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  • Multiferroicity in atomic van der Waals heterostructures

    Gong, Cheng; Kim, Eun Mi; Wang, Yuan; Lee, Geunsik; Zhang, Xiang (Nature Communications, Springer Science and Business Media LLC, 2019-06-14) [Article]
    Materials that are simultaneously ferromagnetic and ferroelectric – multiferroics – promise the control of disparate ferroic orders, leading to technological advances in microwave magnetoelectric applications and next generation of spintronics. Single-phase multiferroics are challenged by the opposite d-orbital occupations imposed by the two ferroics, and heterogeneous nanocomposite multiferroics demand ingredients’ structural compatibility with the resultant multiferroicity exclusively at inter-materials boundaries. Here we propose the two-dimensional heterostructure multiferroics by stacking up atomic layers of ferromagnetic Cr2Ge2Te6 and ferroelectric In2Se3, thereby leading to all-atomic multiferroicity. Through first-principles density functional theory calculations, we find as In2Se3 reverses its polarization, the magnetism of Cr2Ge2Te6 is switched, and correspondingly In2Se3 becomes a switchable magnetic semiconductor due to proximity effect. This unprecedented multiferroic duality (i.e., switchable ferromagnet and switchable magnetic semiconductor) enables both layers for logic applications. Van der Waals heterostructure multiferroics open the door for exploring the low-dimensional magnetoelectric physics and spintronic applications based on artificial superlattices.
  • Magnetic Attributes of NiFe2O4 Nanoparticles: Influence of Dysprosium Ions (Dy3+) Substitution

    Almessiere, Munirah Abdullah; Slimani, Y.; Güngüneş, H.; Ali, S.; Manikandan, A.; Ercan, I.; Baykal, A.; Trukhanov, A.V. (Nanomaterials, MDPI AG, 2019-05-31) [Article]
    his paper reports the influence of dysprosium ion (Dy3+) substitution on the structural and magnetic properties of NiDyxFe2−xO4 (0.0 ≤ x ≤ 0.1) nanoparticles (NPs) prepared using a hydrothermal method. The structure and morphology of the as-synthesized NPs were characterized via X-ray diffraction (XRD), scanning and transmission electron microscope (SEM, and TEM) analyses. 57Fe Mössbauer spectra were recorded to determine the Dy3+ content dependent variation in the line width, isomer shift, quadrupole splitting, and hyperfine magnetic fields. Furthermore, the magnetic properties of the prepared NPs were also investigated by zero-field cooled (ZFC) and field cooled (FC) magnetizations and AC susceptibility measurements. The MZFC (T) results showed a blocking temperature (TB). Below TB, the products behave as ferromagnetic (FM) and act superparamagnetic (SPM) above TB. The MFC (T) curves indicated the existence of super-spin glass (SSG) behavior below Ts (spin-glass freezing temperature). The AC susceptibility measurements confirmed the existence of the two transition temperatures (i.e., TB and Ts). Numerous models, e.g., Neel–Arrhenius (N–A), Vogel–Fulcher (V–F), and critical slowing down (CSD), were used to investigate the dynamics of the systems. It was found that the Dy substitution enhanced the magnetic interactions.
  • Fruity flavors from waste: A novel process to upgrade crude glycerol to ethyl valerate

    Ganigué, Ramon; Naert, Pieter; Candry, Pieter; de Smedt, Jonas; Stevens, Christian V.; Rabaey, Korneel (Bioresource Technology, Elsevier BV, 2019-05-28) [Article]
    Valeric acid and its ester derivatives are chemical compounds with a high industrial interest. Here we report a new approach to produce them from crude glycerol, by combining propionic acid fermentation with chain elongation. Propionic acid was produced by Propionibacterium acidipropionici (8.49 ± 1.40 g·L−1). In the subsequent mixed population chain elongation, valeric acid was the dominant product (5.3 ± 0.69 g·L−1) of the chain elongation process. Residual glycerol negatively impacted the selectivity of mixed culture chain elongation towards valeric acid, whereas this was unaffected when Clostridium kluyveri was used as bio-catalyst. Valeric acid could be selectively isolated and upgraded to ethyl valerate by using dodecane as extractant and medium for esterification, whereas shorter-chain carboxylic acids could be recovered by using a 10 wt% solution of trioctylphosphine oxide (TOPO) in dodecane. Overall, our work shows that the combined fermentation, electrochemistry and homogeneous catalysis enables fine chemical production from side streams.
  • A New pW CMOS Sub-Hertz Timer

    Shahid, Hamza; Alzaher, Hussain (Arabian Journal for Science and Engineering, Springer Science and Business Media LLC, 2019-05-25) [Article]
    A low-voltage and ultra-low power sub-Hertz timer using transistor operating in sub-threshold region is proposed. The sub-Hertz operation is achieved by controlling the amount of currents charging and discharging the timer’s capacitor instead of using large passive components. Pulse width modulation is accomplished by sizing the transistors in charging and discharging control blocks. The timer is working from a single supply voltage of as low as 0.4 V. The circuit is designed in a standard CMOS 150 nm and simulated using Cadence. Simulation results show an oscillation frequency of as low as 0.0217 Hz (a period of 46 s) while using integrable capacitor (100 pF). Its average power consumption for one period is 13.91 pW.
  • Topological Protection Can Arise from Thermal Fluctuations and Interactions

    Pedro, Ricardo Pablo; Paulose, Jayson; Souslov, Anton; Dresselhaus, Mildred; Vitelli, Vincenzo (Physical Review Letters, American Physical Society (APS), 2019-03-21) [Article]
    Topological quantum and classical materials can exhibit robust properties that are protected against disorder, for example, for noninteracting particles and linear waves. Here, we demonstrate how to construct topologically protected states that arise from the combination of strong interactions and thermal fluctuations inherent to soft materials or miniaturized mechanical structures. Specifically, we consider fluctuating lines under tension (e.g., polymer or vortex lines), subject to a class of spatially modulated substrate potentials. At equilibrium, the lines acquire a collective tilt proportional to an integer topological invariant called the Chern number. This quantized tilt is robust against substrate disorder, as verified by classical Langevin dynamics simulations. This robustness arises because excitations in this system of thermally fluctuating lines are gapped by virtue of interline interactions. We establish the topological underpinning of this pattern via a mapping that we develop between the interacting-lines system and a hitherto unexplored generalization of Thouless pumping to imaginary time. Our work points to a new class of classical topological phenomena in which the topological signature manifests itself in a structural property observed at finite temperature rather than a transport measurement.
  • Structural control of nonnative ligand binding in engineered mutants of phosphoenolpyruvate carboxykinase

    Tang, Henry Yue Hin; Shin, David S; Hura, Gregory L.; Yang, Yue; Hu, Xiaoyu; Lightstone, Felice C; McGee, Matthew D; Padgett, Hal S; Yannone, Steven M; Tainer, John A. (Biochemistry, American Chemical Society (ACS), 2018-10-30) [Article]
    Protein engineering to alter recognition underlying ligand binding and activity has enormous potential. Here, ligand binding for E. coli phosphoenolpyruvate carboxykinase (PEPCK), which converts oxaloacetate into CO2 and phosphoenolpyruvate as the first committed step in gluconeogenesis, was engineered to accommodate alternative ligands as an exemplary system with structural information. From our identification of bicarbonate binding in the PEPCK active site at the supposed CO2 binding site, we probed binding of nonnative ligands with three oxygen atoms arranged to resemble bicarbonate geometry. Crystal structures of PEPCK and point mutants with bound nonnative ligands thiosulfate and methanesulfonate along with strained ATP plus reoriented oxaloacetate intermediates and unexpected bicarbonate were solved and analyzed. The mutations successfully altered the bound ligand position and orientation, as well as its specificity: mutated PEPCKs bound either thiosulfate or methanesulfonate, but never both. Computational calculations predicted a methanesulfonate binding mutant and revealed that release of active site ordered solvent exerts a strong influence on ligand binding. Besides nonnative ligand binding, one mutant altered the Mn2+ coordination sphere: instead of the canonical octahedral ligand arrangement, the mutant in question only had a five-coordinate arrangement. From this work, critical features of ligand binding, position, and metal ion co-factor geometry required for all downstream events can be engineered with small numbers of mutations to provide insights into fundamental underpinnings of protein-ligand recognition. Through structural and computational knowledge, the combination of designed and random mutations aids robust design of predetermined changes to ligand binding and activity in order to engineer protein function.
  • Synthesis and Characterization of Cu Decorated Zeolite A@void@Et-PMO Nanocomposites for Removal of Methylene Blue by a Heterogeneous Fenton Reaction

    Li, Xiayu; Zeng, Shangjing; Qu, Xuejian; Dai, Jinyu; Liu, Xiaofang; Wang, Runwei; Zhang, Zongtao; Qiu, Shilun (MDPI AG, 2018-10-29) [Preprint]
    The development of novel porous composite materials for organic dye degradation and removal has received increasing attention due to water contamination problem. In this paper, hydrothermal synthesized nano zeolite A have been encapsulated with porous periodic mesoporous organosilica (PMO) through a simple modified StÖber method an organosilane-directed growth-induced etching strategy, the obtained yolk-shell structured sample was further functionalized by the impregnation of copper, realizing the composite material with hierarchical porous and catalytic properties. The morphology, porosity and metal content of the zeolite Cu/A and Cu/A@Et-PMO were fully characterized. As compared to the parent material, the composite Cu/A@Et-PMO have an efficient adsorption and catalytic degradation performance on methylene blue (MB), the removal efficiency reached as high as 95% of 60 mg/L MB with 10min. These novel structured porous composites may have great potential for adsorption and degradation application including waste effluents.
  • Structure regulation of amino acids derived nitrogen doped porous carbon nanosheet through facile solid state assembly method

    Wang, Yu; Pan, Ying; Zhu, Liangkui; Guo, Ningning; Wang, Runwei; Zhang, Zongtao; Qiu, Shilun (Microporous and Mesoporous Materials, Elsevier BV, 2018-10-16) [Article]
    Carbon nanosheets are widely used in electrocatalysis. Structure control is a great challenge in preparation of carbon materials. Here, a facial solid state assembly method is applied to prepare carbon nanosheets. By choosing amino acids as precursors, structure regulation of carbon nanosheets could be realized via switching the side chains of organic linkers, showing structure evolution from dense monolithic to porous nanosheets. Graphene-like carbon nanosheet constructed foam superstructure was also obtained. Owing to high porosity (BET surface area 1680 m2 g−1 with hierarchical pore structure) and nitrogen (8.23 wt%) modified graphitic frameworks, glutamic acid derived nitrogen doped porous carbon nanosheet superstructure showed high ORR activity (onset potential 0.9 V vs. RHE).
  • Three dimensional simulation on the transport and quantum efficiency of UVC-LEDs with random alloy fluctuations

    Chen, Hung-Hsiang; Speck, James S.; Weisbuch, Claude; Wu, Yuh-Renn (Applied Physics Letters, AIP Publishing, 2018-10-11) [Article]
    The active regions of ultraviolet light emitting diodes (UVLEDs) for UVB and ultra-violet band C wavelengths are composed of AlGaN alloy quantum barriers (QBs) and quantum wells (QWs). The use of alloy QBs and QWs facilitates the formation of percolative paths for carrier injection but also decreases carrier confinement within the QWs. We applied the recently developed Localization Landscape (LL) theory for a full 3D simulation of the LEDs. LL theory describes the effective quantum potential of the quantum states for electrons and holes in a random disordered system with a high computational speed. The results show that the potential fluctuations in the n-AlGaN buffer layer, QWs, and QBs provide percolative paths for carrier injection into the top (p-side) QW. Several properties due to compositional disorder are observed: (1) The peak internal quantum efficiency is larger when disorder is present, due to carrier localization, than for a simulation without fluctuations. (2) The droop is larger mainly due to poor hole injection and weaker blocking ability of the electron blocking layer caused by the fluctuating potentials. (3) Carriers are less confined in the QW and extend into the QBs due to the alloy potential fluctuations. The wave function extension into the QBs enhances TM emission as shown from a k·p simulation of wave-functions admixture, which should then lead to poor light extraction.
  • Design and techno-economic optimization of a rotary chemical looping combustion power plant with CO2 capture

    Iloeje, Chukwunwike O.; Zhao, Zhenlong; GHONIEM, AHMED F. (Applied Energy, Elsevier BV, 2018-09-29) [Article]
    The rotary chemical looping combustion reactor design - which utilizes oxygen carriers in a matrix of micro channels for indirect fuel conversion - provides a viable path for fossil-based electric power generation with CO2 capture. Its thermally integrated matrix of micro channels minimizes irreversibilities associated with heat transfer in the reactor, and establishes multiscale coupling between oxygen carrier kinetics, reactor geometry and plant operating conditions. In this study, we implement an optimization framework that exploits this multiscale coupling for simultaneous reactor design and power plant economic optimization. Results for the methane-fueled power plant reveal optimized thermal efficiencies of 54–56% for a rotary chemical looping recuperative Brayton cycle plant, with compressor pressure ratio in the 3–7 range. By switching from an efficiency to an economic objective, we identified solutions that reduced electricity cost by about 11%; by performing scaling and technology maturity projections, we show competitive economics for the rotary chemical looping plant with CO2 capture.
  • Clustering algorithms to analyze molecular dynamics simulation trajectories for complex chemical and biological systems

    Peng, Jun-hui; Wang, Wei; Yu, Ye-qing; Gu, Han-lin; Huang, Xuhui (Chinese Journal of Chemical Physics, AIP Publishing, 2018-09-25) [Article]
    Molecular dynamics (MD) simulation has become a powerful tool to investigate the structure-function relationship of proteins and other biological macromolecules at atomic resolution and biologically relevant timescales. MD simulations often produce massive datasets containing millions of snapshots describing proteins in motion. Therefore, clustering algorithms have been in high demand to be developed and applied to classify these MD snapshots and gain biological insights. There mainly exist two categories of clustering algorithms that aim to group protein conformations into clusters based on the similarity of their shape (geometric clustering) and kinetics (kinetic clustering). In this paper, we review a series of frequently used clustering algorithms applied in MD simulations, including divisive algorithms, agglomerative algorithms (single-linkage, complete-linkage, average-linkage, centroid-linkage and ward-linkage), center-based algorithms (K-Means, K-Medoids, K-Centers, and APM), density-based algorithms (neighbor-based, DBSCAN, density-peaks, and Robust-DB), and spectral-based algorithms (PCCA and PCCA+). In particular, differences between geometric and kinetic clustering metrics will be discussed along with the performances of different clustering algorithms. We note that there does not exist a one-size-fits-all algorithm in the classification of MD datasets. For a specific application, the right choice of clustering algorithm should be based on the purpose of clustering, and the intrinsic properties of the MD conformational ensembles. Therefore, a main focus of our review is to describe the merits and limitations of each clustering algorithm. We expect that this review would be helpful to guide researchers to choose appropriate clustering algorithms for their own MD datasets.
  • Functional Nanomaterials and Nanostructures Enhancing Electrochemical Biosensors and Lab-on-a-Chip Performances: Recent Progress, Applications, and Future Perspective

    Wongkaew, Nongnoot; Simsek, Marcel; Griesche, Christian; Baeumner, Antje J. (Chemical Reviews, American Chemical Society (ACS), 2018-09-24) [Article]
    Electrochemical biosensors and associated lab-on-a-chip devices are the analytical system of choice when rapid and on-site results are needed in medical diagnostics and food safety, for environmental protection, process control, wastewater treatment, and life sciences discovery research among many others. A premier example is the glucose sensor used by diabetic patients. Current research focuses on developing sensors for specific analytes in these application fields and addresses challenges that need to be solved before viable commercial products can be designed. These challenges typically include the lowering of the limit of detection, the integration of sample preparation into the device and hence analysis directly within a sample matrix, finding strategies for long-term in vivo use, etc. Today, functional nanomaterials are synthesized, investigated, and applied in electrochemical biosensors and lab-on-a-chip devices to assist in this endeavor. This review answers many questions around the nanomaterials used, their inherent properties and the chemistries they offer that are of interest to the analytical systems, and their roles in analytical applications in the past 5 years (2013–2018), and it gives a quantitative assessment of their positive effects on the analyses. Furthermore, to facilitate an insightful understanding on how functional nanomaterials can be beneficial and effectively implemented into electrochemical biosensor-based lab-on-a-chip devices, seminal studies discussing important fundamental knowledge regarding device fabrication and nanomaterials are comprehensively included here. The review ultimately gives answers to the ultimate question: “Are they really needed or can bulk materials accomplish the same?” Finally, challenges and future directions are also discussed.
  • Nitridation of optimised TiO2 nanorods through PECVD towards neural electrode application

    Sait, Roaa; Govindarajan, Sridhar; Cross, Richard (Materialia, Elsevier BV, 2018-09-18) [Article]
    A neural electrode interface material is a key component for effective stimulation and recording of neural activity. The fundamental requirement of a neural electrode is for it to be able to deliver adequate charge to targeted neuronal population. Coating electrode surfaces with nanostructured material not only provides an increase in surface area, providing relatively more active sites for charge delivery than planar systems, but also allows for the reduction of electrode dimension to reduce invasiveness and increase selectivity. In this work, titanium nitride nanowires (TiN-NWs) synthesised by novel nitridation process in Plasma Enhanced Chemical Vapour Deposition (PECVD) is suggested as an enhanced coating material for neural electrodes. The synthesis involved the solution growth of crystalline titanium oxide nanorods (TiO2-NRs) from a sputtered TiN nucleation layer followed by nitridation. TiO2-NRs exhibited high aspect ratio of 23.1 and were converted into TiN after one hour of nitridation at 600°C. Evidence of conversion was studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM). The nitridation temperature and time reported here are the lowest and shortest as compared to the literature. The near-stoichiometric TiN-NWs (x=0.49) achieved in this work were used subsequently for electrochemical characterisation through Cyclic Voltammetry (CV). The capacitance of relatively high aspect TiN-NWs was 3.78 mF/cm2, which was a 5-fold enhancement compared to thin film of TiN layer (0.7 mF/cm2). A stability test of the nanowires were performed in which the capacitance remained relatively unchanged.
  • Elastic-Beam Triboelectric Nanogenerator for High-Performance Multifunctional Applications: Sensitive Scale, Acceleration/Force/Vibration Sensor, and Intelligent Keyboard

    Chen, Yuliang; Wang, Yi-Cheng; Zhang, Ying; Zou, Haiyang; Lin, Zhiming; Zhang, Guobin; Zou, Chongwen; Wang, Zhong Lin (Advanced Energy Materials, Wiley, 2018-09-03) [Article]
    Exploiting novel devices for either collecting energy or self-powered sensors is vital for Internet of Things, sensor networks, and big data. Triboelectric nanogenerators (TENGs) have been proved as an effective solution for both energy harvesting and self-powered sensing. The traditional triboelectric nanogenerators are usually based on four modes: contact-separation mode, lateral sliding mode, single-electrode mode, and freestanding triboelectric-layer mode. Since the reciprocating displacement/force is necessary for all working modes, developing efficient elastic TENG is going to be important and urgent. Here, a kind of elastic-beam TENG with arc-stainless steel foil is developed, whose structure is quite simple, and its working states depend on the contact area and separating distance as proved by experiments and theoretical calculations. This structure is different from traditional structures, e.g., direct sliding or contact-separation structures, whose working states mainly depend on contact area or separating distance. This triboelectric nanogenerator shows advanced mechanical and electrical performance, such as high sensitivity, elasticity, and ultrahigh frequency response, which encourage applications as a force sensor, sensitivity scale, acceleration sensor, vibration sensor, and intelligent keyboard.
  • Chemical functional group descriptor for ignition propensity of large hydrocarbon liquid fuels

    Dussan, Karla; Won, Sang Hee; Ure, Andrew D.; Dryer, Frederick L.; Dooley, Stephen (Proceedings of the Combustion Institute, Elsevier BV, 2018-08-30) [Article]
    The chemical functional group approach is investigated to verify the fundamental applicability of low-dimensional descriptors in the prediction of global combustion behavior, as described by homogeneous reflected shock ignition delay times. Three key chemical functional groups, CH2, CH3 and benzyl-type, are used to represent n-alkyl, iso-alkyl, and aromatic functionalities, respectively. To examine whether such descriptors can appropriately reflect the influences of these functionalities on ignition delay, Quantitative Structure-Property Relationship (QSPR) regression analysis is performed with the formulation of analytical models based on a fundamental Arrhenius-type description. The models are trained using literature measurements of reflected shock ignition delay times for stoichiometric fuel/air mixtures at 20 atm. Sensitivity analyses applied to the QSPR regression models show that the CH2 functional group dominates chemical kinetic behaviors at low temperature, while the chemical kinetic impacts of CH2, CH3, and benzyl-type functional groups all diminish as temperature increases. Further analyses of constant-volume adiabatic ignition delay predictions using detailed chemical kinetic models demonstrate influences of n-alkyl, iso-alkyl, and aromatic functionalities at both low and high temperature, consistent with those found for the QSPR regression models. Finally, 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy is used to directly quantify the chemical functional group compositions of both petroleum-derived and alternative jet fuels. Combining the QSPR model with NMR spectra interpretation, the applicability of current approach as an expeditious tool to accurately characterize the ignition propensity of real transportation fuels is demonstrated by comparison with experimental measurements.
  • Architecture and Preparation of Hollow Catalytic Devices

    Li, Bowen; Zeng, Hua Chun (Advanced Materials, Wiley, 2018-08-30) [Article]
    Since pioneering work done in the late 1990s, synthesis of functional hollow materials has experienced a rapid growth over the past two decades while their applications have been proven to be advantageous across many technological fields. In the field of heterogeneous catalysis, the development of micro- and nanoscale hollow materials as catalytic devices has also yielded promising results, because of their higher activity, stability, and selectivity. Herein, the architecture and preparation of these catalysts with tailorable composition and morphology are reviewed. First, synthesis of hollow materials is introduced according to the classification of template mediated, template free, and combined approaches. Second, different architectural designs of hollow catalytic devices, such as those without functionalization, with active components supported onto hollow materials, with active components incorporated within porous shells, and with active components confined within interior cavities, are evaluated respectively. The observed catalytic performances of this new class of catalysts are correlated to structural merits of individual configuration. Examples that demonstrate synthetic approaches and architected configurations are provided. Lastly, possible future directions are proposed to advance this type of hollow catalytic devices on the basis of our personal perspectives.
  • Absolute adsorption of light hydrocarbons and carbon dioxide in shale rock and isolated kerogen

    Wu, Tianhao; Zhao, Huangjing; Tesson, Stéphane; Firoozabadi, Abbas (Fuel, Elsevier BV, 2018-08-28) [Article]
    Natural gas production from shale formations has changed the energy landscape. Knowledge of adsorption in the subsurface shale formations improves resource assessment. The excess adsorption is directly measurable from experiments. Evaluation of fluid content in shale is based on the absolute adsorption. At high pressure relevant to subsurface conditions, the computation of absolute adsorption from excess adsorption has shortcomings when the conventional models are used. In this work, we first present the excess sorption data of light hydrocarbons and carbon dioxide in subsurface shale rock and in isolated kerogen. Gravimetric method was used in our measurements. The results show that, at high pressure, the excess adsorption of ethane and carbon dioxide decreases significantly as pressure increases. Excess adsorption of ethane at 60 °C for the shale sample investigated becomes negative at high pressure. The conventional models may provide a non-monotonic absolute adsorption and even magnify the unphysical negative adsorption. In addition to the proposed model based on adsorbed layer volume, we also account for effective sample volume due to the pore volume accessibility by different molecules, as well as the swelling of kerogen. The adsorption data from subsurface shale and the method for analysis presented in this work set the stage for prediction capability in hydrocarbon production from shale reservoirs.
  • A bilayered PVA/PLGA-bioresorbable shuttle to improve the implantation of flexible neural probes

    Pas, Jolien; Rutz, Alexandra L.; Quilichini, Pascale; Slézia, Andrea; Ghestem, Antoine; Kaszas, Attila; Donahue, Mary; Curto, Vincenzo; O’Connor, Rodney P.; bernard, christophe; Williamson, Adam; Malliaras, George (Journal of Neural Engineering, IOP Publishing, 2018-08-22) [Article]
    Objective: Neural electrophysiology is often conducted with traditional, rigid depth probes. The mechanical mismatch between these probes and soft brain tissue is unfavorable for tissue interfacing. Making probes compliant can improve biocompatibility, but as a consequence, they become more difficult to insert into the brain. Therefore, new methods for inserting compliant neural probes must be developed. \n Approach: Here, we present a new bioresorbable shuttle based on the hydrolytically degradable poly(vinyl alcohol) (PVA) and poly(lactic-co-glycolic acid) (PLGA). We show how to fabricate the PVA/PLGA shuttles on flexible and thin parylene probes. The method consists of PDMS molding used to fabricate a PVA shuttle aligned with the probe and to also impart a sharp tip necessary for piercing brain tissue. The PVA shuttle is then dip-coated with PLGA to create a bi-layered shuttle. \n Main results: While single layered PVA shuttles are able to penetrate agarose brain models, only limited depths were achieved and repositioning was not possible due to the fast degradation. We demonstrate that a bilayered approach incorporating a slower dissolving PLGA layer prolongs degradation and enables facile insertion for at least several millimeters depth. Impedances of electrodes before and after shuttle preparation were characterized and showed that careful deposition of PLGA is required to maintain low impedance. Facilitated by the shuttles, compliant parylene probes were also successfully implanted into anaesthetized mice and enabled the recording of high quality local field potentials. \n Significance: This work thereby presents a solution towards addressing a key challenge of implanting compliant neural probes using a two polymer system. PVA and PLGA are polymers with properties ideal for translation: commercially available, biocompatible with FDA-approved uses and bioresorbable. By presenting new ways to implant compliant neural probes, we can begin to fully evaluate their chronic biocompatibility and performance compared to traditional, rigid electronics.
  • Diffusivity of Mono- and Divalent Salts and Water in Polyelectrolyte Desalination Membranes

    Aryal, Dipak; Ganesan, Venkat (The Journal of Physical Chemistry B, American Chemical Society (ACS), 2018-08-14) [Article]
    The dynamics of ions and solvent molecules in polyelectrolyte desalination membranes is key to water purification technologies in which selective transport of the different components is desired. Recent experimental and our computational results have shown that nontrivial mechanisms underlie the transport properties of salt ions and water in charged polymer membranes. Explicitly, in polymer electrolytes, we found a reversal in the salt concentration dependence of the mobilities of Na+, Cl– salt ions and water molecules when compared with aqueous solutions. Motivated by such results, in this study, we have used atomistic molecular dynamics simulations to probe whether the mechanisms deduced in our earlier work apply to other salt systems and to mixtures of salts. Specifically, we report results for the ion diffusivities in aqueous KCl, MgCl2, and a 1:1 mixture of NaCl and MgCl2 salt solutions at different concentrations (ranging from 0.06 to 1 M) and investigate, at the molecular level, the mechanisms underlying the behaviors of salt and water transport properties. Our results show that diffusion of salt ions and water in charged polymer membranes are in general influenced by their association with polymer charge groups and ion pairing effects. Divalent ions are more strongly coupled with the polymeric ionic groups than monovalent salt ions and exhibit diffusivity trends that are distinct relative to monovalent salts. Further, we demonstrate that the mobilities of water molecules are influenced by coordination of water with polymer charge groups and their ion pairing tendencies and also exhibit distinct trends in monovalent and divalent salt solutions.
  • Translating Catalysis to Chemiresistive Sensing

    Schroeder, Vera; Swager, Timothy M. (Journal of the American Chemical Society, American Chemical Society (ACS), 2018-08-14) [Article]
    Activating molecules or functional groups with high chemoselectivity in complex environments is the central goal of transition-metal-based catalysis. Promoting strong interactions between a selected substrate and a catalytic system can also be used to create highly selective and customizable sensors, and these concepts are widely recognized for enzymatic processes. We demonstrate the successful translation of organometallic reactions to sensing capability. Specifically, we have developed single-walled carbon nanotube (SWCNT) chemiresistive sensors for the highly selective detection of acrylates using conditions for the aerobic oxidative Heck reaction. The sensors mirror the catalytic processes and selectively respond to electron-deficient alkenes by adapting a catalytic reaction system to modulate the doping levels in carbon nanotubes. The sensors readily detect acrylates at parts per million (ppm) levels in untreated air. The concepts presented here are generally applicable and can guide future sensor development based upon known catalytic processes.

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