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Continuous and in situ detection of biomarkers in biofluids (for example, sweat) can provide critical health data but is limited by biofluid accessibility. Here we report a sensor design that enables in situ detection of solid-state biomarkers ubiquitously present on human skin. We deploy an ionic-electronic bilayer hydrogel to facilitate the sequential dissolution, diffusion and electrochemical reaction of solid-state analytes. We demonstrate continuous monitoring of water-soluble analytes (for example, solid lactate) and water-insoluble analytes (for example, solid cholesterol) with ultralow detection limits of 0.51 and 0.26 nmol cm-2, respectively. Additionally, the bilayer hydrogel electrochemical interface reduces motion artefacts by a factor of three compared with conventional liquid-sensing electrochemical interfaces. In a clinical study, solid-state epidermal biomarkers measured by our stretchable wearable sensors showed a high correlation with biomarkers in human blood and dynamically correlated with physiological activities. These results present routes to universal platforms for biomarker monitoring without the need for biofluid acquisition.
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Biomarcadores , Epiderme , Hidrogéis , Dispositivos Eletrônicos Vestíveis , Biomarcadores/sangue , Biomarcadores/análise , Humanos , Hidrogéis/química , Epiderme/metabolismo , Eletrônica , Técnicas Eletroquímicas/métodos , Técnicas Biossensoriais/instrumentação , Técnicas Biossensoriais/métodosRESUMO
OBJECTIVE: This research investigates how particle parameters, such as zeta potential, size, functional group, material composition, and hydrophobicity affect their affinity and deposition of particles onto hair. METHODS: Streaming potential was used as the technique for analysis. The streaming potential data obtained was then converted to surface coverage data. Scanning electron microscopy (SEM) was also done to visualize particle localization on the hair surface. RESULTS: This study found stronger particle affinity on healthy than on damaged (oxidatively bleached) hair, due to diminished interaction sites from the removal of the hair shaft's external lipid layer. SEM imaging supported these findings and offered insights into particle localization. Hydrophilic silica particles accumulated along the exposed hydrophilic cuticle edges of healthy hair, due to hydrogen bonding with the exposed endocuticle. This localization is hypothesized to be due to the limited hydrophilic binding sites on the hydrophobic healthy hair cuticle surface. In damaged hair, an abundance of hydrophilic sites across the cuticle surface results in more dispersed binding. Hydrogen bonding and electrostatic attraction were shown to be the predominant forces influencing deposition, with hydrophobic interactions playing a less influential role. The affinity studies also proved that electrostatic attractions work over a longer range and are more effective at lower particle conditions compared with hydrogen bonding which only start to play a bigger role at higher particle concentrations. Steric hindrance of bulky side groups acted as a significant repulsive force. Results also revealed that larger particles deposit poorly on both healthy and damaged hair compared with smaller ones. Compared with neutrally charged silica nanoparticles (SN-2), positively charged PMMA particles (PN+16) have a stronger affinity to healthy hair, with highly charged particles (PN+49) depositing most rapidly. CONCLUSION: This study provides a fundamental understanding of how particle-surface parameters influence their affinity to hair and how damaging hair affects deposition.
OBJECTIF: Cette étude examine comment les paramètres des particules, tels que le potentiel zêta, la taille, le groupe fonctionnel, la composition du matériau et l'hydrophobie, affectent l'affinité et le dépôt des particules sur les cheveux. MÉTHODES: Le potentiel d'écoulement a été utilisé comme technique d'analyse. Les données de potentiel d'écoulement obtenues ont ensuite été converties en données de couverture de surface. Une microscopie électronique à balayage (MEB) a également été réalisée pour visualiser la localisation des particules à la surface des cheveux. RÉSULTATS: Cette étude a mis en évidence une affinité plus forte des particules sur des cheveux sains que sur des cheveux abîmés (décolorés par oxydation), en raison de la diminution des sites d'interaction due à l'élimination de la couche lipidique externe de la tige du cheveu. L'imagerie MEB a confirmé ces résultats et a permis d'obtenir des informations sur la localisation des particules. Des particules de silice hydrophile se sont accumulées en bordure des cuticules hydrophiles exposées des cheveux sains, en raison de la liaison de l'hydrogène avec l'endocuticule exposée. Il est supposé que cette localisation est due au nombre réduit de sites de liaison hydrophiles à la surface hydrophobe saine de la cuticule capillaire. Sur des cheveux abîmés, l'abondance de sites hydrophiles sur la surface des cuticules entraîne une liaison plus dispersée. La liaison de l'hydrogène et l'attraction électrostatique se sont avérées être les forces prédominantes qui influencent le dépôt, les interactions hydrophobes jouant un rôle moins influent. Les études d'affinité ont également démontré que les attractions électrostatiques fonctionnent sur une plus longue plage et sont plus efficaces dans des conditions de concentration de particules inférieures par rapport à la liaison de l'hydrogène qui ne commence à jouer un rôle plus important qu'à des concentrations de particules plus élevées. L'entrave stérique des groupes latéraux volumineux a agi comme une force répulsive significative. Les résultats ont également révélé que les particules plus grosses se déposent faiblement sur des cheveux sains et des cheveux abîmés par rapport aux particules plus petites. Par rapport aux nanoparticules de silice à charge neutre (SN2), les particules de PMMA à charge positive (PN+16) ont une affinité plus forte avec les cheveux sains, les particules fortement chargées (PN+49) se déposant le plus rapidement. CONCLUSION: Cette étude apporte une compréhension fondamentale de la façon dont les paramètres de la surface et des particules influencent leur affinité avec les cheveux et dans quelle mesure les cheveux abîmés affectent les dépôts.
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The origin of the condensation of water begins at the nanoscale, a length-scale that is challenging to probe for liquids. In this work we directly image heterogeneous nucleation of water nanodroplets by in situ transmission electron microscopy. Using gold nanoparticles bound to a flat surface as heterogeneous nucleation sites, we observe nucleation and growth of water nanodroplets. The growth of nanodroplet radii follows the power law: R(t)~(t-t 0) ß , where ß~0.2-0.3.
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Previous studies have reported persistent rotational behavior between adherent cell-cell pairs cultured on micropatterned substrates, and this rotation is often accompanied by a sigmoidal deflection of the cell-cell interface. Interestingly, the cell-cell rotation runs in the opposite reference frame from what could be expected of single cell locomotion. Specifically, the rotation of the cell pair consists of each individual cell protruding from the inwardly regressive arm of the cell-cell interface, and retracting from the other outwardly protrusive arm. To this author's knowledge, the cause of this elusive behavior has not yet been clarified. Here, we propose a physical model based on particle dynamics, accounting for actomyosin forcing, viscous dissipation, and cortical tension. The results show that a correlation in actomyosin force vectors leads to both persistent rotational behavior and interfacial deflection in a simulated cell cluster. Significantly, the model, without any artificial cues, spontaneously and consistently reproduces the same rotational reference frame as experimentally observed. Further analyses show that the interfacial deflection depends predominantly on cortical tension, whereas the cluster rotation depends predominantly on actomyosin forcing. Together, these results corroborate the hypothesis that both rotational and morphological phenomena are, in fact, physically coupled by an intracellular torque of a common origin.
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Fenômenos Biofísicos , Modelos Biológicos , Rotação , Actomiosina/metabolismo , Fenômenos Biomecânicos , Adesão CelularRESUMO
We simulated a pulsed direct current (DC) planar magnetron discharge using fluid model, solving for species continuity, momentum, and energy transfer equations, coupled with Poisson equation and Lorentz force for electromagnetism. Based on a validated DC magnetron model, an asymmetric bipolar potential waveform is applied at the cathode at 50-200 kHz frequency and 50-80% duty cycle. Our results show that pulsing leads to increased electron density and electron temperature, but decreased deposition rate over non-pulsed DC magnetron, trends consistent with those reported by experimental studies. Increasing pulse frequency increases electron temperature but reduces the electron density and deposition rate, whereas increasing duty cycle decreases both electron temperature and density but increases deposition rate. We found that the time-averaged electron density scales inversely with the frequency, and time-averaged discharge voltage magnitude scales with the duty cycle. Our results are readily applicable to modulated pulse power magnetron sputtering and can be extended to alternating current (AC) reactive sputtering processes.
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Platinum-based metal catalysts are considered excellent converters in various catalytic reactions, particularly in fuel cell applications. The atomic structure at the nanocrystal surface and the metal interface both influence the catalytic performance, controlling the efficiency of the electrochemical reactions. Here we report the synthesis of Ag/Pt and Ag/Pd core/shell nanocrystals and insight into the formation mechanism of these bimetallic core/shell nanocrystals when undergoing oxygen plasma treatment. We carefully designed the oxidation treatment that determines the structural and compositional evolution. The accelerated oxidation-triggered diffusion of Ag toward the outer metal shell leads to the Kirkendall effect. After prolonged oxygen plasma treatment, most core/shell nanocrystals evolve into hollow spheres. At the same time, a minor fraction of the metal remains unchanged with a well-protected Ag core and a monocrystalline Pt or Pd shell. We hypothesize that the O2 plasma disturbs the Pt or Pd shell surface and introduces active O species that react with the diffused Ag from the inside out. Based on EDX elemental mapping, combined with several electron microscopic techniques, we deduced the formation mechanism of the hollow structures to be as follows: (I) the oxidation of Ag within the Pt or Pd lattice causes a disrupted crystal lattice of Pt or Pd; (II) nanochannels arise at the defect locations on the Pt or Pd shell; (III) the remaining Ag atoms pass through these nanochannels and leave a hollow crystal behind. Our findings deepen the understanding of interface dynamics of bimetallic nanostructured catalysts under an oxidative environment and unveil an alternative approach for catalyst pretreatment.
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Variational quantum algorithms offer a promising new paradigm for solving partial differential equations on near-term quantum computers. Here, we propose a variational quantum algorithm for solving a general evolution equation through implicit time-stepping of the Laplacian operator. The use of encoded source states informed by preceding solution vectors results in faster convergence compared to random re-initialization. Through statevector simulations of the heat equation, we demonstrate how the time complexity of our algorithm scales with the Ansatz volume for gradient estimation and how the time-to-solution scales with the diffusion parameter. Our proposed algorithm extends economically to higher-order time-stepping schemes, such as the Crank-Nicolson method. We present a semi-implicit scheme for solving systems of evolution equations with non-linear terms, such as the reaction-diffusion and the incompressible Navier-Stokes equations, and demonstrate its validity by proof-of-concept results.
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Materials (e.g., brick or wood) are generally perceived as unintelligent. Even the highly researched "smart" materials are only capable of extremely primitive analytical functions (e.g., simple logical operations). Here, a material is shown to have the ability to perform (i.e., without a computer), an advanced mathematical operation in calculus: the temporal derivative. It consists of a stimuli-responsive material coated asymmetrically with an adaptive impermeable layer. Its ability to analyze the derivative is shown by experiments, numerical modeling, and theory (i.e., scaling between derivative and response). This class of freestanding stimuli-responsive materials is demonstrated to serve effectively as a derivative controller for controlled delivery and self-regulation. Its fast response realizes the same designed functionality and efficiency as complex industrial derivative controllers widely used in manufacturing. These results illustrate the possibility to associate specifically designed materials directly with higher concepts of mathematics for the development of "intelligent" material-based systems.
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The Covid-19 pandemic has focused attention on airborne transmission of viruses. Using realistic air flow simulation, we model droplet dispersion from coughing and study the transmission risk related to SARS-CoV-2. Although this model defines most airborne droplets as 8-16 µm in diameter, we infer that larger droplets of 32-40 µm in diameter may potentially be more infectious due to higher viral content. Use of face masks is therefore recommended for both personal and social protection. We found social distancing effective at reducing transmission potential across all droplet sizes. However, the presence of a human body 1 m away modifies the aerodynamics so that downstream droplet dispersion is enhanced, which has implications on safe distancing in queues. At 1 m distance, we found that an average of 0.55 viral copies is inhaled for a cough at median loading, scalable up to 340 copies at peak loading. Droplet evaporation results in significant reduction in droplet counts, but airborne transmission remains possible even under low humidity conditions.
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Microbiologia do Ar , COVID-19/transmissão , Tosse/virologia , SARS-CoV-2/fisiologia , Humanos , Hidrodinâmica , Máscaras , Modelos Biológicos , Tamanho da Partícula , Medição de RiscoRESUMO
The COVID-19 pandemic has led to many countries oscillating between various states of lock-down as they seek to balance keeping the economy and essential services running and minimizing the risk of further transmission. Decisions are made about which activities to keep open across a range of social settings and venues guided only by ad hoc heuristics regarding social distancing and personal hygiene. Hence, we propose the dual use of computational fluid dynamic simulations and surrogate aerosol measurements for location-specific assessment of risk of infection across different real-world settings. We propose a 3-tiered risk assessment scheme to facilitate classification of scenarios into risk levels based on simulations and experiments. Threshold values of <54 and >840 viral copies and <5% and >40% of original aerosol concentration are chosen to stratify low, medium, and high risk. This can help prioritize allowable activities and guide implementation of phased lockdowns or re-opening. Using a public bus in Singapore as a case study, we evaluate the relative risk of infection across scenarios such as different activities and passenger positions and demonstrate the effectiveness of our risk assessment methodology as a simple and easily interpretable framework. For example, this study revealed that the bus's air-conditioning greatly influences dispersion and increases the risk of certain seats and that talking can result in similar relative risk to coughing for passengers around an infected person. Both numerical and experimental approaches show similar relative risk levels with a Spearman's correlation coefficient of 0.74 despite differing observables, demonstrating applicability of this risk assessment methodology to other scenarios.
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The ongoing Covid-19 pandemic has focused our attention on airborne droplet transmission. In this study, we simulate the dispersion of cough droplets in a tropical outdoor environment, accounting for the effects of non-volatile components on droplet evaporation. The effects of relative humidity, wind speed, and social distancing on evaporative droplet transport are investigated. Transmission risks are evaluated based on SARS-CoV-2 viral deposition on a person standing 1 m or 2 m away from the cougher. Our results show that the travel distance for a 100 µm droplet can be up to 6.6 m under a wind speed of 2 m/s. This can be further increased under dry conditions. We found that the travel distance of a small droplet is relatively insensitive to relative humidity. For a millimetric droplet, the projected distance can be more than 1 m, even in still air. Significantly greater droplets and viral deposition are found on a body 1 m away from a cougher, compared to 2 m. Despite low inhalation exposure based on a single cough, infection risks may still manifest through successive coughs or higher viral loadings.
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We study heterogeneous condensation growth of water droplets on micron-sized particles resting on a level substrate. Through numerical simulations on equilibrium droplet profiles, we find multiple wetting states towards complete wetting of the particle. Specifically, a partially wetting droplet could undergo a spontaneous transition to complete wetting during condensation growth, for contact angles above a threshold minimum. In addition, we find a competitive wetting behavior between the particle and the substrate, and interestingly, a reversal of the wetting dependence on contact angles during late stages of droplet growth. Using quasi-steady assumption, we simulate a growing droplet under a constant condensation flux, and the results are in good agreement with our experimental observations. As a geometric approximation for particle clusters, we propose and validate a pancake model, and with it, show that a particle cluster has greater wetting tendency compared to a single particle. Together, our results indicate a strong interplay between contact angle, capillarity and geometry during condensation growth.
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We investigate the axisymmetric homogeneous growth of 10-100 nm water nanodroplets on a substrate surface. The main mechanism of droplet growth is attributed to the accumulation of laterally diffusing water monomers, formed by the absorption of water vapour in the environment onto the substrate. Under assumptions of quasi-steady thermodynamic equilibrium, the nanodroplet evolves according to the augmented Young-Laplace equation. Using continuum theory, we model the dynamics of nanodroplet growth including the coupled effects of disjoining pressure, contact angle and monomer diffusion. Our numerical results show that the initial droplet growth is dominated by monomer diffusion, and the steady late growth rate of droplet radius follows a power law of 1/3, which is unaffected by the substrate disjoining pressure. Instead, the disjoining pressure modifies the growth rate of the droplet height, which then follows a power law of 1/4. We demonstrate how spatial depletion of monomers could lead to a growth arrest of the nanodroplet, as observed experimentally. This work has further implications on the growth kinetics, transport and phase transition of liquids at the nanoscale.
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Modelos Químicos , Água/química , Coloides/química , Cinética , Nanotecnologia , Propriedades de SuperfícieRESUMO
Nanoscale defects on a substrate affect the sliding motion of water droplets. Using in situ transmission electron microscopy imaging, we visualized the depinning dynamics of water nanodroplets from gold nanoparticles on a flat SiNx surface. Our observations showed that nanoscale pinning effects of the gold nanoparticle oppose the lateral forces, resulting in stretching, even breakup, of the water nanodroplet. Using continuum long wave theory, we modeled the dynamics of a nanodroplet depinning from a nanoparticle of comparable length scales, and the model results are consistent with experimental findings and show formation of a capillary bridge prior to nanodroplet depinning. Our findings have important implications on surface cleaning at the nanoscale.
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Cytoplasmic streaming occurs in diverse cell types, where it generally serves a transport function. Here, we examine streaming in multicellular fungal hyphae and identify an additional function wherein regimented streaming forms distinct cytoplasmic subcompartments. In the hypha, cytoplasm flows directionally from cell to cell through septal pores. Using live-cell imaging and computer simulations, we identify a flow pattern that produces vortices (eddies) on the upstream side of the septum. Nuclei can be immobilized in these microfluidic eddies, where they form multinucleate aggregates and accumulate foci of the HDA-2 histone deacetylase-associated factor, SPA-19. Pores experiencing flow degenerate in the absence of SPA-19, suggesting that eddy-trapped nuclei function to reinforce the septum. Together, our data show that eddies comprise a subcellular niche favoring nuclear differentiation and that subcompartments can be self-organized as a consequence of regimented cytoplasmic streaming.
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Compartimento Celular , Corrente Citoplasmática , Diferenciação Celular , Núcleo Celular/metabolismo , Parede Celular/metabolismo , Genes Fúngicos , Hifas/citologia , Hifas/crescimento & desenvolvimento , Microtúbulos/metabolismo , Mutação , Neurospora/citologia , Neurospora/genética , Neurospora/fisiologia , Reologia , Estresse Mecânico , Frações Subcelulares/metabolismoRESUMO
Cell entry into a micro-channel has potential applications in cell sorting and cancer diagnostics. In this paper, we numerically model breast cancer cell entry into a constricted micro-channel. Our results indicate that the cell velocity decreases during entry and increases after entry, an observation in agreement with experiments. We found that the cell entry time depend strongly on the cortical stiffness and is minimum at some critical cortical elasticity. In addition, we found that for the same entry time, a stiff nucleus is displaced toward the cell front, whereas a viscous nucleus is displaced toward the rear. In comparison, the nucleus is less sensitive to the viscosity of the cytoplasm. These observations suggest that specific intra-cellular properties can be deduced non-invasively during cell entry, through the inspection of the nucleus using suitable illumination techniques, such as fluorescent labeling.
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Neoplasias da Mama/patologia , Modelos Teóricos , Núcleo Celular/metabolismo , Citoplasma/metabolismo , Feminino , Humanos , ViscosidadeRESUMO
Pathogenicity of Bacillus anthracis depends on the faithful inheritance of plasmid pXO1, in a process that requires the plasmid encoded tubulin-related protein Ba-TubZ. Here we show, using heterologous expression in Schizosaccharomyces pombe, that Ba-TubZ assembles into a dynamic polymer in the absence of other B. anthracis proteins and can generate force capable of deforming the fission yeast nuclear envelope. The polymer bundles contain 27 ± 15 protofilaments/µm assuming that each protofilament spans the entire length. Thinner appearing buckled and thicker appearing straight filaments of Ba-TubZ were both capable of inducing nuclear envelope deformation. Unlike the related protein Bt-TubZ from Bacillus thuringiensis, which undergoes treadmilling upon expression in fission yeast, Ba-TubZ polymers did not undergo detectable treadmilling. Instead, in fluorescence recovery after photobleaching experiments, it displayed a different turnover behavior characterized by moderate fluorescence recovery along the entire length of the polymer. Modeling Ba-TubZ bundles as Euler-Bernoulli beams that buckle under compressive loads when pushed against the nuclear envelope allowed us to estimate that Ba-TubZ generates forces in the order of 1-10 nN. We propose that polymerization based filament elongation and force generation might aid faithful segregation of the virulence plasmid.
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Bacillus anthracis/metabolismo , Proteínas de Bactérias/metabolismo , Multimerização Proteica/fisiologia , Bacillus anthracis/genética , Bacillus anthracis/patogenicidade , Bacillus thuringiensis/genética , Bacillus thuringiensis/metabolismo , Proteínas de Bactérias/genética , Membrana Nuclear/genética , Membrana Nuclear/metabolismo , Plasmídeos/genética , Plasmídeos/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismoRESUMO
In eukaryotes, cytokinesis is accomplished by an actomyosin-based contractile ring. Although in Caenorhabditis elegans embryos larger cells divide at a faster rate than smaller cells, it remains unknown whether a similar mode of scalability operates in other cells. We investigated cytokinesis in the filamentous fungus Neurospora crassa, which exhibits a wide range of hyphal circumferences. We found that N. crassa cells divide using an actomyosin ring and larger rings constricted faster than smaller rings. However, unlike in C. elegans, the total amount of myosin remained constant throughout constriction, and there was a size-dependent increase in the starting concentration of myosin in the ring. We predict that the increased number of ring-associated myosin motors in larger rings leads to the increased constriction rate. Accordingly, reduction or inhibition of ring-associated myosin slows down the rate of constriction. Because the mechanical characteristics of contractile rings are conserved, we predict that these findings will be relevant to actomyosin ring constriction in other cell types.
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Actomiosina/metabolismo , Citocinese/fisiologia , Miosinas/metabolismo , Neurospora crassa/citologia , Actinas/metabolismo , Actinas/fisiologia , Actomiosina/genética , Membrana Celular/metabolismo , Membrana Celular/fisiologia , Tamanho Celular , Miosinas/genética , Neurospora crassa/genética , Neurospora crassa/fisiologiaRESUMO
Membrane waves have been observed near the leading edge of a motile cell. Such phenomenon is the result of the interplay between hydrodynamics and adhesive dynamics. Here we consider membrane dynamics on a thin fluid gap supported by adhesive bonds. Using coupled lubrication theory and adhesive dynamics, we derive an evolution equation to account for membrane tension, bending, adhesion, and viscous lubrication. Four adhesion scenarios are examined: no adhesion, uniform adhesion, clustered adhesion, and focal adhesion. Two contrasting traveling wave types are found, namely, tension and adhesion waves. Tension waves disperse with time and space, whereas adhesion waves show increased amplitudes and are highly persistent. We show that the transition from tension to adhesion waves depends on a necessary, but insufficient, criterion that the wave amplitude must exceed a critical gap height, which is dependent on adhesion binding probability. We also show that strong adhesion results in sharp tension-to-adhesion wave transitions. The present work could explain the strong persistence of the waves observed in adhered cells using differential inference contrast (DIC) microscopy and the observation that the wavelengths decrease shortly after leading edge retraction.