.125 gPt kW−1). This study paves a new way to develop high-performance low-Pt ORR catalysts for PEMFCs.
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| 9. |
- Zhang, Yue-Jiao, et al.
(author)
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Probing the Electronic Structure of Heterogeneous Metal Interfaces by Transition Metal Shelled Gold Nanoparticle-Enhanced Raman Spectroscopy
- 2016
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:37, s. 20684-20691
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Journal article (peer-reviewed)abstract
- In heterogeneous catalysis, characterization of heterogeneous metal interfaces of bimetallic catalysts is a crucial step to elucidate the catalytic performance and is a key to develop advanced catalysts. However, analytical techniques such as X-ray photoelectron spectroscopy can only work in vacuum conditions and are difficult to use for in situ analysis. Here, we present efficient and convenient core-shell nano particle-enhanced Raman spectroscopy to explore the in situ electronic structures of heterogeneous interfaces (Au@Pd and Au@Pt core-shell NPs) by varying the shell thickness. The experimental observations reported here clearly show that Pd donates electrons to Au, while Pt accepts electrons from Au at the heterogeneous interfaces. This conclusion gains further support from ex situ X-ray photoelectron spectroscopy results. The Au core greatly affects the electronic structures of both the Pd and Pt shells as well as catalytic behaviors. Finally, the as prepared core-shell nanoparticles were used to demonstrate their improved catalytic properties in real electrocatalytic systems such as methanol oxidation and oxygen reduction reactions.
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