Rapid One-Pot Preparation of Large Freestanding Nanoparticle-Polymer Films.

2D arrays of metal nanoparticles formed at liquid-liquid interfaces have been fixed in situ to a thin polymer support to create freestanding large (cm2 ) composite films where the particles remain exposed rather than being trapped within the polymer. Applications of these flexible robust 2D nanoparticle arrays as sensors, thin film conductors, antimicrobial coatings, and dip-in catalysts are shown.

A Method for Promoting Assembly of Metallic and Nonmetallic Nanoparticles into Interfacial Monolayer Films.

Two-dimensional metal nanoparticle arrays are normally constructed at liquid-oil interfaces by modifying the surfaces of the constituent nanoparticles so that they self-assemble. Here we present a general and facile new approach for promoting such interfacial assembly without any surface modification. The method use salts that have hydrophobic ions of opposite charge to the nanoparticles, which sit in the oil layer and thus reduce the Coulombic repulsion between the particles in the organic phase, allowing the particles to sit in close proximity to each other at the interface. The advantage of this method is that because it does not require the surface of the particles to be modified it allows nonmetallic particles including TiO2 and SiO2 to be assembled into dense interfacial layers using the same procedure as is used for metallic particles. This opens up a route to a new family of nanostructured functional materials.

Surface-Enhanced Raman Spectroscopy as a Probe of the Surface Chemistry of Nanostructured Materials.

Surface-enhanced Raman spectroscopy (SERS) is now widely used as a rapid and inexpensive tool for chemical/biochemical analysis. The method can give enormous increases in the intensities of the Raman signals of low-concentration molecular targets if they are adsorbed on suitable enhancing substrates, which are typically composed of nanostructured Ag or Au. However, the features of SERS that allow it to be used as a chemical sensor also mean that it can be used as a powerful probe of the surface chemistry of any nanostructured material that can provide SERS enhancement. This is important because it is the surface chemistry that controls how these materials interact with their local environment and, in real applications, this interaction can be more important than more commonly measured properties such as morphology or plasmonic absorption. Here, the opportunity that this approach to SERS provides is illustrated with examples where the surface chemistry is both characterized and controlled in order to create functional nanomaterials.

Stable and uniform SERS signals from self-assembled two-dimensional interfacial arrays of optically coupled Ag nanoparticles.

Densely packed interfacial nanoparticle films form spontaneously when aqueous Ag colloid is shaken with CH2Cl2 in the presence of a "promoter" such as 10(-4) mol dm(-3) tetrabutylammonium nitrate (TBA(+)NO3(-)), which induces rapid self-assembly of the nanoparticles at the liquid/liquid interface without adsorbing onto their surfaces. The particles within these reflective, metal-like liquid films (MeLLFs) are optically coupled and give strong SERS enhancement, similar to that obtained for the same colloid aggregated with optimized concentration of metal salt. However, unlike aggregated colloids their structure means they do not sediment out of solution so they give SERS spectra that are stable for >20 h) and have good uniformity (relative standard deviation in absolute intensity over 1 mm(2) array of 25 points was 1.1%). Since the films lie at the aqueous/organic interface they are open to adsorption of analytes from either of the phases and can be probed in situ to detect both water- and nonwater-soluble analytes. The detection limit for mercaptobenzoic acid (MBA) added to the organic layer was found to be <2 ppb. These materials therefore combine many of the best features of both patterned surfaces and metal colloids for quantitative SERS analysis.