Electrochemical Studies of Nanoscale Objects: Proteins and Inorganic Nanoparticles

Conformational transitions of proteins play a crucial role in many biochemical and biophysical reactions. Understanding the conformational changes of a protein upon adsorption to a substrate is very important in biotechnology, e.g. the development of modern protein chip technology, biocompatibility of implants, and many other ones. This research program used cytochrome c, an electron carrier in the respiratory chain, as a model to probe how surface adsorption affects the folding of a protein. My work investigates the interaction of protein horse heart cytochrome c when it is electrostatically adsorbed or covalently attached onto a 1 nm thick monolayer film, which covers an Au surface. After changing the pH value of the solutions or adding the denaturants into the solutions, the conformation of cytochrome c changes and causes a change of the peak current of cyclic voltammgram. In addition, the denatured cytochrome c's peroxidase activity has been studied and compared at different pH. Assemblies of CdSe and CdTe nanoparticles (NPs) on a dithiol coated Au electrode were created and their electronic energetics were quantified. This research describes the energy level alignment of the filled and unfilled electronic states of nanoparticles with respect to the Au Fermi level. Using cyclic voltammetry it was possible to measure the energy of the filled states of the NPs with respect to the Au substrate, and by using photoemission spectroscopy it was possible to independently measure both the filled state energies and those of the unfilled states with respect to the vacuum level. Comparison of these two different measures shows good agreement with the IUPAC accepted value of the absolute electrode potential. In contrast to the common model of energy level alignment, the experimental findings show that the filled states become 'pinned' to the Fermi level of the Au electrode, even for moderately small NP sizes. Photophysical and photoinduced electron transfer processes that follow the excitation of the NP assemblies are probed by photoelectrochemical measurements. For bilayer assemblies of two different NPs on a Au substrate, the photocurrent response of the bilayer assemblies depends on the ordering of differently sized nanoparticles with respect to the surface