The Physics of Antimicrobial Activity of Ionic Liquids.

The bactericidal potency of ionic liquids (ILs) is well-established, yet their precise mechanism of action remains elusive. Here, we show evidence that the bactericidal action of ILs primarily involves the permeabilization of the bacterial cell membrane. Our findings reveal that ILs exert their effects by directly interacting with the lipid bilayer and enhancing the membrane dynamics. Lateral lipid diffusion is accelerated, which in turn augments membrane permeability, ultimately leading to bacterial death. Furthermore, our results establish a significant connection: an increase in the alkyl chain length of ILs correlates with a notable enhancement in both lipid lateral diffusion and antimicrobial potency. This underscores a compelling correlation between membrane dynamics and antimicrobial effectiveness, providing valuable insights for the rational design and optimization of IL-based antimicrobial agents in healthcare applications.

Correction: Quantifying the three-dimensional facial morphology of the laboratory rat with a focus on the vibrissae.

[This corrects the article DOI: 10.1371/journal.pone.0194981.].

Spatial arrangement of the whiskers of harbor seals ( Phoca vitulina ) compared to whisker arrangements of mice ( Mus musculus ) and rats ( Rattus norvegicus ).

Most mammals have specialized facial hairs known as vibrissae (whiskers), sensitive tactile structures that subserve both touch and flow sensing. Different animals have different numbers and geometric arrangements of whiskers, and it seems nearly self-evident that these differences would correlate with functional and behavioral use. To date, however, cross-species comparisons of three-dimensional (3D) whisker array geometry have been limited because standard morphometric techniques cannot be applied. Our laboratory recently developed a novel approach to enable quantitative, cross-species vibrissal array comparisons. Here we quantify the 3D morphology of the vibrissal array of the harbor seal ( Phoca vitulina ), construct a CAD model of the array, and compare array morphologies of harbor seals, mice ( Mus musculus ) and rats ( Rattus norvegicus ). In all three species whisker arclength decreases from caudal to rostral, whisker curvature increases from caudal to rostral, and whiskers emerge from the face in smooth orientation gradients. Two aspects of whisker orientation are strikingly consistent across species: the elevation angle is constant within a row, and the twist of the whisker about its own axis varies smoothly in a diagonal gradient across the array. We suggest that invariant whisker elevation within a row may aid localization behaviors, while variable twist-orientation may help the animal sense stimulus direction. We anticipate this work will serve as a starting point for quantitative comparisons of vibrissal arrays across species, help clarify the mechanical basis by which seal vibrissae enable efficient wake detection and following, and enable the creation of whole-body biomechanical models for neuroscience and robotics.

Leveraging plasmonic hot electrons to quench defect emission in metal-semiconductor nanostructured hybrids.

Modeling light-matter interactions in hybrid plasmonic materials is vital to their widening relevance from optoelectronics to photocatalysis. Here, we explore photoluminescence (PL) from ZnO nanorods (ZNRs) embedded with gold nanoparticles (Au NPs). A progressive increase in Au NP concentration introduces significant structural disorder and defects in ZNRs, which paradoxically quenches defect related visible PL while intensifying the near band edge (NBE) emission. Under UV excitation, the simulated semi-classical model realizes PL from ZnO with sub-bandgap defect states, eliciting visible emissions that are absorbed by Au NPs to generate a non-equilibrium hot carrier distribution. The photo-stimulated hot carriers, transferred to ZnO, substantially modify its steady-state luminescence, reducing NBE emission lifetime and altering the abundance of ionized defect states, finally reducing visible emission. The simulations show that the change in the interfacial band bending at the Au-ZnO interface under optical illumination facilitates charge transfer between the components. This work provides a general foundation to observe and model the hot carrier dynamics and strong light-matter interactions in hybrid plasmonic systems.

Comparative morphology of the whiskers and faces of mice (Mus musculus) and rats (Rattus norvegicus).

Understanding neural function requires quantification of the sensory signals that an animal's brain evolved to interpret. These signals in turn depend on the morphology and mechanics of the animal's sensory structures. Although the house mouse (Mus musculus) is one of the most common model species used in neuroscience, the spatial arrangement of its facial sensors has not yet been quantified. To address this gap, the present study quantifies the facial morphology of the mouse, with a particular focus on the geometry of its vibrissae (whiskers). The study develops equations that establish relationships between the three-dimensional (3D) locations of whisker basepoints, whisker geometry (arclength, curvature) and the 3D angles at which the whiskers emerge from the face. Additionally, the positions of facial sensory organs are quantified relative to bregma-lambda. Comparisons with the Norway rat (Rattus norvegicus) indicate that when normalized for head size, the whiskers of these two species have similar spacing density. The rostral-caudal distances between facial landmarks of the rat are a factor of ∼2.0 greater than the mouse, while the scale of bilateral distances is larger and more variable. We interpret these data to suggest that the larger size of rats compared with mice is a derived (apomorphic) trait. As rodents are increasingly important models in behavioral neuroscience, the morphological model developed here will help researchers generate naturalistic, multimodal patterns of stimulation for neurophysiological experiments and allow the generation of synthetic datasets and simulations to close the loop between brain, body and environment.

Frequency dependent impedance response analysis of nanocrystalline ZnO chemiresistors.

ZnO is a widely studied gas sensor material and is used in many commercial sensor devices. However, selectivity towards any particular gas remains an issue due to lack of complete knowledge of the gas sensing mechanism of oxide surfaces. In this paper, we have studied the frequency dependent gas sensor response of ZnO nanoparticles of a diameter of nearly 30 nm. A small rise of synthesis temperature from 85 °C to 95 °C in the solvothermal process, shows coarsening by joining and thereby distinct loss of grain boundaries as seen from transmission electron micrographs. This leads to a substantial reduction in impedance, Z (GΩ to MΩ), and rises in resonance frequencyfres(from 1 to 10 Hz) at room temperature. From temperature dependent studies it is observed that the grain boundaries show a Correlated Barrier Hopping mechanism of transport and the hopping range in the grain boundary region is typically 1 nm with a hopping energy of 153 meV. On the other hand, within the grain, it shows a change of transport type from low temperature tunneling to beyond 300 °C as polaron hopping. The presence of disorder (defects) as the hopping sites. The temperature dependence offresagrees with different predicted oxygen chemisorbed species between 200 °C to 400 °C. As opposed to the traditional DC response, the AC response in the imaginary part of (Z″) shows gas specific resonance frequencies for each gas, such as NO2, ethanol, and H2. Among the two reducing gases, ethanol and hydrogen; the former shows good dependence on concentration in Z″ whereas the latter shows a good response infresas well as capacitance. Thus, the results of frequency dependent response allow us to investigate greater details of the gas sensing mechanism in ZnO, which may be exploited for selective gas sensing.

On the intrinsic curvature of animal whiskers.

Facial vibrissae (whiskers) are thin, tapered, flexible, hair-like structures that are an important source of tactile sensory information for many species of mammals. In contrast to insect antennae, whiskers have no sensors along their lengths. Instead, when a whisker touches an object, the resulting deformation is transmitted to mechanoreceptors in a follicle at the whisker base. Previous work has shown that the mechanical signals transmitted along the whisker will depend strongly on the whisker's geometric parameters, specifically on its taper (how diameter varies with arc length) and on the way in which the whisker curves, often called "intrinsic curvature." Although previous studies have largely agreed on how to define taper, multiple methods have been used to quantify intrinsic curvature. The present work compares and contrasts different mathematical approaches towards quantifying this important parameter. We begin by reviewing and clarifying the definition of "intrinsic curvature," and then show results of fitting whisker shapes with several different functions, including polynomial, fractional exponent, elliptical, and Cesàro. Comparisons are performed across ten species of whiskered animals, ranging from rodents to pinnipeds. We conclude with a discussion of the advantages and disadvantages of using the various models for different modeling situations. The fractional exponent model offers an approach towards developing a species-specific parameter to characterize whisker shapes within a species. Constructing models of how the whisker curves is important for the creation of mechanical models of tactile sensory acquisition behaviors, for studies of comparative evolution, morphology, and anatomy, and for designing artificial systems that can begin to emulate the whisker-based tactile sensing of animals.

Demonstration of three-dimensional contact point determination and contour reconstruction during active whisking behavior of an awake rat.

The rodent vibrissal (whisker) system has been studied for decades as a model of active touch sensing. There are no sensors along the length of a whisker; all sensing occurs at the whisker base. Therefore, a large open question in many neuroscience studies is how an animal could estimate the three-dimensional (3D) location at which a whisker makes contact with an object. In the present work we simulated the shape of a real rat whisker to demonstrate the existence of several unique mappings from triplets of mechanical signals at the whisker base to the three-dimensional whisker-object contact point. We then used high speed video to record whisker deflections as an awake rat whisked against a peg, and used the mechanics resulting from those deflections to extract the contact points along the peg surface. These results demonstrate that measurement of specific mechanical triplets at the base of a biological whisker can enable 3D contact point determination during natural whisking behavior. The approach is viable even though the biological whisker has non-ideal, non-planar curvature, and even given the rat's real-world choices of whisking parameters. Visual intuition for the quality of the approach is provided in a video that shows the contour of the peg gradually emerging during active whisking behavior.

Symmetric domain segmentation in WS2flakes: correlating spatially resolved photoluminescence, conductance with valley polarization.

The incidence of intra-flake heterogeneity of spectroscopic and electrical properties in chemical vapour deposited (CVD) WS2flakes is explored in a multi-physics investigation via spatially resolved spectroscopic maps correlated with electrical, electronic and mechanical properties. The investigation demonstrates that the three-fold symmetric segregation of spectroscopic response, in topographically uniform WS2flakes are accompanied by commensurate segmentation of electronic properties e.g. local carrier density and the differences in the mechanics of tip-sample interactions, evidenced via scanning probe microscopy phase maps. Overall, the differences are understood to originate from point defects, namely sulfur vacancies within the flake along with a dominant role played by the substrate. While evolution of the multi-physics maps upon sulfur annealing elucidates the role played by sulfur vacancy, substrate-induced effects are investigated by contrasting data from WS2flake on Si and Au surfaces. Local charge depletion induced by the nature of the sample-substrate junction in case of WS2on Au is seen to invert the electrical response with comprehensible effects on their spectroscopic properties. Finally, the role of these optoelectronic properties in preserving valley polarization that affects valleytronic applications in WS2flakes, is investigated via circular polarization discriminated photoluminescence experiments. The study provides a thorough understanding of spatial heterogeneity in optoelectronic properties of WS2and other transition metal chalcogenides, which are critical for device fabrication and potential applications.

Impaired trigeminal control of ingestive behavior in the Prrxl1-/- mouse is associated with a lemniscal-biased orosensory deafferentation.

Although peripheral deafferentation studies have demonstrated a critical role for trigeminal afference in modulating the orosensorimotor control of eating and drinking, the central trigeminal pathways mediating that control, as well as the timescale of control, remain to be elucidated. In rodents, three ascending somatosensory pathways process and relay orofacial mechanosensory input: the lemniscal, paralemniscal, and extralemniscal. Two of these pathways (the lemniscal and extralemniscal) exhibit highly structured topographic representations of the orofacial sensory surface, as exemplified by the one-to-one somatotopic mapping between vibrissae on the animals' face and barrelettes in brainstem, barreloids in thalamus, and barrels in cortex. Here we use the Prrxl1 knockout mouse model (also known as the DRG11 knockout) to investigate ingestive behavior deficits that may be associated with disruption of the lemniscal pathway. The Prrxl1 deletion disrupts somatotopic patterning and axonal projections throughout the lemniscal pathway but spares patterning in the extralemniscal nucleus. Our data reveal an imprecise and inefficient ingestive phenotype. Drinking behavior exhibits deficits on the timescales of milliseconds to seconds. Eating behavior shows deficits over an even broader range of timescales. An analysis of food acquisition and consummatory rate showed deficits on the timescale of seconds, and analysis of body weight suggested deficits on the scale of long term appetitive control. We suggest that ordered assembly of trigeminal sensory information along the lemniscal pathway is critical for the rapid and precise modulation of motor circuits driving eating and drinking action sequences.

A novel stimulator to investigate the tuning of multi-whisker responsive neurons for speed and the direction of global motion: Contact-sensitive moving stimulator for multi-whisker stimulation.

BACKGROUND: The rodent vibrissal (whisker) systcnsorimotor integration and active tactile sensing. Experiments on the vibrissal system often require highly repeatable stimulation of multiple whiskers and the ability to vary stimulation parameters across a wide range. The stimulator must also be easy to position and adjust. Developing a multi-whisker stimulation system that meets these criteria remains challenging. NEW METHOD: We describe a novel multi-whisker stimulator to assess neural selectivity for the direction of global motion. The device can generate repeatable, linear sweeps of tactile stimulation across the whisker array in any direction and with a range of speeds. A fiber optic beam break detects the interval of whisker contact as the stimulator passes through the array. RESULTS: We demonstrate the device's function and utility by recording from a small number of multi-whisker-responsive neurons in the trigeminal brainstem. Neurons had higher firing rates in response to faster stimulation speeds; some also exhibited strong direction-of-motion tuning. COMPARISON WITH EXISTING METHODS: The stimulator complements more standard piezo-electric stimulators, which offer precise control but typically stimulate only single whiskers, require whisker trimming, and travel through small angles. It also complements non-contact methods of stimulation such as air-puffs and electromagnetic-induced stimulation. Tradeoffs include stimulation speed and frequency, and the inability to stimulate whiskers individually. CONCLUSIONS: The stimulator could be used - in either anesthetized or awake, head-fixed preparations - as an approach to studying global motion selectivity of multi-whisker sensitive neurons at multiple levels of the vibrissal-trigeminal system.

Continuous, multidimensional coding of 3D complex tactile stimuli by primary sensory neurons of the vibrissal system.

Across all sensory modalities, first-stage sensory neurons are an information bottleneck: they must convey all information available for an animal to perceive and act in its environment. Our understanding of coding properties of primary sensory neurons in the auditory and visual systems has been aided by the use of increasingly complex, naturalistic stimulus sets. By comparison, encoding properties of primary somatosensory afferents are poorly understood. Here, we use the rodent whisker system to examine how tactile information is represented in primary sensory neurons of the trigeminal ganglion (Vg). Vg neurons have long been thought to segregate into functional classes associated with separate streams of information processing. However, this view is based on Vg responses to restricted stimulus sets which potentially underreport the coding capabilities of these neurons. In contrast, the current study records Vg responses to complex three-dimensional (3D) stimulation while quantifying the complete 3D whisker shape and mechanics, thereby beginning to reveal their full representational capabilities. The results show that individual Vg neurons simultaneously represent multiple mechanical features of a stimulus, do not preferentially encode principal components of the stimuli, and represent continuous and tiled variations of all available mechanical information. These results directly contrast with proposed codes in which subpopulations of Vg neurons encode select stimulus features. Instead, individual Vg neurons likely overcome the information bottleneck by encoding large regions of a complex sensory space. This proposed tiled and multidimensional representation at the Vg directly constrains the computations performed by more central neurons of the vibrissotrigeminal pathway.

A dynamical model for generating synthetic data to quantify active tactile sensing behavior in the rat.

As it becomes possible to simulate increasingly complex neural networks, it becomes correspondingly important to model the sensory information that animals actively acquire: the biomechanics of sensory acquisition directly determines the sensory input and therefore neural processing. Here, we exploit the tractable mechanics of the well-studied rodent vibrissal ("whisker") system to present a model that can simulate the signals acquired by a full sensor array actively sampling the environment. Rodents actively "whisk" ∼60 vibrissae (whiskers) to obtain tactile information, and this system is therefore ideal to study closed-loop sensorimotor processing. The simulation framework presented here, WHISKiT Physics, incorporates realistic morphology of the rat whisker array to predict the time-varying mechanical signals generated at each whisker base during sensory acquisition. Single-whisker dynamics were optimized based on experimental data and then validated against free tip oscillations and dynamic responses to collisions. The model is then extrapolated to include all whiskers in the array, incorporating each whisker's individual geometry. Simulation examples in laboratory and natural environments demonstrate that WHISKiT Physics can predict input signals during various behaviors, currently impossible in the biological animal. In one exemplary use of the model, the results suggest that active whisking increases in-plane whisker bending compared to passive stimulation and that principal component analysis can reveal the relative contributions of whisker identity and mechanics at each whisker base to the vibrissotactile response. These results highlight how interactions between array morphology and individual whisker geometry and dynamics shape the signals that the brain must process.

Constraints on the deformation of the vibrissa within the follicle.

Nearly all mammals have a vibrissal system specialized for tactile sensation, composed of whiskers growing from sensor-rich follicles in the skin. When a whisker deflects against an object, it deforms within the follicle and exerts forces on the mechanoreceptors inside. In addition, during active whisking behavior, muscle contractions around the follicle and increases in blood pressure in the ring sinus will affect the whisker deformation profile. To date, however, it is not yet possible to experimentally measure how the whisker deforms in an intact follicle or its effects on different groups of mechanoreceptors. The present study develops a novel model to predict vibrissal deformation within the follicle sinus complex. The model is based on experimental results from a previous ex vivo study on whisker deformation within the follicle, and on a new histological analysis of follicle tissue. It is then used to simulate whisker deformation within the follicle during passive touch and active whisking. Results suggest that the most likely whisker deformation profile is "S-shaped," crossing the midline of the follicle right below the ring sinus. Simulations of active whisking indicate that an increase in overall muscle stiffness, an increase in the ratio between deep and superficial intrinsic muscle stiffness, and an increase in sinus blood pressure will all enhance tactile sensitivity. Finally, we discuss how the deformation profiles might map to the responses of primary afferents of each mechanoreceptor type. The mechanical model presented in this study is an important first step in simulating mechanical interactions within whisker follicles.

Refractive index-assisted UV/Vis spectrophotometry to overcome spectral interference by impurities.

A major challenge hindering the application of techniques like UV/Vis spectrophotometry in determining concentration is spectral interference from contaminants. Since molar absorptivities vary significantly, even minuscule amounts of specific contaminants may cause relatively large errors in UV/Vis spectrophotometry based quantification. Current methods to deal with this are slow, cost-intensive, or ineffective for unknown interferents. We propose constrained refractometry as an expedient technique to aid UV/Vis spectrophotometry, avoiding large errors due to spectral interference. Based on a modified Lorentz Lorenz equation, the technique helps not only in detecting and reducing error from unknown contaminants but also in identifying the significant impurity. Experimental results show a significant reduction of error in concentration determination even for multiple unknown interfering contaminants.

Controlling the macroscopic electrical properties of reduced graphene oxide by nanoscale writing of electronic channels.

The allure of all-carbon electronics stems from the spread of its physical properties across all its allotropes. The scheme also harbours unique challenges, such as tunability of band gap, variability of doping and defect control. Here, we explore the technique of scanning probe tip-induced nanoscale reduction of graphene oxide (GO), which nucleates conducting, [Formula: see text] rich graphitic regions on the insulating GO background. The flexibility of direct writing is supplemented with control over the degree of reduction and tunability of band gap through macroscopic control parameters. The fabricated reduced GO channels and ensuing devices are investigated via spectroscopy and temperature and bias-dependent electrical transport and correlated with spatially resolved electronic properties, using surface potentiometry. The presence of carrier localization effects, induced by the phase-separated [Formula: see text] domains, and large local electric field fluctuations are reflected in the non-linear transport across the channels. Together, the results indicate a complex transport phenomenon, which may be variously dominated by tunnelling or variable range hopping or activated depending on the electronic state of the material.

Tapered Polymer Whiskers to Enable Three-Dimensional Tactile Feature Extraction.

Many mammals use their vibrissae (whiskers) to tactually explore their surrounding environment. Vibrissae are thin tapered structures that transmit mechanical signals to a wealth of mechanical receptors (sensors) located in a follicle at each vibrissal base. A recent study has shown that-provided that the whisker is tapered-three mechanical signals at the base are sufficient to determine the three-dimensional location at which a whisker made contact with an object. However, creating biomimetic tapered whiskers has proved challenging from both materials and manufacturing standpoints. This study develops and characterizes an artificial whisker for use as part of a sensory input device that is a biomimic of the biological rat whisker neurosensory system. A novel manufacturing process termed surface conforming fiber drawing (SCFD) is developed to produce artificial whiskers that meet the requirements to be a successful mechanical and geometric mimic of the biological rat vibrissae. Testing the sensory capabilities of the artificial whisker shows improved performance over previous nontapered filaments. SCFD-manufactured tapered whiskers demonstrate the ability to predict contact point locations with a median distance error of 0.47 cm.

Thickness induced metal to insulator charge transport and unusual hydrogen response in granular palladium nanofilms.

This work reports a systematic study of the evolution of charge transport properties in granular ultra-thin films of palladium of thicknesses varying between 6 nm and 2 nm. While the films with thickness >4 nm exhibit metallic behaviour, that at 3 nm thickness undergoes a metal-insulator transition at 19.5 K. In contrast, the 2 nm thick film remained insulating at all temperatures, with transport following Mott's variable range hopping. At room temperature, while the thicker films exhibit resistance decrease upon H2 exposure, the insulating film showed an anomalous initial resistance increase before switching to a subsequent decrease. The nanostructure dependent transport and the ensuing H2 response is modeled on a percolation model, which also explores the relevance of film thickness as a macroscopic control parameter to engineer the desired system response in granular metal films.

Complement C6 deficiency exacerbates pathophysiology after spinal cord injury.

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

Lack of Association between Poor Glycemic Control in T2DM and Subclinical Hypothyroidism.

BACKGROUND: Hypothyroidism is a highly prevalent and multifactorial disorder and has been implicated in the causation of dyslipidemia, dermatological diseases, atherosclerosis, and myocardial dysfunction, as well as endothelial dysfunction. The relationship between subclinical hypothyroidism and type 2 diabetes mellitus is not well established. In the present study, we attempt to find out the prevalence of subclinical hypothyroidism in type 2 diabetes mellitus and its association with glycemic control. MATERIALS AND METHODS: This was an observational study in which 205 consecutive patients of T2DM visiting the outpatient department of medicine were recruited. Serum TSH, free thyroxine, free triiodothyronine, and lipid profile, as well as HbA1c assays, were done in the study participants, and they were categorized into three groups by HbA1c: <7%, 7-9%, and >9%. RESULTS: There is a high prevalence of subclinical hypothyroidism in type 2 DM patients. Mean HbA1c in diabetics without SCH was 7.89%, whereas it was 8.33% in diabetics with SCH. This difference was statistically not significant. TSH was not found to be significantly associated with HbA1c. CONCLUSION: High prevalence of SCH in T2DM patients suggests that there is a need for regular follow-up to check the progression of SCH to overt hypothyroidism. High serum TSH is not a predictor of poor glycemic control.