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Perovskite-based photoluminescent detection of lead particles in gunshot residue
Full text linkGunshot residue (GSR) analysis is crucial for forensic investigations of shooting incidents, but current methods are time-consuming, laborious, and provide limited spatial resolution. We introduce photoluminescent lead analysis (PL-Pb) for instant high-resolution GSR detection. Lead particles in GSR react into lead halide perovskite semiconductors that emit bright green light under ultraviolet irradiation. PL-Pb enables trace detection of GSR, including ricochet markings, bullet wipes, and combustion plumes. Our method visualizes fine details like rifling patterns and facilitates and extends shooting distance reconstructions. We find that PL-Pb is also suitable for rapid presumptive testing of shooting suspect’s hands, clothes, shoes, and other relevant objects. The instant results, sensitivity, and spatial resolution of perovskite-based detection of lead-containing micro-traces offer unprecedented opportunities for forensic investigations and environmental studies on lead particles
Nongenetic adaptation by collective migration
Full text linkCell populations must adjust their phenotypic composition to adapt to changing environments. One adaptation strategy is to maintain distinct phenotypic subsets within the population and to modulate their relative abundances via gene regulation. Another strategy involves genetic mutations, which can be augmented by stress-response pathways. Here, we studied how a migrating bacterial population regulates its phenotypic distribution to traverse diverse environments. We generated isogenic Escherichia coli populations with varying distributions of swimming behaviors and observed their phenotype distributions during migration in liquid and porous environments. We found that the migrating populations became enriched with high-performing swimming phenotypes in each environment, allowing the populations to adapt without requiring mutations or gene regulation. This adaptation is dynamic and rapid, reversing in a few doubling times when migration ceases. By measuring the chemoreceptor abundance distributions during migration toward different attractants, we demonstrated that adaptation acts on multiple chemotaxis-related traits simultaneously. These measurements are consistent with a general mechanism in which adaptation results from a balance between cell growth generating diversity and collective migration eliminating underperforming phenotypes. Thus, collective migration enables cell populations with continuous, multidimensional phenotypes to flexibly and rapidly adapt their phenotypic composition to diverse environmental conditions
Quantifying the genetic origins of body plan scaling
Full text linkMany of the higher organisms have remarkably consistent body proportions where, within a given species, the sizes of the different body parts, such as the head or the legs, scale with the size of the organism. To probe the origins of body plan scaling, one should study early stages of development where this property is established. Drosophila melanogaster is arguably the most suited organism for such a study since decades of research have enabled measurements of the relevant developmental markers with unprecedented precision. Specifically, we now have access to the expression profiles of all developmental genes that jointly orchestrate the body plan formation of the fruit fly through a complex network of interactions. The richness and quality of measurement data in the fly embryo call for a comparable level of quantitative rigor in studying the question of spatial scaling—a challenge that Nikolić et al. embark on in their recent PNAS publication (1)
Physical synchronization of soft self-oscillating limbs for fast and autonomous locomotion
Full text linkAnimals achieve robust locomotion by offloading regulation from the brain to physical couplings within the body. In contrast, locomotion in artificial systems often depends on centralized processors. Here, we introduce a rapid and autonomous locomotion strategy with synchronized gaits emerging through physical interactions between self-oscillating limbs and the environment, without control signals. Each limb is a single soft tube that only requires a constant flow of air to perform cyclic stepping motions at frequencies reaching 300 hertz. Physical synchronization of several of these self-oscillating limbs enables locomotion speeds that are orders of magnitude faster than those of comparable state-of-the-art robots. Through body-environment dynamics, these seemingly simple devices exhibit autonomy, including obstacle avoidance, amphibious gait transitions, and phototaxis
Metasurface-Based Phosphor-Converted Micro-LED Architecture for Displays – Creating Guided Modes for Enhanced Directionality
Full text linkPhosphor-converted micro-light emitting diodes (micro-LEDs) are a crucial technology for display applications but face significant challenges in light extraction because of the high refractive index of the blue pump die chip. In this study, we design and experimentally demonstrate a nanophotonic approach that overcomes this issue, achieving up to a 3-fold increase in light extraction efficiency. Our approach involves engineering the local density of optical states (LDOS) to generate quasi-guided modes within the phosphor layer by strategically inserting a thin low-index spacer in combination with a metasurface for mode extraction. We demonstrate the trade-offs between blue light pumping, LDOS enhancement at the converted emission wavelength, and radiation pattern control using a stratified system solver for dipole emission. Experimentally, the integration of plasmonic antennas and a silica spacer resulted in a 3-fold overall brightness enhancement, with nearly a 4-fold increase in forward emission. This nanophotonic metasurface waveguide design is a critical advancement for producing bright, directional micro-LEDs, particularly in augmented/virtual reality (AR/VR) devices and smartwatch displays, without the need for bulky secondary optics or reflectors
Trigger factor accelerates nascent chain compaction and folding
Full text linkConformational control of nascent chains is poorly understood. Chaperones are known to stabilize, unfold, and disaggregate polypeptides away from the ribosome. In comparison, much less is known about the elementary conformational control mechanisms at the ribosome. Yet, proteins encounter major folding and aggregation challenges during translation. Here, using selective ribosome profiling and optical tweezers with correlated single-molecule fluorescence, with dihydrofolate reductase (DHFR) as a model system, we show that the Escherichia coli chaperone trigger factor (TF) accelerates nascent chain folding. TF scans nascent chains by transient binding events, and then locks into a stable binding mode as the chain collapses and folds. This interplay is reciprocal: TF binding collapses nascent chains and stabilizes partial folds, while nascent chain compaction prolongs TF binding. Ongoing translation controls these cooperative effects, with TF-accelerated folding depending on the emergence of a peptide segment that is central to the core DHFR beta-sheet. The folding acceleration we report here impacts processes that depend on folding occurring cotranslationally, including cotranslational protein assembly, protein aggregation, and translational pausing, and may be relevant to other domains of life
How Many Mobile Ions Can Electrical Measurements Detect in Perovskite Solar Cells?
Full text linkIn recent years, mobile ions have been assigned to various degradation mechanisms in perovskite solar cells. Some of these include nonreversible degradation, like migration into charge transport layers (CTLs) (1) or reaction with electrodes. (2) Others focus on the electrostatic effects due to mobile ions. Most importantly, the accumulation of a large density of mobile ions at the interface between perovskite and charge transport layers can lead to screening of the built-in potential, which can result in enhanced interface and bulk recombination, reducing the short-circuit current density and fill-factor. (3) The accumulation of mobile ions has also been connected to a decrease in open-circuit voltage. (4) To obtain a comprehensive understanding of the impact of mobile ions on the device physics of perovskite solar cells, accurately determining the density and diffusion coefficient of mobile ions in perovskites is of utmost importance. However, measured ion densities cover multiple orders of magnitude from 1015 cm–3 to 1019 cm–3. (3,5−7) To determine ion densities, electrical measurements like transient current measurements, also known as bias-assisted charge extraction, (3) capacitance frequency, also known as impedance spectroscopy, (8,9) transient capacitance measurements, also known as transient ion drift measurements, (9) and low-frequency Mott–Schottky measurements (5) have been applied. Here, we illustrate that it becomes impossible to determine the ion density if it is high enough to screen a significant portion of the built-in field. To illustrate the difficulty of extracting high ion densities from the different electrical measurements, we carried out drift-diffusion simulations. For the transport layers, we chose parameters resembling thin organic transport layers 2PACz and C60. We assume that ionic transport is mediated by halide vacancies, (10−12) and their charge is compensated by nonmobile negatively charged ions. (13) We carried out the simulations for different mobile ion densities ranging from 1016 to 1020 cm–3, and a typical ionic conductivity σion = eμionNion of 1.6 · 10–10S/cm, where e is the elementary charge, μion is the ionic mobility, and Nion is the density of mobile ions. The complete simulation parameters are listed in the Supporting Information. We emphasize that the absolute values of the presented results are only valid for the parameter set studied in this work
Design of a Soft Robotic Artificial Cardiac Wall
Full text linkIn cardiovascular engineering, the recent introduction of soft robotic technologies sheds new light on the future of implantable cardiac devices, enabling the replication of complex bioinspired architectures and motions. To support human heart function, assistive devices and total artificial hearts have been developed. However, the system's functionality, hemocompatibility, and overall implantability are still open challenges.
Methods: Here, the design of a soft robotic artificial cardiac wall is presented: the action of a bioinspired myocardium of pneu-matic McKibben actuators in a double helix is coupled with an engineered passive and deformable endocardial layer made of silicone. The correlation between the helix angle of the actuators and the ejection fraction of the artificial cardiac wall was pre-liminarily studied with a simplified analytical model. A FEM model was introduced to represent the complex deformation of the endocardial layer during the actuation of the cardiac wall.
Results: Experimental tests report an ejection fraction of 68%, i.e., 77.2 ± 0.4 mL against 90 mmHg, satisfying the minimum physiological requirements and, therefore, proving the concept's functionality.
Conclusions: The conceived device paves the way for a new generation of innovative approaches where engineered bioinspira-tion might be the key to future artificial cardiac pumps that could support or even substitute the human failing heart
Enantiopurity by Directed Evolution of Crystal Stabilities and Nonequilibrium Crystallization
Full text linkCrystallization is a powerful method to isolate enantiopure molecules from racemates if enantiomers self-sort into separate enantiopure crystals. Unfortunately, this behavior is unpredictable and rare (5–10%), as both enantiomers predominantly crystallize together to form racemic crystals, hindering any such chiral sorting. These unfavorable statistics might be overcome using nonequilibrium conditions. Therefore, we systematically characterize energy differences (ΔGΦ) between racemic and enantiopure crystal phases for libraries of target molecules (phenylglycine, praziquantel) with different chemical modifications. Surprisingly, these libraries reveal wide but similar continuous distributions of ΔGΦ, wherein similar chemical modifications group together. This grouping allows a directed evolution strategy to discover racemic crystals with low ΔGΦ for isolating desired enantiomers by crystallization under nonequilibrium conditions. Comparison with over a hundred previously reported compounds suggests that as many as half of all chiral molecules may kinetically form enantiopure crystals (∼50%). These insights open new previously unconsidered possibilities for isolating enantiopure molecules
Defect passivation and enhanced UV emission in β-Ga2O3 via remote fluorine plasma treatment
Full text linkThis study investigates the incorporation of fluorene (F) donors in β-Ga2O3 and its effects on luminescence, defect structure and carrier dynamics. Monoclinic β-Ga2O3 nanowires (NWs) are synthesized via chemical vapour deposition and subsequently doped with F using remote SF6 plasma treatment, leveraging their nanoscale cross sections. Photoelectron spectroscopy reveals F incorporation at oxygen sites and the formation of strong Ga–F bonds without sulfur contamination, while the monoclinic crystal structure remains intact. The impact of F doping is assessed using hyperspectral cathodoluminescence (CL) mapping and time-resolved spectroscopy of individual NWs. The β-Ga2O3 NWs exhibit a strong characteristic UV peak at 3.40 eV, associated with self-trapped holes, and visible defect-related emissions. After F incorporation, an additional UV emission at 3.64 eV emerges, attributed to shallow F donor-deep acceptor pair recombination, while the defect-related emissions are strongly supressed as F atoms occupy oxygen vacancies. Carrier lifetime increases from 9.2 ns to 17.0 ns with increasing F concentration along the nanowire. The work highlights the utility of F plasma processing to passivate intrinsic defects in Ga2O3 and the influence of F donors on the UV emission of β-Ga2O3