Nanoporous Gold Thin Films as Substrates to Analyze Liquids by Cryo-atom Probe Tomography.

Cryogenic atom probe tomography (cryo-APT) is being developed to enable nanoscale compositional analyses of frozen liquids. Yet, the availability of readily available substrates that allow for the fixation of liquids while providing sufficient strength to their interface is still an issue. Here, we propose the use of 1-2-µm-thick binary alloy film of gold-silver sputtered onto flat silicon, with sufficient adhesion without an additional layer. Through chemical dealloying, we successfully fabricate a nanoporous substrate, with an open-pore structure, which is mounted on a microarray of Si posts by lift-out in the focused-ion beam system, allowing for cryogenic fixation of liquids. We present cryo-APT results obtained after cryogenic sharpening, vacuum cryo-transfer, and analysis of pure water on the top and inside the nanoporous film. We demonstrate that this new substrate has the requisite characteristics for facilitating cryo-APT of frozen liquids, with a relatively lower volume of precious metals. This complete workflow represents an improved approach for frozen liquid analysis, from preparation of the films to the successful fixation of the liquid in the porous network, to cryo-APT.

Correction: Electron microscope loading and in situ nanoindentation of water ice at cryogenic temperatures.

[This corrects the article DOI: 10.1371/journal.pone.0281703.].

Quasi-"In Situ" Analysis of the Reactive Liquid-Solid Interface during Magnesium Corrosion Using Cryo-Atom Probe Tomography.

The early stages of corrosion occurring at liquid-solid interfaces control the evolution of the material's degradation process, yet due to their transient state, their analysis remains a formidable challenge. Here corrosion tests are performed on a MgCa alloy, a candidate material for biodegradable implants using pure water as a model system. The corrosion reaction is suspended by plunge freezing into liquid nitrogen. The evolution of the early-stage corrosion process on the nanoscale by correlating cryo-atom probe tomography (APT) with transmission-electron microscopy (TEM) and spectroscopy, is studied. The outward growth of Mg hydroxide Mg(OH)2 and the inward growth of an intermediate corrosion layer consisting of hydrloxides of different compositions, mostly monohydroxide Mg(OH) instead of the expected MgO layer, are observed. In addition, Ca partitions to these newly formed hydroxides and oxides. Density-functional theory calculations suggest a domain of stability for this previously experimental unreported Mg(OH) phase. This new approach and these new findings advance the understanding of the early stages of magnesium corrosion, and in general reactions and processes at liquid-solid interfaces, which can further facilitate the development of corrosion-resistant materials or better control of the biodegradation rate of future implants.

In Situ Metallic Coating of Atom Probe Specimen for Enhanced Yield, Performance, and Increased Field-of-View.

Atom probe tomography requires needle-shaped specimens with a diameter typically below 100 nm, making them both very fragile and reactive, and defects (notches at grain boundaries or precipitates) are known to affect the yield and data quality. The use of a conformal coating directly on the sharpened specimen has been proposed to increase yield and reduce background. However, to date, these coatings have been applied ex situ and mostly are not uniform. Here, we report on the controlled focused-ion beam in situ deposition of a thin metal film on specimens immediately after specimen preparation. Different metallic targets e.g. Cr were attached to a micromanipulator via a conventional lift-out method and sputtered using Ga or Xe ions. We showcase the many advantages of coating specimens from metallic to nonmetallic materials. We have identified an increase in data quality and yield, an improvement of the mass resolution, as well as an increase in the effective field-of-view. This wider field-of-view enables visualization of the entire original specimen, allowing to detect the complete surface oxide layer around the specimen. The ease of implementation of the approach makes it very attractive for generalizing its use across a very wide range of atom probe analyses.

Scalable substrate development for aqueous sample preparation for atom probe tomography.

Reliable and consistent preparation of atom probe tomography (APT) specimens from aqueous and hydrated biological specimens remains a significant challenge. One particularly difficult process step is the use of a focused ion beam (FIB) instrument for preparing the required needle-shaped specimen, typically involving a 'lift-out' procedure of a small sample of material. Here, two alternative substrate designs are introduced that enable using FIB only for sharpening, along with example APT datasets. The first design is a laser-cut FIB-style half-grid close to those used for transmission electron microscopy (TEM) that can be used in a grid holder compatible with APT pucks. The second design is a larger, standalone self-supporting substrate called a 'crown', with several specimen positions, which self-aligns in APT pucks, prepared by electrical discharge machining (EDM). Both designs are made nanoporous, to provide strength to the liquid-substrate interface, using chemical and vacuum dealloying. Alpha brass, a simple, widely available, lower-cost alternative to previously proposed substrates, was selected for this work. The resulting designs and APT data are presented and suggestions are provided to help drive wider community adoption.

A Versatile and Reproducible Cryo-sample Preparation Methodology for Atom Probe Studies.

Repeatable and reliable site-specific preparation of specimens for atom probe tomography (APT) at cryogenic temperatures has proven challenging. A generalized workflow is required for cryogenic specimen preparation including lift-out via focused ion beam and in situ deposition of capping layers, to strengthen specimens that will be exposed to high electric field and stresses during field evaporation in APT and protect them from environment during transfer into the atom probe. Here, we build on existing protocols and showcase preparation and analysis of a variety of metals, oxides, and supported frozen liquids and battery materials. We demonstrate reliable in situ deposition of a metallic capping layer that significantly improves the atom probe data quality for challenging material systems, particularly battery cathode materials which are subjected to delithiation during the atom probe analysis itself. Our workflow design is versatile and transferable widely to other instruments.

Electron microscope loading and in situ nanoindentation of water ice at cryogenic temperatures.

Interest in the technique of low temperature environmental nanoindentation has gained momentum in recent years. Low temperature indentation apparatuses can, for instance, be used for systematic measurements of the mechanical properties of ice in the laboratory, in order to accurately determine the inputs for the constitutive equations describing the rheologic behaviour of natural ice (i.e., the Glen flow law). These properties are essential to predict the movement of glaciers and ice sheets over time as a response to a changing climate. Herein, we introduce a new experimental setup and protocol for electron microscope loading and in situ nanoindentation of water ice. Preliminary testing on pure water ice yield elastic modulus and hardness measurements of 4.1 GPa and 176 MPa, respectively, which fall within the range of previously published values. Our approach demonstrates the potential of low temperature, in situ, instrumented nanoindentation of ice under controlled conditions in the SEM, opening the possibility for investigating individual structural elements and systematic studies across species and concentration of impurities to refine to constitutive equations for natural ice.

Understanding the Degradation of a Model Si Anode in a Li-Ion Battery at the Atomic Scale.

To advance the understanding of the degradation of the liquid electrolyte and Si electrode, and their interface, we exploit the latest developments in cryo-atom probe tomography. We evidence Si anode corrosion from the decomposition of the Li salt before charge-discharge cycles even begin. Volume shrinkage during delithiation leads to the development of nanograins from recrystallization in regions left amorphous by the lithiation. The newly created grain boundaries facilitate pulverization of nanoscale Si fragments, and one is found floating in the electrolyte. P is segregated to these grain boundaries, which confirms the decomposition of the electrolyte. As structural defects are bound to assist the nucleation of Li-rich phases in subsequent lithiations and accelerate the electrolyte's decomposition, these insights into the developed nanoscale microstructure interacting with the electrolyte contribute to understanding the self-catalyzed/accelerated degradation Si anodes and can inform new battery designs unaffected by these life-limiting factors.

Status and Direction of Atom Probe Analysis of Frozen Liquids.

Imaging of liquids and cryogenic biological materials by electron microscopy has been recently enabled by innovative approaches for specimen preparation and the fast development of optimized instruments for cryo-enabled electron microscopy (cryo-EM). Yet, cryo-EM typically lacks advanced analytical capabilities, in particular for light elements. With the development of protocols for frozen wet specimen preparation, atom probe tomography (APT) could advantageously complement insights gained by cryo-EM. Here, we report on different approaches that have been recently proposed to enable the analysis of relatively large volumes of frozen liquids from either a flat substrate or the fractured surface of a wire. Both allowed for analyzing water ice layers which are several micrometers thick consisting of pure water, pure heavy water, and aqueous solutions. We discuss the merits of both approaches and prospects for further developments in this area. Preliminary results raise numerous questions, in part concerning the physics underpinning field evaporation. We discuss these aspects and lay out some of the challenges regarding the APT analysis of frozen liquids.

Pathologically stiff erythrocytes impede contraction of blood clots.

BACKGROUND: Blood clot contraction, volume shrinkage of the clot, is driven by platelet contraction and accompanied by compaction of the erythrocytes and their gradual shape change from biconcave to polyhedral, with the resulting cells named polyhedrocytes. OBJECTIVES: Here, we examined the role of erythrocyte rigidity on clot contraction and erythrocyte shape transformation. METHODS: We used an optical tracking methodology that allowed us to quantify changes in contracting clot size over time. RESULTS AND CONCLUSIONS: Erythrocyte rigidity has been shown to be increased in sickle cell disease (SCD), and in our experiments erythrocytes from SCD patients were 4-fold stiffer than those from healthy subjects. On average, the final extent of clot contraction was reduced by 53% in the clots from the blood of patients with SCD compared to healthy individuals, and there was significantly less polyhedrocyte formation. To test if this reduction in clot contraction was due to the increase in erythrocyte rigidity, we used stiffening of erythrocytes via chemical cross-linking (glutaraldehyde), rigidifying Wrightb antibodies (Wrb ), and naturally more rigid llama ovalocytes. Results revealed that stiffening erythrocytes result in impaired clot contraction and fewer polyhedrocytes. These results demonstrate the role of erythrocyte rigidity in the contraction of blood clots and suggest that the impaired clot contraction/shrinkage in SCD is due to the reduced erythrocyte deformability, which may be an underappreciated mechanism that aggravates obstructiveness of erythrocyte-rich (micro)thrombi in SCD.

Platelet heterogeneity enhances blood clot volumetric contraction: An example of asynchrono-mechanical amplification.

Physiological processes such as blood clotting and wound healing as well as pathologies such as fibroses and musculoskeletal contractures, all involve biological materials composed of a contracting cellular population within a fibrous matrix, yet how the microscale interactions among the cells and the matrix lead to the resultant emergent behavior at the macroscale tissue level remains poorly understood. Platelets, the anucleate cell fragments that do not divide nor synthesize extracellular matrix, represent an ideal model to study such systems. During blood clot contraction, microscopic platelets actively pull fibers to shrink the macroscale clot to less than 10% of its initial volume. We discovered that platelets utilize a new emergent behavior, asynchrono-mechanical amplification, to enhanced volumetric material contraction and to magnify contractile forces. This behavior is triggered by the heterogeneity in the timing of a population of actuators. This result indicates that cell heterogeneity, often attributed to stochastic cell-to-cell variability, can carry an essential biophysical function, thereby highlighting the importance of considering 4 dimensions (space + time) in cell-matrix biomaterials. This concept of amplification via heterogeneity can be harnessed to increase mechanical efficiency in diverse systems including implantable biomaterials, swarm robotics, and active polymer composites.

Transitioning Clinical Care for People Who Use Drugs to Telemedicine: Lessons Learned One Year into the COVID-19 Pandemic.

Background: As a harm reduction-focused primary care clinic for people who use drugs, the Respectful and Equitable Access to Comprehensive Healthcare (REACH) Program faced multiple barriers due to the COVID-19 pandemic. We describe and evaluate how the telemedicine-driven adaptations REACH made allowed the program to engage its patients. Methods: REACH expanded its telemedicine capabilities by transitioning its in-person clinic and methods of connecting with referrals to telemedicine. The program provided patients with phones to increase access to needed technology. Results: Throughout 2020, patient visits continuously shifted from being entirely in-person, to entirely telemedicine, to a hybrid model. Clinic show rates averaged 71% with this hybrid model, compared with 57% pre-COVID-19. Phones were distributed to 88 patients, 77% of which engaged in at least one telemedicine visit. Conclusions: Telemedicine allowed REACH to provide uninterrupted care during the pandemic. The program is now refining its hybrid model of telemedicine and in-person care to more equitably serve all patients.

Spatially resolved 3D metabolomic profiling in tissues.

Spatially resolved RNA and protein molecular analyses have revealed unexpected heterogeneity of cells. Metabolic analysis of individual cells complements these single-cell studies. Here, we present a three-dimensional spatially resolved metabolomic profiling framework (3D-SMF) to map out the spatial organization of metabolic fragments and protein signatures in immune cells of human tonsils. In this method, 3D metabolic profiles were acquired by time-of-flight secondary ion mass spectrometry to profile up to 189 compounds. Ion beams were used to measure sub-5-nanometer layers of tissue across 150 sections of a tonsil. To incorporate cell specificity, tonsil tissues were labeled by an isotope-tagged antibody library. To explore relations of metabolic and cellular features, we carried out data reduction, 3D spatial correlations and classifications, unsupervised K-means clustering, and network analyses. Immune cells exhibited spatially distinct lipidomic fragment distributions in lymphatic tissue. The 3D-SMF pipeline affects studying the immune cells in health and disease.

COVID-19, nationalism, and the politics of crisis: A scholarly exchange.

In this article, several scholars of nationalism discuss the potential for the COVID-19 pandemic to impact the development of nationalism and world politics. To structure the discussion, the contributors respond to three questions: (1) how should we understand the relationship between nationalism and COVID-19; (2) will COVID-19 fuel ethnic and nationalist conflict; and (3) will COVID-19 reinforce or erode the nation-state in the long run? The contributors formulated their responses to these questions near to the outset of the pandemic, amid intense uncertainty. This made it acutely difficult, if not impossible, to make predictions. Nevertheless, it was felt that a historically and theoretically informed discussion would shed light on the types of political processes that could be triggered by the COVID-19 pandemic. In doing so, the aim is to help orient researchers and policy-makers as they grapple with what has rapidly become the most urgent issue of our times.

Corrigendum to "Community-Acquired Cavitary Pseudomonas Pneumonia Linked to Use of a Home Humidifier".

[This corrects the article DOI: 10.1155/2017/5474916.].

Highly selective aptamer based organic electrochemical biosensor with pico-level detection.

An organic aptamer functionalized electrochemical transistor has been developed to detect the presence of epinephrine molecule which acts as an excitatory neurotransmitter. The abnormalities in the level of epinephrine are the direct symptoms of some diseases such as Takotsubo cardiomyopathy, myocardial infarction, arrhythmias and other heart related diseases. The present approach is based on immobilization of aptamers on the gate electrode which selectively binds to epinephrine with high affinity. The introduction of epinephrine in the system causes screening of negative charge of aptamers as well as the production of Faradaic current due to oxidation of epinephrine. The synergistic effect of these two events decreases the overall channel current which was seen in both transfer characteristics and current-time curve. Additional experiments against common interfering agents (dopamine, ascorbic acid, DOPAC etc) showed no decrease in the current which indicates high specificity of the sensor. Overall, the incorporation of aptamers in the transistor has allowed us to obtain a sensor exhibiting the lowest limit of detection for epinephrine (90 pM) till date which is comparable to normal physiological level. This approach provides a real-time detection of a large range of biomolecules and viral proteins in a time and cost-effective manner and has applications in point-of-care testing tool for several diagnostic applications.

In Situ XPS Investigation of Transformations at Crystallographically Oriented MoS2 Interfaces.

Nanoscale transition-metal dichalcogenide (TMDC) materials, such as MoS2, exhibit promising behavior in next-generation electronics and energy-storage devices. TMDCs have a highly anisotropic crystal structure, with edge sites and basal planes exhibiting different structural, chemical, and electronic properties. In virtually all applications, two-dimensional or bulk TMDCs must be interfaced with other materials (such as electrical contacts in a transistor). The presence of edge sites vs basal planes (i.e., the crystallographic orientation of the TMDC) could influence the chemical and electronic properties of these solid-state interfaces, but such effects are not well understood. Here, we use in situ X-ray photoelectron spectroscopy (XPS) to investigate how the crystallography and structure of MoS2 influence chemical transformations at solid-state interfaces with various other materials. MoS2 materials with controllably aligned crystal structures (horizontal vs vertical orientation of basal planes) were fabricated, and in situ XPS was carried out by sputter-depositing three different materials (Li, Ge, and Ag) onto MoS2 within an XPS instrument while periodically collecting photoelectron spectra; these deposited materials are of interest due to their application in electronic devices or energy storage. The results showed that Li reacts readily with both crystallographic orientations of MoS2 to form metallic Mo and Li2S, while Ag showed very little chemical or electronic interaction with either type of MoS2. In contrast, Ge showed significant chemical interactions with MoS2 basal planes, but only minor chemical changes were observed when Ge contacted MoS2 edge sites. These findings have implications for electronic transport and band alignment at these interfaces, which is of significant interest for a variety of applications.

Community-Acquired Cavitary Pseudomonas Pneumonia Linked to Use of a Home Humidifier.

Pseudomonas aeruginosa is an opportunistic pathogen that rarely causes pneumonia in otherwise healthy patients. We describe a case of community-acquired P. aeruginosa pneumonia in a previously healthy individual who likely acquired the infection from a home humidifier.

Associations Between Asthma Control and Airway Obstruction and Performance of Activities of Daily Living in Older Adults with Asthma.

OBJECTIVES: To determine the effect of asthma on functional limitations of older adults in the United States. DESIGN: Analyses were conducted with data from the Asthma Beliefs and Literacy in the Elderly study, a prospective cohort study of people aged 60 and older with asthma. SETTING: Participants were recruited from urban primary care and pulmonary specialty practices in New York City and Chicago between 2010 and 2012. PARTICIPANTS: Individuals aged 60 and older with asthma (380 women, 72 men, mean age 67.5 ± 6.8 (range 60-98), 40% Latino, 30% black). MEASUREMENTS: Characteristics of participants with and without activity of daily living (ADL) limitations were compared using the chi-square test. Generalized estimating equations were used to model the relationships between poor asthma control (Asthma Control Questionnaire (ACQ) score >1.5) and severity of airway obstruction (forced expiratory volume in 1-second (FEV1 )) and number of ADL limitations. RESULTS: Participants with one or more ADL limitations were more likely to be female (90% vs 81%, P = .02) and Latino (58% vs 32%, P < .001), have less than a high school education (53% vs 27%, P < .001) and an income of $1,350 per month or less (79% vs 46%, P < .001), and be unmarried (78% vs 64%, P = .003). In the adjusted analysis, poorer ACQ scores (odds ratio (OR) = 1.6, 95% confidence interval (CI) = 1.0-2.4; P = .05) but not severity of airway obstruction (OR = 1.1, 95% CI = 0.6-1.9) was associated with greater ADL limitations. CONCLUSION: Older adults reporting poor asthma control are more likely to have ADL limitations than those with controlled asthma, although one-time spirometry may not adequately identify those at risk of physical impairment from asthma.