Investigations of redox-labeled silica and gold nanoparticles in solution and as films on electrodes

Chapter One serves as a background for Au nanoparticles (AuNP) and silica nanoparticles (SiNP). A brief history of the synthesis and characterization of AuNPs will be followed by a discussion on the recent application of the particles in sensing and energy-related applications. The second portion of the chapter will be a discussion on the functionalization of SiNPs and their application in a variety of sensing systems.Chapter Two discusses the irreversible adsorption onto electrode surfaces of highly ionic, mixed-monolayer AuNPs containing an N,N,N-triethylammonium terminated thiol and an 6-(ferrocenylhexane) thiol. The AuNP films are entropically stabilized due to the multidentate nature of the particles and can be transferred to NP-free electrolyte solutions for further investigation. The most interesting aspect of the film is the ability to monitor ion and accompanying solvent transfer between the film and electrolyte solution despite the films being one to two monolayers thick. Comparisons will be drawn to ion transfer between two immiscible electrolyte solutions.Chapter Three will discuss the controlled growth of films of highly ionic, mixed monolayer AuNPs containing deprotonated mercaptoundecanoic acid and 6-(ferrocenylhexane) thiol. The controlled deposition of films of AuNPs without the addition of a metal ion to facilitate binding between particles provides a new route to controlling film thicknesses for applications in Surface Enhanced Raman Spectroscopy and energy storage. Electrochemical quartz crystal microbalance studies, impedance spectroscopy and theoretical modeling show that the large peak-to-peak separation for the ferrocene/ferrocenium couple in cyclic voltammograms arises solely from uncompensated resistance effects within the film, i.e., the rates of ion permeation.Chapter Four examines ferrocenated SiNPs as charge storage devices. Focus is initially on the surface functionalization. Spectroscopic characterizations are used to estimate the number ferrocenes per particle. Next, a variety of electrochemical investigations confirm that approximately 600 ferrocenes reside on the surface of the particles. Several interesting investigations are discussed relating to formation of a slurry of SiNPs upon addition of supporting electrolyte or acetonitrile for electrochemical investigations. Despite the formation of the slurry, reproducible electrochemistry was obtained.