Macroscopic ordering of polystyrene carboxylate-modified nanospheres self-assembled at the water-air interface.

We present results from an experimental study of ordering characteristics in monolayers of polystyrene nanospheres self-assembled at a water-air interface. We demonstrate that the interaction of spheres, governed by the dissemination of surface charge, leads to the formation of macroscopic close-packed ordered areas or "domains" with a well-defined orientation of the lattice axes over areas of 25 mm(2). It was found that by changing the surface chemistry of the spheres it is possible to modify the balance between the attractive and repulsive forces and thus to control the ordering characteristics. We implemented a model that simulates the process of self-assembly and examines the ordering characteristics for layers with different ratio between attractive and repulsive forces. A good qualitative agreement was found between the simulations and experiment. These studies are technologically relevant as a method of producing nanosphere templates for large area patterned materials.

Spectroscopy on the wing: naturally inspired SERS substrates for biochemical analysis.

We show that naturally occurring chitinous nanostructures found on the wings of the Graphium butterfly can be used as substrates for surface-enhanced Raman scattering when coated with a thin film of gold or silver. The substrates were found to exhibit excellent biocompatibility and sensitivity, making them ideal for protein assaying. An assay using avidin/biotin binding showed that the substrates could be used to quantify protein binding directly from changes in the surface-enhanced Raman scattering (SERS) spectra and were sensitive over a concentration range comparable with a typical enzyme-linked immunosorbent assays (ELISA) assay. A biomimetic version of the wing nanostructures produced using a highly reproducible, large-scale fabrication process, yielded comparable enhancement factors and biocompatibility. The excellent biocompatibility of the wings and biomimetic substrates is unparalleled by other lithographically produced substrates, and this could pave the way for widespread application of ultrasensitive SERS-based bioassays.