Sensitivity enhancement of bimodal waveguide interferometric sensor based on regional mode engineering.

In this paper, we propose a novel bimodal waveguide based on regional mode engineering (BiMW-RME). Leveraging the orthogonality of the guided modes, the form of patterned SiO2 cladding on the bimodal waveguide can reduce the interaction between the reference mode and the analyte, thereby significantly improving sensitivity. The proposed BiMW-RME sensor experimentally demonstrates a phase sensitivity of 2766 π rad/RIU/cm and a detection limit of 2.44×1-5 RIU. The sensitivity is 2.7 times higher than that of the conventional BiMW sensor on the same SOI platform. The proposed design strategy demonstrates a significant improvement in the sensor's sensitivity, presenting a novel approach to enhancing common-path interferometric sensor performance.

Theoretical Insight into the Palladium-Catalyzed Prenylation and Geranylation of Oxindoles with Isoprene.

This work presents a comprehensive mechanistic study of the ligand-controlled palladium-catalyzed prenylation (with C5 added) and geranylation (with C10 added) reactions of oxindole with isoprene. The calculated results indicate that the prenylation with the bis-phosphine ligand and geranylation with the monophosphine ligand fundamentally share a common mechanism. This mechanism involves the formation of two crucial species: a η3-allyl-Pd(II) cation and an oxindole carbon anion. Furthermore, the reactions necessitate the assistance of a second oxindole molecule, which serves as a Brønsted acid, providing a proton to generate the oxindole nitrogen anion. The oxindole nitrogen anion then acts as a Brønsted base, abstracting a C-H proton from another oxindole molecule to form an oxindole carbon anion. These mechanistic details differ significantly from those proposed in the experimental work. The present calculations do not support the presence of the Pd-H species and the η3, η3-diallyl-Pd(II) intermediate, which were previously suggested in experiments. The theoretical results rationalize the experimental finding that the bis-phosphine ligand favors the prenylation of oxindole, while the monophosphine ligand enables the geranylation of oxindole.

A Cu2+ fluorescent chemosensor suitable for quantitative detection of tyrosinase in potatoes over a wide pH range.

Cu2+ as an important trace element plays an essential role in various biologic processes due to the unique redox active nature. For this reason, much effort has been made to develop effective methods for Cu2+ detection. In this study, a novel structure fluorescent chemosensor, 1-(6-(((5-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ4, 5λ4-dipyrrolo[1, 2-c:2', 1'-f][1, 3, 2] diazaborinin-10-yl)quinolin-8-yl)oxy)methyl)pyridin-2-yl)-N, N-bis(pyridin-2-ylmethyl)methanamine (1), was synthesized and characterized by 1H and 13C nuclear magnetic resonance spectroscopy, and electrospray ionization mass spectrometry. Sensor 1 showed an obviously "on-off" fluorescence response to Cu2+ with a 1:1 binding stoichiometry by UV-vis and fluorescence spectrophotometry. The detection limit of sensor 1 to Cu2+ was determined to be 1.9 µM, and the stable pH range for Cu2+ detection was from 3 to 13. Sensor 1 can be used for recognition and detection of tyrosinase in potatoes.

On-Chip Fabrication-Tolerant Exceptional Points Based on Dual-Scatterer Engineering.

The intriguing and anomalous optical characteristics of exceptional points (EPs) in optical resonators have attracted significant attention. While EP-related phenomena have been observed by perturbing resonators with off-chip components, implementing EPs fully on-chip remains challenging due to their extreme susceptibility to fabrication errors. In this Letter, we propose a succinct and compact approach to reach EP in an on-chip integrated silicon microring resonator by manipulating the evolution of backscatterings with two nanocylinders of disparate diameters. The theoretical analysis unveils that the fabrication constraints could be significantly relieved by increasing the difference in diameters of the nanocylinders. The evolution from non-EP to EP is traced experimentally through the step-by-step tuning of the angular and radial positions of nanocylinders. The proposed method opens a pathway toward the on-chip high-density integration of non-Hermitian devices.

Efficient generation of functional neurons from mouse embryonic stem cells via neurogenin-2 expression.

The production of induced neuronal (iN) cells from human embryonic stem cells (ESCs) and induced pluripotent stem cells by the forced expression of proneural transcription factors is rapid, efficient and reproducible. The ability to generate large numbers of human neurons in such a robust manner enables large-scale studies of human neural differentiation and neuropsychiatric diseases. Surprisingly, similar transcription factor-based approaches for converting mouse ESCs into iN cells have been challenging, primarily because of low cell survival. Here, we provide a detailed approach for the efficient and reproducible generation of functional iN cells from mouse ESC cultures by the genetically induced expression of neurogenin-2. The resulting iN cells display mature pre- and postsynaptic specializations and form synaptic networks. Our method provides the basis for studying neuronal development and enables the direct comparison of cellular phenotypes in mouse and human neurons generated in an equivalent way. The procedure requires 14 d and can be carried out by users with expertise in stem cell culture.

Direct Formation of Electronic Excited NO2 Contributes to the High Yield of HONO during Photosensitized Renoxification.

Photosensitized renoxification of HNO3 is found to produce HONO in an unexpectedly high yield, which has been considered an important source for atmospheric HONO. Conventionally, the production of HONO is ascribed to the secondary photolysis of the primarily formed NO2. In this study, by using humic acid (HA) as a model environmental photosensitizer, we provide evidence of the direct formation of NO2 in its electronic excited state (NO2*) as a key intermediate during the photosensitizing renoxification of HNO3. Moreover, the high HONO yield originates from the heterogeneous reaction of the primarily formed NO2* with the co-adsorbed water molecules on HA. Such a mechanism is supported by the increase of the product selectivity of HONO with relative humidity. Further luminescence measurements demonstrate clearly the occurrence of an electronic excited state (NO2*) from photolysis of adsorbed HNO3 on HA. This work deepens our understanding of the formation of atmospheric HONO and gives insight into the transformation of RNS.

Dynamic signatures of microplastic distribution across the water column of Yangtze River Estuary: Complicated implication of tidal effects.

Riverine microplastic (MP) discharge into the ocean contributes greatly to global MP contamination, yet our understanding of this process remains primitive. To deepen our interpretation of the dynamic MP variation throughout the estuarine water columns, we sampled at Xuliujing, the saltwater intrusion node of the Yangtze River Estuary, over the course of ebb and flood tides in four seasons (July and October 2017, January and May 2018 respectively). We observed that the collision of downstream and upstream currents contributed to the high MP concentration and that the mean MP abundance fluctuated with the tide. A model of microplastics residual net flux (MPRF-MODEL), taking the seasonal abundance and vertical distribution of MP along with current velocity into consideration, was developed to predict the net flux of MP throughout the full water columns. 2154 ± 359.7 t/year of MP was estimated to flow into the East China Sea via the River in 2017-2018. Our study suggests that riverine MP flux can be overestimated due to reciprocating current carried MP from the estuary. Using the tidal and seasonal variation in MP distribution, we calculated the tide impact factor index (TIFI) for the Yangtze River Estuary to be between 38.11% and 58.05%. In summary, this study provides a baseline of MP flux research in the Yangtze River for similar tidal-controlled rivers and a contextual understanding of how to appropriately sample and accurately estimate in a dynamic estuary system. The redistribution of microplastics may be impacted by complex tide processes. Although not observed in this study, it may merit investigation.

Amyloid-ß Protein Precursor Regulates Electrophysiological Properties in the Hippocampus via Altered Kv1.4 Expression and Function in Mice.

BACKGROUND: Amyloid-ß protein precursor (AßPP) is enriched in neurons. However, the mechanism underlying AßPP regulation of neuronal activity is poorly understood. Potassium channels are critically involved in neuronal excitability. In hippocampus, A-type potassium channels are highly expressed and involved in determining neuronal spiking. OBJECTIVE: We explored hippocampal local field potential (LFP) and spiking in the presence and absence of AßPP, and the potential involvement of an A-type potassium channel. METHODS: We used in vivo extracellular recording and whole-cell patch-clamp recording to determine neuronal activity, current density of A-type potassium currents, and western blot to detect changes in related protein levels. RESULTS: Abnormal LFP was observed in AßPP-/- mice, including reduced beta and gamma power, and increased epsilon and ripple power. The firing rate of glutamatergic neurons reduced significantly, in line with an increased action potential rheobase. Given that A-type potassium channels regulate neuronal firing, we measured the protein levels and function of two major A-type potassium channels and found that the post-transcriptional level of Kv1.4, but not Kv4.2, was significantly increased in the AßPP-/- mice. This resulted in a marked increase in the peak time of A-type transient outward potassium currents in both glutamatergic and gamma-aminobutyric acid-ergic (GABAergic) neurons. Furthermore, a mechanistic experiment using human embryonic kidney 293 (HEK293) cells revealed that the AßPP deficiency-induced increase in Kv1.4 may not involve protein-protein interaction between AßPP and Kv1.4. CONCLUSION: This study suggests that AßPP modulates neuronal firing and oscillatory activity in the hippocampus, and Kv1.4 may be involved in mediating the modulation.

Rapid Redox Cycling of Fe(II)/Fe(III) in Microdroplets during Iron-Citric Acid Photochemistry.

Fe(III) and carboxylic acids are common compositions in atmospheric microdroplet systems like clouds, fogs, and aerosols. Although photochemical processes of Fe(III)-carboxylate complexes have been extensively studied in bulk aqueous solution, relevant information on the dynamic microdroplet system, which may be largely different from the bulk phase, is rare. With the help of the custom-made ultrasonic-based dynamic microdroplet photochemical system, this study examines the photochemical process of Fe(III)-citric acid complexes in microdroplets for the first time. We find that when the degradation extent of citric acid is similar between the microdroplet system and the bulk solution, the significantly lower Fe(II) ratio is present in microdroplet samples due to the rapider reoxidation of photogenerated Fe(II). However, by replacing citric acid with benzoic acid, no much difference in the Fe(II) ratio between microdroplets and bulk solution is observed, which indicates distinct reoxidation pathways of Fe(II). Moreover, the presence of •OH scavenger, namely, methanol, greatly accelerates the reoxidation of photogenerated Fe(II) in both citric acid and benzoic acid situations. Further experiments reveal that the high availability of O2 and the citric acid- or methanol-derived carbon-centered radicals are responsible for the rapider reoxidation of Fe(II) in iron-citric acid microdroplets by prolonging the length of HO2•- and H2O2-involved radical reaction chains. The results in this study may provide a new understanding about iron-citric acid photochemistry in atmospheric liquid particles, which can further influence the photoactivity of particles and the formation of secondary organic aerosols.

Palladium-catalyzed generation of CO from formic acid for alkoxycarbonylation of internal alkenes involves a PTSA-assisted NH-Pd mechanism: a DFT mechanistic study.

DFT calculations have been performed to find the mechanism of the alkyloxycarbonylation of an internal alkene with HCOOH catalyzed by a palladium complex with P,N hemilabile ligands. Four different cycles have been explored in detail, and a plausible catalytic cycle involves the decomposition of HCOOH/HCOOMe to CO, internal alkene isomerization, terminal alkene insertion, CO migratory insertion and methanolysis. It is shown that decomposition and isomerization processes involve a cooperative P,N hemilabile ligand and Pd(0) (NH-Pd) rather than the Pd(II) hydride (Pd-H) mechanism. Intriguingly, the simultaneous presence of PTSA acts as a hydrogen shuttle (H-shuttle), assisting CO generation and methanolysis. With such a mechanism, the rate-determining transition state corresponds to internal alkene isomerization, which is consistent with the experimental observation that isomerization was the slow step in this process. The back-bonding between palladium and olefin and rapid hydrogen transfer in the presence of a PTSA H-shuttle are responsible for the moderate barriers. In addition, a careful study of the solvent effect indicates that polar solvents, which are capable of hydrogen bonding, can promote the catalytic reactions. Mechanistic insights gained by this theoretical study have not only rationalized the experimental observations well but also have implications for new reaction development.

Erratum: Corrigendum: The distribution and behavioral characteristics of plateau pikas (Ochotonacurzoniae). ZooKeys 1059: 157-171. https://doi.org/10.3897/zookeys.1059.63581.

[This corrects the article DOI: 10.3897/zookeys.1059.63581.].

Enhancing the flame retardancy and UV resistance of polyamide 6 by introducing ternary supramolecular aggregates.

An integrated multi-functional additive was fabricated by successively grafting melamine (MEL) and phytic acid (PhA) on multiwalled carbon-nanotubes (MWNCTs), and was then applied in PA6 to improve the flame retardancy and light aging resistance of the composite. The limit oxygen index of PA6 composite containing 7 wt% PhA-MEL-MWCNTs was increased to 26.4 from 21.0. The smoke and CO release were significantly reduced by 48% and 88% respectively, and the severe melt dripping of PA6 in burning was eliminated. It is proved that PhA-MEL-MWCNTs can absorb ultraviolet (UV) radiation, and hence significantly reduces the mechanical property loss of the PA6 composite after UV aging. The tensile strength of the aged PA6/7 wt%PhA-MEL-MWCNTs composite sample only decreased by 18.1%, which was significantly lower than the loss rate of the control aged PA6 sample (62.5%). This protocol provides a new opportunity for fabricating long-life flame retardant polyamide composites.

RTN4/NoGo-receptor binding to BAI adhesion-GPCRs regulates neuronal development.

RTN4-binding proteins were widely studied as "NoGo" receptors, but their physiological interactors and roles remain elusive. Similarly, BAI adhesion-GPCRs were associated with numerous activities, but their ligands and functions remain unclear. Using unbiased approaches, we observed an unexpected convergence: RTN4 receptors are high-affinity ligands for BAI adhesion-GPCRs. A single thrombospondin type 1-repeat (TSR) domain of BAIs binds to the leucine-rich repeat domain of all three RTN4-receptor isoforms with nanomolar affinity. In the 1.65 Å crystal structure of the BAI1/RTN4-receptor complex, C-mannosylation of tryptophan and O-fucosylation of threonine in the BAI TSR-domains creates a RTN4-receptor/BAI interface shaped by unusual glycoconjugates that enables high-affinity interactions. In human neurons, RTN4 receptors regulate dendritic arborization, axonal elongation, and synapse formation by differential binding to glial versus neuronal BAIs, thereby controlling neural network activity. Thus, BAI binding to RTN4/NoGo receptors represents a receptor-ligand axis that, enabled by rare post-translational modifications, controls development of synaptic circuits.

Sequence logic at enhancers governs a dual mechanism of endodermal organ fate induction by FOXA pioneer factors.

FOXA pioneer transcription factors (TFs) associate with primed enhancers in endodermal organ precursors. Using a human stem cell model of pancreas differentiation, we here discover that only a subset of pancreatic enhancers is FOXA-primed, whereas the majority is unprimed and engages FOXA upon lineage induction. Primed enhancers are enriched for signal-dependent TF motifs and harbor abundant and strong FOXA motifs. Unprimed enhancers harbor fewer, more degenerate FOXA motifs, and FOXA recruitment to unprimed but not primed enhancers requires pancreatic TFs. Strengthening FOXA motifs at an unprimed enhancer near NKX6.1 renders FOXA recruitment pancreatic TF-independent, induces priming, and broadens the NKX6.1 expression domain. We make analogous observations about FOXA binding during hepatic and lung development. Our findings suggest a dual role for FOXA in endodermal organ development: first, FOXA facilitates signal-dependent lineage initiation via enhancer priming, and second, FOXA enforces organ cell type-specific gene expression via indirect recruitment by lineage-specific TFs.

The distribution and behavioral characteristics of plateau pikas (Ochotonacurzoniae).

Plateau pikas (Ochotonacurzoniae) are regarded as one of the main causes of the degradation of alpine meadows in the Qinghai-Tibet Plateau (QTP). The population density of plateau pikas is directly related to the degree of grassland damage. In this study, field observation was conducted for one week in the southeastern QTP in August 2019. A random encounter model (REM) was used to estimate the population density of plateau pikas from photographs and videos, and the frequencies of different behaviors were calculated. In addition, the effects of water-source distance and terrain on the distribution of plateau pikas and the frequencies of different pika behaviors under different population densities were explored. The observations and knowledge derived from this study provide a reference for the population control of plateau pikas.

A density estimation model of plateau pika (Ochotona curzoniae) supporting camera-monitoring programs.

As an important species in the Qinghai-Tibet Plateau, the roles played by plateau pikas in grassland degradation and protection are controversial. The behavior characteristics and population density of this species are important in answering this question, but these traits have not been fully elucidated to date. Camera-capture methods have been used widely in recent years to characterize or calculate population density with the advantage of simple operation and nonintrusive investigation. However, establishing the relationship between actual population density and monitoring data with the condition that individual identification is not possible is a major challenge for this method. In this study, a model composed of a behavioral module and a burrow system module is proposed and applied to simulate the moving path of each individual pika. Based on Monte Carlo method, the model is used to develop the relationship between population density and recorded capture number, which is compared with the results derived from the random encounter model (REM) based on field observations. The simulated results mixed with the calculated density based on observation data could reach R 2 = 0.98 using linear fitting, with proper parameter settings. A novel index named activity intensity of pikas per population density is also proposed, providing information on both the ecological physical characteristics and monitoring space. The influence of different parameters on this index, mainly the pika number per burrow system, pika activity time outside the burrow, and activity intensity, is discussed. The proposed methodology can be applied to different scenarios in further studies when behavioral characteristics of pikas change for such reasons as climate change and vegetation degradation.

Solution-Processed Transparent Conducting Electrodes for Flexible Organic Solar Cells with 16.61% Efficiency.

Nonfullerene organic solar cells (OSCs) have achieved breakthrough with pushing the efficiency exceeding 17%. While this shed light on OSC commercialization, high-performance flexible OSCs should be pursued through solution manufacturing. Herein, we report a solution-processed flexible OSC based on a transparent conducting PEDOT:PSS anode doped with trifluoromethanesulfonic acid (CF3SO3H). Through a low-concentration and low-temperature CF3SO3H doping, the conducting polymer anodes exhibited a main sheet resistance of 35 Ω sq-1 (minimum value: 32 Ω sq-1), a raised work function (≈ 5.0 eV), a superior wettability, and a high electrical stability. The high work function minimized the energy level mismatch among the anodes, hole-transporting layers and electron-donors of the active layers, thereby leading to an enhanced carrier extraction. The solution-processed flexible OSCs yielded a record-high efficiency of 16.41% (maximum value: 16.61%). Besides, the flexible OSCs afforded the 1000 cyclic bending tests at the radius of 1.5 mm and the long-time thermal treatments at 85 °C, demonstrating a high flexibility and a good thermal stability.

Cross-platform validation of neurotransmitter release impairments in schizophrenia patient-derived NRXN1-mutant neurons.

Heterozygous NRXN1 deletions constitute the most prevalent currently known single-gene mutation associated with schizophrenia, and additionally predispose to multiple other neurodevelopmental disorders. Engineered heterozygous NRXN1 deletions impaired neurotransmitter release in human neurons, suggesting a synaptic pathophysiological mechanism. Utilizing this observation for drug discovery, however, requires confidence in its robustness and validity. Here, we describe a multicenter effort to test the generality of this pivotal observation, using independent analyses at two laboratories of patient-derived and newly engineered human neurons with heterozygous NRXN1 deletions. Using neurons transdifferentiated from induced pluripotent stem cells that were derived from schizophrenia patients carrying heterozygous NRXN1 deletions, we observed the same synaptic impairment as in engineered NRXN1-deficient neurons. This impairment manifested as a large decrease in spontaneous synaptic events, in evoked synaptic responses, and in synaptic paired-pulse depression. Nrxn1-deficient mouse neurons generated from embryonic stem cells by the same method as human neurons did not exhibit impaired neurotransmitter release, suggesting a human-specific phenotype. Human NRXN1 deletions produced a reproducible increase in the levels of CASK, an intracellular NRXN1-binding protein, and were associated with characteristic gene-expression changes. Thus, heterozygous NRXN1 deletions robustly impair synaptic function in human neurons regardless of genetic background, enabling future drug discovery efforts.

Subwavelength structure enabled ultra-long waveguide grating antenna.

Because of the high index contrast, current silicon photonics based optical phased arrays cannot achieve small beam divergence and large field-of-view simultaneously without increasing fabrication complexity. To resolve the dilemma, we propose an ultra-long waveguide grating antenna formed by placing subwavelength segments within the evanescent field of a conventional strip waveguide. Bound state in the continuum effect is leveraged to suppress the sidewall emission. As a proof of concept, we theoretically demonstrated a millimeter-long through-etched waveguide grating antenna with a divergence angle of 0.081° and a feature size compatible with current silicon photonics foundries.