Sehoon Chang

Porous Substrates for Label-Free Molecular Level Detection of Nonresonant Organic Molecules

We report on the design of practical surface enhanced Raman scattering (SERS) substrate based upon 3D alumina membranes with cylindrical nanopores chemically modified with polyelectrolyte coating and loaded with gold nanoparticle clusters. These substrates allow for a molecular-level, label-free detection of common plastic explosive materials (TNT, DNT) down to 5-10 zeptograms or 15-30 molecules and a common liquid explosive (HMTD) down to 1 picogram. Such a sensitive detection of organic molecules by utilizing efficient SERS substrates opens the path for affordable and label-free detection of trace amount of practically important chemical compounds.

Nanoporous Membranes with Mixed Nanoclusters for Raman-Based Label-Free Monitoring of Peroxide Compounds

Monitoring trace amounts of peroxide-based molecules is challenging because of the lack of common optical signatures (fluorescence or absorption in UV-vis range) or chemical functionality easily detectable with common routines. To overcome this issue, we suggest a photochemical decomposition approach followed by the analysis of chemical fragments by a fast, sensitive, and reliable Raman spectroscopic method. To facilitate this approach, we employed a novel design of surface-enhanced Raman scattering (SERS)-active nanoporous substrate based on porous alumina membranes decorated with mixed nanoclusters composed of gold nanorods and nanoparticles. The detectable amount of HMTD below 2 pg demonstrated here is about 3 orders of magnitude lower than the current limit of detection. We suggest that laser-induced photocatalytic decomposition onto nanoparticle clusters is critical for achieving label-free detection of unstable and nonresonant organic molecules.

pH-Triggered SERS via Modulated Plasmonic Coupling in Individual Bimetallic Nanocobs

Abstract : In this Communication, we demonstrate the pH-triggered SPR and SERS properties of silver nanowires functionalized with gold nanoparticles in both solution and dry states. In contrast with previous examples of such bimetallic nanocobs, we utilize here a responsive polyacrylic acid (PAA) nanocoating that acts as a linker between the nanoparticles and nanowire. The pH-responsive nature of the PAA nanocoating, which is sensitive to the environmental pH, is employed to vary the separation distance between the gold nanoparticles and the silver nanowire and thus control plasmon coupling. Moreover, placing nanoparticles inside a polymer-gel layer in close proximity to the nanowire surface effectively prevents any potential aggregation of nanoparticles under variable environmental conditions, in contrast with regular nanoparticle solutions, which easily precipitate with changing conditions.

Density-controlled, solution-based growth of ZnO nanorod arrays via layer-by-layer polymer thin films for enhanced field emission

A simple, scalable, and cost-effective technique for controlling the growth density of ZnO nanorod arrays based on a layer-by-layer polyelectrolyte polymer film is demonstrated. The ZnO nanorods were synthesized using a low temperature (T = 90u2009°C), solution-based method. The density-control technique utilizes a polymer thin film pre-coated on the substrate to control the mass transport of the reactant to the substrate. The density-controlled arrays were investigated as potential field emission candidates. The field emission results revealed that an emitter density of 7xa0nanorodsxa0µm(-2) and a tapered nanorod morphology generated a high field enhancement factor of 5884. This novel technique shows promise for applications in flat panel display technology.

SERS Effects in Silver‐Decorated Cylindrical Nanopores

Optimization of pore diameter, the placement of nanoparticles, and the transmission of surface-enhanced Raman scattering (SERS) substrates are found to be very critical for achieving high SERS activity in porous alumina-membrane-based substrates. SERS substrates with a pore diameter of 355 nm incorporating silver nanoparticles show very high SERS activity with enhancement factors of 10(10) .