Highly Sunlight Reflective and Infrared Semi-Transparent Nanomesh Textiles

Radiative cooling in textiles is one of the important factors enabling cooling of the human body for thermal comfort. In particular, under an intense sunlight environment such as that experienced with outdoor exercise and sports activities, high near-infrared (NIR) reflectance to block sunlight energy influx along with high IR transmittance in textiles for substantial thermal emission from the human body would be highly desirable. This investigation demonstrates that a nanoscale geometric control of textile structure alone, instead of complicated introduction of specialty polymer materials and composites, can enable such desirable NIR and IR optical properties in textiles. A diameter-dependent Mie scattering event in fibers and associated optical and thermal behavior were simulated in relation to a nonwoven, nanomesh textile. As an example, a nanomesh structure made of PVDF (polyvinylidene fluoride) electrospun fibers with ∼600 nm average diameter was examined, which exhibited a significant radiative cooling performance with over 90% solar and NIR reflectance to profoundly block the sunlight energy influx as well as ∼50% IR transmittance for human body radiative heat dissipation. An extraordinary cooling effect, as much as 12 °C, was obtained on a simulated skin compared to the normal textile fabric materials. Such a powerful radiative cooling performance together with IR transmitting capability by the nanomesh textile offers a way to efficiently manage sunlight radiation energy to make persons, devices, and transport vehicles cooler and help to save energy in an outdoor sunlight environment as well as indoor conditions

Enhanced Cellular Mobility Guided by TiO2 Nanotube Surfaces

The in vitro endothelial response of primary bovine aortic endothelial cells (BAECs) was investigated on a flat Ti surface vs a nanostructured TiO2 nanotube surface. The nanotopography provided nanoscale cues that facilitated cellular probing, cell sensing, and especially cell migration, where more organized actin cytoskeletal filaments formed lamellipodia and locomotive morphologies. Motile cell protrusions were able to probe down into the nanotube pores for contact stimulation, and focal adhesions were formed and disassembled readily for enhanced advancement of cellular fronts, which was not observed on a flat substrate of titanium. NOx and endothelin-1 functional assays confirmed that the nanotubes also up-regulated an antithrombic cellular state for maintaining vascular tone. The enhanced endothelial response to TiO2 nanotubes is significant for a potential modification of vascular stent surfaces in order to increase the rate and reliability of endothelialization and endothelial cell migration onto the stent for repairing arterial injury after activation

Dye-Sensitized Solar Cell Constructed with Titanium Mesh and 3-D Array of TiO₂ Nanotubes

We have designed and constructed dye sensitized solar cells based on new, 3-D configurations of TiO2 nanotubes. The overall efficiency of our best cells is 5.0% under standard air mass 1.5 global (AM 1.5 G) solar conditions, and the incident photon-to-current efficiency exceeds 60% over a broad part of the visible spectrum. Unlike prior nanotube-based cells where tubes are grown vertically in a 2-D array, the anodes of the present cells consist of tubes that extend radially in a 3-D array from a grid of fine titanium wires. The nanotubes are tens of micrometers in length, and the radial nature of the anode allows the photon absorption path length to exceed the electron transport distance (nanotube length). The cells are front-illuminated and do not require a transparent conductive oxide substrate at either the anode or cathode. The use of 3-D configured nanotubes and low-resistance titanium metal substrates are expected to enhance the performance and simplify the construction of large area dye-sensitized solar cells

Carbon Nanotubes: How Strong Is Their Bond with the Substrate?

A reliable quantification technique for interpreting nanomaterial−substrate bond strength is highly desired to predict efficient, long-term performance of nanomaterial-based devices. Adopting a novel nanoscratch-based technique, here we demonstrate quantification of carbon nanotube (CNT)−substrate adhesion strength for dense CNT structure and for patterned carbon nanocone (CNC) structures. Debonding energy for a single CNT is illustrated to range between 1 and 10 pJ, and the variation is strongly dependent on the nature of the interface between CNTs, catalysts, and substrates. Our proposed technique could be adopted for characterization of bonding strength between a wide variety of nanotubes, nanowires, and other one-dimensional nanostructured materials and their underlying substrates

Site-Specific Patterning of Highly Ordered Nanocrystal Superlattices through Biomolecular Surface Confinement

With the increasing demand in recent years for high-performance devices for both energy and health applications, there has been extensive research to direct the assembly of nanoparticles into meso- or macroscale single two- and three-dimensional crystals of arbitrary configuration or orientation. Inorganic nanoparticle arrays can have intriguing physical properties that differ from either individual nanoparticles or bulk materials. For most device applications, it is necessary to fabricate two-dimensional nanoparticle superlattices at programmed sites on a surface. However, it has remained a significant challenge to generate patterned arrays with long-range positional order because most highly ordered close-packed nanocrystal arrays are typically obtained by kinetically driven evaporation processes. In this report, we demonstrate a method to generate patterned nanocrystal superlattices by confining nanoparticles to geometrically defined 2-D DNA sites on a surface and using associative biomolecular interparticle interactions to produce thermodynamically stable arrays of hexagonally packed nanocrystals with significant long-range order observed over 1−2 μm. We also demonstrate the role of chemical and geometrical confinement on particle packing and obtaining long-range order. Finally, we also demonstrate that the formation of DNA-mediated nanocrystal superlattices requires both interparticle DNA hybridization and solvent-less thermal annealing

Magnetically Guided Nano–Micro Shaping and Slicing of Silicon

Silicon is one of the most important materials for modern electronics, telecom, and photovoltaic (PV) solar cells. With the rapidly expanding use of Si in the global economy, it would be highly desirable to reduce the overall use of Si material, especially to make the PVs more affordable and widely used as a renewable energy source. Here we report the first successful direction-guided, nano/microshaping of silicon, the intended direction of which is dictated by an applied magnetic field. Micrometer thin, massively parallel silicon sheets, very tall Si microneedles, zigzag bent Si nanowires, and tunnel drilling into Si substrates have all been demonstrated. The technique, utilizing narrow array of Au/Fe/Au trilayer etch lines, is particularly effective in producing only micrometer-thick Si sheets by rapid and inexpensive means with only 5 μm level slicing loss of Si material, thus practically eliminating the waste (and also the use) of Si material compared to the ∼200 μm kerf loss per slicing and ∼200 μm thick wafer in the typical saw-cut Si solar cell preparation. We expect that such nano/microshaping will enable a whole new family of novel Si geometries and exciting applications, including flexible Si circuits and highly antireflective zigzag nanowire coatings

Magnetically Vectored Nanocapsules for Tumor Penetration and Remotely Switchable On-Demand Drug Release

Nanocapsules containing intentionally trapped magnetic nanoparticles and defined anticancer drugs have been prepared to provide a powerful magnetic vector under moderate gradient magnetic fields. These nanocapsules can penetrate into the interior of tumors and allow a controlled on−off switchable release of the drug cargo via remote RF field. This smart drug delivery system is compact as all the components can be self-contained in 80−150 nm capsules. In vitro as well as in vivo results indicate that these nanocapsules can be enriched near the mouse breast tumor and are effective in reducing tumor cell growth

Natural-basalt-originated hierarchical nano porous zeolite with strong and selective gas separation capability

Nanostructured zeolite 13X, synthesized from basalt rock via alkali fusion and hydrothermal procedures, demonstrates excellent adsorption performance for light gases (CO2, CH4, N2, and H2). Its robust CO2 separation properties, evident in the adsorption capacity and selectivity order (CO2 >> CH4 > N2 >> H2). The measured adsorption isotherms fit well with the Sips equation, and heterogeneous adsorption behaviors correlate with the isosteric heat of adsorption and adsorption energy distribution. Predicted selectivities via ideal adsorbed solution theory range from 990 to 1,415 (CO2/H2), 244–360 (CO2/N2), and 135–254 (CO2/CH4), indicating significant potential for adsorptive CO2 separation. Natural-basalt-originated, nanostructured zeolite has been created for strong and selective gas adsorption characteristics useful for engineering applications including energy source creation and environmental cleaning, with the selectivity strongly correlated with polarizability.</p

High-Yielding and Photolabile Approaches to the Covalent Attachment of Biomolecules to Surfaces via Hydrazone Chemistry

The development of strategies to couple biomolecules covalently to surfaces is necessary for constructing sensing arrays for biological and biomedical applications. One attractive conjugation reaction is hydrazone formationthe reaction of a hydrazine with an aldehyde or ketoneas both hydrazines and aldehydes/ketones are largely bioorthogonal, which makes this particular reaction suitable for conjugating biomolecules to a variety of substrates. We show that the mild reaction conditions afforded by hydrazone conjugation enable the conjugation of DNA and proteins to the substrate surface in significantly higher yields than can be achieved with traditional bioconjugation techniques, such as maleimide chemistry. Next, we designed and synthesized a photocaged aryl ketone that can be conjugated to a surface and photochemically activated to provide a suitable partner for subsequent hydrazone formation between the surface-anchored ketone and DNA- or protein-hydrazines. Finally, we exploit the latent functionality of the photocaged ketone and pattern multiple biomolecules on the same substrate, effectively demonstrating a strategy for designing substrates with well-defined domains of different biomolecules. We expect that this approach can be extended to the production of multiplexed assays by using an appropriate mask with sequential photoexposure and biomolecule conjugation steps

Electrochemical Properties and Myocyte Interaction of Carbon Nanotube Microelectrodes

Arrays of carbon nanotube (CNT) microelectrodes (nominal geometric surface areas 20−200 μm2) were fabricated by photolithography with chemical vapor deposition of randomly oriented CNTs. Raman spectroscopy showed strong peak intensities in both G and D bands (G/D = 0.86), indicative of significant disorder in the graphitic layers of the randomly oriented CNTs. The impedance spectra of gold and CNT microelectrodes were compared using equivalent circuit models. Compared to planar gold surfaces, pristine nanotubes lowered the overall electrode impedance at 1 kHz by 75%, while nanotubes treated in O2 plasma reduced the impedance by 95%. Cyclic voltammetry in potassium ferricyanide showed potential peak separations of 133 and 198 mV for gold and carbon nanotube electrodes, respectively. The interaction of cultured cardiac myocytes with randomly oriented and vertically aligned CNTs was investigated by the sectioning of myocytes using focused-ion-beam milling. Vertically aligned nanotubes deposited by plasma-enhanced chemical vapor deposition (PECVD) were observed to penetrate the membrane of neonatal-rat ventricular myocytes, while randomly oriented CNTs remained external to the cells. These results demonstrated that CNT electrodes can be leveraged to reduce impedance and enhance biological interfaces for microelectrodes of subcellular size