Department of Materials Science and Engineering

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Computational Design of Single-Peptide Nanocages with Nanoparticle Templating
(Molecules, 2022-02-12) Villegas, José A.; Sinha, Nairiti J.; Teramoto, Naozumi; Von Bargen, Christopher D.; Pochan, Darrin J.; Saven, Jeffery G.
Protein complexes perform a diversity of functions in natural biological systems. While computational protein design has enabled the development of symmetric protein complexes with spherical shapes and hollow interiors, the individual subunits often comprise large proteins. Peptides have also been applied to self-assembly, and it is of interest to explore such short sequences as building blocks of large, designed complexes. Coiled-coil peptides are promising subunits as they have a symmetric structure that can undergo further assembly. Here, an α-helical 29-residue peptide that forms a tetrameric coiled coil was computationally designed to assemble into a spherical cage that is approximately 9 nm in diameter and presents an interior cavity. The assembly comprises 48 copies of the designed peptide sequence. The design strategy allowed breaking the side chain conformational symmetry within the peptide dimer that formed the building block (asymmetric unit) of the cage. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques showed that one of the seven designed peptide candidates assembled into individual nanocages of the size and shape. The stability of assembled nanocages was found to be sensitive to the assembly pathway and final solution conditions (pH and ionic strength). The nanocages templated the growth of size-specific Au nanoparticles. The computational design serves to illustrate the possibility of designing target assemblies with pre-determined specific dimensions using short, modular coiled-coil forming peptide sequences.
Effects of composition and thermal treatment on VOC-limiting defects in single-crystalline Cu2ZnSnSe4 solar cells
(Progress in Photovoltaics, 2021-11-19) Lloyd, Michael A.; Ma, Xiangyu; Kuba, Austin G.; McCandless, Brian E.; Doty, Matthew F.; Birkmire, Robert
Single-crystalline Cu2ZnSnSe4 (CZTSe) solar cells with open circuit voltages reaching 500 mV are achieved through a combination of composition control and a low-temperature thermal ordering treatment. A comparison of the device results for Cu-poor CZTSe with Cu/Zn + Sn ratios of 0.77 and 0.86 is presented with and without the implementation of a 130°C absorber annealing treatment. An increase in bandgap energy is observed via external quantum efficiency measurements with both the decrease in Cu content and the implementation of the order anneal, the latter of which also leads to a decrease in Urbach energy. Defect characterization performed with admittance spectroscopy on devices is demonstrated as insufficient because of low-temperature current barriers. Photoluminescence (PL) on crystal surfaces however enables a qualitative comparison of the defect landscape between crystal compositions and annealing treatments. Both a highly compensated and a lightly doped defect model are used to fit PL as a function of laser fluence to identify defects contributing to each observed recombination channel. The PL signatures attributed to the ZnSn defect become unresolvable with a decrease in Cu/Zn + Sn ratio from 0.86 to 0.77. Furthermore, a decrease in Cu–Zn disorder is observed upon the implementation of the annealing treatment through both a comparison of potential fluctuation depths and of both PL models.
Electronically Conductive Hydrogels by in Situ Polymerization of a Water-Soluble EDOT-Derived Monomer
(Advanced Engineering Materials, 2022-05-13) Nguyen, Dan My; Wu, Yuhang; Nolin, Abigail; Lo, Chun-Yuan; Guo, Tianzheng; Dhong, Charles; Martin, David C.; Kayser, Laure V.
Electronically conductive hydrogels have gained popularity in bioelectronic interfaces because their mechanical properties are similar to biological tissues, potentially preventing scaring in implanted electronics. Hydrogels have low elastic moduli, due to their high water content, which facilitates their integration with biological tissues. To achieve electronically conductive hydrogels, however, requires the integration of conducting polymers or nanoparticles. These “hard” components increase the elastic modulus of the hydrogel, removing their desirable compatibility with biological tissues, or lead to the heterogeneous distribution of the conductive material in the hydrogel scaffold. A general strategy to transform hydrogels into electronically conductive hydrogels without affecting the mechanical properties of the parent hydrogel is still lacking. Herein, a two-step method is reported for imparting conductivity to a range of different hydrogels by in-situ polymerization of a water-soluble and neutral conducting polymer precursor: 3,4–ethylenedioxythiophene diethylene glycol (EDOT-DEG). The resulting conductive hydrogels are homogenous, have conductivities around 0.3 S m−1, low impedance, and maintain an elastic modulus of 5–15 kPa, which is similar to the preformed hydrogel. The simple preparation and desirable properties of the conductive hydrogels are likely to lead to new materials and applications in tissue engineering, neural interfaces, biosensors, and electrostimulation.
Estrogenic activity of lignin-derivable alternatives to bisphenol A assessed via molecular docking simulations
(RSC Advances, 2021-06-23) Amitrano, Alice; Mahajan, Jignesh S.; Korley, LaShanda T. J.; Epps, Thomas H. III
Lignin-derivable bisphenols are potential alternatives to bisphenol A (BPA), a suspected endocrine disruptor; however, a greater understanding of structure–activity relationships (SARs) associated with such lignin-derivable building blocks is necessary to move replacement efforts forward. This study focuses on the prediction of bisphenol estrogenic activity (EA) to inform the design of potentially safer BPA alternatives. To achieve this goal, the binding affinities to estrogen receptor alpha (ERα) of lignin-derivable bisphenols were calculated via molecular docking simulations and correlated to median effective concentration (EC50) values using an empirical correlation curve created from known EC50 values and binding affinities of commercial (bis)phenols. Based on the correlation curve, lignin-derivable bisphenols with binding affinities weaker than ∼−6.0 kcal mol−1 were expected to exhibit no EA, and further analysis suggested that having two methoxy groups on an aromatic ring of the bio-derivable bisphenol was largely responsible for the reduction in binding to ERα. Such dimethoxy aromatics are readily sourced from the depolymerization of hardwood biomass. Additionally, bulkier substituents on the bridging carbon of lignin-bisphenols, like diethyl or dimethoxy, were shown to weaken binding to ERα. And, as the bio-derivable aromatics maintain major structural similarities to BPA, the resultant polymeric materials should possess comparable/equivalent thermal (e.g., glass transition temperatures, thermal decomposition temperatures) and mechanical (e.g., tensile strength, modulus) properties to those of polymers derived from BPA. Hence, the SARs established in this work can facilitate the development of sustainable polymers that maintain the performance of existing BPA-based materials while simultaneously reducing estrogenic potential.
An image analysis method for quantifying precision and disorder in nanofabricated photonic structures
(Nanotechnology, 2022-11-28) Carfagno, Henry; Garcia, Pedro David; Doty, Matthew F.
Disorder is an essential parameter in photonic systems and devices, influencing phenomena such as the robustness of topological photonic states and the Anderson localization of modes in waveguides. We develop and demonstrate a method for both analyzing and visualizing positional, size, and shape disorder in periodic structures such as photonic crystals. This analysis method shows selectivity for disorder type and sensitivity to disorder down to less than 1%. We show that the method can be applied to more complex shapes such as those used in topological photonics. The method provides a powerful tool for process development and quality control, including analyzing the precision of E-beam lithography before patterns are transferred; quantifying the precision limits of lithography, deposition, or etch processes; and studying the intentional displacement of individual objects within otherwise periodic arrays.
Impact of collagen-like peptide (CLP) heterotrimeric triple helix design on helical thermal stability and hierarchical assembly: a coarse-grained molecular dynamics simulation study
(Soft Matter, 2022-04-05) Taylor, Phillip A.; Kloxin, April M.; Jayaraman, Arthi
Collagen-like peptides (CLP) are multifunctional materials garnering a lot of recent interest from the biomaterials community due to their hierarchical assembly and tunable physicochemical properties. In this work, we present a computational study that links the design of CLP heterotrimers to the thermal stability of the triple helix and their self-assembly into fibrillar aggregates and percolated networks. Unlike homotrimeric helices, the CLP heterotrimeric triple helices in this study are made of CLP strands of different chain lengths that result in ‘sticky’ ends with available hydrogen bonding groups. These ‘sticky’ ends at one end or both ends of the CLP heterotrimer then facilitate inter-helix hydrogen bonding leading to self-assembly into fibrils (clusters) and percolated networks. We consider the cases of three sticky end lengths – two, four, and six repeat units – present entirely on one end or split between two ends of the CLP heterotrimer. We observe in CLP heterotrimer melting curves generated using coarse grained Langevin dynamics simulations at low CLP concentration that increasing sticky end length results in lower melting temperatures for both one and two sticky ended CLP designs. At higher CLP concentrations, we observe non-monotonic trends in cluster sizes with increasing sticky end length with one sticky end but not for two sticky ends with the same number of available hydrogen bonding groups as the one sticky end; this nonmonotonicity stems from the formation of turn structures stabilized by hydrogen bonds at the single, sticky end for sticky end lengths greater than four repeat units. With increasing CLP concentration, heterotrimers also form percolated networks with increasing sticky end length with a minimum sticky end length of four repeat units required to observe percolation. Overall, this work informs the design of thermoresponsive, peptide-based biomaterials with desired morphologies using strand length and dispersity as a handle for tuning thermal stability and formation of supramolecular structures.
Intramolecular structure and dynamics in computationally designed peptide-based polymers displaying tunable chain stiffness
(Physical Review Materials, 2021-09-07) Sinha, Nairiti J.; Shi, Yi; Kloxin, Christopher J.; Saven, Jeffery G.; Faraone, Antonio; Jensen, Grethe V.; Pochan, Darrin J
Polymers assembled using computationally designed coiled coil bundlemers display tunable stiffness via control of interbundlemer covalent connectivity as confirmed using small-angle neutron scattering. Neutron spin echo spectroscopy reveals that rigid rod polymers show a decay rate Γ∼Q2 (Q is the scattering vector) expected of straight cylinders. Semirigid polymers assembled using bundlemers linked via 4-armed organic linker show flexible segmental dynamics at mid-Q and Γ∼Q2 behavior at high Q. The results give insight into linker flexibility-dependent interbundlemer dynamics in the hybrid polymers.
A Life Cycle Greenhouse Gas Model of a Yellow Poplar Forest Residue Reductive Catalytic Fractionation Biorefinery
(Environmental Engineering Science, 2022-09-13) Luo, Yuqing; O’Dea, Robert M.; Gupta, Yagya; Chang, Jeffrey; Sadula, Sunitha; Soh, Li Pei; Robbins, Allison M.; Levia, Delphis F.; Vlachos, Dionisios G.; Epps, Thomas H. III; Ierapetritou, Marianthi
The incentive to reduce greenhouse gas (GHG) emissions has motivated the development of lignocellulosic biomass conversion technologies, especially those associated with the carbohydrate fraction. However, improving the overall biomass valorization necessitates using lignin and understanding the impact of different tree parts (leaves, bark, twigs/branchlets) on the deconstruction of lignin, cellulose, and hemicellulose toward value-added products. In this work, we explore the production of chemicals from a yellow poplar-based integrated biorefinery. Yellow poplar (Liriodendron tulipifera L.) is an ideal candidate as a second-generation biomass feedstock, given that it is relatively widespread in the eastern United States. Herein, we evaluate and compare how the different proportions of cellulose, hemicellulose (xylan), and lignin among leaves, bark, and twigs/branchlets of yellow poplar, both individually and as a composite mix, influence the life-cycle GHG model of a yellow poplar biorefinery. For example, the processing GHG emissions were reduced by 1,110 kg carbon dioxide (CO2)-eq, 654 kg CO2-eq, and 849 kg CO2-eq per metric ton of twigs/branchlets, leaves, and bark, respectively. Finally, a sensitivity analysis illustrates the robustness of this biorefinery to uncertainties of the feedstock xylan/glucan ratio and carbon content.
Light and microwave driven spin pumping across FeGaB–BiSb interface
(Physical Review Materials, 2021-12-16) Sharma, Vinay; Wu, Weipeng; Bajracharya, Prabesh; To, Duy Quang; Johnson, Anthony; Janotti, Anderson; Bryant, Garnett W.; Gundlach, Lars; Jungfleisch, M. Benjamin; Budhani, Ramesh C.
Three-dimensional (3D) topological insulators (TIs) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet (FM) Fe78Ga13B9 (FeGaB) and 3D TI Bi85Sb15 (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. DC magnetization measurements establish the soft magnetic character of FeGaB films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing magnetization and large value of spin mixing conductance (5.03×1019m–2) as the spin angular momentum leaks into the TI layer. Magnetic field controlled bipolar DC voltage generated across the TI layer by inverse spin Hall effect is analyzed to extract the values of spin Hall angle and spin diffusion length of BiSb. The spin pumping parameters derived from the measurements of the femtosecond light-pulse-induced terahertz emission are consistent with the result of FMR. The Kubo-Bastin formula and tight-binding model calculations shed light on the thickness-dependent spin-Hall conductivity of the TI films, with predictions that are in remarkable agreement with the experimental data. Our results suggest that room temperature deposited amorphous and polycrystalline heterostructures provide a promising platform for creating novel spin orbit torque devices.
Lignin-derivable alternatives to petroleum-derived non-isocyanate polyurethane thermosets with enhanced toughness
(Materials Advances, 2022-11-30) Mhatre, Sampanna V.; Mahajan, Jignesh S.; Epps, Thomas H., III; Korley, LaShanda T. J.
The structural similarities between lignin-derivable bisguaiacols and petroleum-derived bisphenol A/F (BPA/BPF) suggest that bisguaiacols could be ideal biobased alternatives to BPA/BPF in non-isocyanate polyurethane (NIPU) thermosets. Herein, bisguaiacol/bisphenol-derived cyclic carbonates with variations in methoxy content and bridging-carbon substitution were cured with two triamines of different chain lengths, and the impact of these differences on the thermomechanical properties of NIPU networks was examined. The methoxy groups present in the lignin-derivable cyclic carbonates led to thermosets with significantly improved toughness (∼49–59 MJ m−3) and elongation at break (εb ∼195–278%) vs. the BPA/BPF-based benchmarks (toughness ∼ 26–35 MJ m−3, εb ∼ 86–166%). Furthermore, the addition of dimethyl substitution on the bridging carbon resulted in increased yield strength (σy) – from ∼28 MPa for networks with unsubstituted bridging carbons to ∼45 MPa for the dimethyl-substituted materials. These enhancements to mechanical properties were achieved while retaining essential thermoset properties, such as application-relevant moduli and thermal stabilities. Finally, the triamine crosslinkers provided substantial tunability of thermomechanical properties and produced NIPUs that ranged from rigid materials with a high yield strength (σy ∼ 65–88 MPa) to flexible and tough networks. Overall, the structure-property relationships presented highlight a promising framework for the design of versatile, bio-derivable, NIPU thermosets.
Load and release of gambogic acid via dual-target ellipsoidal-Fe3O4@SiO2@mSiO2-C18@dopamine hydrochloride -graphene quantum dots-folic acid and its inhibition to VX2 tumor cells
(Nanotechnology, 2022-12-19) Dong, Mengyang; Liu, Wenwen; Yang, Yuxiang; Xie, Meng; Yuan, Hongming; Ni, Chaoying
Ellipsoidal-Fe3O4@SiO2@mSiO2-C18@dopamine hydrochloride-graphene quantum dots-folic acid (ellipsoidal-HMNPs@PDA-GQDs-FA), a dual-functional drug carrier, was stepwise constructed. The α-Fe2O3 ellipsoidal nanoparticles were prepared by a hydrothermal method, and then coated with SiO2 by Stöber method. The resulting core–shell structure, Fe3O4@SiO2@mSiO2-C18 magnetic nano hollow spheres, abbreviated as HMNPs, was finally grafted with graphene quantum dots (GQDs), dopamine hydrochloride (PDA) and folic acid (FA) by amide reaction to obtain HMNPs@PDA-GQDs-FA. Transmission electron microscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy and element analysis proved the successful construction of the HMNPs@PDA-GQDs-FA nanoscale carrier-cargo composite. The carrier HMNPs@PDA-GQDs-FA has higher load (51.63 ± 1.53%) and release (38.56 ± 1.95%) capacity for gambogic acid (GA). Cytotoxicity test showed that the cell survival rate was above 95%, suggesting the cytotoxicity of the carrier-cargo was very low. The cell lethality (74.91 ± 1.2%) is greatly improved after loading GA because of the magnetic targeting of HMNPs, the targeting performance of FA to tumor cells, and the pH response to the surrounding environment of tumor cells of PDA. All results showed that HMNPs@PDA-GQDs-FA had good biocompatibility and could be used in the treatment of VX2 tumor cells after loading GA.
Machine Learning-Enhanced Computational Reverse-Engineering Analysis for Scattering Experiments (CREASE) for Analyzing Fibrillar Structures in Polymer Solutions
(Macromolecules, 2022-12-27) Wu, Zijie; Jayaraman, Arthi
In this work, we present a machine learning (ML)-enhanced computational reverse-engineering analysis of scattering experiments (CREASE) approach to analyze the small-angle scattering profiles from polymer solutions with assembled semiflexible fibrils with dispersity in fibril diameters (e.g., aqueous solutions of methylcellulose fibrils). This work is an improvement over the original CREASE method [Beltran-Villegas, D. J.; J. Am. Chem. Soc., 2019, 141, 14916−14930], which identifies relevant dimensions of assembled structures in polymer solutions from their small-angle scattering profiles without relying on traditional analytical models. Here, we improve the original CREASE approach by incorporating ML for analyzing assembled semiflexible fibrillar structures with disperse fibril diameters. We first validate our CREASE approach without ML by taking as input the scattering profiles of in silico structures with known dimensions (diameter, Kuhn length) and reproducing as output those known dimensions within error. We then show how the incorporation of ML (specifically an artificial neural network, denoted as NN) within the CREASE approach improves the speed of workflow without sacrificing the accuracy of the determined fibrillar dimensions. Finally, we apply NN-enhanced CREASE to experimental small-angle X-ray scattering profiles from methylcellulose fibrils obtained by Lodge, Bates, and co-workers [Schmidt, P. W.; Macromolecules, 2018, 51, 7767−7775] to determine fibril diameter distribution and compare NN-enhanced CREASE’s output with their fibril diameter distribution fitted using analytical models. The diameter distributions of methylcellulose fibrils from NN-enhanced CREASE are similar to those obtained from analytical model fits, confirming the results by Lodge, Bates, and co-workers that methylcellulose form fibrils with consistent average diameters of ∼15–20 nm regardless of the molecular weight of methylcellulose chains. The successful implementation of NN-enhanced CREASE in handling experimental scattering profiles of complex macromolecular assembled structures with dispersity in dimensions demonstrates its potential for application toward other unconventional fibrillar systems that may not have appropriate analytical models.
Matrix Adhesiveness Regulates Myofibroblast Differentiation from Vocal Fold Fibroblasts in a Bio-orthogonally Cross-linked Hydrogel
(ACS Applied Materials and Interfaces, 2022-11-23) Song, Jiyeon; Gao, Hanyuan; Zhang, He; George, Olivia J.; Hillman, Ashlyn S.; Fox, Joseph M.; Jia, Xinqiao
Repeated mechanical and chemical insults cause an irreversible alteration of extracellular matrix (ECM) composition and properties, giving rise to vocal fold scarring that is refractory to treatment. Although it is well known that fibroblast activation to myofibroblast is the key to the development of the pathology, the lack of a physiologically relevant in vitro model of vocal folds impedes mechanistic investigations on how ECM cues promote myofibroblast differentiation. Herein, we describe a bio-orthogonally cross-linked hydrogel platform that recapitulates the alteration of matrix adhesiveness due to enhanced fibronectin deposition when vocal fold wound healing is initiated. The synthetic ECM (sECM) was established via the cycloaddition reaction of tetrazine (Tz) with slow (norbornene, Nb)- and fast (trans-cyclooctene, TCO)-reacting dienophiles. The relatively slow Tz–Nb ligation allowed the establishment of the covalent hydrogel network for 3D cell encapsulation, while the rapid and efficient Tz–TCO reaction enabled precise conjugation of the cell-adhesive RGDSP peptide in the hydrogel network. To mimic the dynamic changes of ECM composition during wound healing, RGDSP was conjugated to cell-laden hydrogel constructs via a diffusion-controlled bioorthognal ligation method 3 days post encapsulation. At a low RGDSP concentration (0.2 mM), fibroblasts residing in the hydrogel remained quiescent when maintained in transforming growth factor beta 1 (TGF-β1)-conditioned media. However, at a high concentration (2 mM), RGDSP potentiated TGF-β1-induced myofibroblast differentiation, as evidenced by the formation of an actin cytoskeleton network, including F-actin and alpha-smooth muscle actin. The RGDSP-driven fibroblast activation to myofibroblast was accompanied with an increase in the expression of wound healing-related genes, the secretion of profibrotic cytokines, and matrix contraction required for tissue remodeling. This work represents the first step toward the establishment of a 3D hydrogel-based cellular model for studying myofibroblast differentiation in a defined niche associated with vocal fold scarring.
Megakaryocyte membrane-wrapped nanoparticles for targeted cargo delivery to hematopoietic stem and progenitor cells
(Bioengineering and Translational Medicine, 2022-11-29) Das, Samik; Harris, Jenna C.; Winter, Erica J.; Kao, Chen-Yuan; Day, Emily S.; Papoutsakis, Eleftherios Terry
Hematopoietic stem and progenitor cells (HSPCs) are desirable targets for gene therapy but are notoriously difficult to target and transfect. Existing viral vector-based delivery methods are not effective in HSPCs due to their cytotoxicity, limited HSPC uptake and lack of target specificity (tropism). Poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) are attractive, nontoxic carriers that can encapsulate various cargo and enable its controlled release. To engineer PLGA NP tropism for HSPCs, megakaryocyte (Mk) membranes, which possess HSPC-targeting moieties, were extracted and wrapped around PLGA NPs, producing MkNPs. In vitro, fluorophore-labeled MkNPs are internalized by HSPCs within 24 h and were selectively taken up by HSPCs versus other physiologically related cell types. Using membranes from megakaryoblastic CHRF-288 cells containing the same HSPC-targeting moieties as Mks, CHRF-wrapped NPs (CHNPs) loaded with small interfering RNA facilitated efficient RNA interference upon delivery to HSPCs in vitro. HSPC targeting was conserved in vivo, as poly(ethylene glycol)–PLGA NPs wrapped in CHRF membranes specifically targeted and were taken up by murine bone marrow HSPCs following intravenous administration. These findings suggest that MkNPs and CHNPs are effective and promising vehicles for targeted cargo delivery to HSPCs.
Mid- to Far-Infrared Anisotropic Dielectric Function of HfS2 and HfSe2
(Advanced Optical Materials, 2022-09-06) Kowalski, Ryan A.; Nolen, Joshua Ryan; Varnavides, Georgios; Silva, Sebastian Mika; Allen, Jack E.; Ciccarino, Christopher J.; Juraschek, Dominik M.; Law, Stephanie; Narang, Prineha; Caldwell, Joshua D.
The far-infrared (far-IR) remains a relatively underexplored region of the electromagnetic spectrum extending roughly from 20 to 100 µm in free-space wavelength. Research within this range has been restricted due to a lack of optical materials that can be optimized to reduce losses and increase sensitivity, as well as by the long free-space wavelengths associated with this spectral region. Here the exceptionally broad Reststrahlen bands of two Hf-based transition metal dichalcogenides (TMDs) that can support surface phonon polaritons (SPhPs) within the mid-infrared (mid-IR) into the terahertz (THz) are reported. In this vein, the IR transmission and reflectance spectra of hafnium disulfide (HfS2) and hafnium diselenide (HfSe2) flakes are measured and their corresponding dielectric functions are extracted. These exceptionally broad Reststrahlen bands (HfS2: 165 cm−1; HfSe2: 95 cm−1) dramatically exceed that of the more commonly explored molybdenum- (Mo) and tungsten- (W) based TMDs (≈5–10 cm−1), which results from the over sevenfold increase in the Born effective charge of the Hf-containing compounds. This work therefore identifies a class of materials for nanophotonic and sensing applications in the mid- to far-IR, such as deeply sub-diffractional hyperbolic and polaritonic optical antennas, as is predicted via electromagnetic simulations using the extracted dielectric function.
Modeling Structural Colors from Disordered One-Component Colloidal Nanoparticle-Based Supraballs Using Combined Experimental and Simulation Techniques
(ACS Materials Letters, 2022-09-05) Patil, Anvay; Heil, Christian M.; Vanthournout, Bram; Singla, Saranshu; Hu, Ziying; Ilavsky, Jan; Gianneschi, Nathan C.; Shawkey, Matthew D.; Sinha, Sunil K.; Jayaraman, Arthi; Dhinojwala, Ali
Bright, saturated structural colors in birds have inspired synthesis of self-assembled, disordered arrays of assembled nanoparticles with varied particle spacings and refractive indices. However, predicting colors of assembled nanoparticles, and thereby guiding their synthesis, remains challenging due to the effects of multiple scattering and strong absorption. Here, we use a computational approach to first reconstruct the nanoparticles’ assembled structures from small-angle scattering measurements and then input the reconstructed structures to a finite-difference time-domain method to predict their color and reflectance. This computational approach is successfully validated by comparing its predictions against experimentally measured reflectance and provides a pathway for reverse engineering colloidal assemblies with desired optical and photothermal properties.
Nanofocusing performance of plasmonic probes based on gradient permittivity materials
(Journal of Optics, 2022-05-06) Wang, Dongxue; Zhang, Ze; Wang, Jianwei; Ma, Ke; Gao, Hua; Wang, Xi
Probe is the core component of an optical scanning probe microscope such as scattering-type scanning near-field optical microscopy (s-SNOM). Its ability of concentrating and localizing light determines the detection sensitivity of nanoscale spectroscopy. In this paper, a novel plasmonic probe made of a gradient permittivity material (GPM) is proposed and its nanofocusing performance is studied theoretically and numerically. Compared with conventional plasmonic probes, this probe has at least two outstanding advantages: first, it does not need extra structures for surface plasmon polaritons excitation or localized surface plasmon resonance, simplifying the probe system; second, the inherent nanofocusing effects of the conical probe structure can be further reinforced dramatically by designing the distribution of the probe permittivity. As a result, the strong near-field enhancement and localization at the tip apex improve both spectral sensitivity and spatial resolution of a s-SNOM. We also numerically demonstrate that a GPM probe as well as its enhanced nanofocusing effects can be realized by conventional semiconductor materials with designed doping distributions. The proposed novel plasmonic probe promises to facilitate subsequent nanoscale spectroscopy applications.
Observation of nonlinear planar Hall effect in magnetic-insulator–topological-insulator heterostructures
(Physical Review B, 2022-10-10) Wang, Yang; Mambakkam, Sivakumar V.; Huang, Yue-Xin; Wang, Yong; Ji, Yi; Xiao, Cong; Yang, Shengyuan A.; Law, Stephanie A.; Xiao, John Q.
Interfacing topological insulators (TIs) with magnetic insulators (MIs) have been widely used to study the interaction between topological surface states and magnetism. Previous transport studies typically interpret the suppression of weak antilocalization or appearance of the anomalous Hall effect as signatures of the magnetic proximity effect (MPE) imposed to TIs. Here, we report the observation of the nonlinear planar Hall effect (NPHE) in Bi2Se3 films grown on MI thulium and yttrium-iron-garnet (TmIG and YIG) substrates, which is an order of magnitude larger than that in Bi2Se3 grown on nonmagnetic gadolinium-gallium-garnet (GGG) substrate. The nonlinear Hall resistance in TmIG/Bi2Se3 depends linearly on the external magnetic field, while that in YIG/Bi2Se3 exhibits an extra hysteresis loop around zero field. The magnitude of the NPHE is found to scale inversely with carrier density. We speculate that the observed NPHE is related to the MPE-induced exchange gap opening and out-of-plane spin textures in the TI surface states, which may be used as an alternative transport signature of the MPE in MI/TI heterostructures.
Peptide-based assembled nanostructures that can direct cellular responses
(Biomedical Materials, 2022-09-29) Huang, Haofu; Kiick, Kristi
Natural originated materials have been well-studied over the past several decades owing to their higher biocompatibility compared to the traditional polymers. Peptides, consisting of amino acids, are among the most popular programmable building blocks, which is becoming a growing interest in nanobiotechnology. Structures assembled using those biomimetic peptides allow the exploration of chemical sequences beyond those been routinely used in biology. In this review, we discussed the most recent experimental discoveries on the peptide-based assembled nanostructures and their potential application at the cellular level such as drug delivery. In particular, we explored the fundamental principles of peptide self-assembly and the most recent development in improving their interactions with biological systems. We believe that as the fundamental knowledge of the peptide assemblies evolves, the more sophisticated and versatile nanostructures can be built, with promising biomedical applications.
Polymer solution structure and dynamics within pores of hexagonally close-packed nanoparticles
(Soft Matter, 2022-10-20) Heil, Christian M.; Jayaraman, Arthi
Using coarse-grained molecular dynamics simulations, we examine structure and dynamics of polymer solutions under confinement within the pores of a hexagonally close-packed (HCP) nanoparticle system with nanoparticle diameter fifty times that of the polymer Kuhn segment size. We model a condition where the polymer chain is in a good solvent (i.e., polymer–polymer interaction is purely repulsive and polymer–solvent and solvent–solvent interactions are attractive) and the polymer–nanoparticle and solvent–nanoparticle interactions are purely repulsive. We probe three polymer lengths (N = 10, 114, and 228 Kuhn segments) and three solution concentrations (1, 10, and 25%v) to understand how the polymer chain conformations and chain center-of-mass diffusion change under confinement within the pores of the HCP nanoparticle structure from those seen in bulk. The known trend of bulk polymer Rg2 decreasing with increasing concentration no longer holds when confined in the pores of HCP nanoparticle structure; for example, for the 114-mer, the HCP 〈Rg2〉 at 1%v concentration is lower than HCP 〈Rg2〉 at 10%v concentration. The 〈Rg2〉 of the 114-mer and 228-mer exhibit the largest percent decline going from bulk to HCP at the 1%v concentration and the smallest percent decline at the 25%v concentration. We also provide insight into how the confinement ratio (CR) of polymer chain size to pore size within tetrahedral and octahedral pores in the HCP arrangement of nanoparticles affects the chain conformation and diffusion at various concentrations. At the same concentration, the N = 114 has significantly more movement between pores than the N = 228 chains. For the N = 114 polymer, the diffusion between pores (i.e., inter-pore diffusion) accelerates the overall diffusion rate for the confined HCP system while for the N = 228 polymer, the polymer diffusion in the entire HCP is dominated by the diffusion within the tetrahedral or octahedral pores with minor contributions from inter-pore diffusion. These findings augment the fundamental understanding of macromolecular diffusion through large, densely packed nanoparticle assemblies and are relevant to research focused on fabrication of polymer composite materials for chemical separations, storage, optics, and photonics. We perform coarse-grained molecular dynamics simulations to understand structure and dynamics of polymer solutions under confinement within hexagonal close packed nanoparticles with radii much larger than the polymer chain's bulk radius of gyration.

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