Organic/inorganic hybrid nanostructures for chemical plasmonic sensors
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The work presented in this dissertation suggests novel design of chemical plasmonic sensors which have been developed based on Localized Surface Plasmon Resonance (LSPR), and Surface-enhanced Raman scattering (SERS) phenomena. The goal of the study is to understand the SERS phenomena for 3D hybrid (organic/inorganic) templates and to design of the templates for trace-level detection of selected chemical analytes relevant to liquid explosives and hazardous chemicals. The key design criteria for the development of the SERS templates are utilizing selective polymeric nanocoatings within cylindrical nanopores for promoting selective adsorption of chemical analyte molecules, maximizing specific surface area, and optimizing concentration of hot spots with efficient light interaction inside nanochannels. The organic/inorganic hybrid templates are optimized through a comprehensive understanding of the LSPR properties of the gold nanoparticles, gold nanorods, interaction of light with highly porous alumina template, and the choice of physical and chemical attributes of the selective coating. Furthermore, novel method to assemble silver nanoparticles in 3D as the active SERS-active substrate has been demonstrated by uniform, in situ growth of silver nanoparticles from electroless deposited silver seeds excluding any adhesive polymer layer on template. This approach can be the optimal for SERS sensing applications because it is not necessary to separate the Raman bands of the polyelectrolyte binding layer from those of the desired analyte. The fabrication method is an efficient, simple and fast way to assemble nanoparticles into 3D nanostructures. Addressable Raman markers from silver nanowire crossbars with silver nanoparticles are also introduced and studied. Assembly of silver nanowire crossbar structure is achieved by simple, double-step capillary transfer lithography. The on/off SERS properties can be observed on silver nanowire crossbars with silver nanoparticles depending on the exact location and orientation of decorated silver nanoparticles nearby silver nanowire crossbars. As an alternative approach for the template-assisted nanostructure design, porous alumina membrane (PAM) can be utilized as a sacrificial template for the fabrication of the nanotube structure. The study seeks to investigate the design aspects of polymeric/inorganic hybrid nanotube structures with plasmonic properties, which can be dynamically tuned by external stimuli such as pH. This research suggests several different organic/inorganic nanostructure assemblies by various template-assisted techniques. The polymeric/inorganic hybrid nanostructures including SERS property, pH responsive characteristics, and large surface area will enable us to understand and design the novel chemical plasmonic sensors.