The Rational Design And Lithographic Fabrication Of Surface Enchanced Ie Enhanced Raman Spectroscopy Substrates PDF Download

The design and fabrication of nanoparticles (NPs) and NP assemblies to sustain intense electromagnetic field enhancement for surface enhanced Raman scattering (SERS)-based imaging and sensing have recently gained significant attention. In SERS, the intrinsic optical properties of plasmonic NPs are used to overcome the relatively low Raman cross-sections and thereby increase sensitivity. Sharp features in anisotropic NPs and interparticle gaps within NP assemblies have been identified as the locations where the highest SERS enhancements can be achieved, also known as "hot spots". Many attempts have been reported that deal with the bottom-up assembly of NPs to achieve highly reproducible, sensitive, and well characterized SERS substrates, but it still remains a challenge to attain monodisperse, highly reproducible "hot spots" and directional assembly. The focus of this dissertation is to develop synthetic protocols for controlled engineering of NPs with SERS "hot spots", and thereby to contribute to the advancement of SERS-based sensing and imaging applications. In this dissertation, the development of SERS substrates has evolved from dimers of spherical gold NPs (SP), to star-shaped gold NPs (ST), and finally to assembled superstructures of ST and SPs. The kinetically controlled assembly of SPs into dimers was achieved by using Raman active dithiolated linker molecules, with the highest yield reported for this method to the best of our knowledge, leading to SERS tags with a reproducible SERS enhancement on the order of 105. NP dimers, surface-functionalized to target U87 glioblastoma cancer cells, demonstrated a fast, reliable, and selective SERS-based detection of the diseased cells that outperforms fluorescence. The morphology of the STs was modified to possess longer and sharper spikes with a narrower tip curvature thereby increasing the electromagnetic field localization at the tips. SERS substrates were designed by periodically and reproducibly immobilizing STs on a planar substrate with high surface coverage and limited to no clustering, thus enabling femtomolar detection of organic analytes with an outstanding 109 SERS enhancement. Finally, the core-satellite assemblies of ST with SPs were achieved through conjugation linker chemistry. These assemblies demonstrated SERS enhancement of two orders of magnitudes greater than isolated STs thereby improving the sensitivity of potential SERS-based imaging and sensing applications.