Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock.

Optical atomic clocks1,2 use electronic energy levels to precisely keep track of time. A clock based on nuclear energy levels promises a next-generation platform for precision metrology and fundamental physics studies. Thorium-229 nuclei exhibit a uniquely low-energy nuclear transition within reach of state-of-the-art vacuum ultraviolet (VUV) laser light sources and have, therefore, been proposed for construction of a nuclear clock3,4. However, quantum-state-resolved spectroscopy of the 229mTh isomer to determine the underlying nuclear structure and establish a direct frequency connection with existing atomic clocks has yet to be performed. Here, we use a VUV frequency comb to directly excite the narrow 229Th nuclear clock transition in a solid-state CaF2 host material and determine the absolute transition frequency. We stabilize the fundamental frequency comb to the JILA 87Sr clock2 and coherently upconvert the fundamental to its seventh harmonic in the VUV range by using a femtosecond enhancement cavity. This VUV comb establishes a frequency link between nuclear and electronic energy levels and allows us to directly measure the frequency ratio of the 229Th nuclear clock transition and the 87Sr atomic clock. We also precisely measure the nuclear quadrupole splittings and extract intrinsic properties of the isomer. These results mark the start of nuclear-based solid-state optical clocks and demonstrate the first comparison, to our knowledge, of nuclear and atomic clocks for fundamental physics studies. This work represents a confluence of precision metrology, ultrafast strong-field physics, nuclear physics and fundamental physics.

Tunable itinerant spin dynamics with polar molecules.

Strongly interacting spins underlie many intriguing phenomena and applications1-4 ranging from magnetism to quantum information processing. Interacting spins combined with motion show exotic spin transport phenomena, such as superfluidity arising from pairing of spins induced by spin attraction5,6. To understand these complex phenomena, an interacting spin system with high controllability is desired. Quantum spin dynamics have been studied on different platforms with varying capabilities7-13. Here we demonstrate tunable itinerant spin dynamics enabled by dipolar interactions using a gas of potassium-rubidium molecules confined to two-dimensional planes, where a spin-1/2 system is encoded into the molecular rotational levels. The dipolar interaction gives rise to a shift of the rotational transition frequency and a collision-limited Ramsey contrast decay that emerges from the coupled spin and motion. Both the Ising and spin-exchange interactions are precisely tuned by varying the strength and orientation of an electric field, as well as the internal molecular state. This full tunability enables both static and dynamical control of the spin Hamiltonian, allowing reversal of the coherent spin dynamics. Our work establishes an interacting spin platform that allows for exploration of many-body spin dynamics and spin-motion physics using the strong, tunable dipolar interaction.

Redox conditions correlated with vibronic coupling modulate quantum beats in photosynthetic pigment-protein complexes.

Quantum coherences, observed as time-dependent beats in ultrafast spectroscopic experiments, arise when light-matter interactions prepare systems in superpositions of states with differing energy and fixed phase across the ensemble. Such coherences have been observed in photosynthetic systems following ultrafast laser excitation, but what these coherences imply about the underlying energy transfer dynamics remains subject to debate. Recent work showed that redox conditions tune vibronic coupling in the Fenna-Matthews-Olson (FMO) pigment-protein complex in green sulfur bacteria, raising the question of whether redox conditions may also affect the long-lived (>100 fs) quantum coherences observed in this complex. In this work, we perform ultrafast two-dimensional electronic spectroscopy measurements on the FMO complex under both oxidizing and reducing conditions. We observe that many excited-state coherences are exclusively present in reducing conditions and are absent or attenuated in oxidizing conditions. Reducing conditions mimic the natural conditions of the complex more closely. Further, the presence of these coherences correlates with the vibronic coupling that produces faster, more efficient energy transfer through the complex under reducing conditions. The growth of coherences across the waiting time and the number of beating frequencies across hundreds of wavenumbers in the power spectra suggest that the beats are excited-state coherences with a mostly vibrational character whose phase relationship is maintained through the energy transfer process. Our results suggest that excitonic energy transfer proceeds through a coherent mechanism in this complex and that the coherences may provide a tool to disentangle coherent relaxation from energy transfer driven by stochastic environmental fluctuations.

Photosynthesis tunes quantum-mechanical mixing of electronic and vibrational states to steer exciton energy transfer.

Photosynthetic species evolved to protect their light-harvesting apparatus from photoxidative damage driven by intracellular redox conditions or environmental conditions. The Fenna-Matthews-Olson (FMO) pigment-protein complex from green sulfur bacteria exhibits redox-dependent quenching behavior partially due to two internal cysteine residues. Here, we show evidence that a photosynthetic complex exploits the quantum mechanics of vibronic mixing to activate an oxidative photoprotective mechanism. We use two-dimensional electronic spectroscopy (2DES) to capture energy transfer dynamics in wild-type and cysteine-deficient FMO mutant proteins under both reducing and oxidizing conditions. Under reducing conditions, we find equal energy transfer through the exciton 4-1 and 4-2-1 pathways because the exciton 4-1 energy gap is vibronically coupled with a bacteriochlorophyll-a vibrational mode. Under oxidizing conditions, however, the resonance of the exciton 4-1 energy gap is detuned from the vibrational mode, causing excitons to preferentially steer through the indirect 4-2-1 pathway to increase the likelihood of exciton quenching. We use a Redfield model to show that the complex achieves this effect by tuning the site III energy via the redox state of its internal cysteine residues. This result shows how pigment-protein complexes exploit the quantum mechanics of vibronic coupling to steer energy transfer.

Leveraging Dynamical Symmetries in Two-Dimensional Electronic Spectra to Extract Population Transfer Pathways.

We present a method to deterministically isolate population transfer kinetics from two-dimensional electronic spectroscopic signals. Central to this analysis is the characterization of how all possible subensembles of excited state systems evolve through the population time. When these dynamics are diagrammatically mapped by using double-sided Feynman pathways where population time dynamics are included, a useful symmetry emerges between excited state absorption and ground state bleach recovery dynamics of diagonal and below diagonal cross-peak signals. This symmetry allows removal of pathways from the spectra to isolate signals that evolve according to energy transfer kinetics. We describe a regression procedure to fit to energy transfer time constants and characterize the accuracy of the method in a variety of complex excited state systems using simulated two-dimensional spectra. Our results show that the method is robust for extracting ultrafast energy transfer in multistate excitonic systems, systems containing dark states that affect the signal kinetics, and systems with interfering vibrational relaxation pathways. This procedure can be used to accurately extract energy transfer kinetics from a wide variety of condensed phase systems.

Correlates of post-traumatic growth among nursing professionals: A cross-sectional analysis.

AIMS: Among nursing professionals, our aims were to examine (a) self-reported traumatic experiences, (b) differences in post-traumatic growth (i.e. positive psychological growth after experiencing a traumatic event) by nursing professional level and (c) demographic, work-related, behavioural and traumatic experience covariates of post-traumatic growth. BACKGROUND: Trauma experience among nursing professionals is higher than observed in the general population. Due to the nature of their work environment, workplace trauma rates are particularly alarming. Understanding post-traumatic growth among nursing professionals may guide interventions to enhance well-being. METHOD: A secondary analysis of cross-sectional survey data from nursing professionals (N = 299). Demographic, work-related, behavioural, trauma experience categories and post-traumatic growth variables were examined. RESULTS: Advanced practice nurses and clinical nurses reported higher rates of workplace trauma, as compared to nursing assistants. Higher post-traumatic growth scores were associated with having a postgraduate degree, serving the paediatric population and lower frequency of alcohol use. Lower post-traumatic growth scores were associated with being married/widowed, being an advanced practice provider or clinical nurse, working in the intensive care unit and reporting workplace, family/personal stress and undisclosed trauma. CONCLUSIONS: Nursing professionals have several demographic, work-related, behavioural and traumatic experience-related variables associated with and that explain variances in post-traumatic growth. IMPLICATION FOR NURSING MANAGEMENT: Targeted screening and individualized treatment based on nursing professional level should be considered to support trauma recovery and post-traumatic growth.

Compassion Satisfaction, Burnout, and Secondary Traumatic Stress Among Nursing Staff at an Academic Medical Center: A Cross-Sectional Analysis.

BACKGROUND: Although several studies have recently described compassion satisfaction (CS), burnout (BO), and secondary traumatic stress (STS) in nurses, few to date have examined these issues across nursing specialties. Such examination is needed to inform future nursing-subspecialty tailored interventions. AIMS: To examine (1) differences in CS, BO, and STS across nursing specialties and (2) differences associated with demographic, work-related, and behavioral factors among nurses. METHOD: A secondary analysis of survey responses from nurses (N = 350) at an academic medical center. Demographic, behavioral, work-related, and professional quality of life variables were analyzed using hierarchical regression analyses. RESULTS: CS, BO, and STS scores significantly varied across specialties with emergency nurses experiencing significantly elevated rates of BO and STS, and lowest rates of CS; scores were also differentially associated with demographic, work-related, behavioral, and workplace violence variables. CONCLUSIONS: Key differences in CS, BO, and STS by nursing specialty suggests the importance of tailoring BO and STS mitigative interventions. BO and STS risk factors should be assessed in nurses (e.g., behavioral health problems and poor sleep quality) and specialty-specific interventions (e.g., reducing workplace violence exposure in emergency settings) may be considered to improve CS while reducing BO and STS among nurses.

Health-Related Quality of Life After Polytrauma: A Systematic Review.

BACKGROUND: Following hospital discharge after traumatic injuries, many patients' rehabilitation is inhibited by poor health-related quality of life (HRQoL). OBJECTIVE: The purpose of this review is to identify factors that influence the HRQoL of polytrauma patients after hospital discharge. METHODS: A systematic literature search was performed in CINAHL and PubMed databases for English-language articles published between January 2015 and January 2020. Articles that dealt with pediatric or narrow adult populations, exclusively considered brain and spinal cord injuries, burn injuries, or isolated fractures were excluded. In total, 22 nonexperimental cohort studies were eligible for inclusion. RESULTS: Based on these studies, with minor disagreements explainable by deficient sampling, variables that impacted HRQoL fell into 11 categories: demographics, preinjury HRQoL, preexisting conditions, mental health status, injury type and location, injury severity, course of hospitalization, time after injury, financial and employment status, functional capacity, and pain. CONCLUSION: The finding with the greatest implications was that mental health, positive coping, self-efficacy, and perception of physical state significantly influence HRQoL after injury and, along with other modifiable variables, can be optimized by directed treatment. Additionally, targeted assessments and interventions can be utilized to improve quality of life for patients with nonmodifiable risk factors.

Depressive Symptoms Predict Delayed Ambulation After Traumatic Injury.

BACKGROUND: Impaired psychological state, such as anxiety and depressive symptoms, occurs in up to 40% of patients hospitalized for traumatic injury. These symptoms, in the acute period, may delay engagement in activity, such as ambulation, following injury. The purpose of this study was to determine whether baseline anxiety and depressive symptoms predicted delayed (>48 hr from admission) ambulation in patients hospitalized for major traumatic injury. METHODS: Adults (n = 19) admitted for major trauma (Injury Severity Score [ISS] = 15) provided a baseline measure of anxiety and depressive symptoms (Hospital Anxiety and Depression Scale [HADS]). Logistic regression was used to determine the predictive power of baseline HADS Anxiety and HADS Depression subscale scores for delayed ambulation while controlling for ISS. RESULTS: At baseline, anxiety was present in 32% of patients; 21% reported depressive symptoms. Baseline HADS Anxiety score did not predict the ambulation group. However, for each 1 point increase in baseline HADS Depression score, the likelihood of patients ambulating after 48 hr from admission increased by 67% (odds ratio = 1.67; 95% CI [1.02, 2.72]; p = .041). CONCLUSION: Worsening depressive symptoms were associated with delayed ambulation in the acute period following injury. Future, larger scale investigations are needed to further elucidate the relationship between psychological symptoms and the acute recovery period from trauma to better inform clinicians and guide development of interventions to improve patient outcomes.

Leveraging scatter in two-dimensional spectroscopy: passive phase drift correction enables a global phasing protocol.

Phase stability between pulse pairs defining Fourier-transform time delays can limit resolution and complicates development and adoption of multidimensional coherent spectroscopies. We demonstrate a data processing procedure to correct the long-term phase drift of the nonlinear signal during two-dimensional (2D) experiments based on the relative phase between scattered excitation pulses and a global phasing procedure to generate fully absorptive 2D electronic spectra of wafer-scale monolayer MoS2. Our correction results in a ∼30-fold increase in effective long-term signal phase stability, from ∼λ/2 to ∼λ/70 with negligible extra experimental time and no additional optical components. This scatter-based drift correction should be applicable to other interferometric techniques as well, significantly lowering the practical experimental requirements for this class of measurements.

Factors Associated With Burnout in Trauma Nurses.

BACKGROUND: Burnout is a psychological syndrome resulting from repeated stressors experienced in the workplace that centers on emotional exhaustion, detachment from the job, and a sense of ineffectiveness. It has been previously demonstrated that burnout exists in the health care workforce, but there has been limited investigation of burnout in nurses who primarily provide care for patients who have been traumatically injured. The purpose of this study was to explore factors associated with burnout reported by trauma nurses. METHODS: This was a secondary analysis of a cross-sectional survey distributed at a large, academic Level I trauma center that serves both adult and pediatric patients. For this analysis, only the Burnout subscale of the Professional Quality of Life scale Version 5 (ProQOL) was used. Multivariate hierarchical regression was used to determine factors associated with burnout reported by trauma nurses. RESULTS: Protective factors included being female, being married, and better quality of sleep. Risk factors included having a mental health diagnosis and working with adult populations. CONCLUSIONS: These results provide an important contribution to the burnout risk profile for trauma nurses and may provide insight into future investigations as well as development and testing of tailored interventions to mitigate burnout in trauma nurses.

A Psychometric Analysis of CIWA-Ar in Acutely Ill and Injured Hospitalized Patients.

Alcohol withdrawal syndrome (AWS) manifests after alcohol-dependent individuals suddenly cease alcohol consumption. Clinical Institute Withdrawal Assessment-Alcohol, revised (CIWA-Ar) is a widely used tool to assess and guide treatment of AWS. CIWA-Ar was developed in voluntarily detoxification centers, and the reliability and validity of CIWA-Ar have been minimally evaluated in hospitalized patients. We performed a retrospective chart review of 479 cases of screening and treatment of AWS using CIWA-Ar, of which 118 were admitted to a trauma/orthopedic (T/O) service and 361 to an internal medicine (IM) service. Exploratory factor analyses with varimax rotation were applied for each population, and reliability testing was performed on the determined subscales. Exploratory factor analyses yielded 2 unique structures, each explaining 56% of the variance of CIWA-Ar. The IM group had a 3-factor structure with the Physical Disturbances (23%), Anxiety (19%), and Confusion (14%) subscales. The T/O group had a 2-factor structure with the Neurological Disturbances (36%) and Physical Disturbances (20%) subscales. Overall, Cronbach's alphas were acceptable (0.74 and 0.82 for IM and T/O, respectively); however, Cronbach's alphas for the IM subscales were 0.66 and 0.69 for physical disturbances and anxiety, respectively. Cronbach's alpha for the Confusion subscale was not calculated because only 1 scale item loaded. The subscales of the T/O factor structure yielded Cronbach's alphas of 0.81 for neurological disturbances and 0.62 for physical disturbances. Our analyses did not support the reliability or validity of CIWA-Ar in acutely ill or injured patients, warranting further investigation and tool development for AWS management in the hospital setting.

Use of Plasma-Based Trauma Transfusion Protocols at Level IV Trauma Centers.

Early initiation of a high ratio massive transfusion can lower trauma patient mortality by 80%. Long transport times from rural Level IV trauma centers therefore require that damage control resuscitation begin before patient transfer. This study evaluates the current use of fresh frozen plasma (FFP) at Level IV trauma centers and the feasibility of implementing trauma transfusion protocols at these centers. Demographic and clinical data were collected for trauma patients at all state Level IV trauma centers who would have met criteria for massive transfusion protocol (MTP) activation based on the Assessment of Blood Consumption (ABC) score. All state Level IV trauma centers were also surveyed to determine availability of blood bank plasma resources. A total of 760 adult trauma patients presented to a Level IV trauma center during the study period. Three hundred sixty-eight patients (48.4%) were transferred to a higher level of care. Because FAST (Focused Assessment with Sonography for Trauma) results were not available in the state registry data, we included all blunt trauma patients with an ABC score of 1 as "potential ABC-positive patients." Forty-two (5.5%) patients were potentially ABC positive. Fifteen of 22 Level IV centers responded to our survey. Seventy-three percent of respondents have FFP available. Mean time to FFP availability was 63.1 min. Median total length of stay from registration to emergency department discharge for potentially ABC-positive patients was 2 hr. Because most Level IV trauma centers have FFP and thaw times are such that administration would not delay transport to a higher level of care, we recommend implementation of MTPs at Level IV trauma centers to reduce hemorrhage-associated mortality.

CE: Breaking Through the Bottleneck: Acuity Adaptability in Noncritical Trauma Care.

BACKGROUND: Achieving efficient throughput of patients is a challenge faced by many hospital systems. Factors that can impede efficient throughput include increased ED use, high surgical volumes, lack of available beds, and the complexities of coordinating multiple patient transfers in response to changing care needs. Traditionally, many hospital inpatient units operate via a fixed acuity model, relying on multiple intrahospital transfers to move patients along the care continuum. In contrast, the acuity-adaptable model allows care to occur in the same room despite fluctuations in clinical condition, removing the need for transfer. This model has been shown to be a safe and cost-effective approach to improving throughput in populations with predictable courses of hospitalization, but has been minimally evaluated in other populations, such as patients hospitalized for traumatic injury. PURPOSE: This quality improvement project aimed to evaluate implementation of an acuity-adaptable model on a 20-bed noncritical trauma unit. Specifically, we sought to examine and compare the pre- and postimplementation metrics for throughput efficiency, resource utilization, and nursing quality indicators; and to determine the model's impact on patient transfers for changes in level of care. METHODS: This was a retrospective, comparative analysis of 1,371 noncritical trauma patients admitted to a level 1 trauma center before and after the implementation of an acuity-adaptable model. Outcomes of interest included throughput efficiency, resource utilization, and quality of nursing care. Inferential statistics were used to compare patients pre- and postimplementation, and logistic regression analyses were performed to determine the impact of the acuity-adaptable model on patient transfers. RESULTS: Postimplementation, the median ED boarding time was reduced by 6.2 hours, patients more often remained in their assigned room following a change in level of care, more progressive care patient days occurred, fall and hospital-acquired pressure injury index rates decreased respectively by 0.9 and 0.3 occurrences per 1,000 patient days, and patients were more often discharged to home. Logistic regression analyses revealed that under the new model, patients were more than nine times more likely to remain in the same room for care after a change in acuity and 81.6% less likely to change rooms after a change in acuity. An increase of over $11,000 in average daily bed charges occurred postimplementation as a result of increased progressive care-level bed capacity. CONCLUSIONS: The implementation of an acuity-adaptable model on a dedicated noncritical trauma unit improved throughput efficiency and resource utilization without sacrificing quality of care. As hospitals continue to face increasing demand for services as well as numerous barriers to meeting such demand, leaders remain challenged to find innovative ways to optimize operational efficiency and resource utilization while ensuring delivery of high-quality care. The findings of this study demonstrate the value of the acuity-adaptable model in achieving these goals in a noncritical trauma care population.

Original Research: Breaking Through the Bottleneck: Acuity Adaptability in Noncritical Trauma Care.

BACKGROUND: Achieving efficient throughput of patients is a challenge faced by many hospital systems. Factors that can impede efficient throughput include increased ED use, high surgical volumes, lack of available beds, and the complexities of coordinating multiple patient transfers in response to changing care needs. Traditionally, many hospital inpatient units operate via a fixed acuity model, relying on multiple intrahospital transfers to move patients along the care continuum. In contrast, the acuity-adaptable model allows care to occur in the same room despite fluctuations in clinical condition, removing the need for transfer. This model has been shown to be a safe and cost-effective approach to improving throughput in populations with predictable courses of hospitalization, but has been minimally evaluated in other populations, such as patients hospitalized for traumatic injury. PURPOSE: This quality improvement project aimed to evaluate implementation of an acuity-adaptable model on a 20-bed noncritical trauma unit. Specifically, we sought to examine and compare the pre- and postimplementation metrics for throughput efficiency, resource utilization, and nursing quality indicators; and to determine the model's impact on patient transfers for changes in level of care. METHODS: This was a retrospective, comparative analysis of 1,371 noncritical trauma patients admitted to a level 1 trauma center before and after the implementation of an acuity-adaptable model. Outcomes of interest included throughput efficiency, resource utilization, and quality of nursing care. Inferential statistics were used to compare patients pre- and postimplementation, and logistic regression analyses were performed to determine the impact of the acuity-adaptable model on patient transfers. RESULTS: Postimplementation, the median ED boarding time was reduced by 6.2 hours, patients more often remained in their assigned room following a change in level of care, more progressive care patient days occurred, fall and hospital-acquired pressure injury index rates decreased respectively by 0.9 and 0.3 occurrences per 1,000 patient days, and patients were more often discharged to home. Logistic regression analyses revealed that under the new model, patients were more than nine times more likely to remain in the same room for care after a change in acuity and 81.6% less likely to change rooms after a change in acuity. An increase of over $11,000 in average daily bed charges occurred postimplementation as a result of increased progressive care-level bed capacity. CONCLUSIONS: The implementation of an acuity-adaptable model on a dedicated noncritical trauma unit improved throughput efficiency and resource utilization without sacrificing quality of care. As hospitals continue to face increasing demand for services as well as numerous barriers to meeting such demand, leaders remain challenged to find innovative ways to optimize operational efficiency and resource utilization while ensuring delivery of high-quality care. The findings of this study demonstrate the value of the acuity-adaptable model in achieving these goals in a noncritical trauma care population.

Feasibility and Acceptability of a Novel Intensive Care Unit Communication Intervention ("Let's Talk") and Initial Assessment Using the Multiple Goals Theory of Communication.

Background: Family members of intensive care unit (ICU) patients often report poor communication, feeling unprepared for ICU family meetings, and poor psychological outcomes after decision-making. The objective of this study was to create a tool to prepare families for ICU family meetings and assess feasibility of using Communication Quality Analysis (CQA) to measure communication quality of family meetings. Methods: This observational study was conducted at an academic tertiary care center in Hershey, PA from March 2019 to 2020. Phase 1a involved conceptual design. Phase 1b entailed acceptability testing of 2 versions of the tool (text-only, comic) with 9 family members of non-capacitated ICU patients; thematic analysis of semi-strucutred interviews was conducted. Phase 1c assessed feasibility of applying CQA to audio-recorded ICU family meetings (n = 17); 3 analysts used CQA to assess 6 domains of communication quality. Wilcoxon Signed Rank tests were used to interpret CQA scores. Results: Four themes emerged from Phase 1b interviews: participants 1) found the tool useful for meeting preparation and organizing thoughts, 2) appreciated emotional content, 3) preferred the comic form (67%), and 4) had indifferent or negative perceptions about specific elements. In Phase 1c, clinicians scored higher on the CQA content and engagement domains; family members scored higher on the emotion domain. CQA scores in the relationship and face domains had the lowest quality ratings. Conclusions: Let's Talk may help families become better prepared for ICU family meetings. CQA provides a feasible approach to assessing communication quality that identifies specific areas of strengths and weaknesses in communication.

Adopting duplex sequencing technology for genetic toxicity testing: A proof-of-concept mutagenesis experiment with N-ethyl-N-nitrosourea (ENU)-exposed rats.

Duplex sequencing (DS) is an error-corrected next-generation sequencing method in which molecular barcodes informatically link PCR-copies back to their source DNA strands, enabling computational removal of errors in consensus sequences. The resulting background of less than one artifactual mutation per 107 nucleotides allows for direct detection of somatic mutations. TwinStrand Biosciences, Inc. has developed a DS-based mutagenesis assay to sample the rat genome, which can be applied to genetic toxicity testing. To evaluate this assay for early detection of mutagenesis, a time-course study was conducted using male Hsd:Sprague Dawley SD rats (3 per group) administered a single dose of 40 mg/kg N-ethyl-N-nitrosourea (ENU) via gavage, with mutation frequency (MF) and spectrum analyzed in stomach, bone marrow, blood, and liver tissues at 3 h, 24 h, 7 d, and 28 d post-exposure. Significant increases in MF were observed in ENU-exposed rats as early as 24 h for stomach (site of contact) and bone marrow (a highly proliferative tissue) and at 7 d for liver and blood. The canonical, mutational signature of ENU was established by 7 d post-exposure in all four tissues. Interlaboratory analysis of a subset of samples from different tissues and time points demonstrated remarkable reproducibility for both MF and spectrum. These results demonstrate that MF and spectrum can be evaluated successfully by directly sequencing targeted regions of DNA obtained from various tissues⁠, a considerable advancement compared to currently used in vivo gene mutation assays.

Adopting Duplex Sequencing™ Technology for Genetic Toxicity Testing: A Proof-of-Concept Mutagenesis Experiment with N-Ethyl-N-Nitrosourea (ENU)-Exposed Rats.

Duplex sequencing (DuplexSeq) is an error-corrected next-generation sequencing (ecNGS) method in which molecular barcodes informatically link PCR-copies back to their source DNA strands, enabling computational removal of errors by comparing grouped strand sequencing reads. The resulting background of less than one artifactual mutation per 10 7 nucleotides allows for direct detection of somatic mutations. TwinStrand Biosciences, Inc. has developed a DuplexSeq-based mutagenesis assay to sample the rat genome, which can be applied to genetic toxicity testing. To evaluate this assay for early detection of mutagenesis, a time-course study was conducted using male Hsd:Sprague Dawley SD rats (3 per group) administered a single dose of 40 mg/kg N-ethyl-N-nitrosourea (ENU) via gavage, with mutation frequency (MF) and spectrum analyzed in stomach, bone marrow, blood, and liver tissues at 3 h, 24 h, 7 d, and 28 d post-exposure. Significant increases in MF were observed in ENU-exposed rats as early as 24 h for stomach (site of contact) and bone marrow (a highly proliferative tissue) and at 7 d for liver and blood. The canonical, mutational signature of ENU was established by 7 d post-exposure in all four tissues. Interlaboratory analysis of a subset of samples from different tissues and time points demonstrated remarkable reproducibility for both MF and spectrum. These results demonstrate that MF and spectrum can be evaluated successfully by directly sequencing targeted regions of DNA obtained from various tissues, a considerable advancement compared to currently used in vivo gene mutation assays. HIGHLIGHTS: DuplexSeq is an ultra-accurate NGS technology that directly quantifies mutationsENU-dependent mutagenesis was detected 24 h post-exposure in proliferative tissuesMultiple tissues exhibited the canonical ENU mutation spectrum 7 d after exposureResults obtained with DuplexSeq were highly concordant between laboratoriesThe Rat-50 Mutagenesis Assay is promising for applications in genetic toxicology.

Annihilation of Excess Excitations along Phycocyanin Rods Precedes Downhill Flow to Allophycocyanin Cores in the Phycobilisome of Synechococcus elongatus PCC 7942.

Cyanobacterial phycobilisome complexes absorb visible sunlight and funnel photogenerated excitons to the photosystems where charge separation occurs. In the phycobilisome complex of Synechococcus elongatus PCC 7942, phycocyanin protein rods that absorb bluer wavelengths are assembled on allophycocyanin cores that absorb redder wavelengths. This arrangement creates a natural energy gradient toward the reaction centers of the photosystems. Here, we employ broadband pump-probe spectroscopy to observe the fate of excess excitations in the phycobilisome complex of this organism. We show that excess excitons are quenched through exciton-exciton annihilation along the phycocyanin rods prior to transfer to the allophycocyanin cores. Our observations are especially relevant in comparison to other antenna proteins, where exciton annihilation primarily occurs in the lowest-energy chlorophylls. The observed effect could play a limited photoprotective role in physiological light fluences. The exciton decay dynamics is faster in the intact phycobilisome than in isolated C-phycocyanin trimers studied in earlier work, confirming that this effect is an emergent property of the complex assembly. Using the obtained annihilation data, we calculate exciton hopping times of 2.2-6.4 ps in the phycocyanin rods. This value agrees with earlier FRET calculations of exciton hopping times along phycocyanin hexamers by Sauer and Scheer.

Sub-10 fs Intervalley Exciton Coupling in Monolayer MoS2 Revealed by Helicity-Resolved Two-Dimensional Electronic Spectroscopy.

The valley pseudospin at the K and K' high-symmetry points in monolayer transition metal dichalcogenides (TMDs) has potential as an optically addressable degree of freedom in next-generation optoelectronics. However, intervalley scattering and relaxation of charge carriers leads to valley depolarization and limits practical applications. In addition, enhanced Coulomb interactions lead to pronounced excitonic effects that dominate the optical response and initial valley depolarization dynamics but complicate the interpretation of ultrafast spectroscopic experiments at short time delays. Employing broadband helicity-resolved two-dimensional electronic spectroscopy (2DES), we observe ultrafast (∼10 fs) intervalley coupling between all A and B valley exciton states that results in a complete breakdown of the valley index in large-area monolayer MoS2 films. These couplings and subsequent dynamics exhibit minimal excitation fluence or temperature dependence and are robust toward changes in sample grain size and inherent strain. Our observations strongly suggest that this direct intervalley coupling on the time scale of optical excitation is an inherent property of large-area MoS2 distinct from dynamic carrier or exciton scattering, phonon-driven processes, and multiexciton effects. This ultrafast intervalley coupling poses a fundamental challenge for exciton-based valleytronics in monolayer TMDs and must be overcome to fully realize large-area valleytronic devices.