Self-assembled arrays of hemispherical gallium nanoparticles deposited by molecular beam epitaxy on a sapphire support are explored as a new type of substrate for ultraviolet plasmonics. Spin-casting a 5 nm film of crystal violet upon these nanoparticles permitted the demonstration of surface-enhanced Raman spectra, fluorescence, and degradation following excitation by a HeCd laser operating at 325 nm. Measured local Raman enhancement factors exceeding 10(7) demonstrate the potential of gallium nanoparticle arrays for plasmonically enhanced ultraviolet detection and remediation.

Surface-enhanced Raman Scattering (SERS) is studied in sub-wavelength metallic gratings on a substrate using a rigorous electromagnetic approach. In the ultraviolet SERS is limited by the metallic dampening, yet enhancements as large as 10(5) are predicted. It is shown that these enhancements are directly linked to the spectral position of the plasmonic band edge of the metal/substrate surface plasmon. A simple methodology is presented for selecting the grating pitch to produce optimal enhancement for a given laser frequency.

In this study we investigated the differentiation of human neural progenitor cells (hNPCs) in vitro to evaluate their differentiation potential and in vivo to explore their viability and behavior following transplantation. Progenitors were maintained as neurospheres in media containing basic fibroblast growth factor and epidermal growth factor. Micropatterned polystyrene substrates were fabricated and coated with ECL (entactin, collagen, and laminin) to provide physical and chemical guidance during the differentiation of the hNPCs. The hNPCs growing on the micropatterned substrates showed no differences in proliferation or differentiation potential compared with those hNPCs growing on the nonpatterned substrates. However, hNPCs cultured on the micropatterned substrates were aligned in the direction of the micropattern compared with those cells growing on the nonpatterned substrates. Furthermore, hNPC migration was directed in alignment with the micropatterned substrates. Transplantation of the hNPCs into the developing retina was used to evaluate their behavior in vivo. Cells displayed extensive survival, differentiation, and morphological integration following xenotransplant into the retina, even in the absence of immunosuppression. Taken together, our results show that these multipotent hNPCs are a neurogenic progenitor population that can be maintained in culture for extended periods. Although the micropatterned substrates have no major effect on the proliferation or differentiation of the hNPCs, they clearly promoted alignment and directed neurite outgrowth along the pattern as well as directing migration of the cells. These approaches may provide important strategies to guide the growth and differentiation of NPCs in vitro and in vivo.

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