Xianzhong Lang

Controlled assembly of highly Raman-enhancing silver nanocap arrays templated by porous anodic alumina membranes.

A convenient nanoscale technique is reported for the fabrication of highly ordered hemispherical silver nanocap arrays templated by porous anodic alumina (PAA) membranes as robust and cost-efficient surface-enhanced Raman scattering (SERS) substrates. This geometry produces a high Raman signal due to its periodic hexagonal arrangements and control of the gap between the nanostructures in the sub-10-nm regime. The surface structure can be tuned further to optimize the enhancement factor according to optional PAA fabrication and silver deposition parameters. Finite-difference time-domain calculations indicate that the structure may possess excellent SERS characteristics due to the high density and abundance of hot spots.

High-Sensitivity and Stable Cellular Fluorescence Imaging by Patterned Silver Nanocap Arrays

Patterned silver nanocap arrays (PSNAs) prepared on porous anodic alumina templates by a simple coating technique yield enhanced sensitivity and stability in cellular fluorescence imaging. Microstructural analysis, surface-enhanced Raman scattering mapping, and finite difference time domain simulation indicate that the hot spots are evenly distributed on the substrate. Ag1522 or Chinese Hamster Ovary cells are labeled by phalloidin-fluorscein isothiocyanate (P-FITC) on the cytoskeletons and the fluorescence signals from the fluorophores bound on the cell cytoskeletons on the PSNAs are enhanced 8-fold compared to those on glass used in conventional imaging. In addition to the intensity enhancement, the photostability is improved dramatically. Spectral analysis suggests that the PSNAs can create more excitons in the light-emitting P-FITC because of plasmon resonance energy transfer from the silver nanocaps to the nearby P-FITC. They can also act as plasmonic antennae by converting a part of the nonradiative near-field emission from the fluorophores to the far field consequently enhancing the emission.

Tailoring light emission properties of organic emitter by coupling to resonance-tuned silver nanoantenna arrays

A convenient nanotechnique is reported to tailor the light emission properties of organic emitter poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) by coupling to resonance-tuned silver nanoantenna arrays. It is revealed experimentally and theoretically that the enhanced photoluminescence from the MEH-PPV/silver nanoantenna complex may originate from the energy transfer effect in the surface plasmon resonance coupling between the MEH-PPV and silver nanocaps and from local electromagnetic field enhancement of nanogaps between the silver nanocaps in the background of the light-emitting MEH-PPV. The results are corroborated by the finite difference time domain simulation results.

Silver nanovoid arrays for surface-enhanced Raman scattering.

Highly ordered silver nanovoid arrays are fabricated on porous anodic alumina membranes to produce robust and cost-efficient surface-enhanced Raman scattering (SERS) substrates. Plasmonic tunability can be accomplished by adjusting the topography with different anode voltages. Evenly distributed plasmonic fields, high average enhancement factor, and excellent ambient stability due to the natural protective layer are some of the unique advantages, and the silver nanovoid arrays are applicable to sensing devices.

Modulation of surface-enhanced Raman spectra by depth selective excitation of embedded indium tin oxide nanoisland arrays

Embedded transparent conducting indium tin oxide (ITO) nanoisland arrays were prepared by pulsed laser deposition of ITO films on roughened Si templates and post-annealing to investigate the surface-enhanced Raman scattering activities. Considerable Raman enhancement of a rhodamine 6G probe during Ar+ laser excitation was observed and modulated by the thickness of the ITO film due to the exponentially decaying field of the localized surface plasmon polaritons at the interface. Because the Raman-enhancing functional layer is protected at the ITO/Si interface, this system is reusable and also believed to be immune to contamination and other surface activities.

Trace detection of multiwalled carbon nanotubes using Raman-enhancing silver nanocap arrays

A convenient strategy is demonstrated for trace detection of multiwalled carbon nanotubes (MWNTs) using Raman-enhancing silver nanocap arrays. Microstructural analysis indicates that the hot spots are evenly distributed on the substrate. A brief analytical methodology to evaluate the dispersity of adsorbed MWNTs with different ultra-low concentrations by 2D point-by-point Raman mapping is proposed. The detection limit of this method was found to be 3 ppb. Our results open new possibilities for applying surface-enhanced Raman scattering to trace detection of an inorganic probe.

Band-gap-dependent emissions from conjugated polymers coupled silver nanocap array

The optical properties of poly(2,5-dioctyloxy-p-phenylene) (PPP) and poly[3-(2,5,8-trioxanonyl) thiophene] (P3TT) coupled silver nanocap array have been investigated. The absorption spectrum of P3TT and the emission spectrum of PPP match the absorption of the silver nanocap array. Plasmon energy transfer occurs from the silver nanocap array to P3TT or from PPP to the silver nanocap array, resulting in the largely increased or decreased photoluminescence (PL), respectively. The PL enhancement of the P3TT coupled silver nanocap array is more than 9-fold; whereas the PL intensity of the PPP coupled silver nanocap array is less than one-tenth of the PPP film.

Tunable Surface-Enhanced Raman Scattering from High-Density Gold Semishell Arrays with Controllable Dimensions

A convenient reproducible technique is reported for the fabrication of large-area gold semishell arrays by mechanically pressing porous anodic alumina (PAA) stamps into gold/polymer bilayer structures that serve as robust and cost-efficient surface-enhanced Raman-scattering (SERS) substrates. The surface structure can be tuned further to optimize the enhancement factor according to optional PAA fabrication parameters and imprinting pressures. Finite-difference time-domain calculations indicate that the structure may possess excellent SERS characteristics due to the high density and abundance of hot spots.

Modulating emission from acceptor in donor-acceptor diblock copolymers by plasmon resonance energy transfer

We have investigated the optical properties of all-conjugated block copolymers, poly (2,5-dioctyloxy-p-phenylene)-b-poly[3-(2,5,8-trioxanonyl) thiophene] (PPP-b-P3TT), coupled silver nanocap array. The photoluminescence (PL) enhancement of the acceptor is increased with the mole fraction of the P3TT block in the coupled copolymer. The emission from the PPP blocks and the absorption of the P3TT blocks match the plasmon resonance frequency of the silver nanocap array. The emission from the PPP blocks is absorbed by the silver nanocap array to propagate surface plasmons or surface plasmon polaritons near the interfaces of the conjugated polymer/silver nanocap array, whose energies can be transferred to the P3TT blocks. As a result, more than 14-fold PL enhancement of the P3TT blocks has been observed in the coupled copolymer by photoexcitation at the absorption maximum of the PPP blocks.