Robust estimation of bacterial cell count from optical density

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

Graphitic Carbon Nitride For Electrochemical Energy Conversion And Storage

Owing to the rising pressure on the requirement of commercializing sustainable and environmentally friendly energy technologies such as proton exchange membrane fuel cells (PEMFCs), metal-Air batteries, and water splitting electrolyzers, it is urgent to develop highly efficient electrocatalysts to replace costly platinum group metals. Graphitic carbon nitrides (g-C3N4) have attracted intensive focus due to their unique properties and impressive performance in challenging the widely accepted nitrogen-doped carbon materials in electrocatalytic fields. However, the relatively poor conductivity limits further improvement of g-C3N4-based electrocatalysts. Thus, this Review is primarily focused on recent progress in the functionalization of g-C3N4 materials for oxygen reduction and water splitting reactions. Especially, an innovative and in-depth understanding of g-C3N4 materials is presented by systematically summarizing the function of g-C3N4 materials, such as serving as active sites, coordination complexes, and supporter/protective coatings, in contributing to the catalytic performance. Finally, the main challenges and future perspectives of g-C3N4-based nanomaterials in electrocatalytic fields are also discussed. It should be noted that in the text we acknowledge that many (in fact, most) of the g-C3N4 materials have been polymeric amorphous phases within the C-N-H system. To avoid debate and confusion on the naming of previously reported graphitic carbon nitride materials in our Review, we decided to call all these of materials g-C3N4 in accordance with previous reports

Amorphous Mof Introduced N-Doped Graphene: An Efficient And Versatile Electrocatalyst For Zinc-Air Battery And Water Splitting

Recently, developing metal-organic framework (MOF) derived carbon-based electrocatalysts has become more and more popular for large-scale application of renewable energy devices. However, the rational conversion of MOFs into a versatile platform for high-efficiency catalyst is still very challenging. Moreover, the relationship between the crystallinity of MOF precursor and the catalytic activity of resultant carbon-based catalyst is still not well-understood. In this work, a strategy for the synthesis of sheet-like mesoporous nitrogen-doped graphene (MNG) derived from amorphous MOFs is demonstrated. The amorphous MOF derived MNG showed much higher catalytic activity than that of nitrogen-doped carbon (MNC) derived from highly crystallized MOFs. This rationally designed MNG catalyst served as a multifunctional electrode in a zinc-air battery and a water splitting device, both of which showed electrocatalytic performance superior to those of platinum group metal (PGM) catalysts. The characterization analysis confirmed that the enhanced activity of amorphous MOF derived MNG was primarily attributed to the optimal properties of electronic conductivity, graphitization degree, and high specific surface area

Amorphous MOF Introduced N‑Doped Graphene: An Efficient and Versatile Electrocatalyst for Zinc–Air Battery and Water Splitting

Recently, developing metal–organic framework (MOF) derived carbon-based electrocatalysts has become more and more popular for large-scale application of renewable energy devices. However, the rational conversion of MOFs into a versatile platform for high-efficiency catalyst is still very challenging. Moreover, the relationship between the crystallinity of MOF precursor and the catalytic activity of resultant carbon-based catalyst is still not well-understood. In this work, a strategy for the synthesis of sheet-like mesoporous nitrogen-doped graphene (MNG) derived from amorphous MOFs is demonstrated. The amorphous MOF derived MNG showed much higher catalytic activity than that of nitrogen-doped carbon (MNC) derived from highly crystallized MOFs. This rationally designed MNG catalyst served as a multifunctional electrode in a zinc–air battery and a water splitting device, both of which showed electrocatalytic performance superior to those of platinum group metal (PGM) catalysts. The characterization analysis confirmed that the enhanced activity of amorphous MOF derived MNG was primarily attributed to the optimal properties of electronic conductivity, graphitization degree, and high specific surface area

Phosphorus And Aluminum Codoped Porous Nio Nanosheets As Highly Efficient Electrocatalysts For Overall Water Splitting

We present a facile way to fabricate phosphorus and aluminum codoped nickel oxide-based nanosheets by using layered double hydroxide (AlNi-LDH) as precursors, which showed an overall water-splitting performance in alkaline solution. The codoping of phosphorus and aluminum into nickel oxide nanosheets leads to an optimum balance among surface chemical state, electrochemically active surface area, and density of active sites. As a result, it can afford a current density of 100 mA cm-2 at the overpotential of 310 mV for oxygen evolution reaction (OER) and a current density of 10 mA cm-2 at the overpotential of 138 mV for hydrogen evolution reaction (HER) in 1 M KOH. When it was used as a bifunctional catalyst in a two-electrode water-splitting device, a potential of 1.56 V was achieved at the current density of 10 mA cm-2

Nickel Sulfide Freestanding Holey Films As Air-Breathing Electrodes For Flexible Zn-Air Batteries

In this work, a combination of bottom-up electrochemical deposition and top-down electrochemical etching strategies followed by a subsequent sulfuration treatment was employed to rationally synthesize a nickel sulfide (NiSx) freestanding holey film (FHF). Owing to the holey structure along with the optimal electrochemically active surface area and active sites, the as-prepared NiSx FHF showed an impressive bifunctional electrocatalytic performance toward both oxygen evolution and reduction reactions. The holey and freestanding features provide the NiSx FHF with promising characteristics to be used as an ideal air-breathing cathode in flexible Zn-air batteries (ZABs). As a proof-of-concept, the rationally designed NiSx FHF achieved remarkable rechargeability and flexibility in a ZAB configuration

Enhancing Electron Transfer And Electrocatalytic Activity On Crystalline Carbon-Conjugated G-C3N4

Carbon nitride (g-C3N4) materials are electro-activated for oxygen reduction (ORR) and oxygen evolution (OER) reactions when they are supported by conductive carbons. However, the electrocatalytic process on semiconductor-based heterostructures such as carbon-supported g-C3N4 still suffers from a huge energy loss because of poor electron mobility. Here, we demonstrated a concept that the conjugation of g-C3N4 with crystalline carbon can improve the in-plane electron mobility and make interior triazine units more electro-active for ORR and OER. As a result, the Co metal coordinated g-C3N4 with crystalline carbons (Co-C3N4/C) showed a remarkable electrocatalytic performance toward both ORR and OER. For example, it displayed an onset potential of 0.95 V for ORR and an overpotential of 1.65 V for OER at 10 mA cm-2, which are comparable and even better than those of benchmark Pt, RuO2, and other carbon nitride-based electrocatalysts. As a proof-of-concept application, we employed this catalyst as an air electrode in the rechargeable aluminum-air battery, which showed more rechargeable and practicable than those of Pt/C and RuO2 catalysts in two-electrode coin battery. The characterization results identified that the good performance of Co-C3N4/C was primarily attributed to the enhanced in-plane electron mobility by crystalline carbon conjugation and the Co-coordinated g-C3N4 along with nitrogen-doped carbons

Surface-Modified Porous Carbon Nitride Composites As Highly Efficient Electrocatalyst For Zn-Air Batteries

Porous carbon nitride (PCN) composites are fabricated using a top-down strategy, followed by additions of graphene and CoSx nanoparticles. This subsequently enhances conductivity and catalytic activity of PCN (abbreviated as CoSx@PCN/rGO) and is achieved by one-step sulfuration of PCN/graphene oxides (GO) composite materials. As a result, the as-prepared CoSx@PCN/rGO catalysts display excellent activity and stability toward both oxygen evolution and reduction reactions, surpassing electrocatalytic performance shown by state-of-the-art Pt, RuO2 and other carbon nitrides. Remarkably, the CoSx@PCN/rGO bifunctional activity allows for applications in zinc-air batteries, which show better rechargeability than Pt/C. The enhanced catalytic performance of CoSx@PCN/rGO can primarily be attributed to the highly porous morphology and sufficiently exposed active sites that are favorable for electrocatalytic reactions

Understanding Synergism Of Cobalt Metal And Copper Oxide Toward Highly Efficient Electrocatalytic Oxygen Evolution

Understanding the synergism of bimetallic transition metal (TM)-based catalysts for oxygen evolution reaction (OER) is very difficult because it is complicated to identify the surface active sites in a bimetal system. Herein, we rationally designed Cu oxide (CuOx) nanoarray film (NF) as an example to investigate the synergism and doping effects of iron group metals on OER. This is an advantage because CuOx is electrocatalytically inert and oxidatively stable, which is much better than carbon-based platforms. Especially, cobalt (Co) shows a much stronger synergism as compared with nickel (Ni) and iron (Fe). By introducing Co into the inert CuOx NFs, the Co active sites can be correlated to the OER activity by rationally regulating the morphology of CuOx NFs. In addition, the phase transformation from Cu2O to CuO occurs during the OER testing, further boosting the OER activity of Co-doped CuOx NF due to the hybridization change of Co active site. As a result, the Co-doped CuOx NF with 0.30 at. % Co (denoted as Co0.30CuOx) shows a remarkable OER activity (an overpotential of 0.29 V at 10 mA cm-2) in basic solution, superior to those of the state-of-the-art OER catalysts. Both experimental and computational studies indicate that the introduction of Co-dopant in CuOx changes the rate-limiting step from M-OHads → M-Oads to M-Oads → M-OOHads and decreases the theoretical onset potential by 0.31 V. The optimal concentration of Co-dopant in CuOx nanocrystals renders the favorable surface properties for the electron transfer, the adsorption, and desorption of OER-relevant intermediates. Moreover, the small size of CuOx nanocrystals contributes to the large electrochemically active surface area, which enables the sufficient Co active sites to the electrolyte

New Polyphenols from a Deep Sea Spiromastix sp. Fungus, and Their Antibacterial Activities

Eleven new polyphenols namely spiromastols A–K (1–11) were isolated from the fermentation broth of a deep sea-derived fungus Spiromastix sp. MCCC 3A00308. Their structures were determined by extensive NMR data and mass spectroscopic analysis in association with chemical conversion. The structures are classified as diphenyl ethers, diphenyl esters and isocoumarin derivatives, while the n-propyl group in the analogues is rarely found in natural products. Compounds 1–3 exhibited potent inhibitory effects against a panel of bacterial strains, including Xanthomanes vesicatoria, Pseudomonas lachrymans, Agrobacterium tumefaciens, Ralstonia solanacearum, Bacillus thuringensis, Staphylococcus aureus and Bacillus subtilis, with minimal inhibitory concentration (MIC) values ranging from 0.25 to 4 µg/mL. The structure-activity relationships are discussed, while the polychlorinated analogues 1–3 are assumed to be a promising structural model for further development as antibacterial agents