Zhulin Huang

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.

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.

Polyacrylic acid sodium salt film entrapped Ag-nanocubes as molecule traps for SERS detection

AbstractSurface-enhanced Raman spectroscopy (SERS) is a fast analytical technique for trace chemicals; however, it requires the active SERS-substrates to adsorb analytes, thus limiting target species to those with the desired affinity for substrates. Here we present networked polyacrylic acid sodium salt (PAAS) film entrapped Ag-nanocubes (denoted as Ag-nanocubes@PAAS) as an effective SERS-substrate for analytes with and without high affinity. Once the analyte aqueous solution is cast on the dry Ag-nanocubes@PAAS substrate, the bibulous PAAS becomes swollen forcing the Ag-nanocubes loose, while the analytes diffuse in the interstices among the Ag-nanocubes. When dried, the PAAS shrinks and pulls the Ag-nanocubes back to their previous aggregated state, while the PAAS network “detains” the analytes in the small gaps between the Ag-nanocubes for SERS detection. The strategy has been proven effective for not only singleanalytes but also multi-analytes without strong affinity for Ag, showing its potential in SERS-based simultaneous multi-analyte detection of both adsorbable and non-adsorbable pollutants in the environment.

Gap-tunable Ag-nanorod arrays on alumina nanotip arrays as effective SERS substrates

Large area arrays of length-tunable alumina nanotips on the joints of hexagonally patterned conical-pores in an anodic aluminum oxide (AAO) template are achieved via a repeated process of anodizing Al foil for pore growth downwards and phosphoric acid etching for pore-widening. By top-view sputtering Ag on the alumina nanotip arrays, hexagonally patterned arrays of Ag-nanorods (Ag-NRs) on the alumina nanotips and uniformly distributed Ag-nanoparticles (Ag-NPs) on the upper rim of the inner surface of the conical-pores are obtained and they exhibit strong surface-enhanced Raman scattering (SERS) activity due to the high density of sub-10 nm gaps between the nearest neighboring Ag-NRs and between the adjacent Ag-NPs. The resultant nanostructures are tailored to attain an optimal SERS enhancement factor of ∼3.2 × 107 by tuning the Ag-sputtering duration. SERS measurements demonstrate that the as-fabricated large-scale Ag-nanostructures can serve as highly sensitive and reproducible SERS substrates. Finite element method calculation also confirms that the fabricated substrates possess excellent SERS activity. By modifying the Ag-NR arrays with mono-6-thio-β-cyclodextrin, the SERS detection limit of PCB-77 (a congener of polychlorinated biphenyls (PCBs)) reaches 10−6 M, showing potential in SERS-based rapid detection of trace PCBs, a kind of global environmental hazardous material.

Hexagonally arranged arrays of urchin-like Ag hemispheres decorated with Ag nanoparticles for surface-enhanced Raman scattering substrates

The surface topography of noble metal particles is a significant factor in tailoring surface-enhanced Raman scattering (SERS) properties. Here, we present a simple fabrication route to hexagonally arranged arrays of surface-roughened urchinlike Ag hemispheres (Ag-HSs) decorated with Ag nanoparticles (Ag-NPs) for highly active and reproducible SERS substrates. The urchin-like Ag-HS arrays are achieved by sputtering Ag onto the top surface of a highly ordered porous anodic aluminum oxide (AAO) template to form ordered arrays of smooth Ag-HSs and then by electrodepositing Ag-NPs onto the surface of each Ag-HS. Owing to the ordered arrangement of the Ag-HSs and the improved surface roughness, the urchin-like hierarchical Ag-HS arrays can provide sufficient and uniform “hot spots” for reproducible and highly active SERS effects. Using the urchin-like Ag-HS arrays as SERS substrates, 10−7 M dibutyl phthalate (a member of plasticizers family) and 1.5 × 10−5 M PCB-77 (one congener of polychlorinated biphenyl, a notorious class of pollutants) are identified, showing promising potential for these substrates in the rapid recognition of organic pollutants.

Tapered Optical Fiber Probe Assembled with Plasmonic Nanostructures for Surface-Enhanced Raman Scattering Application

Optical fiber-Raman devices integrated with plasmonic nanostructures have promising potentials for in situ probing remote liquid samples and biological samples. In this system, the fiber probe is required to simultaneously demonstrate stable surface enhanced Raman scattering (SERS) signals and high sensitivity toward the target species. Here we demonstrate a generic approach to integrate presynthesized plasmonic nanostructures with tapered fiber probes that are prepared by a dipping-etching method, through reversed electrostatic attraction between the silane couple agent modified silica fiber probe and the nanostructures. Using this approach, both negatively and positively charged plasmonic nanostructures with various morphologies (such as Au nanosphere, Ag nanocube, Au nanorod, Au@Ag core-shell nanorod) can be stably assembled on the tapered silica fiber probes. Attributed to the electrostatic force between the plasmonic units and the fiber surface, the nanostructures do not disperse in liquid samples easily, making the relative standard deviation of SERS signals as low as 2% in analyte solution. Importantly, the detection sensitivity of the system can be optimized by adjusting the cone angle (from 3.6° to 22°) and the morphology of nanostructures assembled on the fiber. Thus, the nanostructures-sensitized optical fiber-Raman probes show great potentials in the applications of SERS-based environmental detection of liquid samples.

Nano-petri-dish Array Assisted Glancing Angle Sputtering for Ag-NP Assembled Bi-nanoring Arrays as Effective SERS Substrates

Nano-petri-dish array assisted glancing angle Ag-sputtering was reported to synthesize Ag-nanoparticle (Ag-NP) assembled bi-nanoring arrays as surface-enhanced Raman scattering (SERS) substrates. By manipulating the sputtering-Ag duration, the gaps between the Ag-NPs in the bi-nanorings are tunable to acquire optimal electromagnetic field enhancement, and the ordered bi-nanoring arrays ensure excellent reproducibility for Raman measurement. Such as-fabricated Ag-NPs assembled nanoring arrays exhibit excellent SERS performance, not only 1 × 10(-12) M rhodamine 6G has been identified, but also polychlorinated biphenyls with a low concentration down to 1 × 10(-9) M has been recognized, showing great potential in the detection of trace organic pollutants in the environment.

Urchin-like Au-nanoparticles@Ag-nanohemisphere arrays as active SERS-substrates for recognition of PCBs

A simple fabrication route is developed for ordered urchin-like Au-nanoparticles decorated Ag-nanohemisphere nanodot arrays with a highly active and reproducible surface-enhanced Raman scattering effect for rapid recognition of 4-chlorinated biphenyl.

An ordered array of hierarchical spheres for surface-enhanced Raman scattering detection of traces of pesticide.

An ordered array of hierarchically-structured core-nanosphere@space-layer@shell-nanoparticles has been fabricated for surface-enhanced Raman scattering (SERS) detection. To fabricate this hierarchically-structured chip, a long-range ordered array of Au/Ag-nanospheres is first patterned in the nano-bowls on the planar surface of ordered nanoporous anodic titanium oxide template. A ultra-thin alumina middle space-layer is then conformally coated on the Au/Ag-nanospheres, and Ag-nanoparticles are finally deposited on the surface of the alumina space-layer to form an ordered array of Au/Ag-nanosphere@Al2O3-layer@Ag-nanoparticles. Finite-difference time-domain simulation shows that SERS hot spots are created between the neighboring Ag-nanoparticles. The ordered array of hierarchical nanostructures is used as the SERS-substrate for a trial detection of methyl parathion (a pesticide) in water and a limit of detection of 1 nM is reached, indicating its promising potential in rapid monitoring of organic pollutants in aquatic environment.

Plasmonic nanorod arrays for enhancement of single-molecule detection

We fabricated silver nanorod arrays producing enhanced fluorescence and evaluated the photophysical behaviors of single probes immobilized on nanorods. The observation of bright emission indicated that a highly enhanced field was created near the nanorod. A considerable enhancement in fluorescence of up to a factor of two orders of magnitude was observed as compared to the emission on the controlled substrate.