A native chemical chaperone in the human eye lens.

Cataract is one of the most prevalent protein aggregation disorders and still the most common cause of vision loss worldwide. The metabolically quiescent core region of the human lens lacks cellular or protein turnover; it has therefore evolved remarkable mechanisms to resist light-scattering protein aggregation for a lifetime. We now report that one such mechanism involves an unusually abundant lens metabolite, myo-inositol, suppressing aggregation of lens crystallins. We quantified aggregation suppression using our previously well-characterized in vitro aggregation assays of oxidation-mimicking human γD-crystallin variants and investigated myo-inositol's molecular mechanism of action using solution NMR, negative-stain TEM, differential scanning fluorometry, thermal scanning Raman spectroscopy, turbidimetry in redox buffers, and free thiol quantitation. Unlike many known chemical chaperones, myo-inositol's primary target was not the native, unfolded, or final aggregated states of the protein; rather, we propose that it was the rate-limiting bimolecular step on the aggregation pathway. Given recent metabolomic evidence that it is severely depleted in human cataractous lenses compared to age-matched controls, we suggest that maintaining or restoring healthy levels of myo-inositol in the lens may be a simple, safe, and globally accessible strategy to prevent or delay lens opacification due to age-onset cataract.

Establishment of perpendicular protrusion of type I collagen on TiO2 nanotube surface as a priming site of peri-implant connective fibers.

Natural teeth are supported by connective tissue collagen fibers that insert perpendicularly in the tooth cementum. Perpendicular insertion plays an important role in the maintenance of the junction between the oral epithelium and the periodontal connective tissue. Most titanium dental implant surfaces have no micro or macro structure to support perpendicularly oriented collagen attachment. Without this tight biologic seal to resist bacterial invasion and epithelial downgrowth, progressive bone loss in peri-implantitis is seen around dental implants. The purpose of this study was to establish the perpendicularly oriented collagen attachment to titanium oxide nanotube (TNT), and to assess its binding stability. TNT was prepared on the titanium-surface by anodization. Scanning electron microscopy (SEM) showed a regularly aligned TNT with an average 67 nm-diameter when anodized at 30 V for 3 h. Subsequently, collagen type I (CoI) was electrophoretically fused to anodic TNT in native polyacrylamide gel system where negatively charged CoI-C term was perpendicularly navigated to TNT. SEM and atomic force microscopy (AFM) were used to analyze CoI on the TiO2 and TNT surface. Several tens of nanometers of CoI protrusion were recorded by AFM. These protrusions may be long enough to be priming sites for cell-secreted CoI. CoI laid parallel to the titanium surface when fused by a chemical linker. Binding resistance of CoI against drastic ultrasonication was measured by Fourier-transform infrared spectroscopy attenuated total reflection (FTIR-ATR). The electrophoretically fused CoI in the titanium nanotube (TNT-CoIEPF) showed the significantly greatest binding resistance than the other groups (P < 0.01, a 1-way ANOVA and Tukey HSD post hoc test). Furthermore, TNT-CoIEPF surface rejected epithelial cell stretching and epithelial sheet formation. Chemically linked horizontal CoI on titanium oxide (TiO2) facilitated epithelial cell stretching and sheet formation.

Reactivity of a stable copper-dioxygen complex.

We report the isolation of a room temperature stable dipyrromethene Cu(O2) complex featuring a side-on O2 coordination. Reactivity studies highlight the unique ability of the dioxygen adduct for both hydrogen-atom abstraction and acid/base chemistry towards phenols, demonstrating that side-on superoxide species can be reactive entities.

Controlling the Roughness of Langmuir-Blodgett Monolayers.

Controlling the surface roughness of thin films with nanoscale precision is of significant interest for the rational design of surface coatings. Although wrinkling and buckling of Langmuir monolayers under compression has been demonstrated for several years, there is currently no method to precisely control this behavior during compression and thereby modify the surface roughness of deposited films. Here, we combine conventional Langmuir phase analysis with a novel dynamic viscoelasticity measurement to simply and accurately observe the jamming transition of monolayers of silica spheres, graphene oxide, and surfactant. By overcompressing beyond this point, the surface roughness of the deposited monolayer can be precisely controlled. This technique could be used to tune the surface properties of a variety of materials from lipids to nanoparticles.

Intracellular Delivery Using Nanosecond-Laser Excitation of Large-Area Plasmonic Substrates.

Efficiently delivering functional cargo to millions of cells on the time scale of minutes will revolutionize gene therapy, drug discovery, and high-throughput screening. Recent studies of intracellular delivery with thermoplasmonic structured surfaces show promising results but in most cases require time- or cost-intensive fabrication or lead to unreproducible surfaces. We designed and fabricated large-area (14 × 14 mm), photolithography-based, template-stripped plasmonic substrates that are nanosecond laser-activated to form transient pores in cells for cargo entry. We optimized fabrication to produce plasmonic structures that are ultrasmooth and precisely patterned over large areas. We used flow cytometry to characterize the delivery efficiency of cargos ranging in size from 0.6 to 2000 kDa to cells (up to 95% for the smallest molecule) and viability of cells (up to 98%). This technique offers a throughput of 50000 cells/min, which can be scaled up as necessary. This technique is also cost-effective as each large-area photolithography substrate can be used to deliver cargo to millions of cells, and switching to a nanosecond laser makes the setup cheaper and easier to use. The approach we present offers additional desirable features: spatial selectivity, reproducibility, minimal residual fragments, and cost-effective fabrication. This research supports the development of safer genetic and viral disease therapies as well as research tools for fundamental biological research that rely on effectively delivering molecules to millions of living cells.

Facet-Selective Epitaxy of Compound Semiconductors on Faceted Silicon Nanowires.

Integration of compound semiconductors with silicon (Si) has been a long-standing goal for the semiconductor industry, as direct band gap compound semiconductors offer, for example, attractive photonic properties not possible with Si devices. However, mismatches in lattice constant, thermal expansion coefficient, and polarity between Si and compound semiconductors render growth of epitaxial heterostructures challenging. Nanowires (NWs) are a promising platform for the integration of Si and compound semiconductors since their limited surface area can alleviate such material mismatch issues. Here, we demonstrate facet-selective growth of cadmium sulfide (CdS) on Si NWs. Aberration-corrected transmission electron microscopy analysis shows that crystalline CdS is grown epitaxially on the {111} and {110} surface facets of the Si NWs but that the Si{113} facets remain bare. Further analysis of CdS on Si NWs grown at higher deposition rates to yield a conformal shell reveals a thin oxide layer on the Si{113} facet. This observation and control experiments suggest that facet-selective growth is enabled by the formation of an oxide, which prevents subsequent shell growth on the Si{113} NW facets. Further studies of facet-selective epitaxial growth of CdS shells on micro-to-mesoscale wires, which allows tuning of the lateral width of the compound semiconductor layer without lithographic patterning, and InP shell growth on Si NWs demonstrate the generality of our growth technique. In addition, photoluminescence imaging and spectroscopy show that the epitaxial shells display strong and clean band edge emission, confirming their high photonic quality, and thus suggesting that facet-selective epitaxy on NW substrates represents a promising route to integration of compound semiconductors on Si.

Peering at a buried polymer-crystal interface: probing heterogeneous nucleation by sum frequency generation vibrational spectroscopy.

Sum frequency generation vibrational spectroscopy (SFG-VS) has been applied to investigate the selective crystallization of two forms of acetaminophen (ACM) on polymer surfaces. To our knowledge, this is the first account of SFG-VS being applied to study a polymer-crystal interface. SFG elucidates the molecular-level interactions governing phase selection at this buried interface, providing insight into the process of polymer-induced heteronucleation (PIHn) in solution as well as from the vapor phase. ACM heteronucleates from supersaturated aqueous solution in the metastable orthorhombic crystal form on poly(methyl methacrylate) (PMMA) surfaces, whereas the thermodynamically stable monoclinic crystal form is observed to form on poly(n-butyl methacrylate) (PBMA) surfaces. When the ACM crystals were grown by sublimation, only the monoclinic form was observed on both PMMA and PBMA. SFG-VS results indicate that hydrogen bonds are formed between PMMA C═O groups and the orthorhombic ACM crystals at the PMMA-ACM interface. At PBMA-monoclinic ACM interfaces, no hydrogen bond formation was observed. This research demonstrates that SFG-VS can be used to probe molecular interactions at polymer-crystal interfaces. Understanding the interfacial molecular interactions will ultimately provide a rational basis for improving methods for polymorph discovery and selection based on heteronucleation on polymer surfaces.

Deducing 2D crystal structure at the liquid/solid interface with atomic resolution: a combined STM and SFG study.

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and C=O groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

Solventless adhesive bonding using reactive polymer coatings.

A novel solventless adhesive bonding (SAB) process is reported, which is applicable to a wide range of materials including, but not limited to, poly(dimethylsiloxane) (PDMS). The bonding is achieved through reactions between two complementary polymer coatings, poly(4-aminomethyl-p-xylylene-co-p-xylylene) and poly(4-formyl-p-xylylene-co-p-xylylene), which are prepared by chemical vapor deposition (CVD) polymerization of the corresponding [2.2]paracyclophanes and can be deposited on complementary microfluidic units to be bonded. These CVD-based polymer films form well-adherent coatings on a range of different substrate materials including polymers, glass, silicon, metals, or paper and can be stored for extended periods prior to bonding without losing their bonding capability. Tensile stress data are measured on PDMS with various substrates and compared favorably to current methods such as oxygen plasma and UV/ozone. Sum frequency generation (SFG) has been used to probe the presence of amine and aldehyde groups on the surface after CVD polymerization and their conversion during bonding. In addition to bonding, unreacted functional groups present on the luminal surface of microfluidic channels provide free chemical groups for further surface modification. Fluorescently labeled molecules including rhodamine-conjugated streptavidin and atto-655 NHS ester were used to verify the presence of active functional groups on the luminal surfaces after bonding.