An Automated Gradient Titration Fluorescence Methodology for High-Resolution Identification of Aqueous Two-Polymer Phase Extraction Conditions for Single-Wall Carbon Nanotubes.

A significant advance in rate and precision of identifying the co-surfactant concentrations leading to differential extraction of specific single-wall carbon nanotube (SWCNT) species in aqueous two-polymer phase extraction experiments is reported. These gains are achieved through continuous titration of co-surfactant and other solution components during automated fluorescence measurements on SWCNT dispersions. The resulting fluorescence versus concentration curves display intensity and wavelength shift transitions traceable to the nature of the adsorbed surfactant layer on specific SWCNT structures at the (n,m) species and enantiomer level at high resolution. The increased precision and speed of the titration method resolve previously invisible complexity in the SWCNT fluorescence during the transition from one surfactant dominating the SWCNT interface to the other, offering insight into the fine details of the competitive exchange process. For the first time, we additionally demonstrate that the competitive process of the surfactant switch is direction independent (reversible) and hysteresis-free; the latter data effectively specifies an upper bound for the time scale of the exchange process. Titration curves are compared to literature results and initial advanced parameter variation is conducted for previously unreasonable to investigate solution conditions.

Characterising illness stages and recovery trajectories of eating disorders in young people via remote measurement technology (STORY): a multi-centre prospective cohort study protocol.

BACKGROUND: Eating disorders (EDs) are serious, often chronic, conditions associated with pronounced morbidity, mortality, and dysfunction increasingly affecting young people worldwide. Illness progression, stages and recovery trajectories of EDs are still poorly characterised. The STORY study dynamically and longitudinally assesses young people with different EDs (restricting; bingeing/bulimic presentations) and illness durations (earlier; later stages) compared to healthy controls. Remote measurement technology (RMT) with active and passive sensing is used to advance understanding of the heterogeneity of earlier and more progressed clinical presentations and predictors of recovery or relapse. METHODS: STORY follows 720 young people aged 16-25 with EDs and 120 healthy controls for 12 months. Online self-report questionnaires regularly assess ED symptoms, psychiatric comorbidities, quality of life, and socioeconomic environment. Additional ongoing monitoring using multi-parametric RMT via smartphones and wearable smart rings ('Oura ring') unobtrusively measures individuals' daily behaviour and physiology (e.g., Bluetooth connections, sleep, autonomic arousal). A subgroup of participants completes additional in-person cognitive and neuroimaging assessments at study-baseline and after 12 months. DISCUSSION: By leveraging these large-scale longitudinal data from participants across ED diagnoses and illness durations, the STORY study seeks to elucidate potential biopsychosocial predictors of outcome, their interplay with developmental and socioemotional changes, and barriers and facilitators of recovery. STORY holds the promise of providing actionable findings that can be translated into clinical practice by informing the development of both early intervention and personalised treatment that is tailored to illness stage and individual circumstances, ultimately disrupting the long-term burden of EDs on individuals and their families.

In vitro co-culture of Clostridium scindens with primary human colonic epithelium protects the epithelium against Staphylococcus aureus.

A complex and dynamic network of interactions exists between human gastrointestinal epithelium and intestinal microbiota. Therefore, comprehending intestinal microbe-epithelial cell interactions is critical for the understanding and treatment of intestinal diseases. Primary human colonic epithelial cells derived from a healthy human donor were co-cultured with Clostridium scindens (C. scindens), a probiotic obligate anaerobe; Staphylococcus aureus (S. aureus), a facultative anaerobe and intestinal pathogen; or both bacterial species in tandem. The co-culture hanging basket platform used for these experiments possessed walls of controlled oxygen (O2) permeability to support the formation of an O2 gradient across the intestinal epithelium using cellular O2 consumption, resulting in an anaerobic luminal and aerobic basal compartment. Both the colonic epithelial cells and C. scindens remained viable over 48 h during co-culture. In contrast, co-culture with S. aureus elicited significant damage to colonic epithelial cells within 24 h. To explore the influence of the intestinal pathogen on the epithelium in the presence of the probiotic bacteria, colonic epithelial cells were inoculated sequentially with the two bacterial species. Under these conditions, C. scindens was capable of repressing the production of S. aureus enterotoxin. Surprisingly, although C. scindens converted cholic acid to secondary bile acids in the luminal medium, the growth of S. aureus was not significantly inhibited. Nevertheless, this combination of probiotic and pathogenic bacteria was found to benefit the survival of the colonic epithelial cells compared with co-culture of the epithelial cells with S. aureus alone. This platform thus provides an easy-to-use and low-cost tool to study the interaction between intestinal bacteria and colonic cells in vitro to better understand the interplay of intestinal microbiota with human colonic epithelium.

Mucus-coated, magnetically-propelled fecal surrogate to mimic fecal shear forces on colonic epithelium.

The relationship between the mechanical forces associated with bowel movement and colonic mucosal physiology is understudied. This is partly due to the limited availability of physiologically relevant fecal models that can exert these mechanical stimuli in in vitro colon models in a simple-to-implement manner. In this report, we created a mucus-coated fecal surrogate that was magnetically propelled to produce a controllable sweeping mechanical stimulation on primary intestinal epithelial cell monolayers. The mucus layer was derived from purified porcine stomach mucins, which were first modified with reactive vinyl sulfone (VS) groups followed by reaction with a thiol crosslinker (PEG-4SH) via a Michael addition click reaction. Formation of mucus hydrogel network was achieved at the optimal mixing ratio at 2.5 % w/v mucin-VS and 0.5 % w/v PEG-4SH. The artificial mucus layer possessed similar properties as the native mucus in terms of its storage modulus (66 Pa) and barrier function (resistance to penetration by 1-µm microbeads). This soft, but mechanically resilient mucus layer was covalently linked to a stiff fecal hydrogel surrogate (based on agarose and magnetic particles, with a storage modulus of 4600 Pa). The covalent bonding between the mucus and agarose ensured its stability in the subsequent fecal sliding movement when tested at travel distances as long as 203 m. The mucus layer served as a lubricant and protected epithelial cells from the moving fecal surrogate over a 1 h time without cell damage. To demonstrate its utility, this mucus-coated fecal surrogate was used to mechanically stimulate a fully differentiated, in vitro primary colon epithelium, and the physiological stimulated response of mucin-2 (MUC2), interleukin-8 (IL-8) and serotonin (5HT) secretion was quantified. Compared with a static control, mechanical stimulation caused a significant increase in MUC2 secretion into luminal compartment (6.4 × ), a small but significant increase in IL-8 secretion (2.5 × and 3.5 × , at both luminal and basal compartments, respectively), and no detectable alteration in 5HT secretion. This mucus-coated fecal surrogate is expected to be useful in in vitro colon organ-on-chips and microphysiological systems to facilitate the investigation of feces-induced mechanical stimulation on intestinal physiology and pathology.

Nurse Anesthesia Diversion Prevention: A Knowledge and Needs Gap Analysis.

BACKGROUND: Substance misuse is an occupational health problem for anesthesia providers (APs). More than 10% of nurse anesthetists misuse and divert medications. No standard exists for addressing AP drug diversion. The purpose of this quality improvement project was to evaluate the use of a knowledge and needs assessment to inform the development of a successful drug diversion prevention program for certified registered nurse anesthetists (CRNAs) and student registered nurse anesthetists (SRNAs). METHODS: A 28-item questionnaire, using the health belief model (HBM) and the risk perception attitude (RPA) framework, was developed to assess knowledge, beliefs, and practices of substance misuse and diversion. RPA groups were determined by level of belief in self-risk and perceived efficacy of prevention strategies. The survey was emailed to 100 CRNAs and over 100 SRNAs. Survey results were organized using the RPA framework. FINDINGS: One hundred twelve surveys were completed. The RPA avoidant category (high-risk belief and low perceived efficacy of preventive interventions) comprised 52.5% of CRNAs; SRNAs were divided primarily among the RPA responsive category with high perceived risk and high-efficacy beliefs (38.9%) and the indifferent category of low-risk beliefs and low perceived efficacy (31.9%). CONCLUSIONS/APPLICATIONS TO PRACTICE: Anesthesia providers have varying beliefs regarding drug misuse and diversion risks and perceptions of their ability to be successful with preventive strategies. Failure to address nurse anesthesia needs-based diversion prevention may result in missed opportunities to educate this group. Implementation of RPA-tailored interventions by health care organizations may produce effective, long-term outcomes for drug diversion within the profession.

Surfactant Chemistry and Polymer Choice Affect Single-Wall Carbon Nanotube Extraction Conditions in Aqueous Two-Polymer Phase Extraction.

Quantitative determination of the effects of surfactant chemistry and polymer chain length on the concentration conditions necessary to yield extraction of specific single-wall carbon nanotube (SWNCT) species in an aqueous two-polymer phase extraction (ATPE) separation are reported. In particular, the effects of polyethylene glycol (PEG) chain length, surfactant ratios, and systematic structural variations of alkyl surfactants and bile salts on the surfactant ratios necessary for extraction were investigated using a recently reported fluorescence-based method. Alkyl surfactant tail length was observed to strongly affect the amount of surfactant necessary to cause PEG-phase extraction of nanotube species in ATPE, while variation in the anionic sulfate/sulfonate head group chemistry has less impact on the concentration necessary for extraction. Substitution of different bile salts results in different surfactant packings on the SWCNTs, with substitution greatly affecting the alkyl surfactant concentrations required for (n,m) extraction. Finally, distinct alkyl-to-bile surfactant ratios were found to extract specific (n,m) SWCNTs across the whole effective window of absolute concentrations, supporting the hypothesized competitive adsorption mechanism model of SWCNT sorting. Altogether, these results provide valuable insights into the underlying mechanisms behind ATPE-based SWCNT separations, towards further development and optimization of the ATPE method for SWCNT chirality and handedness sorting.

Monolithic Silica Microbands Enable Thin-Layer Chromatography Analysis of Single Cells.

A picoliter thin-layer chromatography (pTLC) platform was developed for analyzing extremely miniature specimens, such as assay of the contents of a single cell of 1 picoliter volume. The pTLC chip consisted of an array of microscale bands made from highly porous monolithic silica designed to accept picoliter-scale volume samples. pTLC bands were fabricated by combining sol-gel chemistry and microfabrication technology. The width (60-80 µm) and depth (13 µm) of each band is comparable to the size of single cells and acted to reduce the lateral diffusion and confine the movement of compounds along the microbands. Ultrasmall volumes (tens of pL) of model fluorescent compounds were spotted onto the microband by a piezoelectric microdispenser and successfully separated by pTLC. The separation resolution and analyte migration were dependent on the macropore size (ranging from 0.3 to 2.3 µm), which was adjustable by changing the porogen concentration during the sol-gel process. For a 0.3 µm macropore size, attomoles of analyte were detectable by fluorescence using standard microscopy methods. The separation resolution, theoretical plate number, and separation times ranged from 1.3 to 2.1, 4 to 357, and 2 to 8 min, respectively, for the chosen model biological lipids. To demonstrate the capability of pTLC for separating analytes from single mammalian cells, cells loaded with fluorescent lipophilic dyes or sphingosine kinase reporter were spotted on microbands, and the single-cell contents separated by pTLC were detected from their fluorescence. These results demonstrate the potential of pTLC for applications in many areas where miniature specimens and high-throughput parallel analyses are needed.

Human 2D Crypt Model for Assaying Intestinal Stem Cell Proliferation and Differentiation.

Intestine is a common site of adverse drug effects in clinical trials; thus, improved in vitro models for preclinical screening of pharmaceutical compounds are sought. A planar, self-renewing human intestinal monolayer platform based on primary adult gastrointestinal stem cells, termed the 2D crypt model, has been developed to screen for the effects of various compounds on the intestinal epithelium. The 2D crypt platform is based on a standard 12-well plate format and consists of cell culture inserts with a collagen film overlaying an impermeable film patterned with an array of micron-scale holes. This two-chamber format enables a gradient of growth factors to be applied such that the tissue self-organizes into spatially segregated stem and differentiated cell compartments. The patterned monolayer mimics a gut epithelium in possessing a stem cell niche, migrating proliferative and differentiated cells. Once established, the 2D crypts replicate many aspects of in vivo physiology, including cell migration, maturation, and apoptotic cell death. The planar geometry of the system simplifies dosing, sampling, and imaging during assay. An immunofluorescence-based assay was established to quantitatively assess cell density, proliferation, migration, viability, and the abundance and localization of postmitotic lineages as a function of time. The model was used to perform a small-scale screen of compounds, including signaling molecules, endogenous hormones/cytokines, and microbial metabolites, on tissue homeostasis. Hit compounds that significantly impacted proliferation and/or differentiation were readily identified. The 2D crypt platform represents a significant innovation in the development of microphysiological systems for emulating the gut epithelium for compound screens.

A Platform for Co-Culture of Primary Human Colonic Epithelium With Anaerobic Probiotic Bacteria.

An in vitro platform was designed and optimized for the co-culture of probiotic anaerobic bacteria with a primary human colonic epithelium having a goal of assessing the anti-inflammatory impact of the probiotic bacteria. The device maintained a luminal O2 concentration at <1% while also supporting an oxygenated basal compartment at 10% for at least 72 h. Measurement of the transepithelial resistance of a confluent colonic epithelium showed high monolayer integrity while fluorescence assays demonstrated that the monolayer was comprised primarily of goblet cells and colonocytes, the two major differentiated cell subtypes of the colonic epithelium. High monolayer barrier function and viability were maintained during co-culture of the epithelium with the probiotic obligate anaerobe Anaerobutyricum hallii (A. hallii). Importantly the device supported a static co-culture of microbes and colonic epithelium mimicking the largely static or low flow conditions within the colonic lumen. A model inflamed colonic epithelium was generated by the addition of tumor necrosis factor-α (TNF-α) and lipopolysaccharide (LPS) to the basal and luminal epithelium sides, respectively. Co-culture of A. hallii with the LPS/TNF-α treated intestine diminished IL-8 secretion by ≥40% which could be mimicked by co-culture with the A. hallii metabolite butyrate. In contrast, co-culture of the inflamed epithelium with two strains of lactic acid-producing bacteria, Lactobacillus rhamnosus GG (LGG) and Bifidobacterium adolescentis (B. adolescentis), did not diminish epithelial IL-8 secretion. Co-culture with colonic epithelial cells from different donors demonstrated a consistent anti-inflammatory effect by A. hallii, but distinct responses to co-culture with LGG and B. adolescentis. The demonstrated system offers a simple and easily adopted platform for examining the physiologic impact of alterations in the intestinal epithelium that occur in the presence of probiotic bacteria and their metabolites.

Development of a Primary Human Intestinal Epithelium Enriched in L-Cells for Assay of GLP-1 Secretion.

Type 2 diabetes mellitus is a chronic disease associated with obesity and dysregulated human feeding behavior. The hormone glucagon-like peptide 1 (GLP-1), a critical regulator of body weight, food intake, and blood glucose levels, is secreted by enteroendocrine L-cells. The paucity of L-cells in primary intestinal cell cultures including organoids and monolayers has made assays of GLP-1 secretion from primary human cells challenging. In the current paper, an analytical assay pipeline consisting of an optimized human intestinal tissue construct enriched in L-cells paired with standard antibody-based GLP-1 assays was developed to screen compounds for the development of pharmaceuticals to modulate L-cell signaling. The addition of the serotonin receptor agonist Bimu 8, optimization of R-spondin and Noggin concentrations, and utilization of vasoactive intestinal peptide (VIP) increased the density of L-cells in a primary human colonic epithelial monolayer. Additionally, the incorporation of an air-liquid interface culture format increased the L-cell number so that the signal-to-noise ratio of conventional enzyme-linked immunoassays could be used to monitor GLP-1 secretion in compound screens. To demonstrate the utility of the optimized analytical method, 21 types of beverage sweeteners were screened for their ability to stimulate GLP-1 secretion. Stevioside and cyclamate were found to be the most potent inducers of GLP-1 secretion. This platform enables the quantification of GLP-1 secretion from human primary L-cells and will have broad application in understanding L-cell formation and physiology and will improve the identification of modulators of human feeding behavior.

Suspended Collagen Hydrogels to Replicate Human Colonic Epithelial Cell Interactions with Immune Cells.

The human colon plays a critical role in fluid and salt absorption and harbors the largest immune compartment. There is a widespread need for in vitro models of human colon physiology with its innate immune system. A method is described to produce a cassette with a network of struts supporting a suspended, non-chemically cross-linked collagen hydrogel scaffold compatible with the co-culture of primary gastrointestinal epithelium and migratory inflammatory cells. The epithelial monolayer cultured on the suspended collagen possesses a population of polarized and differentiated cells similar to that present in vivo. This epithelial layer displays proper barrier function with a transepithelial electrical resistance (TEER) ≥ 1,500 Ω cm2 and an apparent permeability ≤10-5 cm2 s-1 . Immune cells plated on the basal face of the scaffold transmigrated over a period of 24 h to the epithelial layer in response to epithelial production of IL-8 induced by luminal stimulation of Clostridium difficile Toxin A. These studies demonstrate that this in vitro platform possesses a functional primary colonic epithelial layer with an immune cell compartment capable of recruitment in response to pro-inflammatory cues coming from the epithelium.

A technology of a different sort: microraft arrays.

A common procedure performed throughout biomedical research is the selection and isolation of biological entities such as organelles, cells and organoids from a mixed population. In this review, we describe the development and application of microraft arrays, an analysis and isolation platform which enables a vast range of criteria and strategies to be used when separating biological entities. The microraft arrays are comprised of elastomeric microwells with detachable polymer bases (microrafts) that act as capture and culture sites as well as supporting carriers during cell isolation. The technology is elegant in its simplicity and can be implemented for samples possessing tens to millions of objects yielding a flexible platform for applications such as single-cell RNA sequencing, subcellular organelle capture and assay, high-throughput screening and development of CRISPR gene-edited cell lines, and organoid manipulation and selection. The transparent arrays are compatible with a multitude of imaging modalities enabling selection based on 2D or 3D spatial phenotypes or temporal properties. Each microraft can be individually isolated on demand with retention of high viability due to the near zero hydrodynamic stress imposed upon the cells during microraft release, capture and deposition. The platform has been utilized as a simple manual add-on to a standard microscope or incorporated into fully automated instruments that implement state-of-the-art imaging algorithms and machine learning. The vast array of selection criteria enables separations not possible with conventional sorting methods, thus garnering widespread interest in the biological and pharmaceutical sciences.

Combining secondary ion mass spectrometry image depth profiling and single particle inductively coupled plasma mass spectrometry to investigate the uptake and biodistribution of gold nanoparticles in Caenorhabditis elegans.

Analytical techniques capable of determining the spatial distribution and quantity (mass and/or particle number) of engineered nanomaterials in organisms are essential for characterizing nano-bio interactions and for nanomaterial risk assessments. Here, we combine the use of dynamic secondary ion mass spectrometry (dynamic SIMS) and single particle inductively coupled mass spectrometry (spICP-MS) techniques to determine the biodistribution and quantity of gold nanoparticles (AuNPs) ingested by Caenorhabditis elegans. We report the application of SIMS in image depth profiling mode for visualizing, identifying, and characterizing the biodistribution of AuNPs ingested by nematodes in both the lateral and z (depth) dimensions. In parallel, conventional- and sp-ICP-MS quantified the mean number of AuNPs within the nematode, ranging from 2 to 36 NPs depending on the size of AuNP. The complementary data from both SIMS image depth profiling and spICP-MS provides a complete view of the uptake, translocation, and size distribution of ingested NPs within Caenorhabditis elegans.

Hyperglycemia minimally alters primary self-renewing human colonic epithelial cells while TNFα-promotes severe intestinal epithelial dysfunction.

Hyperglycemia is thought to increase production of inflammatory cytokines and permeability of the large intestine. Resulting intestinal inflammation is then often characterized by excess secretion of tumor necrosis factor alpha (TNFα). Thus, hyperglycemia in hospitalized patients suffering from severe trauma or disease is frequently accompanied by TNFα secretion, and the combined impact of these insults on the intestinal epithelium is poorly understood. This study utilized a simple yet elegant model of the intestinal epithelium, comprised of primary human intestinal stem cells and their differentiated progeny, to investigate the impact of hyperglycemia and inflammatory factors on the colonic epithelium. When compared to epithelium cultured under conditions of physiologic glucose, cells under hyperglycemic conditions displayed decreased mucin-2 (MUC2), as well as diminished alkaline phosphatase (ALP) activity. Conditions of 60 mM glucose potentiated secretion of the cytokine IL-8 suggesting that cytokine secretion during hyperglycemia may be a source of tissue inflammation. TNFα measurably increased secretion of IL-8 and IL-1ß, which was enhanced at 60 mM glucose. Surprisingly, intestinal permeability and paracellular transport were not altered by even extreme levels of hyperglycemia. The presence of TNFα increased MUC2 presence, decreased ALP activity, and negatively impacted monolayer barrier function. When TNFα hyperglycemia and ≤30 mM glucose and were combined, MUC2 and ALP activity remained similar to that of TNFα alone, although synergistic effects were seen at 60 mM glucose. An automated image analysis pipeline was developed to assay changes in properties of the zonula occludens-1 (ZO-1)-demarcated cell boundaries. While hyperglycemia alone had little impact on cell shape and size, cell morphologic properties were extraordinarily sensitive to soluble TNFα. These results suggest that TNFα acted as the dominant modulator of the epithelium relative to glucose, and that control of inflammation rather than glucose may be key to maintaining intestinal homeostasis.

Image-Based Live Cell Sorting.

Technologies capable of cell separation based on cell images provide powerful tools enabling cell selection criteria that rely on spatially or temporally varying properties. Image-based cell sorting (IBCS) systems utilize microfluidic or microarray platforms, each having unique characteristics and applications. The advent of IBCS marks a new paradigm in which cell phenotype and behavior can be explored with high resolution and tied to cellular physiological and omics data, providing a deeper understanding of single-cell physiology and the creation of cell lines with unique properties. Cell sorting guided by high-content image information has far-reaching implications in biomedical research, clinical medicine, and pharmaceutical development.

Enterochromaffin Cell-Enriched Monolayer Platform for Assaying Serotonin Release from Human Primary Intestinal Cells.

Enteroendocrine (EE) cells within the intestinal epithelium produce a range of hormones that have key roles in modulating satiety and feeding behavior in humans. The regulation of hormone release from EE cells as a potential therapeutic strategy to treat metabolic disorders is highly sought after by the pharmaceutical industry. However, functional studies are limited by the scarcity of EE cells (or surrogates) in both in vivo and in vitro systems. Enterochromaffin (EC) cells are a subtype of EE cells that produce serotonin (5HT). Here, we explored simple strategies to enrich EC cells in in vitro monolayer systems derived from human primary intestinal stem cells. During differentiation of the monolayers, the EC cell lineage was significantly altered by both the culture method [air-liquid interface (ALI) vs submerged] and the presence of vasoactive intestinal peptide (VIP). Compared with traditional submerged cultures without VIP, VIP-assisted ALI culture significantly boosted the number of EC cells and their 5HT secretion by up to 430 and 390%, respectively. The method also increased the numbers of other subtypes of EE cells such as L cells. Additionally, this method generated monolayers with enhanced barrier integrity, so that directional (basal or apical) 5HT secretion was measurable. For all donor tissues, the enriched EC cells improved the signal-to-background ratio and reliability of 5HT release assays. The enhancement in the 5HT secretion behavior was consistent over time from a single donor, but significant variation in the amount of secreted 5HT was present among tissues derived from five different donors. To demonstrate the utility of the EC-enriched monolayer system, 13 types of pungent food ingredients were screened for their ability to stimulate 5HT secretion. Curcumin found in the spice turmeric derived from the Curcuma longa plant was found to be the most potent secretagogue. This EC-enriched cell monolayer platform can provide a valuable analytical tool for the high-throughput screening of nutrients and gut microbial components that alter the secretion of 5HT.

Observation of gapped state in rare-earth monopnictide HoSb.

The rare-earth monopnictide family is attracting an intense current interest driven by its unusual extreme magnetoresistance (XMR) property and the potential presence of topologically non-trivial surface states. The experimental observation of non-trivial surface states in this family of materials are not ubiquitous. Here, using high-resolution angle-resolved photoemission spectroscopy, magnetotransport, and parallel first-principles modeling, we examine the nature of electronic states in HoSb. Although we find the presence of bulk band gaps at the [Formula: see text] and X-symmetry points of the Brillouin zone, we do not find these gaps to exhibit band inversion so that HoSb does not host a Dirac semimetal state. Our magnetotransport measurements indicate that HoSb can be characterized as a correlated nearly-complete electron-hole-compensated semimetal. Our analysis reveals that the nearly perfect electron-hole compensation could drive the appearance of non-saturating XMR effect in HoSb.

Observation of Dirac state in half-Heusler material YPtBi.

The prediction of non-trivial topological electronic states in half-Heusler compounds makes these materials good candidates for discovering new physics and devices as half-Heusler phases harbour a variety of electronic ground states, including superconductivity, antiferromagnetism, and heavy-fermion behaviour. Here, we report a systematic studies of electronic properties of a superconducting half-Heusler compound YPtBi, in its normal state, investigated using angle-resolved photoemission spectroscopy. Our data reveal the presence of a Dirac state at the [Formula: see text] point of the Brillouin zone at 500 meV below the Fermi level. We observe the presence of multiple Fermi surface pockets, including two concentric hexagonal and six half-oval shaped pockets at the [Formula: see text] and K points of the Brillouin zone, respectively. Furthermore, our measurements show Rashba-split bands and multiple surface states crossing the Fermi level, this is also supported by the first-principles calculations. Our findings of a Dirac state in YPtBi contribute to the establishing of half-Heusler compounds as a potential platform for novel topological phases.

Experimental observation of drumhead surface states in SrAs3.

The topological nodal-line semimetal (TNS) is a unique class of materials with a one dimensional line node accompanied by a nearly dispersionless two-dimensional surface state. However, a direct observation of the so called drumhead surface state within current nodal-line materials is still elusive. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES) along with first-principles calculations, we report the observation of a topological nodal-loop (TNL) in SrAs3, whereas CaAs3 exhibits a topologically trivial state. Our data reveal that surface projections of the bulk nodal-points are connected by clear drumhead surface states in SrAs3. Furthermore, our magneto-transport and magnetization data clearly suggest the presence (absence) of surface states in SrAs3 (CaAs3). Notably, the observed topological states in SrAs3 are well separated from other bands in the vicinity of the Fermi level. RAs3 where R = Ca, Sr, thus, offers a unique opportunity to realize an archetype nodal-loop semimetal and establish a platform for obtaining a deeper understanding of the quantum phase transitions.

Extreme ultraviolet time- and angle-resolved photoemission setup with 21.5 meV resolution using high-order harmonic generation from a turn-key Yb:KGW amplifier.

Characterizing and controlling electronic properties of quantum materials require direct measurements of nonequilibrium electronic band structures over large regions of momentum space. Here, we demonstrate an experimental apparatus for time- and angle-resolved photoemission spectroscopy using high-order harmonic probe pulses generated by a robust, moderately high power (20 W) Yb:KGW amplifier with a tunable repetition rate between 50 and 150 kHz. By driving high-order harmonic generation (HHG) with the second harmonic of the fundamental 1025 nm laser pulses, we show that single-harmonic probe pulses at 21.8 eV photon energy can be effectively isolated without the use of a monochromator. The on-target photon flux can reach 5 × 1010 photons/s at 50 kHz, and the time resolution is measured to be 320 fs. The relatively long pulse duration of the Yb-driven HHG source allows us to reach an excellent energy resolution of 21.5 meV, which is achieved by suppressing the space-charge broadening using a low photon flux of 1.5 × 108 photons/s at a higher repetition rate of 150 kHz. The capabilities of the setup are demonstrated through measurements in the topological semimetal ZrSiS and the topological insulator Sb2-xGdxTe3.