Intrinsic and well-defined second generation hot spots in gold nanobipyramids: Versus gold nanorods

An effective strategy for regioselective modification and directional assembly of anisotropic nanoparticles is demonstrated to explore the electric field enhancement in assembled gold nanobipyramids compared with gold nanorods. The well-defined secondary plasmonic hot spots between the coupled gold nanobipyramids exhibit the capability for single molecule detection

Patterned Molecular Films of Alkanethiol and PLL-PEG on Gold-Silicate Interfaces: How to Add Functionalities while Retaining Effective Antifouling

Spatial control of surface functionalization and interactions is essential for microarray-based analysis. This study reports the fabrication of two-dimensional molecular films with site-specific functionalities, forming microarrays at discrete locations. Arrays of microsized gold disks were produced on a silicate membrane using microfabrication. On these arrays, orthogonal self-assembly of molecules was performed that can specifically bind to gold or silicate. The gold array elements were functionalized with a range of alkanethiols and the silicate with polymeric poly-l-lysine-grafted-poly(ethylene glycol) (PLL-PEG). The surface functionalization on the gold disk array and the surrounding substrate was characterized at each step using X-ray photoelectron spectroscopy (XPS) to show that alkanethiols are specifically attached to the gold. PLL-PEG was used to provide resistance against nonspecific protein and cell adsorption and attached exclusively to the silicate. The effectiveness of the surface chemistry was validated by the selective self-assembly of a gold nanoparticle monolayer array on the gold regions. In a more sophisticated example, selective adhesion of MCF-7 cells to anti-EpCAM antibody modified gold areas of the gold-silicate surface was demonstrated to give a cell microarray. This study provides a general approach to fabricate chemical patterns on silicon-based devices with the convergence of microfabrication and material-specific surface modification, which may be useful to expand the functionalities and potential applications for patterned biomolecular films. Importantly, the ability to pattern surfaces with different surface chemistries is not limited to planar surfaces using this orthogonal surface-coupling approach

A graphene-based sensor for real time monitoring of sun exposure

The photoreduction of graphene oxide (GO) with titanium dioxide (TiO2) was exploited to fabricate a UV sensor for real time monitoring of sun exposure. The sensor was fabricated by simultaneous deposition of GO sheets and TiO2 nanoparticles onto interdigitated electrodes using an AC electrophoresis deposition method. Changes in the resistance of the GO sheets decorated with TiO2 nanoparticles during repeated cycles of exposure to UV were measured to understand the sensitivity of this sensor to UV radiation. Current-time traces revealed that the fabricated UV sensor retains a memory of each cycle of UV exposure; regardless of whether the sensor is exposed to UV for one long cycle or several short cycles. This memory of the extent of UV exposure is a biomimetic approach, analogous to the response of the skin to sun, and means the sensor requires no power except when the data is read from the sensor

Nanoscale pores introduced into paper via mesoporous silica coatings using sol–gel chemistry

Mesopores, with diameters between 2 and 50 nm, not only increase the specific surface area, but also generate hierarchically porous materials with specific properties such as capillary fluid transport, ion specific pore accessibility, or size exclusion. Paper is a strongly hierarchical, porous material with specific properties, such as capillary force-driven fluid transport. However, paper fibers change their morphology during the initial step of wood disintegration. This results in changes of the porous fiber structure. In particular paper fibers loose their mesopores during the final drying step in the fabrication process. Here, we investigate silica mesopore formation in paper by sol–gel chemistry and evaporation induced self-assembly to specifically introduce and rationally design mesopore formation and distribution in cotton linter and eucalyptus sulfate paper sheets. We demonstrate the importance of synchronizing the solvent evaporation rate and capillary fluid velocity to ensure mesopore formation as well as the influence of the fiber type and sol–gel solution composition. The combination of argon and krypton sorption, SAXS, TEM and CLSM provides systematic analysis of the porous structure and the silica distribution along the cellulose paper fiber length and cross-section. These results provide a deeper understanding of mesopore formation in paper and how the latter is influenced by paper fluidic properties

Coordination Polymer to Atomically Thin, Holey, Metal-Oxide Nanosheets for Tuning Band Alignment

Holey 2D metal oxides have shown great promise as functional materials for energy storage and catalysts. Despite impressive performance, their processing is challenged by the requirement of templates plus capping agents or high temperatures; these materials also exhibit excessive thicknesses and low yields. The present work reports a metal-based coordination polymer (MCP) strategy to synthesize polycrystalline, holey, metal oxide (MO) nanosheets with thicknesses as low as two-unit cells. The process involves rapid exfoliation of bulk-layered, MCPs (Ce-, Ti-, Zr-based) into atomically thin MCPs at room temperature, followed by transformation into holey 2D MOs upon the removal of organic linkers in aqueous solution. Further, this work represents an extra step for decorating the holey nanosheets using precursors of transition metals to engineer their band alignments, establishing a route to optimize their photocatalysis. The work introduces a simple, high-yield, room-temperature, and template-free approach to synthesize ultrathin holey nanosheets with high-level functionalities