| Gold nanoparticles (AuNPs) are at the forefront of many research areas and generally require very specific surface functionalities to be compatible with targeted applications. Suitable modification schemes should be simple, fast, and robust. A common surface modification involves the use of thiols to coat the AuNPs with a thiolate monolayer; however, the lability of the sulfur-gold interaction can create problems in applications where high stability is required. Alternatively, this thesis explored the use of diazonium salts to modify gold nanoparticles.;In recent years diazonium cation grafting onto planar substrates has gained significant attention. The resulting layers show resilience and controllable properties such as film thickness and functionality. In order to extend this surface chemistry to include AuNPs, the conditions necessary for the spontaneous chemisorption of diazonium derived aryl films to pre-formed gold nanoparticles were developed. The spectroscopic characterization of these organic layers on gold nanoparticles provided evidence for a gold-carbon covalent bond. A direct comparison of nitrobenzene diazonium salt derived layers to the thiol analogue was used to show that diazonium salt modification schemes are similarly simple and fast in comparison, but also exhibit marked differences in film structure as they produce multilayers.;Gold nanoparticles are widely used in biosensing applications providing unique optical properties for signal enhancement and detection schemes. In UV-vis spectroscopy, localized surface plasmon resonance (LSPR) of the AuNPs leads to an absorption band. The work presented in this thesis explored the capability of utilizing the LSPR band magnitude in a simple transmission UV-vis measurement to determine the nanoparticle density of adsorbed NPs on a transparent substrate. This led to the development of a new method to incorporate AuNPs as extrinsic labels in a sandwich immunoassay. The analyte, rabbit IgG, is captured on a transparent surface and labeled with AuNPs. This was accomplished by tailoring the surface chemistry of the nanoparticles specifically to the target analyte. Consequently, quantitating the magnitude of the LSPR band determines the number of AuNP-labels present on the biochip surface, which in turn is proportional to the analyte concentration captured. In this fashion detection limits on the order of 100 pM were achieved. |
