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- ItemFast, Label-Free Tracking of Single Viruses and Weakly Scattering Nanoparticles in a Nanofluidic Optical Fiber(Washington, DC : Soc., 2015) Faez, Sanli; Lahini, Yoav; Weidlich, Stefan; Garmann, Rees F.; Wondraczek, Katrin; Zeisberger, Matthias; Schmidt, Markus A.; Orrit, Michel; Manoharan, Vinothan N.High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber having a subwavelength, nanofluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylindrical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions-26 nm in size and 4.6 megadaltons in mass-at rates of over 3 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.
- ItemGas-Phase Fluorination on PLA Improves Cell Adhesion and Spreading(Washington, DC : Soc., 2020) Schroepfer, Michaela; Junghans, Frauke; Voigt, Diana; Meyer, Michael; Breier, Anette; Schulze-Tanzil, Gundula; Prade, InaFor the regeneration or creation of functional tissues, biodegradable biomaterials including polylactic acid (PLA) are widely preferred. Modifications of the material surface are quite common to improve cell-material interactions and thereby support the biological outcome. Typical approaches include a wet chemical treatment with mostly hazardous substances or a functionalization with plasma. In the present study, gas-phase fluorination was applied to functionalize the PLA surfaces in a simple and one-step process. The biological response including biocompatibility, cell adhesion, cell spreading, and proliferation was analyzed in cell culture experiments with fibroblasts L929 and correlated with changes in the surface properties. Surface characterization methods including surface energy and isoelectric point measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were applied to identify the effects of fluorination on PLA. Gas-phase fluorination causes the formation of C-F bonds in the PLA backbone, which induce a shift to a more hydrophilic and polar surface. The slightly negatively charged surface dramatically improves cell adhesion and spreading of cells on the PLA even with low fluorine content. The results indicate that this improved biological response is protein-but not integrin-dependent. Gas-phase fluorination is therefore an efficient technique to improve cellular response to biomaterial surfaces without losing cytocompatibility. Copyright © 2020 American Chemical Society.
- ItemProtein-Assisted Assembly of Modular 3D Plasmonic Raspberry-like Core/Satellite Nanoclusters: Correlation of Structure and Optical Properties(Washington, DC : Soc., 2016) Höller, Roland P. M.; Dulle, Martin; Thomä, Sabrina; Mayer, Martin; Steiner, Anja Maria; Förster, Stephan; Fery, Andreas; Kuttner, Christian; Chanana, MunishWe present a bottom-up assembly route for a large-scale organization of plasmonic nanoparticles (NPs) into three-dimensional (3D) modular assemblies with core/satellite structure. The protein-assisted assembly of small spherical gold or silver NPs with a hydrophilic protein shell (as satellites) onto larger metal NPs (as cores) offers high modularity in sizes and composition at high satellite coverage (close to the jamming limit). The resulting dispersions of metal/metal nanoclusters exhibit high colloidal stability and therefore allow for high concentrations and a precise characterization of the nanocluster architecture in dispersion by small-angle X-ray scattering (SAXS). Strong near-field coupling between the building blocks results in distinct regimes of dominant satellite-to-satellite and core-to-satellite coupling. High robustness against satellite disorder was proved by UV/vis diffuse reflectance (integrating sphere) measurements. Generalized multiparticle Mie theory (GMMT) simulations were employed to describe the electromagnetic coupling within the nanoclusters. The close correlation of structure and optical property allows for the rational design of core/satellite nanoclusters with tailored plasmonics and well-defined near-field enhancement, with perspectives for applications such as surface-enhanced spectroscopies.
- ItemMechanical Robustness of Graphene on Flexible Transparent Substrates(Washington, DC : Soc., 2016) Kang, Moon H.; Prieto López, Lizbeth O.; Chen, Bingan; Teo, Ken; Williams, John A.; Milne, William I.; Cole, Matthew T.This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend–relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium–tin oxide on PET. After 104 bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.
- ItemPolymer Brushes on Graphitic Carbon Nitride for Patterning and as a SERS Active Sensing Layer via Incorporated Nanoparticles(Washington, DC : Soc., 2020) Sheng, Wenbo; Li, Wei; Tan, Deming; Zhang, Panpan; Zhang, En; Sheremet, Evgeniya; Schmidt, Bernhard V.K.J.; Feng, Xinliang; Rodriguez, Raul D.; Jordan, Rainer; Amin, IhsanGraphitic carbon nitride (gCN) has a broad range of promising applications, from energy harvesting and storage to sensing. However, most of the applications are still restricted due to gCN poor dispersibility and limited functional groups. Herein, a direct photografting of gCN using various polymer brushes with tailorable functionalities via UV photopolymerization at ambient conditions is demonstrated. The systematic study of polymer brush-functionalized gCN reveals that the polymerization did not alter the inherent structure of gCN. Compared to the pristine gCN, the gCN-polymer composites show good dispersibility in various solvents such as water, ethanol, and tetrahydrofuran (THF). Patterned polymer brushes on gCN can be realized by employing photomask and microcontact printing technology. The polymer brushes with incorporated silver nanoparticles (AgNPs) on gCN can act as a multifunctional recyclable active sensing layer for surface-enhanced Raman spectroscopy (SERS) detection and photocatalysis. This multifunctionality is shown in consecutive cycles of SERS and photocatalytic degradation processes that can be applied to in situ monitor pollutants, such as dyes or pharmaceutical waste, with high chemical sensitivity as well as to water remediation. This dual functionality provides a significant advantage to our AgNPs/polymer-gCN with regard to state-of-the-art systems reported so far that only allow SERS pollutant detection but not their decomposition. These results may provide a new methodology for the covalent functionalization of gCN and may enable new applications in the field of catalysis, biosensors, and, most interestingly, environmental remediation. Copyright © 2020 American Chemical Society.
- ItemMolecular Insights into Division of Single Human Cancer Cells in On-Chip Transparent Microtubes(Washington, DC : Soc., 2016) Xi, Wang; Schmidt, Christine K.; Sanchez, Samuel; Gracias, David H.; Carazo-Salas, Rafael E.; Butler, Richard; Lawrence, Nicola; Jackson, Stephen P.; Schmidt, Oliver G.In vivo, mammalian cells proliferate within 3D environments consisting of numerous microcavities and channels, which contain a variety of chemical and physical cues. External environments often differ between normal and pathological states, such as the unique spatial constraints that metastasizing cancer cells experience as they circulate the vasculature through arterioles and narrow capillaries, where they can divide and acquire elongated cylindrical shapes. While metastatic tumors cause most cancer deaths, factors impacting early cancer cell proliferation inside the vasculature and those that can promote the formation of secondary tumors remain largely unknown. Prior studies investigating confined mitosis have mainly used 2D cell culture systems. Here, we mimic aspects of metastasizing tumor cells dividing inside blood capillaries by investigating single-cell divisions of living human cancer cells, trapped inside 3D rolled-up, transparent nanomembranes. We assess the molecular effects of tubular confinement on key mitotic features, using optical high- and super-resolution microscopy. Our experiments show that tubular confinement affects the morphology and dynamics of the mitotic spindle, chromosome arrangements, and the organization of the cell cortex. Moreover, we reveal that membrane blebbing and/or associated processes act as a potential genome-safety mechanism, limiting the extent of genomic instability caused by mitosis in confined circumstances, especially in tubular 3D microenvironments. Collectively, our study demonstrates the potential of rolled-up nanomembranes for gaining molecular insights into key cellular events occurring in tubular 3D microenvironments in vivo.
- ItemMechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly(Washington, DC : Soc., 2019) Gupta, Vaibhav; Probst, Patrick T.; Goßler, Fabian R.; Steiner, Anja Maria; Schubert, Jonas; Brasse, Yannic; König, Tobias A.F.; Fery, AndreasWe demonstrate a novel colloidal self-assembly approach toward obtaining mechanically tunable, cost-efficient, and low-loss plasmonic nanostructures that show pronounced optical anisotropy upon mechanical deformation. Soft lithography and template-assisted colloidal self-assembly are used to fabricate a stretchable periodic square lattice of gold nanoparticles on macroscopic areas. We stress the impact of particle size distribution on the resulting optical properties. To this end, lattices of narrowly distributed particles (∼2% standard deviation in diameter) are compared with those composed of polydisperse ones (∼14% standard deviation). The enhanced particle quality sharpens the collective surface lattice resonances by 40% to achieve a full width at half-maximum as low as 16 nm. This high optical quality approaches the theoretical limit for this system, as revealed by electromagnetic simulations. One hundred stretching cycles demonstrate a reversible transformation from a square to a rectangular lattice, accompanied by polarization-dependent optical properties. On the basis of these findings we envisage the potential applications as strain sensors and mechanically tunable filters. © 2019 American Chemical Society.
- ItemGold Aerogels: Three-Dimensional Assembly of Nanoparticles and Their Use as Electrocatalytic Interfaces(Washington, DC : Soc., 2016) Wen, Dan; Liu, Wei; Haubold, Danny; Zhu, Chengzhou; Oschatz, Martin; Holzschuh, Matthias; Wolf, André; Simon, Frank; Kaskel, Stefan; Eychmüller, AlexanderThree-dimensional (3D) porous metal nanostructures have been a long sought-after class of materials due to their collective properties and widespread applications. In this study, we report on a facile and versatile strategy for the formation of Au hydrogel networks involving the dopamine-induced 3D assembly of Au nanoparticles. Following supercritical drying, the resulting Au aerogels exhibit high surface areas and porosity. They are all composed of porous nanowire networks reflecting in their diameters those of the original particles (5–6 nm) via electron microscopy. Furthermore, electrocatalytic tests were carried out in the oxidation of some small molecules with Au aerogels tailored by different functional groups. The beta-cyclodextrin-modified Au aerogel, with a host–guest effect, represents a unique class of porous metal materials of considerable interest and promising applications for electrocatalysis.
- ItemHierarchical Sticker and Sticky Chain Dynamics in Self-Healing Butyl Rubber Ionomers(Washington, DC : Soc., 2019) Mordvinkin, Anton; Suckow, Marcus; Böhme, Frank; Colby, Ralph H.; Creton, Costantino; Saalwächter, KayWe present a detailed comparison of the microscopic dynamics and the macroscopic mechanical behavior of novel butyl rubber ionomers with tunable dynamics of sparse sticky imidazole-based sidegroups that form clusters of about 20 units separated by essentially unperturbed chains. This material platform shows promise for application as self-healing elastomers. Size and thermal stability of the ionic clusters were probed by small-angle X-ray scattering, and the chain and sticker dynamics were studied by a combination of broadband dielectric spectroscopy (BDS) and advanced NMR methods. The results are correlated with the rheological behavior characterized by dynamic-mechanical analysis (DMA). While the NMR-detected chain relaxation and DMA results agree quantitatively and confirm relevant aspects of the sticky-reptation picture on a microscopic level, we stress and explain that apparent master curves are of limited use for such a comparison. The cluster-related relaxation time detected by BDS is much shorter than the elastic chain relaxation time, although the weak conductivity does follow the latter. The systematic trends across the sample series suggest that all relaxations are dominated by a cluster-related activation barrier, but also that the BDS-based cluster relaxation does not seem to be directly associated with the effective sticker lifetime. Nonlinear stress-strain experiments demonstrate a reduction of sticker lifetime on stretching and that the stored stress and the elastic recovery depend on the deformation rate. © 2019 American Chemical Society.
- ItemUltrafast laser inscription of asymmetric integrated waveguide 3 dB couplers for astronomical K-band interferometry at the CHARA array(Washington, DC : Soc., 2021) Benoît, Aurélien; Pike, Fraser A.; Sharma, Tarun K.; MacLachlan, David G.; Dinkelaker, Aline N.; Nayak, Abani S.; Madhav, Kalaga; Roth, Martin M.; Labadie, Lucas; Pedretti, Ettore; Brummelaar, Theo A. ten; Scott, Nic; Coudé du Foresto, Vincent; Thomson, Robert R.We present the fabrication and characterization of 3 dB asymmetric directional couplers for the astronomical K-band at wavelengths between 2.0 and 2.4 µm. The couplers were fabricated in commercial Infrasil silica glass using an ultrafast laser operating at 1030 nm. After optimizing the fabrication parameters, the insertion losses of straight single-mode waveguides were measured to be ∼1.2±0.5dB across the full K-band. We investigate the development of asymmetric 3 dB directional couplers by varying the coupler interaction lengths and by varying the width of one of the waveguide cores to detune the propagation constants of the coupled modes. In this manner, we demonstrate that ultrafast laser inscription is capable of fabricating asymmetric 3 dB directional couplers for future applications in K-band stellar interferometry. Finally, we demonstrate that our couplers exhibit an interferometric fringe contrast of >90%. This technology paves the path for the development of a two-telescope K-band integrated optic beam combiner for interferometry to replace the existing beam combiner (MONA) in Jouvence of the Fiber Linked Unit for Recombination (JouFLU) at the Center for High Angular Resolution Astronomy (CHARA) telescope array.