Guowen Meng

Improved SERS performance from Au nanopillar arrays by abridging the pillar tip spacing by Ag sputtering.

Ag-capped Au nanopillar arrays on a resin supporter (see left upper figure), with a typical adjacent pillar tip gap of 10 nm, show obviously higher surface-enhanced Raman scattering (SERS) sensitivity (right column in red) than that of the bare Au nanopillar array while using 10 nM R6G as probe molecules. The large-area Ag-capped Au nanopillar array has potential in trace detection of special chemicals.

Well‐Defined Nanoclusters as Fluorescent Nanosensors: A Case Study on Au25(SG)18

The fluorescence of nanoparticles has attracted much attention in recent research, but in many cases the underlying mechanisms are difficult to evaluate due to the polydispersity of nanoparticles and their unknown structures, in particular the surface structures. Recent breakthroughs in the syntheses and structure determinations of well-defined gold nanoclusters provide opportunities to conduct in-depth investigations. Devising well-defined nanocluster sensors based on fluorescence change is of particular interest not only for scientific studies but also for practical applications. Herein, the potential of the glutathionate (SG)-capped Au(25) nanocluster as a silver ion sensor is evaluated. The Ag(+) detection limit of approximately 200 nM, based on the fluorescence enhancement and good linear fluorescence response in the silver ion concentration range from 20 nM to 11 μM, in combination with the good selectivity among 20 types of metal cations, makes Au(25) (SG)(18) a good candidate for fluorescent sensors for silver ions. Further experiments reveal three important factors responsible for the unique fluorescence enhancement caused by silver ions: 1) the oxidation state change of Au(25) (SG)(18) ; 2) the interaction of neutral silver species (Ag(0) , reduced by Au(25) (SG)(18) (-) ) with Au(25) (SG)(18) ; and 3) the interaction of Ag(+) with Au(25) (SG)(18.) Experiments demonstrate the very different chemistry of hydrophobic Au(25) (SC(2) H(4) Ph)(18) and hydrophilic Au(25) (SG)(18) in the reaction with silver ions. This work indicates another potential application of gold nanoclusters, offers new strategies for nanocluster-based chemical sensing, and reveals a new way to influence nanocluster chemistry for potential applications.

Electrochemical synthesis of copper nanowires

Large-scale copper nanowires have been fabricated by potentiostatic electrochemical deposition (ECD) of copper sulphate solution within the nanochannels of porous anodic alumina templates. Scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction and x-ray diffraction techniques were used to characterize the copper nanowires obtained. It is found that the individual copper nanowires are dense and continuous, with uniform diameters (60 nm) along the entire lengths of the wires (30 µm). The single-crystal and polycrystal copper nanowires can be prepared by choosing suitable applied potentials in the copper ECD processes. Moreover, the formation of copper oxides in nanochannels is also discussed in detail. The investigation results reveal that a lower overpotential is necessary to fabricate copper nanowires with fine crystalline structures by the potentiostatic ECD technique.

Blue luminescence in porous anodic alumina films: the role of the oxalic impurities

Porous anodic alumina (PAA) films with ordered nanopore arrays have been prepared by electrochemically anodizing aluminium in oxalic acid solutions, and the role of the oxalic impurities in the optical properties of PAA films has been discussed. Photoluminescence (PL) measurements show that the PAA films obtained have a blue PL band with a peak position at around 470 nm; the oxalic impurities, incorporated in the PAA films during the anodization processes and already existing in them, could be being transformed into PL centres and hence responsible for this PL emission.

Fabrication of Highly Ordered InSb Nanowire Arrays by Electrodeposition in Porous Anodic Alumina Membranes

Highly ordered near-stoichiometrical polycrystalline InSb nanowire arrays have been fabricated by direct current (dc) electrodeposition inside the nanochannels of anodic alumina membranes (AAMs) and subsequent annealing. X-ray diffraction patterns and X-ray energy dispersion analysis reveal the change of crystal structure and the ratio of indium to antimony due to the deposition potential. The results show that cubic-phase InSb nanowire arrays can be achieved by using certain deposition potential and subsequent annealing. Transmission electron microscopy and scanning electron microscopy results demonstrate that these InSb nanowires are uniform with diameters about 50 nm, corresponding to the pore diameter of the AAMs. Raman spectrum further demonstrates the InSb nanowire with high crystal quality.

A General Synthetic Approach to Interconnected Nanowire/Nanotube and Nanotube/Nanowire/Nanotube Heterojunctions with Branched Topology

Heterojunctions between nanotubes (NTs) and nanowires (NWs) could provide building blocks for nanoelectronics and nanophotonics, with other applications in barcodes, optical readout, biomolecular separation, catalysis, selfassembly, and magnetic manipulation. Although hybrid NWs (metal/polymer, semiconductor/semiconductor, 9] metal/semiconductor, and metal/metal ), hybrid NTs (metal/metal), NT/NW heterojunctions, and tree-like nano-heterojunctions have beenmade, the corresponding studies demonstrated limited control over the geometry and complexity of the nano-heterojunctions, which ultimately are central to the design of building blocks for nanocircuits, nanodevices, and nanosystems. Herein we show a general synthetic approach to various branched two-segment NW/NT and three-segment NT/NW/NT heterojunctions, based on a combinatorial process of electrodepositing NWs within the branched channels of anodic aluminum oxide (AAO) templates, selectively etching part of the electrodeposited NWs, and growing NTs on the ends of the NWs. The NWs can be metallic or semiconducting, while the NTs can consist of carbon, silicon, and silica; the two NT segments in threesegment NT/NW/NT nanoarchitectures can comprise either the same or different materials. This approach enables excellent control over the geometry, chemical composition, and complexity of the hetero-nanoarchitectures that can be the framework for nanoscale devices and systems. Figure 1 shows schematic depictions of the basic heteronanoarchitectures we have made, which consist of various NT and NW segments placed combinatorially in a Y-shaped topology. The synthesis scheme follows a typical buildingblock concept in which a set of different nanoscale components (NTs and NWs of different materials with distinct properties, in linear and branched topologies) can be connected in a predetermined fashion inside the branched

Electrospun 1,4-DHAQ-Doped Cellulose Nanofiber Films for Reusable Fluorescence Detection of Trace Cu2+ and Further for Cr3+

1,4-Dihydroxyanthraquinone (1,4-DHAQ, a fluorophore) doped cellulose (CL) (denoted as 1,4-DHAQ@CL) microporous nanofiber film has been achieved via simple electrospinning and subsequent deacetylating, and used for highly sensitive and selective fluorescence detection of Cu(2+) in aqueous solution. As the resultant byproduct of Cu(2+)-contaminated 1,4-DHAQ@CL nanofiber film showed recovered fluorescence by extra addition of Cr(3+) nitrate solution, 1,4-DHAQ and Cu(2+) codoped CL (denoted as (1,4-DHAQ)-Cu(2+)@CL)) microporous nanofiber film has been further fabricated for the detection of Cr(3+) in aqueous solution. It was found that the fluorescence intensity of the 1,4-DHAQ@CL microporous nanofiber film linearly decreases with Cu(2+) concentration ranging from 2.5 × 10(-9) to 3.75 × 10(-8) M, while that of the codoped (1,4-DHAQ)-Cu(2+)@CL nanofiber film linearly increases with Cr(3+) concentration from 2.5 × 10(-9) to 2.5 × 10(-8) M, both with high selectivity over many other common heavy metal ions. The sensing mechanism for Cu(2+) is ascribed to the formation of phenolate between 1,4-DHAQ and Cu(2+), while that for Cr(3+) is attributed to the reversing reaction from Cu(2+)-based phenolate to Cu(2+) and Cr(3+)-based excited complex with recovered fluorescence. The sensitive and selective detection of Cu(2+) and Cr(3+) by using the 1,4-DHAQ@CL and the (1,4-DHAQ)-Cu(2+)@CL nanofiber films was further demonstrated in polluted lake waters, thus indicating their potential applications in environmental monitoring of Cu(2+) and Cr(3+) in polluted water. Additionally, both the 1,4-DHAQ@CL and (1,4-DHAQ)-Cu(2+)@CL microporous nanofiber films are reusable for the detection of Cu(2+) and Cr(3+), respectively, after simple treatment. The design concept in this work might also open a door to the design of effective fluorescence probes for other heavy metal ions.

A facile vapor–solid synthetic route to Sb2O3 fibrils and tubules

Sb2O3 fibrils and tubules with lengths of up to several millimeters and diameters of nanometers to submicrometers were achieved by using Sb2S3 nanopowders as starting material. The synthesis can be ascribed to a vapor–solid process where metal catalyst was neither adopted during the synthesis, nor observed at tips of fibrils or tubules. Sb2O3 fibrils and tubules with lateral dimensions in nano- or submicron-scale may show enhanced catalytic and flame retardant performances. 2002 Elsevier Science B.V. All rights reserved.

Ag dendritic nanostructures for rapid detection of polychlorinated biphenyls based on surface-enhanced Raman scattering effect

We report a facile and efficient synthetic route for Ag dendritic nanostructures on Si wafer via an electroless deposition process. The formation of the Ag dendritic nanostructures is based on a self-assembled localized microscopic electrochemical cell model. These Ag dendritic nanostructures have exhibited very strong surface-enhanced Raman scattering (SERS) effect using rhodamine 6G as probe molecules, and have been used as SERS substrate for detection of low concentration polychlorinated biphenyl-77 with fast time response. The Ag dendritic nanostructures reported here have potentials as SERS substrates for fast detecting other polychlorobiphenyls.

Large-scale well-separated Ag nanosheet-assembled micro-hemispheres modified with HS-β-CD as effective SERS substrates for trace detection of PCBs

Large-scale well-separated Ag nanosheet-assembled micro-hemispheres with similar size and morphology were achieved on bare commercial ITO substrates via simple electrodeposition in a mixed aqueous solution of citric acid and AgNO3. It was found that appropriate electrodeposition current density and citric acid concentration are critical to the formation of well-separated nanosheet-assembled micro-hemispheres with similar size and morphology. The well-separated Ag nanosheet-assembled micro-hemispheres with similar size and morphology ensure the good surface-enhanced Raman scattering (SERS) signal reproducibility from different micro-hemispheres, and the sufficient sub-10 nm gaps on the nanosheet-assembled micro-hemispheres guarantee the high SERS sensitivity. By further modifying the Ag nanosheet-assembled micro-hemispheres with mono-6-thio-β-cyclodextrin (HS-β-CD), the SERS detection limit of 3,3′,4,4′-tetrachlorobiphenyl (PCB-77) can be further reduced, and two different polychlorinated biphenyl (PCB) congeners of 2-chlorobiphenyl (PCB-1) and PCB-77 in a mixed solution can be distinguished, indicating that the large-scale well-separated Ag nanosheet-assembled micro-hemispheres modified with HS-β-CD may have great potential as effective SERS substrates for rapid trace detection of PCBs.