Active Accumulation of Spherical Analytes on Plasmonic Hot Spots of Double-Bent Au Strip Arrays by Multiple Dip-Coating

Fountain Pen-Inspired 3D Colloidal Assembly, Consisting of Metallic Nanoparticles on a Femtoliter Scale

The 3D colloidal assemblies composed of nanoparticles (NPs) are closely associated with optical properties such as photonic crystals, localized surface plasmon resonance, and surface-enhanced Raman scattering. However, research on their fabrication remains insufficient. Here, the femtoliter volume of a 3D colloidal assembly is shown, using the evaporation of a fine fountain pen. A nano-fountain pen (NPF) with a micrometer-level tip inner diameter was adopted for the fine evaporation control of the ink solvent. The picoliters of the evaporation occurring at the NFP tip and femtoliter volume of the 3D colloidal assembly were analyzed using a diffusion equation. The shape of the 3D colloidal assembly was dependent on the evaporation regarding the accumulation time and tip size, and they exhibited random close packing. Using gold-, silver-, and platinum-NPs and mixing ratios of them, diverse 3D colloidal assemblies were formed. The spectra regarding a localized surface plasmon resonance of them were changed according to composition and mixing ratio. We expect that this could be widely applied as a simple fabrication tool in order to explore complex metamaterials constructed of nanoparticles, as this method is highly flexible in varying the shape as well as composition ratio of self-assembled structures.

Plasmon-Enhanced Ultraviolet Luminescence in Colloid Solutions and Nanostructures Based on Aluminum and ZnO Nanoparticles

Aluminum nanoparticles attract scientific interest as a promising low-cost material with strong plasmon resonance in the ultraviolet region, which can be used in various fields of photonics. In this paper, for the first time, ultraviolet luminescence of zinc oxide nanoparticles in colloid solutions and nanostructure films in the presence of plasmonic aluminum nanoparticles 60 nm in size with a metal core and an aluminum oxide shell were studied. Mixture colloids of ZnO and Al nanoparticles in isopropyl alcohol solution with concentrations from 0.022 to 0.44 g/L and 0.057 to 0.00285 g/L, correspondingly, were investigated. The enhancement of up to 300% of ZnO emission at 377 nm in colloids mixtures with metal nanoparticles due to formation of Al-ZnO complex agglomerates was achieved. Plasmon nanostructures with different configurations of layers, such as Al on the surface of ZnO, ZnO on Al, sandwich-like structure and samples prepared from a colloidal mixture of ZnO and Al nanoparticles, were fabricated by microplotter printing. We demonstrated that photoluminescence can be boosted 2.4-fold in nanostructures prepared from a colloidal mixture of ZnO and Al nanoparticles, whereas the sandwich-like structure gave only 1.1 times the amplification of luminescence. Calculated theoretical models of photoluminescence enhancement of ideal and weak emitters near aluminum nanoparticles of different sizes showed comparable results with the obtained experimental data.

Nanostructured Materials Based on Noble Metals for Advanced Biological Applications

This special issue focuses on highlighting the progress of last decade regarding the new nanostructured materials based on noble metals, especially gold and silver. Innovative preparations, functionalizations, and characterizations of these nanomaterials are investigated. Moreover, biotechnological applications, and advanced uses of these compounds for environmental sensing are reported. In particular gold and silver nanomaterials are widely studied due to their high stability, amazing chemical–physical features and, for silver, marked antibacterial properties. It is also hoped that the current special issue will encourage multidisciplinary research on noble metal nanomaterials, expanding the range of potential biological applications. This must be associated with improvements in synthetic methods and with economic feasibility studies of the proposed processes, also exploring the ecotoxicological aspects.