Showing papers by "Ralph G. Nuzzo published in 2010"

Waterproof AlInGaP optoelectronics on stretchable substrates with applications in biomedicine and robotics

Abstract: Inorganic light-emitting diodes and photodetectors represent important, established technologies for solid-state lighting, digital imaging and many other applications. Eliminating mechanical and geometrical design constraints imposed by the supporting semiconductor wafers can enable alternative uses in areas such as biomedicine and robotics. Here we describe systems that consist of arrays of interconnected, ultrathin inorganic light-emitting diodes and photodetectors configured in mechanically optimized layouts on unusual substrates. Light-emitting sutures, implantable sheets and illuminated plasmonic crystals that are compatible with complete immersion in biofluids illustrate the suitability of these technologies for use in biomedicine. Waterproof optical-proximity-sensor tapes capable of conformal integration on curved surfaces of gloves and thin, refractive-index monitors wrapped on tubing for intravenous delivery systems demonstrate possibilities in robotics and clinical medicine. These and related systems may create important, unconventional opportunities for optoelectronic devices.

Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

Abstract: Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

Guiding neuron development with planar surface gradients of substrate cues deposited using microfluidic devices

Abstract: Wiring the nervous system relies on the interplay of intrinsic and extrinsic signaling molecules that control neurite extension, neuronal polarity, process maturation and experience-dependent refinement. Extrinsic signals establish and enrich neuron-neuron interactions during development. Understanding how such extrinsic cues direct neurons to establish neural connections in vitro will facilitate the development of organized neural networks for investigating the development and function of nervous system networks. Producing ordered networks of neurons with defined connectivity in vitro presents special technical challenges because the results must be compliant with the biological requirements of rewiring neural networks. Here we demonstrate the ability to form stable, instructive surface-bound gradients of laminin that guide postnatal hippocampal neuron development in vitro. Our work uses a three-channel, interconnected microfluidic device that permits the production of adlayers of planar substrates through the combination of laminar flow, diffusion and physisorption. Through simple flow modifications, a variety of patterns and gradients of laminin (LN) and fluorescein isothiocyanate-conjugated poly-l-lysine (FITC-PLL) were deposited to present neurons with an instructive substratum to guide neuronal development. We present three variations in substrate design that produce distinct growth regimens for postnatal neurons in dispersed cell cultures. In the first approach, diffusion-mediated gradients of LN were formed on cover slips to guide neurons toward increasing LN concentrations. In the second approach, a combined gradient of LN and FITC-PLL was produced using aspiration-driven laminar flow to restrict neuronal growth to a 15 microm wide growth zone at the center of the two superimposed gradients. The last approach demonstrates the capacity to combine binary lines of FITC-PLL in conjunction with surface gradients of LN and bovine serum albumin (BSA) to produce substrate adlayers that provide additional levels of control over growth. This work demonstrates the advantages of spatio-temporal fluid control for patterning surface-bound gradients using a simple microfluidics-based substrate deposition procedure. We anticipate that this microfluidics-based patterning approach will provide instructive patterns and surface-bound gradients to enable a new level of control in guiding neuron development and network formation.

Functional Nanostructured Plasmonic Materials

Abstract: Plasmonic crystals fabricated with precisely controlled arrays of subwavelength metal nanostructures provide a promising platform for sensing and imaging of surface binding events with micrometer spatial resolution over large areas. Soft nanoimprint lithography provides a robust, cost-effective method for producing highly uniform plasmonic crystals of this type with predictable optical properties. The tunable multimode plasmonic resonances of these crystals and their ability for integration into lab-on-a-chip microfluidic systems can both be harnessed to achieve exceptionally high analytical sensitivities down to submonolayer levels using even a common optical microscope, circumventing numerous technical limitations of more conventional surface plasmon resonance techniques. In this article, we highlight some recent advances in this field with an emphasis on the fabrication and characterization of these integrated devices and their demonstrated applications.

Compact monocrystalline silicon solar modules with high voltage outputs and mechanically flexible designs

Abstract: A type of compact (∼cm2) high voltage photovoltaic module that utilizes large collections of ultrathin (∼15 μm), small (∼45 μm wide, ∼1 mm long) silicon solar cells was fabricated and characterized. Integration on thin sheets of plastic yielded flexible modules with per-cell efficiencies of ∼8%, voltage outputs >200 V, and maximum power outputs >1.5 mW.

Conjugated carbon monolayer membranes: methods for synthesis and integration.

Abstract: Monolayer membranes of conjugated carbon represent a class of nanomaterial with demonstrated uses in various areas of electronics, ranging from transparent, flexible, and stretchable thin film conductors, to semiconducting materials in moderate and high-performance field-effect transistors. Although graphene represents the most prominent example, many other more structurally and chemically diverse systems are also of interest. This article provides a review of demonstrated synthetic and integration strategies, and speculates on future directions for the field.

Capillary induced self-assembly of thin foils into 3Dstructures

Abstract: Self-assembly of complex structures is common in nature. Self-assembly principles provide a promising way to fabricate three-dimensional, micro- or millimeter scale devices. In the present paper, we present a generalized analytical study of the self-folding of thin plates into deterministic 3D shapes through fluid–solid interactions. Based on the beam theory, a mechanics model is developed, incorporating the two competing components—a capillary force promoting folding and the bending rigidity of the foil that resists folding into a 3D structure. Through an equivalence argument of thin foils of different geometry, an effective folding parameter, which uniquely characterizes the driving force for folding, has been identified. A criterion for spontaneous folding of any shaped 2D patterned foil based on the effective folding parameter is thus established. The model predictions show excellent agreement with experimental measurements made on a variety of materials, indicating that the assumptions used in the analysis arevalid.

Visualizing Materials Chemistry at Atomic Resolution

Abstract: Analytical electron microscopy—empowered by advances in electron optics and detectors—is poised to radically transform our understanding of the complex phenomena arising from atomic and electronic structure in materials chemistry. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.)

Iridium Ziegler-Type Hydrogenation Catalysts Made from [(1,5-COD)Ir(μ-O2C8H15)]2 and AlEt3: Spectroscopic and Kinetic Evidence for the Irn Species Present and for Nanoparticles as the Fastest Catalyst

Abstract: Ziegler-type hydrogenation catalysts, those made from a group 8−10 transition metal precatalyst and an AlR3 cocatalyst, are often used for large scale industrial polymer hydrogenation; note that Ziegler-type hydrogenation catalysts are not the same as Ziegler−Natta polymerization catalysts. A review of prior studies of Ziegler-type hydrogenation catalysts (Alley et al. J. Mol. Catal. A: Chem. 2010, 315, 1−27) reveals that a ∼50 year old problem is identifying the metal species present before, during, and after Ziegler-type hydrogenation catalysis, and which species are the kinetically best, fastest catalysts—that is, which species are the true hydrogenation catalysts. Also of significant interest is whether what we have termed “Ziegler nanoclusters” are present and what their relative catalytic activity is. Reported herein is the characterization of an Ir Ziegler-type hydrogenation catalyst, a valuable model (vide infra) for the Co-based industrial Ziegler-type hydrogenation catalyst, made from the crysta...

Fabrication of microstructured silicon (μs-Si) from a bulk Si wafer and its use in the printing of high-performance thin-film transistors on plastic substrates

Abstract: In this paper, we report a new fabrication route to generate microstructured, single-crystalline silicon (μs-Si) ribbons using (110) silicon. Two different methods were explored for producing these printable structures. This work also introduces a second-process innovation in the fabrication of microstructured semiconductor objects for printed large-area circuits, namely the direct integration of a high-quality, thermally grown silicon dioxide (SiO2) layer for use as a gate dielectric in top-gate metal-oxide-silicon field effect transistors. We also demonstrate and characterize a soft, conformable lamination process that considerably enhances the mechanical stability of devices printed on plastic, allowing bending radii as small as 0.8 cm. These structures enable a reduction of the bending strains localized at the device interface. These improvements were fully characterized by finite element simulations of the strain distribution present in a descriptive model of the multilayer laminated circuit.

Microfluidic contact printing: a versatile printing platform for patterning biomolecules on hydrogel substrates

Abstract: This work describes a printing platform that utilizes components of two complementary techniques—microcontact printing and microfluidic patterning—to provide a high-throughput, reusable tool for patterning biomolecularly responsive chemical features on soft materials. Hydrogel substrates imprinted with biomolecular targets (e.g., proteins or peptides) are of considerable interest because of their utility in diverse bioanalytical applications such as diagnostics and studies of cells in culture. In the system described here, a track-etched polycarbonate membrane is used to seal a PDMS microfluidic channel device to form a print head. Model ‘inks’—solutions of biotin labeled biomolecular targets—are constantly replenished via perfusion of solution through the membrane and captured on a streptavidin-incorporating polyacrylamide hydrogel-coated substrate placed in conformal contact with the print head. The patterns obtained can be controlled through modifications of channel design and secondary programming via selective membrane wetting. Multiple channel designs have been used to pattern three model classes of biomolecular inks (i.e., peptides, polysaccharides, and proteins). Hydrogels patterned with polylysine are used to illustrate a specific biological application for this soft-patterning method, in this case directing in vitro primary mammalian hippocampal neuronal growth. The short cycle time and reproducibility of this soft-patterning technique are highlighted.

Bifunctional polyacrylamide based polymers for the specific binding of hexahistidine tagged proteins on gold surfaces

Abstract: We describe a modified bifunctional analogue of polyacrylamide that spontaneously forms self-assembled polymeric thin films on Au surfaces. The film is engineered to specifically bind histidine tagged proteins (6His), while simultaneously remaining inherently resistant to the non-specific adsorption of proteins in solution. The backbone of a polyacrylamide-co-n-acryloxysuccinimide copolymer is functionalized via tandem active ester (NHS) couplings with 3-(methylthio)propylamine (MTP) and nitrilotriacetic acid (NTA). The resulting functionalized polymers form stable and exceptionally hydrophilic thin films that are ∼2–5 nm thick, a mass coverage that varies with the MTP graft density. These films are characterized using a variety of techniques (X-ray photoelectron spectroscopy (XPS), reflection absorption infrared spectroscopy (RAIRS), ellipsometry, surface plasmon resonance (SPR), and matrix assisted laser desorption ionization (MALDI)) to establish their structure and function. The protein resistance of the films, as demonstrated by their exposure to solutions of bovine serum albumin (BSA), can be modulated by the amount of MTP grafted to the polymer, which in turn, affects their mass coverage. We show that it is possible to specifically capture hexahistidine tagged proteins with low incidences of nonspecific adsorption using these materials, a discrimination quantified using surface plasmon resonance (SPR) at concentrations down to ∼20 nM. These polymers also bind strongly to the surfaces of Au nanoparticles, stabilizing them against aggregation, providing them with a similar capacity to selectively bind 6His tagged proteins that can then be speciated using MALDI.