Paul J. G. Goulet

New insights into Brust-Schiffrin metal nanoparticle synthesis.

A revised view of Brust-Schiffrin metal nanoparticle syntheses is presented here. Precursor species of these reactions are identified and quantified for Au, Ag, and Cu systems. Contrary to the assumptions of previous reports, tetraalkylammonium metal complexes are shown to be precursors of the two-phase reactions, whereas M(I) thiolates are shown to be precursors of the one-phase reactions. A new scheme is outlined for the two-phase synthesis, and the implications of this scheme are discussed. A new synthetic strategy employing well-defined precursors is also introduced. Finally, M(I) thiolate formation, and its impact on nanoparticle synthesis, is discussed. It is expected that the results presented here will lead to modifications in the manner in which these important syntheses are conducted.

Facile phase transfer of large, water-soluble metal nanoparticles to nonpolar solvents.

The facile phase-transfer of large, water-soluble metal nanoparticles to nonpolar solvent is reported here. Thiol-terminated polystyrene (PS-SH) is ligand-exchanged onto water-soluble metal nanoparticles in single-phase acetone/water mixtures, generating a precipitate. The solvent is then removed and the particles are redissolved in nonpolar solvent. This approach is demonstrated for nanoparticles of different metal (Au and Ag), size (3 to >100 nm), shape (spheres, rods, and wires, etc.), and leaving ligand (citrate, cetyltrimethylammonium bromide, poly(vinylpyrrolidone), and 4-dimethylaminopyridine. The resulting PS-SH-stabilized nanoparticles maintain their initial size and shape, and are highly stable. They are soluble in various organic solvents (toluene, benzene, chloroform, dichloromethane, and tetrahydrofuran), and can be readily dried, purified, and re-dissolved. This method makes possible the utilization of a full range of existing nanoparticle cores in nonpolar solvents with a single ligand. It provides access to numerous nanomaterials that cannot be obtained through direct synthesis in nonpolar solvent, and is expected to be of significant value in a number of applications.

Surface-enhanced resonance raman scattering: single-molecule detection in a Langmuir-Blodgett monolayer.

Surface-enhanced resonance Raman scattering (SERRS) is used for single-molecule detection from spatially resolved 1-μm2 sections of a Langmuir–Blodgett (LB) monolayer deposited onto a Ag film. The target molecule, bis (benzimidazo) thioperylene (BZP), is dispersed in an arachidic acid monomolecular layer containing one BZP molecule per μm2, which is also the probing area of the Raman microscope. For concentrated samples (attomole quantities in the field of view), average SERRS, surface-enhanced fluorescence (SEF), and Raman imaging, including line mapping and global images at different temperatures, were recorded. Single-molecule SERRS spectra, obtained using an LB monolayer, present changes in bandwidth and relative intensities, highlighting the properties of single-molecule SERRS that are lost in average SERRS measurements of mixed LB monolayers obtained at the same temperatures. Also, the dilute system phenomenon of blinking is discussed with regard to results obtained from LB monolayers. The dilution process used in the single-molecule LB SERRS work is independently supported by fluorescence results obtained from very dilute solutions with monomer concentrations down to 10−12 M.

Simultaneous electronic and ionic conduction in ionic liquid imbibed polyacetylene-like conjugated polymer films

Polymer films composed of a polyacetylene-like conjugated polymer and 1-propyl-3-methylimidazolium iodide ionic liquid (IL) were synthesized using a ‘one-pot’ hydroiodic acid catalyzed thermal dehydration of poly(vinyl alcohol) (PVA) precursor polymer blended with the IL. The dehydration of the precursor polymer and the formation of polyene segments, in films reacted at temperatures in the range of 60 to 250 °C, were characterized using thermogravimetry and infrared spectroscopy. In reactions catalyzed by HI, infrared, 13C NMR, and Raman spectroscopies confirmed nearly complete elimination of the hydroxyl groups of PVA at 200 °C, which was below the decomposition temperature of the IL in the blend. In contrast, the synthesis of the polyene–IL blend was not feasible in the absence of the HI catalyst, because pure PVA exhibited peak mass loss at about 280 °C, a temperature at which the IL also showed significant thermal degradation. Electrochemical and mechanical properties of the polyene–IL blends synthesized at 200 °C were investigated. The films exhibited both electronic and ionic conductivities. The charge conduction pathways were identified and quantified using electrochemical impedance spectroscopy (EIS). The electronic and ionic conductivities increased by as much as four orders of magnitude over the temperature range of 25 to 115 °C. The storage and loss moduli of the films were measured using dynamic mechanical analysis (DMA), and elongation at break was determined by tensile testing. Addition of IL to the conjugated polymer not only imparted ionic conductivity to the polyene films, but also greatly improved their mechanical properties, including the elongation at break.

Applications of the Enhancement of Resonance Raman Scattering and Fluorescence by Strongly Coupled Metallic Nanostructures

In this Chapter, we have described several applications of the enhancement of resonance Raman scattering and molecular fluorescence toward the characterization of single molecules, monolayers, and thin solid films on metal-island films, colloidal metal nanoparticles, and nanocomposite films. While this review is by no means extensive, we believe it does serve to shed light on some of the more critical considerations of this work, and also to highlight some of the very powerful potential uses of resonant surface-enhanced spectroscopies.

Surface-Enhancement of Fluorescence Near Noble Metal Nanostructures

In this chapter the phenomenon of surface-enhanced fluorescence has been discussed. Beginning with the discovery of surface-enhanced Raman scattering in the late 1970’s, this review has shown SEF in the context of the broader surface-enhanced spectroscopies. The close relationship of SEF to SERS, due to their common EM enhancement mechanism, in particular, has been stressed. In order to provide a general overview of this topic, several of the most important considerations for the understanding of surface-enhanced fluorescence spectroscopy have been discussed. Included in this discussion were the concepts of EM enhancement, enhanced absorption, radiationless energy transfer to metal surfaces, the distance, coverage, and temperature dependence of SEF, and the effects of quantum efficiencies on enhancement. Also discussed, was the preparation and characteristics of a common enhancing nanoparticle metal substrate for SEF, and the surface-enhanced fluorescence of Langmuir-Blodgett monolayers.